Final Report Summary - SUNPAP (Scale-Up Nanoparticles in Modern Papermaking)
Nano fibrillated cellulose (NFC) is one of the most promising nanomaterials for wide-variety applications. When the project was started, NFC was prepared and applied in papermaking, mainly on a lab scale. The target of the SUNPAP project was to up-scale the NFC production processes and to adapt this nanomaterial for modern papermaking processes via demonstrated pilot lines. The energy consumption of NFC production is high and needs to be reduced. The high potential could be seen with a combination of the mechanical refining and enzymatic pre-treatment before homogenisation or with pre-treating the pulp fibres by oxidative chemicals without intensive refining. Based on these findings, a new pilot line with high-pressure homogenisers was built at CTP in parallel to this project, and the semi-pilot scale rotor- / stator-machine at PTS was completely re-engineered in order to produce NFCs for project partners. Three different NFCs were produced on a large-scale and were used for the production of selected demonstrators. The main conclusion of the material cost calculations was that the chemical costs of chemically pre-treated NFCs outweighed the higher electricity and capital costs of the enzymatically pre-treated NFC. NFC does not only offer possibilities to improve the current products on the market, but makes it possible to develop completely new types of value added products for niche markets. In conventional pigment coating trials, no major benefits were gained via NFC in pigment coating colour. Increased drying demand due to the low solids will limit the used amounts.
There are possibilities to use NFC as a rheology modifier or to improve critical product properties. NFC can give a good grease barrier in multilayer barrier products and can replace partly non-renewable materials. The drying quality of the dispersion coating layer was improved with the use of NFC. As the second-layer barrier, latex or extrusion coating with PE further improved the barrier properties when coated on top of the polyvinyl alcohol and NFC layer. Novel products with active properties are possible with functionalised NFCs. High antibacterial activity of papers could be achieved with thin layers of NFC-TiO2 or ZnO. NFC-TiO2 has significant activity for the oxidation of NO and NOx with low coat weights. Thin layers can be applied with the novel foam applicator installed by VTT on a pilot scale. NFC containing aggregates gave, in most cases, results as good as those from fine NFC. Sustainability assessment showed that the changes in environmental impacts for the pigment coating case were negligible, due to small amounts used. For the bulk structures the trend was positive and radically lower environmental impacts were achieved when the use of NFC enabled lower basis weight due to higher strength. The presence of NFC in demonstrators did not induce large changes in recycling / de-inking. The tested coated board products, including NFC in the coating layer, passed the biodegradability tests and their compostability was confirmed. NFCs are viscous gel-type materials and are used mainly in wet form. The toxicological studies in vitro and in vivo did not indicate any major concerns, except for occupational inhalatory exposure, which can be managed by standard protective measures. NFCs seem to be biodegradable and non-toxic and no big changes in safety or recycling of products containing NFC are expected in the future.
Project context and objectives
The SUNPAP project addressed the competitiveness of the European paper industry by means of nanocellulose-based processes to provide radical product performance improvements, new efficient manufacturing methods and the introduction of new added value functionalities. NFC is the most promising nanomaterial for wide-variety applications in papermaking. When the project was started, NFC was mainly prepared and applied on a lab scale. The target of the project was to scale up the NFC production processes and to adapt this nanomaterial for modern papermaking processes via the demonstrated pilot lines. The scientific work was divided into four research modules which have strong synergy and were well integrated within each other.
The main practical targets of the project are:
- development and up-scaling of novel processes for the energy-efficient production of nanomaterials, namely NFC, on a pilot scale (in module NFC production);
- development and up-scaling of NFC modification processes to address the challenges of papermaking and to provide added value active functionalities (in module NFC processing);
- building and demonstration of pilot lines to alleviate take-up of nanotechnologies, both for the production and the utilisation of NFC, to the modern papermaking processes (in modules NFC production and processing);
- exploitation of innovative sustainable solutions for the whole paper industry value chain by integrated sustainability assessment approaches based on economic, social, and EIAs (in module value chain);
- risk assessments to guarantee the safe introduction of nanotechnologies in the whole value chain of conventional industrial paper production processes and final paper based products (in module health and safety).
The final goal was to enable the introduction of NFC-based processes in various types of applications in the papermaking value chain and the main aims were to develop and demonstrate:
1. high-performance products and environmentally friendly NFC-enabled production processes, demonstrated for graphical papers and packaging boards;
2. functional products and innovative processes enabled by NFC with active functionalities, demonstrated for papers and packaging materials;
3. high-added value fibre-based products with highly specific properties made possible by NFC, demonstrated for fibre-based filters and other selected innovative materials.
The first main target was studied in NFC production and the research work was focused on the material development; NFC production and modification processes and optimising the processes for the up-scaling of NFC production. The activities were directed towards the three main technical challenges of the project, energy-efficient NFC production, and high quantities of NFC and control of NFC suspension rheology. The purpose of module 2 was to produce various types of native and modified NFC batches, which were used in module 3 for the product demonstrations. The main objectives of module NFC production were preparation of NFC from cost-competitive pulp raw materials, development of process concepts for cost-efficient preparation of NFC on a pilot scale, preparation of user-friendly NFC for different kinds of papermaking processes and production of NFC with active properties on a pilot scale for added value paper products. The second main target was studied in NFC processing, which developed the NFC-enabled process and product concepts and finally produced demonstrations of the developed concepts. The proper industry steering was realised by active participation of the industry partners already in the main research tasks. The focus of WP7 was to provide theoretical tools for the optimisation of the rheology of the NFC suspensions.
The overall objectives of module NFC processing were control of reactions and conditions of NFC in wet-end and coating processes, development and design of NFC-enabled product concepts to use the full potential of NFC, in terms of its dimension, optical, strength, specific surface area, and functional properties, prediction of optimal NFC-based process operation parameters by simulation of rheology of suspensions and coatings that include NFC as a main component and demonstrations of the concepts for three selected end-use areas. The fourth main target was studied in the value chain, which was focused on the generation of a holistic view of the value network of the NFC-based processes and products, ranging from raw materials to the end of life of the products, in order to design the demonstrated product concepts for the market areas with the best potential. This module contained three WPs, which were all essential when evaluating the possible success of the NFC product value chain, starting from raw materials and production and ending up at recycling and end-of-life assessment. Here WP1 concentrated on evaluating the financial grounds and means for producing NFC by combining market analysis with production prospects. WP2 determined the sustainability of potential NFC value chains and analysed effects of new products on social, economic and environmental areas. WP3 focused on recyclability and biodegradability issues regarding NFC. This included analysis of both eco-toxicological impacts and biodegradation of new functional materials. An important role of the WPs was the communication with other partners and the delivery of the results to WP10: Risk assessment.
The aims of the module value chain were:
1. assessment of economic grounds for production of NFC-based products and a determination of the most beneficial applications and market areas;
2. evaluation of the economy of the value chain; assessment of profitability for chosen products and determining the most promising value chains for production, taking into account current and emerging market needs;
3. guidance and support for the focus of the project in a sustainable direction, by evaluating sustainability aspects of the developed processes and value added paper products throughout the whole value chain, from raw materials to end-of-life analysis.
The fifth main target was studied in health and safety, which evaluated the toxicity of the nanomaterial used in the project and performed risk assessments in order to provide information about possible obstacles to market access and industrial take-up of the project results. This module contained two WPs. WP9 was devoted to test nanocellulose and functional nanocellulose (NFC and FNFC), and WP10 to do the risk assessment based on the available information and the results supplied by WP1: Market needs, WP2: Sustainability assessments, WP3: Recyclability and biodegradability, WP9: Toxicity and other parts of the project. The aims of the module health and safety were the generation of exposure models for in vitro and in vivo studies, research of the bioactivities of the NFC and functionalised NFC at cellular level, research of systemic toxicity of the NFC and functionalised NFC in in vivo trials, creation of an overall understanding of the environmental, health and safety risks related to the raw materials and products developed and guidance for other parts of the project, to develop low-risk products by serving as an information source
Project results
Material and process studies were made in order to deliver different NFC qualities for application development. Application studies were first carried out on a laboratory scale and continued as product and process studies on a larger scale for final demonstrations. Commercial microcellulose or micro fibrillated cellulose (MFC, Arbocel), which is a coarser material than NFC, was used in some cases as a reference material or when the suitability of test procedures was assessed. The sustainability assessment of the value chains and the risk assessment of the novel processes and products were studied throughout the project.
NFC production (module 2) - process and material development
The main objective of WP4 was to develop concepts for energy-efficient preparation of NFC on a pilot scale and to identify optimal pulp raw materials for NFC preparation. Both targets were the keys to producing cost-efficient NFC. An essential part of WP4 was to deliver NFC samples to other partners for other research tasks. These objectives were considered by taking into account different chemical and enzymatic pre-treatment methods and the influence of pulp composition on NFC fabrication. The results were transferred to different kinds of homogenisation techniques, both in industrially available facilities for the production of micro fibrillated celluloses and pilot-scale rotor-stator-machines and high-pressure homogenisers were used in the experiments.
It was seen that two different routes of the pulp pre-treatments have the highest potential to reduce the energy consumption of NFC production:
1. combining mechanical refining and enzymatic pre-treatment before homogenisation, which, after homogenisation, led to gel-type NFC, containing mainly aggregates of microfibrils;
2. pre-treatment of pulp fibres by means of oxidative chemicals (TEMPO) without intensive mechanical refining before pre-treatment, which after homogenisation led to transparent gels with individual nanofibrils.
Especially in the preparation of NFC-based on enzymatic pre-treatment, the energy consumption in the refining stages varied depending on the used pulp raw material. It was concluded that all commercial pulps can be used, but dissolving pulps were best because of their low refining resistance in the refining stages and their sensitive reaction towards the enzymes. No mechanical refining before the final homogenisation was necessary in the production of NFC with oxidative pre-treatment of the pulps (TEMPO). Even fewer passes at high pressure could be realised because after two passes, the pulps were completely homogenised. The optimisation of the TEMPO oxidation conditions for pilot studies was performed using a design of experiment methodology by means of a composite central design (CCD) on a small scale. The optimisation was based on minimising time and chemical additions in order to maximise the yield, fines content, and number of carboxyl groups. This NFC, produced with low energy consumption using TEMPO oxidation, showed a remarkably lower viscosity than the reference materials, which were the target in WP5. The most suitable high-pressure homogenisers and a rotor- / stator-machine were selected to produce NFC on a pilot scale for other project partners. The high-pressure homogenisers were bought and the pilot line was built at CTP in parallel with this project. The geometries of the tools from the rotor- / stator-machine were completely re-engineered to produce NFC products using a technique not used before at PTS.
In total, more than 100 kg of NFC was produced for other partners:
1. NFC-CTP = enzymatically pre-treated pulp combined with mechanical refining followed by high pressure homogeniser;
2. NFC-TE/CTP = TEMPO-oxidised pre-treated pulp followed by high pressure homogeniser;
3. NFC-TE/PTS = TEMPO-oxidised pre-treated pulp followed by rotor- / stator-machine.
TEMPO pictures showed that an enzymatically pre-treated and homogenised sample (NFC-CTP) was mainly aggregated microfibrils with only partly a nanostructure; NFC with TEMPO oxidation and a homogenised sample (NFC-TE/CTP) contained mainly nanofibrils and NFC with TEMPO oxidation and rotor-stator treatment (NFC-TE/PTS) cut the fibres resulting in short but thick macrofibrils. It was possible to produce different kinds of NFC structures, but it was still hard and time consuming to analyse the NFC properties. For this reason, fractionation tools were developed to reveal more about what is inside NFC samples and NFC quality assurance tools were investigated to establish protocols for reliable quality testing in the production of NFC. In order to characterise the different NFC qualities, a complex fractionation system at VTT was established where the sizes of different fractions could be measured and analysed. Most parts of all produced NFC qualities were in the range of > 0.1 μm. The fractions > 1 μm probably contain mainly aggregates and therefore they do not go through the wide slots. The fraction < 0.1 μm contained mainly dissolved solids. The main objective of WP5 was the development of NFC modification processes to impart innovative functionalities to NFC. The functionalisation of NFC was carried out to achieve development of hydrophobic NFC suspensions with a controlled viscosity profile suitable for the applications in paper production processes and development of NFC with active properties for special paper applications.
NFC surface energy modification to impart hydrophobic properties: Different approaches were applied such as physical adsorption of polymers on the NFC surface and chemical modifications of NFC. Chemical grafting of hydrophobic moieties was studied in organic as well as aqueous media.
Physical adsorption of polymers on the NFC surface: Industrial copolymers, polyvinyl alcohols (PVA), were used for the NFC modifications. Physical adsorption of polyvinyl alcohol on NFC resulted to be a relatively simple method of modifying the NFC viscosity. The addition of polyvinyl alcohol significantly decreased the NFC suspension shear viscosity and the modification did not depend on the different polyvinyl alcohol grades. The effects on suspension viscosity were slow and the studies were carried out on a laboratory scale. By adding polyvinyl alcohol, a significant increase in NFC suspension concentration could be reached without viscosity increasing.
An interesting route for NFC chemical grafting was the nano-emulsion approach, where nano-emulsions containing AKD were produced and mixed with NFC suspension. After removal of the CHCl3 solvent, the NFC-AKD suspension was ready for chemical grafting obtained after the drying process. The activation step can be alternatively performed before application to paper, to obtain a dry NFC-AKD re-dispersible additive or in the paper production process when the paper web is dried. Based on the laboratory work, NFC-AKD suspension displays a significant reduction of viscosity in coating colour formulations with respect to non-modified NFC. Active Innovative inorganic nanoparticles / NFC hybrid systems were developed and the selected NFC functionalisation was obtained by the addition of inorganic nanoparticles. Two main routes were followed: polyelectrolyte assembly and direct physical adsorption. NFC-Ag and NFC-ZnO Nano-composites were obtained by electrostatic assembly of inorganic nanoparticles (Ag and ZnO) on the NFC surface. Different polyelectrolytes were investigated as macromolecular linkers between inorganic fillers and NFC. These nano-composites were applied on paper by coating. The obtained nano-composites and coated paper, showed significant antibacterial activity. NFC-ZnO and NFC-TiO2 nano-composites were prepared by physical adsorption, by mixing NFC and inorganic nanoparticle suspensions. The nano-composites showed strong antibacterial activity, with respect to gram-positive bacteria: Staphylococcus aureus and Bacillus cereus spores and gram-negative Klebsiella pneumonia.
NFC processing (module 3) applications, modelling and demonstrations
The main objective of WP6 was to develop and design NFC-enabled product concepts to utilise the full potential of NFC in both coating and wet-end processes. We aimed to master the composition of coating colours for conventional and advanced coating processes in pilot studies. The target of the wet-end lab studies was to control reactions and conditions of NFC wet-end processes application and to optimise and scale up the NFC application processes from hand sheets to pilot scale for the application of native and functionalised NFCs to value chains. Several lab studies using NFC as a replacement for latex or other co-binders in different types of surface treatments were carried out with various natural NFC and modified or functionalised NFC samples. Surface strength and mottling are critical factors in the conventional pigment coatings. The main findings from NFC in conventional pigment coating were increased viscosity of the coating colours, porosity of the filter cake and porosities of the coating layers when NFC was added to the coating colours and decreased gloss of the coated products. Removal of viscosity modifiers widened the operational window. The surface strength results obtained were inconsistent and partly poor, probably due to the low speed. NFC can be used to improve the barrier properties of the packaging materials. The conclusions of the introduced NFC in a plasticised starch matrix are strong improvement of barrier properties (WVTR), and a positive effect was expected for OTR with no degradation of mechanical properties. The cooking of starch matrix directly in NFC suspensions at 95 degrees Celsius did not have any significant impact on NFC properties and is a good choice for preparing NFC-based coating colours. The study of modified NFC showed that modifications are interesting techniques to reduce the viscosity of NFC suspensions by decreasing interactions between fibrils. The coating colours produced with modified NFC had lower viscosities than colours made with unmodified NFC.
This was an important result because this improved a lot of the processability of NFC-based barrier coating colours, while keeping the same barrier properties. The use of NFCs had a big drawback: their high viscosity at low solids led to formulations with low solid content. Only small amounts of NFC could be introduced. Thin layers of cellulose nanofibrils could be applied on the surface by using a novel foam-coating applicator. The use of air instead of water makes the application of viscous cellulose nanofibril solutions possible. The main focus was on the characterisation of foam and foam-coating trial procedures in order to scale up the use of NFC in the foam-coating process. The stability of the foam is an important foam property, besides the bubble size and bubble size distribution. The best indicator for stability was the back pressure value measured by the foam generator. The main part of the work concentrated on solving technical questions in scaling up the foam-coating application. Using infrared driers instantly after the applicator and the new backing roll for the pilot coating line improved coating quality. The mixing head with fewer pins made a higher solid content of NFC possible, which made higher coat weights possible. Differences in contact angle, air permeability, roughness, and microbiological influence between different natural and modified / functionalised NFCs were noticed. The foam-coating process is a suitable method for the application of NFC on the fibre-based substrates. The highest speed with the current pilot configuration was 300 m/min and with higher speeds an extra air removal device is needed. The solid content of NFC is critical and is low, but it is higher than can be used in spray coating. NFC quality is important; big particles / aggregates can block the applicator. VTT has this technology available for paper and board coating studies on a pilot scale.
It can be used for the application of any novel materials giving special functionalities to products with small addition levels. Lab studies to use NFC as an additive in order to improve strength in the wet-end were carried out. The retention evaluation showed that is necessary to use retention aids to retain the NFC. Retention of NFC in the paper sheet depends strongly on the pulp and retention aid used and on the basis weight. NFC leads to a significantly increased dewatering resistance of hardwood chemical pulp. This negative impact could be reduced by using cationic additives. Especially for softwood chemical pulp and CTMP, the loss in dewatering speed was lower compared to hardwood. Retention aids and special starch products can enhance the dewatering speed when using NFC and NFC is generally capable of improving the paper strength significantly. Especially for the paper board, opportunities based on the small-scale pilot results exist for using the increase in strength to save fibre raw materials. NFC in the outer layers can significantly contribute to the stiffness of paper board. At lower dosages, the loss in bulk could be compensated by an increase in E-modulus. There are opportunities to produce CTMP to a lower SR with higher bulk. The reduced delaminating could be compensated by NFC, while the bending stiffness can be improved.
WP7 had two main objectives: prediction of nonlinear dynamic material interactions in suspensions for varied process conditions, with atomistic models and simulation of rheology of suspensions and coatings, including NFC with continuum level models. Atomistic models were used as qualitative input to the continuum level models. The studies increased scientific understanding of the related phenomena in the characterisation of NFC. The molecular dynamics simulations were carried out to obtain information on the mutual interaction between cellulose fibrils and on the interaction between cellulose fibrils and a calcium carbonate surface. The context was to obtain parameters for the aggregation model. The main finding from the atom-scale molecular dynamics simulations was that pushing crystalline cellulose fibrils towards a calcium carbonate surface led to repulsion, due to a water layer stuck in between two hydrophilic surfaces. There was strong binding between cellulose and calcium carbonate in simulations with an initial structure chosen so that a cellulose fibril was attached to a calcium carbonate surface without a water layer in between. Pulling the cellulose fibril apart from this initial configuration led to disintegration of the fibril instead of simple desorption. For cellulose-cellulose interaction, the situation was similar. The amorphous coverage of the fibrils was important in the binding of the fibrils together. In the aggregation model, the mixing of NFC and calcium carbonate particles with varying particle sizes has been studied.
The model was prepared in the spirit of the Smoluchowski mass balance equations, extending it to allow for interactions between different species of aggregates. The model was applied to study a calcium carbonate NFC mixture suspension. The main finding was that the NFC aspect ratio had a crucial role in the mixing of the two phases, having impact on the amount of excess calcium carbonate. The mass ratio between the different species affected the mixing efficiency and dynamics. The interactions of the carboxylated fibril with non-modified nanocellulose structures were found to have two distinguishable forms: a strong electrostatic repulsion due to a large negative surface charge and weak attractive interaction due to forming dynamic hydrogen bonds. The hydrogen bond formation mostly involves the fibrils corners, probably due to the electrostatics geometry and water structuring and screening effects and is not related to the presence of unmodified groups in some corner chains. The interactions between two unmodified fibrils led to stronger hydrogen bonds and aggregation. Two carboxylated fibrils are immediately and powerfully repelled from each other. The carboxylation prevents fibrils from aggregating into larger forms as has been clarified at the molecular level. Main findings described the influence of shear transients and shear localisation on the rheometer reported as viscosity commonly used to characterise suspensions to help the design of the pilot-scale application of new materials.
The characterisation of the NFC on the basis of viscosity can give results that are misleading if not carefully analysed. With this material, there is no standard rheological characterisation. Viscosity is not unique for such a complex material. This is due to the fact that the Newtonian assumption of stress and shear rate relation contains extra components that are not purely viscous. The model was fitted at qualitative level to experimental rheological data. The fitting was used to simulate the occurrence of shear banding in rotating cylinder geometry. The reported NFC suspension experiments were performed in parallel rotating plate geometry. Similar phenomena can be expected to appear in that case since the shear and stress distributions are more heterogeneous for that particular geometry. It was shown that the perfect power-law scaling observed in the TEMPO-oxidised NFC flow curve is possibly a sign of shear banding.
The suspension viscoelasticity plays an important role in the case of enzymatically pre-treated NFC. Using a viscoelastic Maxwell model, transient effects were observed. The model demonstrated that such transients are measurable only for suspensions with small elastic modulus. With higher elastic modulus, transients are so fast that they will disappear due to the slower settling time of the rheometers. This is reasonable to assume, as the NFC flocks formed of longer fibres in the enzymatically pre-treated case can be assumed to have lower elastic modulus compared to the more compact ones formed of shorter fibres, in the TEMPO-oxidised case. Considering the model response to a decreasing shear ramp, it can be seen as an implication of what happens during a papermaking process. When the wet web is formed, there is a decreasing relative velocity difference between the fluid and the wire, implying a shear gradient decreasing in time. The picture that emerges from the simulations is that the flock formation of the TEMPO-oxidised NFC requires such a long time that no noticeable aggregation can be observed. This is promising for shear bands and other phenomena, which are absent in the dispersed phase, as the relative viscosity differences in this state are small.
Three NFCs were selected to be produced on a large-scale and were used on a pilot scale for the manufacturing of the WP8 demonstrations. The NFCs used were named as NFC-CTP, NFC-TE/CTP and NFC-TE/PTS. Several demonstrators were studied.
Examples are:
- demo 1: conventional coating on board;
- demo 3: coating for inkjet paper based on curtain coating;
- demo 4: foam coating with functionalised NFC;
- demo 5: conventional coating for barrier packaging.
Demo 1: Conventional coating on board
Three NFC grades of the project were tested to see the effect of scaling-up on the behaviour of these NFCs in the pigment coating colours, as partly replacing latex binder. The coating trial was conducted on the KCL pilot coating machine and in conventional technology, a bent blade with jet-applicator was used as a coating head. The results from the KCL pilot plant imply that most of the coated board and printing properties with the coatings containing NFC were close to those of the reference coatings with latex. Because of the big decrease of the coating colour solids, it was concluded to be difficult to get benefits from replacing just part of the latex with NFC. In the continuation tests in Stora Enso's pilot plant, the initial target was fine-tuned. Due to limits of time and material, it was not possible to do industrial conversion to cartons. Some unprinted material was made into small boxes in the lab and showed good convertibility. No major benefits were gained in these trials via NFC in coating colour. There could be some possibilities to improve the bending stiffness of the board by using NFC in surface sizing. In such a case, one can expect clearly increased drying demand.
Demo 3: Curtain coating for inkjet paper
In order to fulfil the market needs in terms of production output for inkjet photo papers, paper manufacturers can either invest in new plants or enhance the productivity of existing machines. The production speed of coated inkjet photo paper is limited by cracking during drying of the coating layer. The cohesion strength between the nano-pigments and the binder competes with the retraction force of the binder during drying. The fibre network of the NFC was assumed to counteract the forces and thus reduce cracking of the coating layer. Inkjet photo paper was coated on a pilot coater at Schoeller Technocell using curtain coating technology, which is comparable to the industrial production machines in the company. Two samples were produced, one reference sample without NFC and another one containing 0.06 % NFC in the coating layer. The use of NFC in the coating had a positive impact on paper quality and production efficiency. The quality was on the same level when printed with pigmented inks or even improved when printed with a dye-based ink printer. Especially water fastness, absorption bronzing and brittleness are better with NFC if dye-based inks are used. Besides the beneficial paper quality improvements, the production speed could be increased by adding NFC to the coating colour. The cracking level was lower with 0.06 % NFC in the coating colours, which is equivalent to a potential for a coating speed increase estimated to be 5-10 %.
Demo 4: Foam coating with functionalised NFC
Thin layers of cellulose nanofibrils can be applied on the surface by using a novel foam-coating applicator in the KCL pilot coater. The applied amounts are smaller than in conventional coating. The influences of thin layers on the fine paper surface with unmodified NFC increased hydrophilicity and reduced air permeability and small scale roughness (PPS S10), resulting in glossier and smoother surfaces. By using NFCs functionalised with inorganic particles, it is possible to create novel activities to paper surface even with low coat weights. These foam-coating trials were carried out at Zimmer with a new coating head, making even higher coat weights possible. High antibacterial activity of papers could be achieved with thin layers of NFC-TiO2 and/or ZnO under both light and dark conditions. NFC-TiO2 has significant activity for the oxidation of NO and NOx in low coat weights.
Demo 5: Conventional coating for barrier packaging
Barrier coatings were continued on a pilot scale. The baseboard was coated on CTP's pilot coater. Coating layers of 10 g/m2 containing mainly polyvinyl alcohol with five parts of NFC in the matrix were applied with a SoftTip blade at a speed of 70 m/min in order to get the gas and grease resistant layer. The reels produced were divided into two parts. One reel was sent to Stora Enso in order to perform the PE extrusion. The second reel was coated once again in the CTP's pilot coater: a 6 g/m2 layer of commercial barrier latex was applied to impart the water resistance. Due to the narrow width of the reels, LDPE extrusion coating was done at Tampere Technical University. A relatively high amount of LDPE coating was used because good hot-sealing properties were targeted. The boards from the final coating trials were converted into small packages. Oxygen barrier measurements were carried out with Oxtran 2/21 (Mocon) apparatus (ASTM D-3985) at higher moisture content. Higher moisture conditions were considered relevant because NFC as a hydrophilic material should absorb moisture and give higher oxygen penetration. The grease barrier was tested using a modified ASTM F119-82 method. Because some barrier films tend to fracture in the conversion, testing was done for a creased sample. There was a target to see if creasing defects would be reduced with the help of PE coating, and samples were PE coated for this reason. PE coating was done on both sides, in order to get a more realistic structure for oxygen-tight packages.
There were large variations in the oxygen barrier results. This was caused by pinholes in the coating layer. Pinholes could be a major problem in higher-speed machines because faster drying is needed. The moisture sensitivity of the coating layer will have an effect. The measurements were made at 50 %. The barrier latex gave a clear improvement when coated on top of the polyvinyl alcohol and NFC layer. The best results were obtained when the polyvinyl alcohol and NFC layer was coated with PE. NFC can give a good grease barrier. Pinholes are a potential problem here. Adding the barrier latex gave good grease resistance in no creased samples but not in creased samples. The PE-coated samples had good grease barrier properties after creasing.
Value chain (module 1), market needs, sustainability, recyclability and biodegradability evaluations
WP1. Market needs
The aim of WP1 was to analyse where, when, and how nanocellulose could be used in selected paper and paperboard end-uses. The tasks included both market and technical feasibility assessments of the products developed. The impact on European competitiveness was evaluated. The work was divided into three different tasks: market assessments, feasibility analyses and evaluation of the impact on Europeans competitiveness. Market assessment was started by mapping and evaluating the market growth potential of paper, paperboard and non-woven end-uses. Future consumer needs were researched to distinguish trends and development drivers. The findings of the analysis were compared with properties that nanocellulose was believed to have. Future key end-use properties were extracted and a nanocellulose opportunity tree for paper and paperboard products could be drawn. The findings showed that there are several potential application areas where nanocellulose could be used. The demand for various carton board products is anticipated to grow significantly. Nanocellulose (NFC) could turn out to be beneficial due to its lightweight but interesting strength and barrier properties.
NFC offers possibilities to improve current products on the market and makes it possible to develop completely new types of value added niche products fitting into all product groups in this study. Feasibility analyses were conducted to evaluate the most promising process routes and applications developed. Several routes were screened during the first phases and three routes were qualified and evaluated. The production concepts in the three routes were different. The results showed that the feasibility of the different routes is different. The main difference was that the chemical costs of the chemically pre-treated NFCs outweighed the higher electricity and capital costs of the enzymatically pre-treated NFC. The target in evaluation of the impact on European competitiveness was to analyse the foreseeable impact that nanocellulose could have on European competitiveness. The target was to identify how results could be used and what the links to other European-level research projects were. The results showed that, for European competitiveness, nanocellulose is one part of the solution. It combined a possibility for global leadership, a renewable raw material basis, synergy across sectors and solutions to challenges facing society, while relying on conventionally globally competitive European industries. In nanocellulose, companies can fill certain niches, EU policies populate others and joint efforts fill in the final missing components for the greatest competitive impact to be realised in a never before seen bio-based ecosystem.
WP2. Sustainability assessments
The objectives were to define the framework and indicators for assessing the sustainability of nanotechnology applications in the paper industry, guide and support the focus of the project in a sustainable direction and to demonstrate sustainability aspects of the developed processes and value added paper products. Two sustainability evaluations were carried out. A first-phase evaluation was carried out at the beginning of the project. During this phase, all potential applications were evaluated by screening. During a second phase, a more detailed approach for selected applications was carried out, which represented the final and complete sustainability assessment. During this evaluation, all three pillars of sustainability were included: economic, environmental and social sustainability. Economic assessment focused on private costs, the bottom line in NFC manufacturing and applications. The socioeconomic impacts included evaluation of suppliers in the supply chain. The social assessment included analyses on the working conditions of NFC manufacturing and application. The consumer's point of view was included, relating to acceptance of nanotechnology.
For the environmental assessment, carbon footprint, acidification and eutrophication potential and fossil resource depletion were selected as indicators, as the data sets were comprehensive for these impact categories. The carbon footprint can be considered to be the most important indicator because one of the constraints of NFC manufacturing is the high energy consumption. A water balance was calculated for the NFC processes as background information for possible future water footprint calculations. The impact of NFC on the product's end of life was speculated. Results from research on recyclability and biodegradability were presented. A four-stage approach was used in the LCA analysis. NFC was produced by modifying dissolving sulphite pulp by chemimechanical means from Domsjo pulp mill in Sweden. Three different preparation methods were used at CTP and PTS. The environmental impacts were calculated based on expert estimations and theoretical data. The environmental impacts for the applications with NFC were calculated for SBS board using NFC in the coating to replace partly latex and for wet-laid non-woven to reduce the basis weight by a small addition of NFC. For the SBS case, the changes in environmental impacts were negligible due to the small amounts replaced in coating. For the wet-laid non-woven, the trend was positive. The use of NFC enabled a lower basis weight and led to more than a 30 % lower environmental impact. The social and economic effects of the application cases varied. The gross value added was positive for the wet-laid non-woven case. In the coated board case, the value added was positive with one NFC production route and negative with the other two. Employment effects were found to be positive in the coated board case and negative in the non-woven case.
WP3 Recyclability and biodegradability evaluations were carried out partly on small-scale samples and partly with the larger amounts received from the demonstration trials.
Recyclability of packaging and de-inkability of graphic papers were carried out. Two types of paper products from WP6 were tested in terms of recycling / de-inkability on a lab scale: introduction of NFCs by foam coating for inkjet printing and partial substitution of latex by MFC in the coating layer for LWC products. It appears that the introduction of NFC in paper products did not modify to a large extent the recyclability / de-inkability compared to the same product made without NFC. De-inking of the inkjet prints was not improved and LWC samples printed with heatset were fully de-inkable. The mechanical properties of the recycled pulp were not modified compared to the reference. In the case of the introduction of NFC by foam coating for inkjet printing, anionic surfactant was required for foam coating, which induced some drawbacks during de-inking even if a slight ink removal improvement was observed. Whatever the nature of the NFC introduced, pigmented inkjet prints could not be considered as de-inkable even if modification of the nature of the NFC could induce some slight improvement in ink removal. The presence of the TEMPO pre-treated NFC led to a change in surface chemistry of the NFC, leading to a more hydrophilic character of the NFC. Besides, this surface chemistry change also induced an increase in the potential risk of paper machine plugging and a slight increase in cationic demand, meaning higher chemical consumption in the wet-end of the paper machine.
In the case of LWC paper printed with heatset offset technology, the partial substitution of latex by MFC and the removal of CMC in the coating layer did not change de-inkability and the risk of deposit on the paper machine wire. The main difference observed corresponded to the nature of MFC: undried MFC led to faster kinetic of flotation, due to a difference in resistive strength of the coating layer, but did not modify the flotation selectivity. For the final tests, three demonstrators were selected, considering only products that will be collected and recycled.
During these tests, special attention was paid to the behaviour of the overall recycling/de-inking line and to the final recycled/de-inked pulp quality:
1. Demo 1 (conventional coating on board): recycling on a pilot scale;
2. Demo 2 (conventional coating on paper LWC): de-inkability on lab and pilot scale in paper for a recycling mixture encountered in wood-containing de-inking lines producing newsprint, SC or LWC papers;
3. Demo 5 (barrier packaging): recyclability on a lab scale.
The presence of NFC in these demonstrators does not induce large changes in recycling/de-inking. The presence of NFC pre-treated by TEMPO enabled a reduction of the resistive strength of the coating layer during re-slushing, leading to smaller mineral filler flakes. This opened energy saving during pulping and deflaking, higher mineral filler content in the de-inked pulp and better cleanliness of the pulp. The possible negative impact seen on was confirmed in large-scale tests with NFC pre-treated by TEMPO. NFCs produced in WP5 were investigated in regards to their biodegradability in an aqueous medium. Standardised methods from ISO, EN and OECD were used. The results showed that the intrinsic biodegradability of cellulose was not modified for most of the functionalised NFC analysed. The 90 % biodegradation limit to claim biodegradability of materials was easily reached within a feasible timeframe. The NFCs used for demonstration of SUNPAP corresponded to biodegradable products in an aqueous medium. Coated paperboards from WP6 were analysed, especially products coated with unmodified NFC and functionalised NFC. The ultimate biodegradability under controlled composting conditions was demonstrated with a biodegradability reaching the 90 % limit within 60-70 days. Two of the demonstrations from WP8 were then analysed to determine if they met the requirements for certification of compostability: ultimate biodegradability in compost, disintegration of the samples and ecotoxicity from compost after disintegration. The different coated papers including NFC products did not have a negative impact on the good biodegradability of paper and board in a compost environment. To complete this assessment, disintegration in compost was tested and the quality of the obtained final compost was analysed as well as the absence of any ecotoxicity effect in respect of seed germination and plant growth. The tested paperboard products passed the different tests and their compostability was confirmed.
Health and safety (module 4) - Toxicity and risk assessment
WP9. Toxicity
Originally, WP9 involved three tasks: characterisation of aerosols and liquid dispersion of NFC and FNFC, elucidation of the effects of NFC and FNFC at cellular level and systemic effects of NFC and FNFC in vivo. During the project, the material characterisation was done in WP4. The work in WP9 was done according to the hazard analysis outlined in WP10. The focus was on the in vitro toxicity and the cellular effects of NFCs. The toxicity was assessed using cytotoxicity assays, which measure the harmful effects of the test materials on cultured mammalian cells, immunotoxicity assays, which give an indication of the potential of the test materials to interfere with the basic immunological phenomena and genotoxicity tests, which detect harmful effects on the DNA or chromosomes. Commercial MFC (Arbocel) was used as a reference material with some of the assays when the suitability of test procedures was assessed. The actual test materials used for in vitro studies included NFC samples prepared with and without enzymatic pre-treatment or with TEMPO oxidation before homogenisation. None of these materials was harmful to exposed cells, indicating a lack of cytotoxicity. In the immunotoxicity assays, there were some marginal indications of inflammatory response in human peripheral lymphocytes, but only when the cells had been exposed to bacterial lipopolysaccharide (LPS) before treatment with NFCs. LPS is a potent immunotoxic agent and the results indicate that although the NFCs are not likely to induce inflammatory responses by themselves, they could have synergistic effects with the microbial contamination in NFCs. In genotoxicity assays, there was an indication of DNA damage caused by the NFCs.
The effects were weak and no clear dose response could be detected. The immunotoxic and genotoxic effects indicated a need for further in vivo studies. The tests included the effects of a selected TEMPO-oxidated NFC on a nematode worm and the so-called pharyngeal aspiration test in a mouse. Despite being a simple organism C. elegans has a digestive system, nervous system, xenobiotic metabolism and developmental cycle which makes it a suitable test organism to study effects that cannot be detected in cell cultures. The mouse pharyngeal aspiration test was chosen because the likely human exposure is via inhalation. Exact doses are applied to the mouse pharynx and subsequently the inflammatory and genotoxic responses of the test material can be assessed from the cells that have been harvested by a bronchoalveolar lavage (BAL) from the exposed cells. While no harmful effects were seen in the C. elegans model, indicating that the NFC does not penetrate the cuticulum or gastrointestinal barrier to an extent that causes detectable damage, the BAL-associated cells harvested from the exposed mice indicated an inflammatory response. No signs of genotoxicity were found in these cells. Taken together, the toxicological results indicate that the tested NFCs do not interfere in the cellular metabolism in a way that would lead to cytotoxicity. The weak indications on in vitro genotoxicity were not confirmed in in vivo trials, while both in vitro and in vivo data indicate that an inflammatory response is possible. This has been taken into account in the risk assessment.
WP10. Risk assessment
This WP was devoted to the risk assessment based on the toxicological data available in the literature and accumulated during the project. The work started with an extensive literature study on the available published toxicological data and risk assessment methodology related to NFC or NFC-type materials. The generated data was used to outline a preliminary risk assessment, mainly based on the in vitro data. In the preliminary assessment, the main identified difficulty was the lack of reliable data or even reliable estimates of likely exposures. Because of this, the so-called control banding (CB) approach was applied. CB is a risk management tool that is applicable when the available data are limited. Two CB scenarios, the so-called CB nanotool and Stoffenmanager nanotool were used. In both scenarios, estimations of hazard and exposure are given scores and the combination of the scores is the basis of the risk estimation. The main difference between the approaches is that the hazard evaluation CB nanotool is based on available toxicological information, while the Stoffenmanager nanotool focuses on the physicochemical aspects of the material to be assessed. Both CB approaches gave NFC a high hazard class. This was a result based on the conservative starting point of the CB tools, which gives high hazard scores to unknown parameters and the highest hazard class to insoluble nanoscale fibres. The toxicological data required by the CB nanotool does not exist for NFC and testing for them was beyond the scope of the project. The current CB scenarios overestimate the hazards and are probably not suitable for NFC-type materials. The toxicological data obtained during the project do not indicate major concerns, except for the occupational inhalatory exposure, which can be managed by standard protective measures. The toxicological testing scheme applied in the project was found to be compatible with the first tier hazard and risk assessment according to the latest ISO standard made for nanomaterial risk evaluation.
Potential impact
When interpreting the results of novel products and their impacts it is important to be aware that assumptions are made and generic data sets were used. Therefore the presented results were strongly case dependent. The results can be seen as trends and indicate that no environmental hazards are likely to arise as a result of including NFC in the applications studied. From an environmental perspective, the main differences between the three different NFC production options can be found from electricity consumption, raw material efficiency and water consumption. Enzymatically pre-treated NFC production is an energy-intensive process with high yield and low water consumption, while chemically pre-treated NFC consumes less energy but more water in the process and stays behind in the yield. NFC can be applied in coatings to reduce the need for latex. This was demonstrated in SBS board pigment coating. The amounts of NFC represented less than 1 % of the total product and the environmental effects were not recognisable. Applying NFC in bulk structures will enable a reduced need for raw materials as demonstrated in the wet-laid non-woven application. With lower weight and less raw materials, all the environmental burdens are significantly lower. When combining both approaches using NFC in bulk structures and barrier coatings in large volume packaging paper and board applications, a significantly lower environmental impact can be expected. The production of NFC is energy-intensive and this is a threat when large amounts of NFC are applied, at least in countries where the grid mix is fossil fuel-based. Low concentrations of NFC increase the drying energy demand of the applied NFC due to the use of water in high volumes. The energy consumption does not seem to be higher than in the production of latex. Another threat is related to the embodied environmental burden of chemicals used in the production of NFC. The oxidation chemicals can cause high economic impacts when the cleaning technologies needed to treat the process effluents are taken into account. Both functionalised NFC and reference natural NFC were assessed for their biodegradability in an aqueous environment. Functionalised NFC showed a lower biodegradation rate than NFC only, but the threshold biodegradation limit of 90 % was reached within the test duration.
The results of the biodegradability tests confirmed that the innovative coated board material containing the natural NFC or even slightly functionalised NFC is suitable for recovery in the organic recovery route. Economic and social sustainability assessment of the demonstrators showed that there is no NFC production route and application that would be the best from every aspect measured by the different indicators. The observations on both application cases are collected under a SWOT analysis framework. From an economic point of view, the application of NFC in coated board does not seem to bring cost savings and has a negative impact on product profitability when compared to the reference product. NFC replaced binder by 1:1 in the case studied. If the replacement ratio could be improved, or if NFC could be used in a bulk structure making leaner products possible, the application would be more feasible. The production of lean products by adding NFC does not decrease the production amounts because in most cases the production capacity in board production machines is limited by the drying capacity and therefore higher speeds can be used. Using NFC in higher added value products as barrier-coated products would make the situation more profitable. The replacement of part of the binder by NFC has a positive employment impact when looking at the total number of people employed directly in the application and indirectly in the supplier' business. The impact on value added is positive only in the case of one NFC production route.
The application of NFC in wet-laid non-woven seems to bring cost savings and has a positive impact on product profitability when compared to the reference product. The cost savings in raw material costs could provide opportunities for entering new market areas. The replacement of part of the binder and fibre by NFC has a positive impact on value added when looking at the total sum of direct changes in the application and indirect changes in the suppliers' business. The total impact on employment is negative. A lower need for raw material leads to a lower environmental burden. The common weakness of both the applications is that the occupational risks related to nano-sized fibres are not yet well known, but this is something that will improve as the research proceeds. A risk-related threat from both applications is that, if the safety issues related to nanomaterials are miscommunicated, it can cause major problems. The production of NFC and its application to paper industry products is a young field of research. More investigation is needed and the sustainability aspect should guide the development. The indicators studied in this assessment could be improved by further work on NFC production and application technologies. It seems evident that nanocellulose will be added in the future, not only in special products for niche markets, but widely in different kinds of packaging paper and board products with high production volumes. More product development work in the area of using NFC to increase strength in bulk structures or create novel functionalities with surface treatments is still needed. The important impact of the project on the scientific community was the high number of publications and dissemination activities that have increased the knowledge of the possibilities and challenges in this area. The development of research facilities carried out in the project or in parallel projects will improve the possibilities to continue the work in the future.
The general framework of the collective dissemination plan can be divided into three groups: a first one, including the set up of the project website and all periodic activities planned from the beginning; a second one, concerning all activities developed during the project and a third one, composed of those activities that were planned but will be implemented after the end of the project, as dictated by the IPR rules agreed among partners. The project website was established and managed by the project coordinator (see http://sunpap.vtt.fi for details). The open access project website was the major channel for advertising events and communicating news and public deliverables, including all lectures given in the two open conferences. It contains links to project partners' websites, as well as a link to confidential material for project partners. The Doha system provided by the project coordinator through the VTT extranet has been widely used by the project partnership for internal communication and for exchanging all the documents developed throughout the project. Common rules for project work were collected in the project manual for internal communication and the agreed rules for making publications and managing foreground were summarised in the intellectual property reights (IPR) management procedures, for appropriate management of the project. The newsletters (see http://sunpap.vtt.fi/publications.htm online) were published on the project website every six months and provided a fast and simple up-to-date means of communication of the most relevant public results.
The first open workshop was organised in Espoo, Finland. The main focus was on the laboratory work carried out in the project. The event had a total of 77 participants, mainly from research organisations and universities from Scandinavia and central Europe. The second event was held in Milan, Italy. There were 81 participants, with industry covering almost 50 % of the audience and significantly more participants from southern Europe. The main focus was on pilot-scale work and demonstrations. The conference was attended by non-European industrial representatives from Japan and Brazil. The programmes and materials can be found on http://sunpap.vtt.fi/events.htm Seven scientific peer-reviewed publications are published and two more have been submitted and accepted to be published soon. Project partners were involved in 40 other dissemination activities. Almost 80 oral presentations or posters were disseminated in workshops and conferences where both the scientific community and industry had representatives.
Exploitation results:
Project results can be widely used in the paper, board, and packaging industry
The use of NFC as an additive in inkjet coating colours showed promising results. The use of NFC in coating colours in order to increase the speed on production lines can be started as soon as suitable NFC quality is on the market. The main impact is better competitiveness with lower environmental impacts. The use of NFC in wet-end applications and in coating applications to produce lean non-woven structures has high potential in niche products. The main impact is lean materials with better competitiveness and lower environmental impacts. The results of the use of NFC in a board bulk structure on a laboratory scale have shown similar potential to those in non-woven applications and these can be widely applied in packaging board applications. The main impact is lean materials with better competitiveness and lower environmental impacts. The results regarding barrier properties, carried out as postgraduate work showed good potential for the use of NFC as an additive in barrier coating and these results can be exploited not only for board materials but for any paper barrier packaging materials. The main impact is lean barrier materials with better competitiveness and lower environmental impacts.
Further product development is needed to fine-tune the multilayer structures for different packaging applications. Foam-coating formulation and process results show high potential for the production of thin layers from nanomaterial, making novel products possible in the future. In this area, more work is needed on both product development and scaling up the running speed. The main impact is lean novel products with better competitiveness and added value. The developed methodology concerning health and safety aspects can be used as background material for the future targets aiming to homogenise and update the current standards in the toxicity-testing field. The safety results will be used in databases, making them available as a solid basis for recommendations and contributing to answering the questions and needs for national regulation and legislation authorities.
Project website: http://sunpap.vtt.fi
Dr Ulla Forsstrom
ulla.forsstrom@vtt.fi via e-mail.
There are possibilities to use NFC as a rheology modifier or to improve critical product properties. NFC can give a good grease barrier in multilayer barrier products and can replace partly non-renewable materials. The drying quality of the dispersion coating layer was improved with the use of NFC. As the second-layer barrier, latex or extrusion coating with PE further improved the barrier properties when coated on top of the polyvinyl alcohol and NFC layer. Novel products with active properties are possible with functionalised NFCs. High antibacterial activity of papers could be achieved with thin layers of NFC-TiO2 or ZnO. NFC-TiO2 has significant activity for the oxidation of NO and NOx with low coat weights. Thin layers can be applied with the novel foam applicator installed by VTT on a pilot scale. NFC containing aggregates gave, in most cases, results as good as those from fine NFC. Sustainability assessment showed that the changes in environmental impacts for the pigment coating case were negligible, due to small amounts used. For the bulk structures the trend was positive and radically lower environmental impacts were achieved when the use of NFC enabled lower basis weight due to higher strength. The presence of NFC in demonstrators did not induce large changes in recycling / de-inking. The tested coated board products, including NFC in the coating layer, passed the biodegradability tests and their compostability was confirmed. NFCs are viscous gel-type materials and are used mainly in wet form. The toxicological studies in vitro and in vivo did not indicate any major concerns, except for occupational inhalatory exposure, which can be managed by standard protective measures. NFCs seem to be biodegradable and non-toxic and no big changes in safety or recycling of products containing NFC are expected in the future.
Project context and objectives
The SUNPAP project addressed the competitiveness of the European paper industry by means of nanocellulose-based processes to provide radical product performance improvements, new efficient manufacturing methods and the introduction of new added value functionalities. NFC is the most promising nanomaterial for wide-variety applications in papermaking. When the project was started, NFC was mainly prepared and applied on a lab scale. The target of the project was to scale up the NFC production processes and to adapt this nanomaterial for modern papermaking processes via the demonstrated pilot lines. The scientific work was divided into four research modules which have strong synergy and were well integrated within each other.
The main practical targets of the project are:
- development and up-scaling of novel processes for the energy-efficient production of nanomaterials, namely NFC, on a pilot scale (in module NFC production);
- development and up-scaling of NFC modification processes to address the challenges of papermaking and to provide added value active functionalities (in module NFC processing);
- building and demonstration of pilot lines to alleviate take-up of nanotechnologies, both for the production and the utilisation of NFC, to the modern papermaking processes (in modules NFC production and processing);
- exploitation of innovative sustainable solutions for the whole paper industry value chain by integrated sustainability assessment approaches based on economic, social, and EIAs (in module value chain);
- risk assessments to guarantee the safe introduction of nanotechnologies in the whole value chain of conventional industrial paper production processes and final paper based products (in module health and safety).
The final goal was to enable the introduction of NFC-based processes in various types of applications in the papermaking value chain and the main aims were to develop and demonstrate:
1. high-performance products and environmentally friendly NFC-enabled production processes, demonstrated for graphical papers and packaging boards;
2. functional products and innovative processes enabled by NFC with active functionalities, demonstrated for papers and packaging materials;
3. high-added value fibre-based products with highly specific properties made possible by NFC, demonstrated for fibre-based filters and other selected innovative materials.
The first main target was studied in NFC production and the research work was focused on the material development; NFC production and modification processes and optimising the processes for the up-scaling of NFC production. The activities were directed towards the three main technical challenges of the project, energy-efficient NFC production, and high quantities of NFC and control of NFC suspension rheology. The purpose of module 2 was to produce various types of native and modified NFC batches, which were used in module 3 for the product demonstrations. The main objectives of module NFC production were preparation of NFC from cost-competitive pulp raw materials, development of process concepts for cost-efficient preparation of NFC on a pilot scale, preparation of user-friendly NFC for different kinds of papermaking processes and production of NFC with active properties on a pilot scale for added value paper products. The second main target was studied in NFC processing, which developed the NFC-enabled process and product concepts and finally produced demonstrations of the developed concepts. The proper industry steering was realised by active participation of the industry partners already in the main research tasks. The focus of WP7 was to provide theoretical tools for the optimisation of the rheology of the NFC suspensions.
The overall objectives of module NFC processing were control of reactions and conditions of NFC in wet-end and coating processes, development and design of NFC-enabled product concepts to use the full potential of NFC, in terms of its dimension, optical, strength, specific surface area, and functional properties, prediction of optimal NFC-based process operation parameters by simulation of rheology of suspensions and coatings that include NFC as a main component and demonstrations of the concepts for three selected end-use areas. The fourth main target was studied in the value chain, which was focused on the generation of a holistic view of the value network of the NFC-based processes and products, ranging from raw materials to the end of life of the products, in order to design the demonstrated product concepts for the market areas with the best potential. This module contained three WPs, which were all essential when evaluating the possible success of the NFC product value chain, starting from raw materials and production and ending up at recycling and end-of-life assessment. Here WP1 concentrated on evaluating the financial grounds and means for producing NFC by combining market analysis with production prospects. WP2 determined the sustainability of potential NFC value chains and analysed effects of new products on social, economic and environmental areas. WP3 focused on recyclability and biodegradability issues regarding NFC. This included analysis of both eco-toxicological impacts and biodegradation of new functional materials. An important role of the WPs was the communication with other partners and the delivery of the results to WP10: Risk assessment.
The aims of the module value chain were:
1. assessment of economic grounds for production of NFC-based products and a determination of the most beneficial applications and market areas;
2. evaluation of the economy of the value chain; assessment of profitability for chosen products and determining the most promising value chains for production, taking into account current and emerging market needs;
3. guidance and support for the focus of the project in a sustainable direction, by evaluating sustainability aspects of the developed processes and value added paper products throughout the whole value chain, from raw materials to end-of-life analysis.
The fifth main target was studied in health and safety, which evaluated the toxicity of the nanomaterial used in the project and performed risk assessments in order to provide information about possible obstacles to market access and industrial take-up of the project results. This module contained two WPs. WP9 was devoted to test nanocellulose and functional nanocellulose (NFC and FNFC), and WP10 to do the risk assessment based on the available information and the results supplied by WP1: Market needs, WP2: Sustainability assessments, WP3: Recyclability and biodegradability, WP9: Toxicity and other parts of the project. The aims of the module health and safety were the generation of exposure models for in vitro and in vivo studies, research of the bioactivities of the NFC and functionalised NFC at cellular level, research of systemic toxicity of the NFC and functionalised NFC in in vivo trials, creation of an overall understanding of the environmental, health and safety risks related to the raw materials and products developed and guidance for other parts of the project, to develop low-risk products by serving as an information source
Project results
Material and process studies were made in order to deliver different NFC qualities for application development. Application studies were first carried out on a laboratory scale and continued as product and process studies on a larger scale for final demonstrations. Commercial microcellulose or micro fibrillated cellulose (MFC, Arbocel), which is a coarser material than NFC, was used in some cases as a reference material or when the suitability of test procedures was assessed. The sustainability assessment of the value chains and the risk assessment of the novel processes and products were studied throughout the project.
NFC production (module 2) - process and material development
The main objective of WP4 was to develop concepts for energy-efficient preparation of NFC on a pilot scale and to identify optimal pulp raw materials for NFC preparation. Both targets were the keys to producing cost-efficient NFC. An essential part of WP4 was to deliver NFC samples to other partners for other research tasks. These objectives were considered by taking into account different chemical and enzymatic pre-treatment methods and the influence of pulp composition on NFC fabrication. The results were transferred to different kinds of homogenisation techniques, both in industrially available facilities for the production of micro fibrillated celluloses and pilot-scale rotor-stator-machines and high-pressure homogenisers were used in the experiments.
It was seen that two different routes of the pulp pre-treatments have the highest potential to reduce the energy consumption of NFC production:
1. combining mechanical refining and enzymatic pre-treatment before homogenisation, which, after homogenisation, led to gel-type NFC, containing mainly aggregates of microfibrils;
2. pre-treatment of pulp fibres by means of oxidative chemicals (TEMPO) without intensive mechanical refining before pre-treatment, which after homogenisation led to transparent gels with individual nanofibrils.
Especially in the preparation of NFC-based on enzymatic pre-treatment, the energy consumption in the refining stages varied depending on the used pulp raw material. It was concluded that all commercial pulps can be used, but dissolving pulps were best because of their low refining resistance in the refining stages and their sensitive reaction towards the enzymes. No mechanical refining before the final homogenisation was necessary in the production of NFC with oxidative pre-treatment of the pulps (TEMPO). Even fewer passes at high pressure could be realised because after two passes, the pulps were completely homogenised. The optimisation of the TEMPO oxidation conditions for pilot studies was performed using a design of experiment methodology by means of a composite central design (CCD) on a small scale. The optimisation was based on minimising time and chemical additions in order to maximise the yield, fines content, and number of carboxyl groups. This NFC, produced with low energy consumption using TEMPO oxidation, showed a remarkably lower viscosity than the reference materials, which were the target in WP5. The most suitable high-pressure homogenisers and a rotor- / stator-machine were selected to produce NFC on a pilot scale for other project partners. The high-pressure homogenisers were bought and the pilot line was built at CTP in parallel with this project. The geometries of the tools from the rotor- / stator-machine were completely re-engineered to produce NFC products using a technique not used before at PTS.
In total, more than 100 kg of NFC was produced for other partners:
1. NFC-CTP = enzymatically pre-treated pulp combined with mechanical refining followed by high pressure homogeniser;
2. NFC-TE/CTP = TEMPO-oxidised pre-treated pulp followed by high pressure homogeniser;
3. NFC-TE/PTS = TEMPO-oxidised pre-treated pulp followed by rotor- / stator-machine.
TEMPO pictures showed that an enzymatically pre-treated and homogenised sample (NFC-CTP) was mainly aggregated microfibrils with only partly a nanostructure; NFC with TEMPO oxidation and a homogenised sample (NFC-TE/CTP) contained mainly nanofibrils and NFC with TEMPO oxidation and rotor-stator treatment (NFC-TE/PTS) cut the fibres resulting in short but thick macrofibrils. It was possible to produce different kinds of NFC structures, but it was still hard and time consuming to analyse the NFC properties. For this reason, fractionation tools were developed to reveal more about what is inside NFC samples and NFC quality assurance tools were investigated to establish protocols for reliable quality testing in the production of NFC. In order to characterise the different NFC qualities, a complex fractionation system at VTT was established where the sizes of different fractions could be measured and analysed. Most parts of all produced NFC qualities were in the range of > 0.1 μm. The fractions > 1 μm probably contain mainly aggregates and therefore they do not go through the wide slots. The fraction < 0.1 μm contained mainly dissolved solids. The main objective of WP5 was the development of NFC modification processes to impart innovative functionalities to NFC. The functionalisation of NFC was carried out to achieve development of hydrophobic NFC suspensions with a controlled viscosity profile suitable for the applications in paper production processes and development of NFC with active properties for special paper applications.
NFC surface energy modification to impart hydrophobic properties: Different approaches were applied such as physical adsorption of polymers on the NFC surface and chemical modifications of NFC. Chemical grafting of hydrophobic moieties was studied in organic as well as aqueous media.
Physical adsorption of polymers on the NFC surface: Industrial copolymers, polyvinyl alcohols (PVA), were used for the NFC modifications. Physical adsorption of polyvinyl alcohol on NFC resulted to be a relatively simple method of modifying the NFC viscosity. The addition of polyvinyl alcohol significantly decreased the NFC suspension shear viscosity and the modification did not depend on the different polyvinyl alcohol grades. The effects on suspension viscosity were slow and the studies were carried out on a laboratory scale. By adding polyvinyl alcohol, a significant increase in NFC suspension concentration could be reached without viscosity increasing.
An interesting route for NFC chemical grafting was the nano-emulsion approach, where nano-emulsions containing AKD were produced and mixed with NFC suspension. After removal of the CHCl3 solvent, the NFC-AKD suspension was ready for chemical grafting obtained after the drying process. The activation step can be alternatively performed before application to paper, to obtain a dry NFC-AKD re-dispersible additive or in the paper production process when the paper web is dried. Based on the laboratory work, NFC-AKD suspension displays a significant reduction of viscosity in coating colour formulations with respect to non-modified NFC. Active Innovative inorganic nanoparticles / NFC hybrid systems were developed and the selected NFC functionalisation was obtained by the addition of inorganic nanoparticles. Two main routes were followed: polyelectrolyte assembly and direct physical adsorption. NFC-Ag and NFC-ZnO Nano-composites were obtained by electrostatic assembly of inorganic nanoparticles (Ag and ZnO) on the NFC surface. Different polyelectrolytes were investigated as macromolecular linkers between inorganic fillers and NFC. These nano-composites were applied on paper by coating. The obtained nano-composites and coated paper, showed significant antibacterial activity. NFC-ZnO and NFC-TiO2 nano-composites were prepared by physical adsorption, by mixing NFC and inorganic nanoparticle suspensions. The nano-composites showed strong antibacterial activity, with respect to gram-positive bacteria: Staphylococcus aureus and Bacillus cereus spores and gram-negative Klebsiella pneumonia.
NFC processing (module 3) applications, modelling and demonstrations
The main objective of WP6 was to develop and design NFC-enabled product concepts to utilise the full potential of NFC in both coating and wet-end processes. We aimed to master the composition of coating colours for conventional and advanced coating processes in pilot studies. The target of the wet-end lab studies was to control reactions and conditions of NFC wet-end processes application and to optimise and scale up the NFC application processes from hand sheets to pilot scale for the application of native and functionalised NFCs to value chains. Several lab studies using NFC as a replacement for latex or other co-binders in different types of surface treatments were carried out with various natural NFC and modified or functionalised NFC samples. Surface strength and mottling are critical factors in the conventional pigment coatings. The main findings from NFC in conventional pigment coating were increased viscosity of the coating colours, porosity of the filter cake and porosities of the coating layers when NFC was added to the coating colours and decreased gloss of the coated products. Removal of viscosity modifiers widened the operational window. The surface strength results obtained were inconsistent and partly poor, probably due to the low speed. NFC can be used to improve the barrier properties of the packaging materials. The conclusions of the introduced NFC in a plasticised starch matrix are strong improvement of barrier properties (WVTR), and a positive effect was expected for OTR with no degradation of mechanical properties. The cooking of starch matrix directly in NFC suspensions at 95 degrees Celsius did not have any significant impact on NFC properties and is a good choice for preparing NFC-based coating colours. The study of modified NFC showed that modifications are interesting techniques to reduce the viscosity of NFC suspensions by decreasing interactions between fibrils. The coating colours produced with modified NFC had lower viscosities than colours made with unmodified NFC.
This was an important result because this improved a lot of the processability of NFC-based barrier coating colours, while keeping the same barrier properties. The use of NFCs had a big drawback: their high viscosity at low solids led to formulations with low solid content. Only small amounts of NFC could be introduced. Thin layers of cellulose nanofibrils could be applied on the surface by using a novel foam-coating applicator. The use of air instead of water makes the application of viscous cellulose nanofibril solutions possible. The main focus was on the characterisation of foam and foam-coating trial procedures in order to scale up the use of NFC in the foam-coating process. The stability of the foam is an important foam property, besides the bubble size and bubble size distribution. The best indicator for stability was the back pressure value measured by the foam generator. The main part of the work concentrated on solving technical questions in scaling up the foam-coating application. Using infrared driers instantly after the applicator and the new backing roll for the pilot coating line improved coating quality. The mixing head with fewer pins made a higher solid content of NFC possible, which made higher coat weights possible. Differences in contact angle, air permeability, roughness, and microbiological influence between different natural and modified / functionalised NFCs were noticed. The foam-coating process is a suitable method for the application of NFC on the fibre-based substrates. The highest speed with the current pilot configuration was 300 m/min and with higher speeds an extra air removal device is needed. The solid content of NFC is critical and is low, but it is higher than can be used in spray coating. NFC quality is important; big particles / aggregates can block the applicator. VTT has this technology available for paper and board coating studies on a pilot scale.
It can be used for the application of any novel materials giving special functionalities to products with small addition levels. Lab studies to use NFC as an additive in order to improve strength in the wet-end were carried out. The retention evaluation showed that is necessary to use retention aids to retain the NFC. Retention of NFC in the paper sheet depends strongly on the pulp and retention aid used and on the basis weight. NFC leads to a significantly increased dewatering resistance of hardwood chemical pulp. This negative impact could be reduced by using cationic additives. Especially for softwood chemical pulp and CTMP, the loss in dewatering speed was lower compared to hardwood. Retention aids and special starch products can enhance the dewatering speed when using NFC and NFC is generally capable of improving the paper strength significantly. Especially for the paper board, opportunities based on the small-scale pilot results exist for using the increase in strength to save fibre raw materials. NFC in the outer layers can significantly contribute to the stiffness of paper board. At lower dosages, the loss in bulk could be compensated by an increase in E-modulus. There are opportunities to produce CTMP to a lower SR with higher bulk. The reduced delaminating could be compensated by NFC, while the bending stiffness can be improved.
WP7 had two main objectives: prediction of nonlinear dynamic material interactions in suspensions for varied process conditions, with atomistic models and simulation of rheology of suspensions and coatings, including NFC with continuum level models. Atomistic models were used as qualitative input to the continuum level models. The studies increased scientific understanding of the related phenomena in the characterisation of NFC. The molecular dynamics simulations were carried out to obtain information on the mutual interaction between cellulose fibrils and on the interaction between cellulose fibrils and a calcium carbonate surface. The context was to obtain parameters for the aggregation model. The main finding from the atom-scale molecular dynamics simulations was that pushing crystalline cellulose fibrils towards a calcium carbonate surface led to repulsion, due to a water layer stuck in between two hydrophilic surfaces. There was strong binding between cellulose and calcium carbonate in simulations with an initial structure chosen so that a cellulose fibril was attached to a calcium carbonate surface without a water layer in between. Pulling the cellulose fibril apart from this initial configuration led to disintegration of the fibril instead of simple desorption. For cellulose-cellulose interaction, the situation was similar. The amorphous coverage of the fibrils was important in the binding of the fibrils together. In the aggregation model, the mixing of NFC and calcium carbonate particles with varying particle sizes has been studied.
The model was prepared in the spirit of the Smoluchowski mass balance equations, extending it to allow for interactions between different species of aggregates. The model was applied to study a calcium carbonate NFC mixture suspension. The main finding was that the NFC aspect ratio had a crucial role in the mixing of the two phases, having impact on the amount of excess calcium carbonate. The mass ratio between the different species affected the mixing efficiency and dynamics. The interactions of the carboxylated fibril with non-modified nanocellulose structures were found to have two distinguishable forms: a strong electrostatic repulsion due to a large negative surface charge and weak attractive interaction due to forming dynamic hydrogen bonds. The hydrogen bond formation mostly involves the fibrils corners, probably due to the electrostatics geometry and water structuring and screening effects and is not related to the presence of unmodified groups in some corner chains. The interactions between two unmodified fibrils led to stronger hydrogen bonds and aggregation. Two carboxylated fibrils are immediately and powerfully repelled from each other. The carboxylation prevents fibrils from aggregating into larger forms as has been clarified at the molecular level. Main findings described the influence of shear transients and shear localisation on the rheometer reported as viscosity commonly used to characterise suspensions to help the design of the pilot-scale application of new materials.
The characterisation of the NFC on the basis of viscosity can give results that are misleading if not carefully analysed. With this material, there is no standard rheological characterisation. Viscosity is not unique for such a complex material. This is due to the fact that the Newtonian assumption of stress and shear rate relation contains extra components that are not purely viscous. The model was fitted at qualitative level to experimental rheological data. The fitting was used to simulate the occurrence of shear banding in rotating cylinder geometry. The reported NFC suspension experiments were performed in parallel rotating plate geometry. Similar phenomena can be expected to appear in that case since the shear and stress distributions are more heterogeneous for that particular geometry. It was shown that the perfect power-law scaling observed in the TEMPO-oxidised NFC flow curve is possibly a sign of shear banding.
The suspension viscoelasticity plays an important role in the case of enzymatically pre-treated NFC. Using a viscoelastic Maxwell model, transient effects were observed. The model demonstrated that such transients are measurable only for suspensions with small elastic modulus. With higher elastic modulus, transients are so fast that they will disappear due to the slower settling time of the rheometers. This is reasonable to assume, as the NFC flocks formed of longer fibres in the enzymatically pre-treated case can be assumed to have lower elastic modulus compared to the more compact ones formed of shorter fibres, in the TEMPO-oxidised case. Considering the model response to a decreasing shear ramp, it can be seen as an implication of what happens during a papermaking process. When the wet web is formed, there is a decreasing relative velocity difference between the fluid and the wire, implying a shear gradient decreasing in time. The picture that emerges from the simulations is that the flock formation of the TEMPO-oxidised NFC requires such a long time that no noticeable aggregation can be observed. This is promising for shear bands and other phenomena, which are absent in the dispersed phase, as the relative viscosity differences in this state are small.
Three NFCs were selected to be produced on a large-scale and were used on a pilot scale for the manufacturing of the WP8 demonstrations. The NFCs used were named as NFC-CTP, NFC-TE/CTP and NFC-TE/PTS. Several demonstrators were studied.
Examples are:
- demo 1: conventional coating on board;
- demo 3: coating for inkjet paper based on curtain coating;
- demo 4: foam coating with functionalised NFC;
- demo 5: conventional coating for barrier packaging.
Demo 1: Conventional coating on board
Three NFC grades of the project were tested to see the effect of scaling-up on the behaviour of these NFCs in the pigment coating colours, as partly replacing latex binder. The coating trial was conducted on the KCL pilot coating machine and in conventional technology, a bent blade with jet-applicator was used as a coating head. The results from the KCL pilot plant imply that most of the coated board and printing properties with the coatings containing NFC were close to those of the reference coatings with latex. Because of the big decrease of the coating colour solids, it was concluded to be difficult to get benefits from replacing just part of the latex with NFC. In the continuation tests in Stora Enso's pilot plant, the initial target was fine-tuned. Due to limits of time and material, it was not possible to do industrial conversion to cartons. Some unprinted material was made into small boxes in the lab and showed good convertibility. No major benefits were gained in these trials via NFC in coating colour. There could be some possibilities to improve the bending stiffness of the board by using NFC in surface sizing. In such a case, one can expect clearly increased drying demand.
Demo 3: Curtain coating for inkjet paper
In order to fulfil the market needs in terms of production output for inkjet photo papers, paper manufacturers can either invest in new plants or enhance the productivity of existing machines. The production speed of coated inkjet photo paper is limited by cracking during drying of the coating layer. The cohesion strength between the nano-pigments and the binder competes with the retraction force of the binder during drying. The fibre network of the NFC was assumed to counteract the forces and thus reduce cracking of the coating layer. Inkjet photo paper was coated on a pilot coater at Schoeller Technocell using curtain coating technology, which is comparable to the industrial production machines in the company. Two samples were produced, one reference sample without NFC and another one containing 0.06 % NFC in the coating layer. The use of NFC in the coating had a positive impact on paper quality and production efficiency. The quality was on the same level when printed with pigmented inks or even improved when printed with a dye-based ink printer. Especially water fastness, absorption bronzing and brittleness are better with NFC if dye-based inks are used. Besides the beneficial paper quality improvements, the production speed could be increased by adding NFC to the coating colour. The cracking level was lower with 0.06 % NFC in the coating colours, which is equivalent to a potential for a coating speed increase estimated to be 5-10 %.
Demo 4: Foam coating with functionalised NFC
Thin layers of cellulose nanofibrils can be applied on the surface by using a novel foam-coating applicator in the KCL pilot coater. The applied amounts are smaller than in conventional coating. The influences of thin layers on the fine paper surface with unmodified NFC increased hydrophilicity and reduced air permeability and small scale roughness (PPS S10), resulting in glossier and smoother surfaces. By using NFCs functionalised with inorganic particles, it is possible to create novel activities to paper surface even with low coat weights. These foam-coating trials were carried out at Zimmer with a new coating head, making even higher coat weights possible. High antibacterial activity of papers could be achieved with thin layers of NFC-TiO2 and/or ZnO under both light and dark conditions. NFC-TiO2 has significant activity for the oxidation of NO and NOx in low coat weights.
Demo 5: Conventional coating for barrier packaging
Barrier coatings were continued on a pilot scale. The baseboard was coated on CTP's pilot coater. Coating layers of 10 g/m2 containing mainly polyvinyl alcohol with five parts of NFC in the matrix were applied with a SoftTip blade at a speed of 70 m/min in order to get the gas and grease resistant layer. The reels produced were divided into two parts. One reel was sent to Stora Enso in order to perform the PE extrusion. The second reel was coated once again in the CTP's pilot coater: a 6 g/m2 layer of commercial barrier latex was applied to impart the water resistance. Due to the narrow width of the reels, LDPE extrusion coating was done at Tampere Technical University. A relatively high amount of LDPE coating was used because good hot-sealing properties were targeted. The boards from the final coating trials were converted into small packages. Oxygen barrier measurements were carried out with Oxtran 2/21 (Mocon) apparatus (ASTM D-3985) at higher moisture content. Higher moisture conditions were considered relevant because NFC as a hydrophilic material should absorb moisture and give higher oxygen penetration. The grease barrier was tested using a modified ASTM F119-82 method. Because some barrier films tend to fracture in the conversion, testing was done for a creased sample. There was a target to see if creasing defects would be reduced with the help of PE coating, and samples were PE coated for this reason. PE coating was done on both sides, in order to get a more realistic structure for oxygen-tight packages.
There were large variations in the oxygen barrier results. This was caused by pinholes in the coating layer. Pinholes could be a major problem in higher-speed machines because faster drying is needed. The moisture sensitivity of the coating layer will have an effect. The measurements were made at 50 %. The barrier latex gave a clear improvement when coated on top of the polyvinyl alcohol and NFC layer. The best results were obtained when the polyvinyl alcohol and NFC layer was coated with PE. NFC can give a good grease barrier. Pinholes are a potential problem here. Adding the barrier latex gave good grease resistance in no creased samples but not in creased samples. The PE-coated samples had good grease barrier properties after creasing.
Value chain (module 1), market needs, sustainability, recyclability and biodegradability evaluations
WP1. Market needs
The aim of WP1 was to analyse where, when, and how nanocellulose could be used in selected paper and paperboard end-uses. The tasks included both market and technical feasibility assessments of the products developed. The impact on European competitiveness was evaluated. The work was divided into three different tasks: market assessments, feasibility analyses and evaluation of the impact on Europeans competitiveness. Market assessment was started by mapping and evaluating the market growth potential of paper, paperboard and non-woven end-uses. Future consumer needs were researched to distinguish trends and development drivers. The findings of the analysis were compared with properties that nanocellulose was believed to have. Future key end-use properties were extracted and a nanocellulose opportunity tree for paper and paperboard products could be drawn. The findings showed that there are several potential application areas where nanocellulose could be used. The demand for various carton board products is anticipated to grow significantly. Nanocellulose (NFC) could turn out to be beneficial due to its lightweight but interesting strength and barrier properties.
NFC offers possibilities to improve current products on the market and makes it possible to develop completely new types of value added niche products fitting into all product groups in this study. Feasibility analyses were conducted to evaluate the most promising process routes and applications developed. Several routes were screened during the first phases and three routes were qualified and evaluated. The production concepts in the three routes were different. The results showed that the feasibility of the different routes is different. The main difference was that the chemical costs of the chemically pre-treated NFCs outweighed the higher electricity and capital costs of the enzymatically pre-treated NFC. The target in evaluation of the impact on European competitiveness was to analyse the foreseeable impact that nanocellulose could have on European competitiveness. The target was to identify how results could be used and what the links to other European-level research projects were. The results showed that, for European competitiveness, nanocellulose is one part of the solution. It combined a possibility for global leadership, a renewable raw material basis, synergy across sectors and solutions to challenges facing society, while relying on conventionally globally competitive European industries. In nanocellulose, companies can fill certain niches, EU policies populate others and joint efforts fill in the final missing components for the greatest competitive impact to be realised in a never before seen bio-based ecosystem.
WP2. Sustainability assessments
The objectives were to define the framework and indicators for assessing the sustainability of nanotechnology applications in the paper industry, guide and support the focus of the project in a sustainable direction and to demonstrate sustainability aspects of the developed processes and value added paper products. Two sustainability evaluations were carried out. A first-phase evaluation was carried out at the beginning of the project. During this phase, all potential applications were evaluated by screening. During a second phase, a more detailed approach for selected applications was carried out, which represented the final and complete sustainability assessment. During this evaluation, all three pillars of sustainability were included: economic, environmental and social sustainability. Economic assessment focused on private costs, the bottom line in NFC manufacturing and applications. The socioeconomic impacts included evaluation of suppliers in the supply chain. The social assessment included analyses on the working conditions of NFC manufacturing and application. The consumer's point of view was included, relating to acceptance of nanotechnology.
For the environmental assessment, carbon footprint, acidification and eutrophication potential and fossil resource depletion were selected as indicators, as the data sets were comprehensive for these impact categories. The carbon footprint can be considered to be the most important indicator because one of the constraints of NFC manufacturing is the high energy consumption. A water balance was calculated for the NFC processes as background information for possible future water footprint calculations. The impact of NFC on the product's end of life was speculated. Results from research on recyclability and biodegradability were presented. A four-stage approach was used in the LCA analysis. NFC was produced by modifying dissolving sulphite pulp by chemimechanical means from Domsjo pulp mill in Sweden. Three different preparation methods were used at CTP and PTS. The environmental impacts were calculated based on expert estimations and theoretical data. The environmental impacts for the applications with NFC were calculated for SBS board using NFC in the coating to replace partly latex and for wet-laid non-woven to reduce the basis weight by a small addition of NFC. For the SBS case, the changes in environmental impacts were negligible due to the small amounts replaced in coating. For the wet-laid non-woven, the trend was positive. The use of NFC enabled a lower basis weight and led to more than a 30 % lower environmental impact. The social and economic effects of the application cases varied. The gross value added was positive for the wet-laid non-woven case. In the coated board case, the value added was positive with one NFC production route and negative with the other two. Employment effects were found to be positive in the coated board case and negative in the non-woven case.
WP3 Recyclability and biodegradability evaluations were carried out partly on small-scale samples and partly with the larger amounts received from the demonstration trials.
Recyclability of packaging and de-inkability of graphic papers were carried out. Two types of paper products from WP6 were tested in terms of recycling / de-inkability on a lab scale: introduction of NFCs by foam coating for inkjet printing and partial substitution of latex by MFC in the coating layer for LWC products. It appears that the introduction of NFC in paper products did not modify to a large extent the recyclability / de-inkability compared to the same product made without NFC. De-inking of the inkjet prints was not improved and LWC samples printed with heatset were fully de-inkable. The mechanical properties of the recycled pulp were not modified compared to the reference. In the case of the introduction of NFC by foam coating for inkjet printing, anionic surfactant was required for foam coating, which induced some drawbacks during de-inking even if a slight ink removal improvement was observed. Whatever the nature of the NFC introduced, pigmented inkjet prints could not be considered as de-inkable even if modification of the nature of the NFC could induce some slight improvement in ink removal. The presence of the TEMPO pre-treated NFC led to a change in surface chemistry of the NFC, leading to a more hydrophilic character of the NFC. Besides, this surface chemistry change also induced an increase in the potential risk of paper machine plugging and a slight increase in cationic demand, meaning higher chemical consumption in the wet-end of the paper machine.
In the case of LWC paper printed with heatset offset technology, the partial substitution of latex by MFC and the removal of CMC in the coating layer did not change de-inkability and the risk of deposit on the paper machine wire. The main difference observed corresponded to the nature of MFC: undried MFC led to faster kinetic of flotation, due to a difference in resistive strength of the coating layer, but did not modify the flotation selectivity. For the final tests, three demonstrators were selected, considering only products that will be collected and recycled.
During these tests, special attention was paid to the behaviour of the overall recycling/de-inking line and to the final recycled/de-inked pulp quality:
1. Demo 1 (conventional coating on board): recycling on a pilot scale;
2. Demo 2 (conventional coating on paper LWC): de-inkability on lab and pilot scale in paper for a recycling mixture encountered in wood-containing de-inking lines producing newsprint, SC or LWC papers;
3. Demo 5 (barrier packaging): recyclability on a lab scale.
The presence of NFC in these demonstrators does not induce large changes in recycling/de-inking. The presence of NFC pre-treated by TEMPO enabled a reduction of the resistive strength of the coating layer during re-slushing, leading to smaller mineral filler flakes. This opened energy saving during pulping and deflaking, higher mineral filler content in the de-inked pulp and better cleanliness of the pulp. The possible negative impact seen on was confirmed in large-scale tests with NFC pre-treated by TEMPO. NFCs produced in WP5 were investigated in regards to their biodegradability in an aqueous medium. Standardised methods from ISO, EN and OECD were used. The results showed that the intrinsic biodegradability of cellulose was not modified for most of the functionalised NFC analysed. The 90 % biodegradation limit to claim biodegradability of materials was easily reached within a feasible timeframe. The NFCs used for demonstration of SUNPAP corresponded to biodegradable products in an aqueous medium. Coated paperboards from WP6 were analysed, especially products coated with unmodified NFC and functionalised NFC. The ultimate biodegradability under controlled composting conditions was demonstrated with a biodegradability reaching the 90 % limit within 60-70 days. Two of the demonstrations from WP8 were then analysed to determine if they met the requirements for certification of compostability: ultimate biodegradability in compost, disintegration of the samples and ecotoxicity from compost after disintegration. The different coated papers including NFC products did not have a negative impact on the good biodegradability of paper and board in a compost environment. To complete this assessment, disintegration in compost was tested and the quality of the obtained final compost was analysed as well as the absence of any ecotoxicity effect in respect of seed germination and plant growth. The tested paperboard products passed the different tests and their compostability was confirmed.
Health and safety (module 4) - Toxicity and risk assessment
WP9. Toxicity
Originally, WP9 involved three tasks: characterisation of aerosols and liquid dispersion of NFC and FNFC, elucidation of the effects of NFC and FNFC at cellular level and systemic effects of NFC and FNFC in vivo. During the project, the material characterisation was done in WP4. The work in WP9 was done according to the hazard analysis outlined in WP10. The focus was on the in vitro toxicity and the cellular effects of NFCs. The toxicity was assessed using cytotoxicity assays, which measure the harmful effects of the test materials on cultured mammalian cells, immunotoxicity assays, which give an indication of the potential of the test materials to interfere with the basic immunological phenomena and genotoxicity tests, which detect harmful effects on the DNA or chromosomes. Commercial MFC (Arbocel) was used as a reference material with some of the assays when the suitability of test procedures was assessed. The actual test materials used for in vitro studies included NFC samples prepared with and without enzymatic pre-treatment or with TEMPO oxidation before homogenisation. None of these materials was harmful to exposed cells, indicating a lack of cytotoxicity. In the immunotoxicity assays, there were some marginal indications of inflammatory response in human peripheral lymphocytes, but only when the cells had been exposed to bacterial lipopolysaccharide (LPS) before treatment with NFCs. LPS is a potent immunotoxic agent and the results indicate that although the NFCs are not likely to induce inflammatory responses by themselves, they could have synergistic effects with the microbial contamination in NFCs. In genotoxicity assays, there was an indication of DNA damage caused by the NFCs.
The effects were weak and no clear dose response could be detected. The immunotoxic and genotoxic effects indicated a need for further in vivo studies. The tests included the effects of a selected TEMPO-oxidated NFC on a nematode worm and the so-called pharyngeal aspiration test in a mouse. Despite being a simple organism C. elegans has a digestive system, nervous system, xenobiotic metabolism and developmental cycle which makes it a suitable test organism to study effects that cannot be detected in cell cultures. The mouse pharyngeal aspiration test was chosen because the likely human exposure is via inhalation. Exact doses are applied to the mouse pharynx and subsequently the inflammatory and genotoxic responses of the test material can be assessed from the cells that have been harvested by a bronchoalveolar lavage (BAL) from the exposed cells. While no harmful effects were seen in the C. elegans model, indicating that the NFC does not penetrate the cuticulum or gastrointestinal barrier to an extent that causes detectable damage, the BAL-associated cells harvested from the exposed mice indicated an inflammatory response. No signs of genotoxicity were found in these cells. Taken together, the toxicological results indicate that the tested NFCs do not interfere in the cellular metabolism in a way that would lead to cytotoxicity. The weak indications on in vitro genotoxicity were not confirmed in in vivo trials, while both in vitro and in vivo data indicate that an inflammatory response is possible. This has been taken into account in the risk assessment.
WP10. Risk assessment
This WP was devoted to the risk assessment based on the toxicological data available in the literature and accumulated during the project. The work started with an extensive literature study on the available published toxicological data and risk assessment methodology related to NFC or NFC-type materials. The generated data was used to outline a preliminary risk assessment, mainly based on the in vitro data. In the preliminary assessment, the main identified difficulty was the lack of reliable data or even reliable estimates of likely exposures. Because of this, the so-called control banding (CB) approach was applied. CB is a risk management tool that is applicable when the available data are limited. Two CB scenarios, the so-called CB nanotool and Stoffenmanager nanotool were used. In both scenarios, estimations of hazard and exposure are given scores and the combination of the scores is the basis of the risk estimation. The main difference between the approaches is that the hazard evaluation CB nanotool is based on available toxicological information, while the Stoffenmanager nanotool focuses on the physicochemical aspects of the material to be assessed. Both CB approaches gave NFC a high hazard class. This was a result based on the conservative starting point of the CB tools, which gives high hazard scores to unknown parameters and the highest hazard class to insoluble nanoscale fibres. The toxicological data required by the CB nanotool does not exist for NFC and testing for them was beyond the scope of the project. The current CB scenarios overestimate the hazards and are probably not suitable for NFC-type materials. The toxicological data obtained during the project do not indicate major concerns, except for the occupational inhalatory exposure, which can be managed by standard protective measures. The toxicological testing scheme applied in the project was found to be compatible with the first tier hazard and risk assessment according to the latest ISO standard made for nanomaterial risk evaluation.
Potential impact
When interpreting the results of novel products and their impacts it is important to be aware that assumptions are made and generic data sets were used. Therefore the presented results were strongly case dependent. The results can be seen as trends and indicate that no environmental hazards are likely to arise as a result of including NFC in the applications studied. From an environmental perspective, the main differences between the three different NFC production options can be found from electricity consumption, raw material efficiency and water consumption. Enzymatically pre-treated NFC production is an energy-intensive process with high yield and low water consumption, while chemically pre-treated NFC consumes less energy but more water in the process and stays behind in the yield. NFC can be applied in coatings to reduce the need for latex. This was demonstrated in SBS board pigment coating. The amounts of NFC represented less than 1 % of the total product and the environmental effects were not recognisable. Applying NFC in bulk structures will enable a reduced need for raw materials as demonstrated in the wet-laid non-woven application. With lower weight and less raw materials, all the environmental burdens are significantly lower. When combining both approaches using NFC in bulk structures and barrier coatings in large volume packaging paper and board applications, a significantly lower environmental impact can be expected. The production of NFC is energy-intensive and this is a threat when large amounts of NFC are applied, at least in countries where the grid mix is fossil fuel-based. Low concentrations of NFC increase the drying energy demand of the applied NFC due to the use of water in high volumes. The energy consumption does not seem to be higher than in the production of latex. Another threat is related to the embodied environmental burden of chemicals used in the production of NFC. The oxidation chemicals can cause high economic impacts when the cleaning technologies needed to treat the process effluents are taken into account. Both functionalised NFC and reference natural NFC were assessed for their biodegradability in an aqueous environment. Functionalised NFC showed a lower biodegradation rate than NFC only, but the threshold biodegradation limit of 90 % was reached within the test duration.
The results of the biodegradability tests confirmed that the innovative coated board material containing the natural NFC or even slightly functionalised NFC is suitable for recovery in the organic recovery route. Economic and social sustainability assessment of the demonstrators showed that there is no NFC production route and application that would be the best from every aspect measured by the different indicators. The observations on both application cases are collected under a SWOT analysis framework. From an economic point of view, the application of NFC in coated board does not seem to bring cost savings and has a negative impact on product profitability when compared to the reference product. NFC replaced binder by 1:1 in the case studied. If the replacement ratio could be improved, or if NFC could be used in a bulk structure making leaner products possible, the application would be more feasible. The production of lean products by adding NFC does not decrease the production amounts because in most cases the production capacity in board production machines is limited by the drying capacity and therefore higher speeds can be used. Using NFC in higher added value products as barrier-coated products would make the situation more profitable. The replacement of part of the binder by NFC has a positive employment impact when looking at the total number of people employed directly in the application and indirectly in the supplier' business. The impact on value added is positive only in the case of one NFC production route.
The application of NFC in wet-laid non-woven seems to bring cost savings and has a positive impact on product profitability when compared to the reference product. The cost savings in raw material costs could provide opportunities for entering new market areas. The replacement of part of the binder and fibre by NFC has a positive impact on value added when looking at the total sum of direct changes in the application and indirect changes in the suppliers' business. The total impact on employment is negative. A lower need for raw material leads to a lower environmental burden. The common weakness of both the applications is that the occupational risks related to nano-sized fibres are not yet well known, but this is something that will improve as the research proceeds. A risk-related threat from both applications is that, if the safety issues related to nanomaterials are miscommunicated, it can cause major problems. The production of NFC and its application to paper industry products is a young field of research. More investigation is needed and the sustainability aspect should guide the development. The indicators studied in this assessment could be improved by further work on NFC production and application technologies. It seems evident that nanocellulose will be added in the future, not only in special products for niche markets, but widely in different kinds of packaging paper and board products with high production volumes. More product development work in the area of using NFC to increase strength in bulk structures or create novel functionalities with surface treatments is still needed. The important impact of the project on the scientific community was the high number of publications and dissemination activities that have increased the knowledge of the possibilities and challenges in this area. The development of research facilities carried out in the project or in parallel projects will improve the possibilities to continue the work in the future.
The general framework of the collective dissemination plan can be divided into three groups: a first one, including the set up of the project website and all periodic activities planned from the beginning; a second one, concerning all activities developed during the project and a third one, composed of those activities that were planned but will be implemented after the end of the project, as dictated by the IPR rules agreed among partners. The project website was established and managed by the project coordinator (see http://sunpap.vtt.fi for details). The open access project website was the major channel for advertising events and communicating news and public deliverables, including all lectures given in the two open conferences. It contains links to project partners' websites, as well as a link to confidential material for project partners. The Doha system provided by the project coordinator through the VTT extranet has been widely used by the project partnership for internal communication and for exchanging all the documents developed throughout the project. Common rules for project work were collected in the project manual for internal communication and the agreed rules for making publications and managing foreground were summarised in the intellectual property reights (IPR) management procedures, for appropriate management of the project. The newsletters (see http://sunpap.vtt.fi/publications.htm online) were published on the project website every six months and provided a fast and simple up-to-date means of communication of the most relevant public results.
The first open workshop was organised in Espoo, Finland. The main focus was on the laboratory work carried out in the project. The event had a total of 77 participants, mainly from research organisations and universities from Scandinavia and central Europe. The second event was held in Milan, Italy. There were 81 participants, with industry covering almost 50 % of the audience and significantly more participants from southern Europe. The main focus was on pilot-scale work and demonstrations. The conference was attended by non-European industrial representatives from Japan and Brazil. The programmes and materials can be found on http://sunpap.vtt.fi/events.htm Seven scientific peer-reviewed publications are published and two more have been submitted and accepted to be published soon. Project partners were involved in 40 other dissemination activities. Almost 80 oral presentations or posters were disseminated in workshops and conferences where both the scientific community and industry had representatives.
Exploitation results:
Project results can be widely used in the paper, board, and packaging industry
The use of NFC as an additive in inkjet coating colours showed promising results. The use of NFC in coating colours in order to increase the speed on production lines can be started as soon as suitable NFC quality is on the market. The main impact is better competitiveness with lower environmental impacts. The use of NFC in wet-end applications and in coating applications to produce lean non-woven structures has high potential in niche products. The main impact is lean materials with better competitiveness and lower environmental impacts. The results of the use of NFC in a board bulk structure on a laboratory scale have shown similar potential to those in non-woven applications and these can be widely applied in packaging board applications. The main impact is lean materials with better competitiveness and lower environmental impacts. The results regarding barrier properties, carried out as postgraduate work showed good potential for the use of NFC as an additive in barrier coating and these results can be exploited not only for board materials but for any paper barrier packaging materials. The main impact is lean barrier materials with better competitiveness and lower environmental impacts.
Further product development is needed to fine-tune the multilayer structures for different packaging applications. Foam-coating formulation and process results show high potential for the production of thin layers from nanomaterial, making novel products possible in the future. In this area, more work is needed on both product development and scaling up the running speed. The main impact is lean novel products with better competitiveness and added value. The developed methodology concerning health and safety aspects can be used as background material for the future targets aiming to homogenise and update the current standards in the toxicity-testing field. The safety results will be used in databases, making them available as a solid basis for recommendations and contributing to answering the questions and needs for national regulation and legislation authorities.
Project website: http://sunpap.vtt.fi
Dr Ulla Forsstrom
ulla.forsstrom@vtt.fi via e-mail.