Nano-systems for the conservation of immoveable and moveable
polymaterial Cultural Heritage in a changing environment
Alkaline earth and semi-metal alkoxides precursors will be synthesized tuning their properties on the basis of the stone, wood and glass-substrate characteristics and the specific functionality to be addressed, leading to a new generation of nano-structured materials tailored specifically for historic materials in a climate change context, merging from the most recent advanced research in the fields of nanotechnologies and conservation science. The development of suitable products for treatment of historic materials will finally halt the current use of inappropriate commercial products, especially polymers, that were designed for completely other purposes than the conservation of cultural heritage and that, in the recent years, show the detrimental effects due to their fast deterioration, that hampers the treated material too.
Central in the project is the synthesis of molecular precursors, nano-coating deposition and related properties assessment finalized to the production of innovative products to update the market of conservation products as a real alternative for unfitting traditional ones. The basis for their production and introduction on the market will be developed during the project.
CONSIGLIO NAZIONALE DELLE RICERCHE
Piazzale Aldo Moro 7
Higher or Secondary Education Establishments
€ 550 186,57
Cristina Sabbioni (Dr.)
Sort by EU Contribution
NEDERLANDSE ORGANISATIE VOOR TOEGEPAST NATUURWETENSCHAPPELIJK ONDERZOEK TNO
€ 184 296,89
FUNDACION TECNALIA RESEARCH & INNOVATION
€ 191 125
Cercle des partenaires du patrimoine-Laboratoire de recherche des monuments historiques
€ 192 840
FRAUNHOFER GESELLSCHAFT ZUR FOERDERUNG DER ANGEWANDTEN FORSCHUNG E.V.
€ 187 900
ASOCIACION DE INVESTIGACION DE LAS INDUSTRIAS DE LA CONSTRUCCION
€ 183 870
€ 233 160
NANOTEGO NANO TEKNOLOJIK URUNLER ARASTIRMA GELISTIRME KIMYA SANAYI VETICARET ANONIM SIRKETI
€ 29 520
BOFIMEX BOUWSTOFFEN BV
€ 157 500
METROPOLITANKAPITEL DER HOHEN DOMKIRCHE KOLN DOMBAUVERWALTUNG
€ 81 600
OPERA DI SANTA CROCE
€ 66 360
ESCHLIMANN ATELIER DE RESTAURATION-PEINTURE SAS
€ 186 060
TOP OBERFLACHEN GMBH
€ 162 040
€ 116 240
Grant agreement ID: 283182
1 November 2011
31 October 2014
€ 3 082 933,62
€ 2 522 698,46
CONSIGLIO NAZIONALE DELLE RICERCHE
This project is featured in...
New conservation products for historic building materials
Grant agreement ID: 283182
1 November 2011
31 October 2014
€ 3 082 933,62
€ 2 522 698,46
CONSIGLIO NAZIONALE DELLE RICERCHE
This project is featured in...
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Final Report Summary - NANOMATCH (Nano-systems for the conservation of immoveable and moveable<br/>polymaterial Cultural Heritage in a changing environment)
The problem of deterioration of heritage materials has become increasingly urgent due to: i) the increase of natural weathering caused by climate change and atmospheric pollution; ii) the current use of inappropriate commercial products and their fast deterioration; iii) the need of a more sustainable management of the built heritage. Therefore, there is the demand to improve the actual products and methodologies or to develop new valid alternatives for the conservation and preservation of monuments, safeguarding their cultural values and improving their future usability. NANOMATCH project addressed these issues combining the most recent advances in the fields of nanotechnologies and conservation science. To address the failure of most used conservation organic products, a new class of highly competitive and performing products was developed.
The starting idea was that alkaline earth and semimetal alkoxides are suitable molecular precursors of consolidants since they create a nano-structured coating adherent to pore walls (stone, stone-like and wood) or to the internal cracks (glass). Particularly calcium alkoxide can be considered as strengthener for stone and as alkaline supply for wood. Concerning glass materials, a molecularly dispersed aluminum alkoxide complex penetrates in the smallest capillaries of corroded glass thanks to its very low viscosity and it behaves as glass-in-glass consolidant. Nano-suspensions of alkoxides of alkali and alkaline earth metals were studied, synthesized in the laboratory and tested on a variety of substrates in order to verify the compatibility and performance. The most advanced technologies and the most sophisticated tools/instruments actually available in the market were employed for this purpose. Workability, efficacy, compatibility and durability were assessed in comparison with commercial products both in laboratory and through exposure of treated model samples (sound and artificially weathered) and degraded historical surfaces in four sites: Cologne Cathedral (DE), Santa Croce Basilica in Florence (IT), Oviedo Cathedral (ES), Stavropoleos Monastery in Bucharest (RO).
Results showed good penetration and microcrystalline crystallization of the consolidant within porous stones without significant aesthetic effects. Thanks to the fast alkoxide reaction time, a good surface cohesive effect was rapidly achieved and after exposure it further increased in the deeper layers. In stone-like materials the treatment performances were quite similar but strictly related to the type of binder and pigment. In wood samples, an effect of preservation against fungal attack and pH acidification was attained in combination with a biocide. The product developed for the glass ensured high transparency even after long-term exposure outdoors and stability under medium relative humidity conditions indoors. Finally, risk assessment of nanoparticles exposure was performed. Measurements successfully demonstrated that any nano-particles release took place neither in their manipulation nor after treatment.
During the three years of the project, a considerable number of aspects were taken into account, moving from the development, evaluation and production of these compounds to the formulation, the performance evaluation, risk assessment and environmental impact to the development of business plans related to entry in the market for those products and the writing of the guidelines for end-users.
These new advanced products offer a variety of possible applications starting from the same class of compounds then tailored in relation to the specific conservation needs. Hence, they mark a new generation of restoring inorganic products, compatible with the original materials, easy applicable to indoor and outdoor Cultural Heritage and low cost.
Project Context and Objectives:
Government authorities, restoration architects and conservation scientists have always had to face the problem of deterioration of historic building materials, in particular stone, wood and glass; an issue that has become more and more urgent since the result of most climate change scenario’s for the 21st century will lead to a clear increase in natural decay and worsening of the impact of atmospheric pollution. In addition in recent years socio-economic developments require a more sustainable use of existing building heritage.
The first important step for the project work was the choice and selection of the materials to be used as representatives for weathered historic substrates for laboratory testing and/or field-exposure, among the typologies considered in the project, i.e. stone, stone-like materials, wood and glass. For the class of stone, three lithotypes with very different, rather extreme properties -for porosity and water absorption coefficient- were selected (Carrara marble, Savonnières limestone, Maastricht limestone). This group was supplemented by two stone types, with less extreme properties, but present in two of the case studies: Laspra dolostone and Albeşti limestone. For stone like materials a rather weak type of lime mortar, representative for mural paintings in historic buildings was chosen. For wood substrates, four different species, both hardwood and softwood, and representative because of their presence in historic buildings, were chosen (oak, pine, poplar and linden). For glass, artificially deteriorated model glasses (porous Vycor glass and glass powders) were selected, representative for medieval stained glass and sodium-rich glasses from the 19th century. As innovation in the market of conservation is a central aspect of the project, also existing commercial products were selected to be tested in comparison with the ones to be developed.
Apart from fundamental parameters and criteria to be taken into account, methods to be used for the laboratory tests and field-exposure measurements were defined and protocols established for the assessment of the properties and features of the new products and of the treated materials.
After these preliminary activities, the following work was dedicated to the assessment of the best chemicals, candidate for the project, to the identification of different synthetic routes and to the exploration of their feasibility to obtain suitable Ca/Mg alkoxides for consolidation of stone and wood and to the optimization of the coating deposition on glass from A18, the conservation product developed in the CONSTGLASS project. Different synthetic routes to obtain Ca/Mg alkoxides were analyzed, and the five most promising were experimentally reproduced in laboratory. An in-depth study on the effect of temperature, solvent polarity and concentration, coordination capacity and of different other parameters that may have an important effect on the final compound characteristics was performed. After optimization of the processes, the only process leading to soluble forms of alkoxides was up-scaled from mg to gr scale. This study was propaedeutic for the Kg lab up-scaling. Moreover, all synthesized alkoxides, their behavior in solution, their carbonation process and their decomposition products were fully characterized and studied through different techniques (i.e. Nuclear Magnetic Resonance (NMR), Electrospray Ionization Mass Spectroscopy (ESI-MS), Infrared (IR), elemental analysis, Inductively Coupled Plasma (ICP), X-ray diffraction (XRD) and SEM-EDAX), in order to define their characteristics and physical-chemical properties.
A careful selection of biocide products to be used in combination with metal alkoxides on stone and wood was also performed, taking into consideration their approval for use in the European Union, their proven safety for cultural heritage applications and the absence of any possible reaction with the alkoxide.
Two alkoxides were finally selected and their production process optimized up to Kg lab-scale. The potential of this work is very high and forms an excellent starting point for:
a new really efficient class of chemicals in the restoration world
a new highly competitive product in the market
an industrial procedure for the alkoxides production.
As far as the glass conservation material A18 is concerned, the improvement of the penetration properties by varying the solid content, the choice of solvents and the introduction of wetting agents were further investigated. Modifications of the formulation were tested (variation of pH-values during synthesis, combination with silica sols) focusing on the network forming process after application. Since the adhesion force at high relative humidity was not satisfactory for A18 as it was developed in CONSTGLASS, the A18 was optimized, including the examination of the complexation process as well as the hydrolysis process. The modified A18 product resulted in a good adhesion to glass even at elevated humidity (at least at 70 % RH).
The second phase of the project was focused on the evaluation of the developed solutions, in comparison with commercial products, in terms of effectiveness, compatibility, performance and long-term behaviour.
All samples of the different substrates necessary to carry out the laboratory testing were prepared: for stone and wood substrates, materials were bought, samples cut to size and artificially weathered by different procedures for selected stone samples (Carrara marble and Maastricht limestone) and by fungi attack for most wood samples. For glass and wall painting substrates, as well as some man-made stone replicas, samples were especially made for the project. Application trials were carried out in laboratory on all substrates (stone, stone-like, wood and glass) in order to optimize the application parameters of the two most promising solutions: calcium tetrahydrofurfuryloxide (Ca(OTHF)2) and calcium ethoxide (Ca(OEt)2). These trials allowed then to select the application solvent, product concentration and application conditions that give the best results. The samples were subsequently treated with the calcium alkoxide solutions and the selected commercial products following the laboratory test protocols that were defined for all the substrates.
On stone substrates, the laboratory tests were carried out to evaluate the compatibility of the products with the substrate, both in term of aesthetic compatibility via colour measurements and in term of physical compatibility via measurements of water transport properties of the treated stone. The efficiency of the treatment was assessed via the evaluation of the penetration depth of the treatment and of its consolidating effect using ultrasonic velocity measurements, drilling resistance measuring system and dynamic modulus of elasticity calculations. A microscopy study also enabled to finely examine the interaction of the products and the stone substrate at the porous network level. Finally the treatment durability was evaluated using three artificial weathering tests in an attempt to simulate natural weathering. The resistance of both treated and untreated stone samples to salt crystallisation, to frost and to thermal shock was tested using appropriate climatic chambers. Compatibility and efficiency of the treatments were also evaluated on common pigments and painted stone-like model samples (i.e. model wall paintings). A first group of experiments focused on pigments themselves and their behaviour when mixed with the two NANOMATCH consolidants, as well as with two salts commonly found in historic buildings (NaCl and Na2SO4). The second set of experiments used model wall painting replicas to evaluate the aesthetic changes induced by the treatments via colour measurements, as well as to assess the surface strengthening effect induced by the treatment using an impact testing device that created impact holes on the sample surface and by measuring the characteristics of the holes using a rugosimeter. For wood substrates, tests were carried out to assess the compatibility and performance of nano-structured materials on these substrates: colorimetry, gloss, water vapour equilibrium uptake and release rate, resistance to abrasion, examination by SEM-EDAX, pH of the wood surface and examination by FT-IR. On glass substrates, the newly modified A18 product was assessed and compared to commercially available glass conservation products through several tests. Bending tests on plated microscopic slides were used to evaluate the product’s adhesive strength and thus its performance. Finally, several artificial weathering experiments in climate chambers were carried out to study the durability of A18 after exposure to simulated sunlight conditions (via ATR-IR and UV-Vis spectroscopies) and after exposure to high and low humidity conditions (via bending test and micro-Raman spectroscopy). Biocide performance assessment was also carried out to evaluate the effectiveness of commercial biocides when they are combined with NANOMATCH consolidants and to understand the interaction between the two types of products. Biocide performance was assessed on three different materials: stone, stone-like (model wall paintings) and wood. For stone substrates, accelerated colonization of the Savonnières and Maastricht limestone samples by a filamentous green algae (Klebsormidium flaccidum) was carried out. For the wall painting replicas, the accelerated colonization was carried out using a melanin fungus (Cladosporium sp.). ATP assay and image analysis of the sample surface condition were the two techniques used to quantify the extent and the speed of colonization. For the wood substrates, the evaluation of the biocide efficiency was carried out following a modified version of EN113 standard. The hardwood species (linden, poplar) were submitted to white rot fungus (Coriolus versicolor) aiming at a 30-40% weight loss and the softwood specie (pine) was submitted to brown rot fungus (Coniophora puteana) aiming at a 20-30% weight loss. The weight loss of the samples at the end of the test was then used to compare the protection provided to the wood by the different biocide-NANOMATCH product combinations.
Apart from the laboratory studies, other activities in the 4 selected sites - S. Croce Basilica, Florence, Italy; Cologne Cathedral, Germany; Oviedo Cathedral, Spain; Stavropoleos Monastery, Bucharest, Romania – were organized to evaluate the compatibility and performance of nano-structured materials after exposure on site. First, preliminary surveys to assess the state of conservation of the historic materials of the 4 substrates and to select the historical samples to be treated were carried out. The microclimatic parameters to be monitored, the instruments to be used and the requirements needed at each site for the experimental campaigns were identified. At the same time, the substrates to be exposed, the treatments to be applied, the exposure conditions and locations were defined. The climatic campaigns and field-exposure tests started between April-May 2013 in all 4 sites and ended in March 2014. From the collected microclimatic data the thermal behaviour, the risks for condensation, salt crystallisation and frost damage were calculated for stone and stone-like substrates; special attention was given to the relative humidity levels close to wood and glass samples. Sampling and analyses of treated and untreated model specimens collected before and after treatments were carried out before and after 10 months of exposure on site using different techniques. In particular, the following analyses were performed. Spectrophotometry, SEM-EDX, optical microscopy, scotch tape test, capillarity water absorption to asses colour changes, cohesion, surface properties, penetration depth and interactions with the substrate on stone samples. Visual observations, spectrophotometry and surface hardness to asses colour changes and consolidating effect on stone-like materials. Spectrophotometry, visual observations, weight changes, surface pH measurements to evaluate possible visible alterations, pH changes, mass variations and efficiency of the biocide treatment on wood. UV-Vis-spectroscopy, ATR-IR-spectroscopy and bending tests to observe the evolution of adhesion strength, colour changes, and potential chemical degradation phenomena on laminated glass pieces. The compatibility and performance assessment of treatments were investigated also on historic surfaces, by means of SEM-EDX and optical microscopy on stone real substrates; colorimetry and scotch tape test on stone-like; aesthetic and physical mass changes, as well as superficial pH and SEM observation on wood; microscopy on micro-fissured original glass.
Essential for bringing the developed NANOMATCH prototypes to the market was the study of any possible hazardous impact of the metal alkoxides on environment and human health during production, application and after conservation treatment, by considering the transformation that the compounds would undergo and the possible environmental release of nanoparticles from the treated substrates. The study on the risk assessment of the alkoxides for stone and wood covered a literature review and the characterisation of nanoparticles released during occupational exposure and in outdoor scenarios. The final report covers guidelines and MSDS sheets on the related risks. The risk assessment of the glass part was actualized for the modified A18-material. Detailed information on safe handling of precursors, solvent, powder A18 and finished product A18-sol are available, as well as its MSDS. Regarding the scale-up of the process for the production of the alkoxides for stone and wood, the basic process followed during the production of the material for the field tests was the basis for the definition of the industrial process. The adjustment of the process parameters and set-up allowed to optimize the system, solving the problem encountered during the application work and reducing the production costs. Also the synthesis route of the A18 glass consolidant was studied and optimized. After various alterations, a synthesis route for amounts up to 100 litres was worked out. The first 100 litres A18 batch size were synthesized successfully. The cost of the product depends strongly on the industrial volumes which will have to be produced. The production costs were estimated for three different annual production volumes and were then used in the business modelling exercise. The benefits were evaluated in the different lab and field tests. The market potential assessment was essential to develop the business model and was assessed through questionnaires. As a result, the total outcome of the market volume for Europe was defined at 20.000 litres (for stone/wood), taking only into account the market for stone consolidation in cultural heritage buildings. For glass, the new material is a product with promising future prospects. However, investigations on the glass consolidation market revealed, that only small volumes can be disposed, now and in the future. It is a very restricted niche market with little growing capacities.
The main target of the NANOMATCH project was to synthesize, test and finally identify innovative materials with improved consolidation effect on stone and stone like materials, filler/pH stabilizer effects on wooden materials or filler for the nanofissures in ancient glass.
As a basis to reach these key S&T objectives of the Nanomatch project, WP1 “Identification of substrates, products and suitability criteria for conservation treatment” had three objectives:
Identification of representative substrates for stone, wood and glass to be treated with Nanomatch and conservation products currently on the market.
Identification and prioritisation of the main environmental parameters for the artificial weathering in function of the evaluation of the present and future trend of pollution concentration and climate.
Definition of compatibility and performance criteria for assessment of the Nanomatch products.
The selection of stones was restricted to calcareous stones since the Ca-alkoxide products developed in the Nanomatch project are mainly meant for the consolidation of calcite-based substrates by deposition of calcite. Stone substrates have been selected on the basis of their Water Absorption Coefficient (WAC) and total porosity (Nt). The choice has been made to select stones which have extreme values for these two properties when compared to the normal range of values found in natural stones, i.e. Carrara marble, Savonnières limestone and Laspra dolomite.
Ideally, the evaluation of consolidants should be carried out on naturally deteriorated stones. However, this poses the problem of the availability of such naturally deteriorated stones in sufficient amount for testing and of the scarce reproducibility of the decay. An alternative is offered by artificially weathered stone substrates. For this, the concept of reaggregated stone has been developed, which guarantees a representative and reproducible weathered substrate to be used for treatment and testing of compatibility and performance. The method consist in grinding the stone, sieving and reassembling the obtained grains by the use of little quantities of hydrated lime.
From the consolidants currently on the market to be used for comparison with the Nanomatch products, calcium hydroxide nanoparticles - CaLoSiL® E25 manufactured by IBZ-Salzchemie (Freiberg, Germany) - and a silicic acid ester - KSE 300 HV manufactured by Remmers (Löningen, Germany) - have been selected.
As substrate for wall paintings, replicas that mimic powdering historic wall paintings have been selected. The replicas have been made of two lime mortar layers, a bottom coarse one (arriccio) and a top fine one (intonaco), covered by a paint layer. The choice has been made to use the same lime mortar composition for all the samples.
From the consolidants currently on the market to be used for comparison with the Nanomatch products, CaLoSiL® E25 manufactured by IBZ-Salzchemie (Freiberg, Germany) and Primal™ E 330 S manufactured by Dow Chemicals (Midland, United States) have been selected.
The Nanomatch products for wood were meant to be surface consolidants for non-structural wood. Therefore, biodeteriorated wood has been selected as substrate, in particular by fungi. The choice of the wood species was based on the ones most commonly used in the past in Europe, both in construction of buildings and manufacturing of objects and to include both hardwood and softwood species which are differently susceptible to various types of wood decay. The wood species selected were oak (Quercus), pine (Pinus sylvestris), poplar (Populus) and linden (Tilia).
From the consolidants currently on the market to be used for comparison with the Nanomatch products, Paraloid™ B72 manufactured by Dow Chemicals (Midland, United States) and Methocel™ A4M manufactured by Dow Chemicals (Midland, United States) have been selected.
Three types of glass substrates have been chosen to evaluate the A18 prototype consolidant: artificially deteriorated model glasses, porous Vycor glass and glass powders, the latter to create homogeneous specimens of various sizes and forms for mechanical testing.
There is currently no commercial product on the market, which can be used to fill fractures in glass that are less than 40 μm and which could be directly compared to the Nanomatch products. Nevertheless, two commercial products have been selected for comparison: Paraloid™ B72 manufactured by Dow Chemicals (Midland, United States) and Ormocer® - G manufactured by Fraunhofer (Munich, Germany).
Identification and prioritisation of the main parameters for the compatibility and performance assessment requires a suitable definition of compatibility. Within the NANOMATCH project, the following definition has been adopted: a treatment can be considered compatible if it does not lead to technical (material) or aesthetic damage to the historical materials. The treatment as such should be as durable as possible.
Compatibility criteria are related to the properties of the consolidated material with respect to those of the untreated material; performance criteria are related to the effectiveness of the treatment and include long-term behaviour. Compatibility criteria include physical requirements (water transport properties, thermal & hydric dilation and porosity / pore size distribution), chemical requirements (absence of harmful chemical reactions, unchanged solubility of the substrate), mechanical requirements (‘hardness’ and coherence) and aesthetic requirements (colour, gloss and structure). Additionally, in case of wood substrates, the treatment should not hamper the possibility of future dendrochronological investigation of treated objects.
To be successful, consolidation products have to meet the following performance criteria: cohesive effect, penetration depth of the product, long term performance with respect to salt crystallization, frost and biological decay.
On the basis of these premises, the following technical requirements have been defined: a good performance is obtained when properties like strength, “hardness” and long term performance of a damaged material increase after treatment with respect to those of the damaged untreated material, and when properties as water transport, thermal and hydric dilation, colour, gloss and structure and, again, strength and “hardness” differ, after treatment, as little as possible from those of the sound, untreated substrate.
An evaluation of the present and future trend of the pollution concentration and climate change was performed by studying the results of previous and on-going EU projects like NOAH’S ARK, VIDRIO, CARAMEL, CULTSTRAT, MULTI-ASSES, TeACH, Climate for Culture as well as recent literature. The main parameters involved in the decay of materials and linked with climate change have been identified as follows: rain, air relative humidity, air temperature, surface temperature, wind and solar radiation. Climate parameters have been considered to be more important than pollution parameters in addressing the objectives of the NANOMATCH project and had the priority in the evaluation of the compatibility, efficiency and performance. Long-term behaviour of treatments has been assessed by both accelerated ageing and field-exposure tests. The ageing has been performed by means of different simulations, by using different climatic conditions (RH, T) and salt concentrations.
The effectiveness of the treatment has been evaluated by comparing untreated and treated specimen after the weathering tests. In case of stone substrates, the accelerated weathering tests selected for the evaluation of the long-term behaviour of the Nanomatch treatments were: freeze-thaw (frost resistance), salt crystallization and thermal shock. The evaluation was based on a combination of visual observation (for frost and salt crystallization test), material loss and mercury intrusion (crystallization test) , length change (thermal shock). For wood substrates, the resistance to white and brown rot and water vapour uptake of treated and untreated specimens have been proposed to evaluate the long term behaviour of the treatment. In case of glass, long‐term behaviour of consolidated glass has been evaluated by testing the resistance to climatic conditions, specifically high humidity and UV‐light. The evaluation of the coating properties (hardness) gave an additional indication to the overall material properties of the new consolidant.
In WP2 the new metal-alkoxides as precursor of nano-structured conservation materials have been synthetized.
Metal alkoxides are chemical species of general formula [M(OR)x]n where M is a metal of valency x, R is an alkyl group and n represents the degree of polymerization. Most of the metal alkoxides are extremely reactive in air turning to corresponding metal oxides or carbonates; consequently their synthesis and handling rigorously require dry conditions. On the other hand, this peculiar behavior in atmospheric conditions makes them suitable for conservation purposes in built Heritage.
Calcium alkoxides, for instance, react in presence of humidity and carbon dioxide to give calcium carbonate, which eventually is the main component of many stones, mortars, plaster and wall paintings in built Heritage. Moreover, extensive studies claim the good potential of calcium carbonate to mitigate the acidification of cellulosic materials, including wood and papers.
Concerning the product for glass conservation, A18 is based on aluminium alkoxides complexated with triethanolamine (TEA). After solvent evaporation, the product undergoes transformation leading to a glass-like material that enables to fill even microfissures of nanometric size in historic glasses. Afterwards, slow ion migration from surrounding bulk glass matrix enhances its adhesion to the original materials as well as it insures its glass-like composition. The properties of this product, firstly developed within the CONSTGLASS EU project, were further improved in the frame of the NANOMATCH EU project.
The research to improve the alkoxide compounds for conservation purposes were carried out in WP2. The activity was completely devoted to find the best synthetic conditions to obtain Ca and Mg alkoxides with the required conservation features and the optimization of the A18 product. In addition, reciprocal influence between alkoxides and biocides was preliminary assessed to avoid any detrimental effect to the whole conservation process. Finally, a first upscaling of the synthesis and a first evaluation of costs were performed to forecast the alkoxides production in a larger scale.
Alkoxides for stone and wood
Form a pure chemical point of view, metal alkoxides are chemical species that can be simply formed by the reaction of metallic Ca with an alcohol. Different starting alcohols lead to different properties of the final product.
In order to evaluate which reactants have to be employed in the synthesis, it is essential to define the characteristics of the target molecules. As previously mentioned, metal alkoxides are sensitive to moisture and oxygen and have a strong tendency to olygomerize giving rise to insoluble clusters. To be employed as conservation materials, the main requirement for the products is high solubility in chosen solvents and moderate reactivity: these molecules should ideally penetrate into substrate pore network, then reactions can take place allowing the appropriated crystalline structure to grow inside the disaggregated materials. The starting alcohol and the used solvents should have a correct degree of volatility in order that these processes take place. In addition, all the involved products and the process must be less toxic, less dangerous and less expensive as possible. Of course, a compromise among these requirements has to be adopted, in order to maximize the benefits.
Many parameters associated with the structure of the molecules (steric hindrance, additional coordinating atoms, length of chain, combination of the three) determine the solubility, the tendency to olygomerize, the reactivity and stability of the alkoxides, and the carbonation process as well. For this reason, many alcohols with different characteristics were tested.
Being solvents the media in which the products are dissolved they strongly impact on cost, safety and health issues. Many traditional solvents and new green solvents were selected and tested with the aims to reduce toxicity, environmental impact, cost, and to choose solvents easy and safe to handle, characterized by an appropriate boiling point and vapor pressure which allow its evaporation but avoid premature setting of the products that could jeopardize the strengthening/protective effects on the substrate.
Among the many synthetic routes available in literature, a selection was performed to be experimentally tested for the production of alkali-earth metal alkoxides on the bases of the toxicity and costs of reagents and yield of synthesis. The following methods were selected for the first syntheses:
• direct reaction between metallic calcium and alcohols (with or without solvents, with or without heating),
• alcoholysis reaction (i.e. an exchange between alcoholic groups),
• Riecke reaction in order to activate the metallic calcium,
• synthesis from calcium hydroxide
• a method involving ammonia
More than 150 reaction were performed and most of them allowed to obtain the desired alkoxides with high yields, but many of the products were almost insoluble. Exclusively the method involving ammonia brought to the final product with a high solubility. In most cases, the solubility of all the synthesized species was very low, therefore no practical or even industrial application could be envisaged, so low that no consolidation effect was detected even with reiterated applications of their solutions.
All synthetized compounds were characterized by NMR spectroscopy, IR, elemental analysis and mass-spectrometry, while ICP-OES measurements to evaluate their solubility.
Among the different compounds synthetized with the ammonia method, two of them were selected for thesting their consolidation properties on the basis of their high solubility. They are:
• Calcium ethoxide [Ca(OEt)2]; it forms a suspension when mixed with the solvents, similarly to Calosil, a commercial dispersion of Ca(OH)2 available in the market and employed as stone consolidant
• Calcium tetrahydrofurfuryl oxide [Ca(OTHF)2]; it is a solid compound, very soluble in most organic solvents, and has many of the required characteristics (the corresponding alcohol is low cost, biodegradable, low viscosity and an acceptable volatility, vapour pressure 3hPa).
A study on alkoxide storage stability was performed for 6 months and it confirmed theyare excellent candidates as new materials in the C.H. conservation field. Some yellowing of the compound took place, probably due to oxidative processes, but it could be avoided by addition of suitable stabilizers. These processes affect only the colour of the solution, not its quality, as the concentration of the alkoxide in the solution did not change during time and no decomposition occurred.
Calcium carbonate coatings developed from alkoxides solutions in different solvents were investigated by XRD, SEM and FT-IR to evaluate the characteristics of the final product and to study the carbonation process.
Analysis of the decomposition process of the alkoxides underlined the complexity of the carbonation and the multiplicity of the parameters involved in this process. The kinetically most favourable phase vaterite is always obtained, but transformation to the thermodynamically stable calcite can be achieved through the addition of water (by aerosol for instance). The choice of the solvent is extremely important to control carbonation rate: the higher is its vapor pressure (fast evaporation rate) the faster is the consequent carbonation occurring. On the other hand, it has been observed that the thermodynamically favored phase calcite is favoured by a slow carbonation.
Despite the availability and use of many commercial products of magnesium alkoxides, studies on subsequent carbonation of Mg compounds can hardly be found in literature in relation to their employment as conservation products. For this reason, we decided to investigate the decomposition behavior of Mg precursors before starting synthetic procedures. For both the investigated magnesium compounds, i.e. Mg methoxide and Mg methylcarbonate, the XRD and IR results evidenced that they gave rise to coatings with a very low degree of cristallinity. Furthermore the identified phases revealed the formation of magnesium carbonate into the required phase magnesite did not occur, while these magnesium compounds preferably convert to different hydrated structure of magnesium carbonate and also magnesium hydroxide. These compounds do not convert directly to magnesite but to other more favoured hydrated magnesium salts, that might be deleterious to stone (possible source of efflorescence). For this reason, magnesium compounds were abandoned as precursors for carbonate formation.
The final production of alkoxides was 3.0-3.5 kg for the two calcium alkoxides for stone/wood conservation, according to the amounts needed for the experimental activities related to the assessment of their efficiency.
To obtain the alkoxide in a soluble form, we investigated a synthesis that employed liquid ammonia, known to be able to melt and solubilize metals and to activate them as well. Working on different parameters (temperature, concentration, reaction time, solvents…) the reaction was studied and optimized. The turning point was the choice to employ a low boiling solvent that could also coordinate the calcium atoms (THF), reducing the tendency of the alkoxide molecules to react with each other to form less soluble oligomeric species. This was confirmed by analytical evidences.
During WP2, trials were carried out to optimize the synthesis also for a wider alkoxides production. Obtained results allow the set-up of a pilot production of kilo-lab amounts in the chemical plant of Abcr and eventually delivered with the activities of the WP5, as a preliminary study for the industrial production of those compounds.
Alkoxides for glass conservation
The new glass consolidant, A18, is based on aluminium alkoxides complexated with tri-ethanolamine (TEA), in the ratio Al:TEA 1:1. After complexation, the released alcohol (e. g. sec-butanol) is removed by rotary evaporation and the resulting powder can be re-dissolved in ethanol for example. In this mixture, oligomers are present (Fig. 2, s. attachment). The nano-sized clusters form stable, slightly yellow solutions, for example in ethanol, which enable the infiltration of microfissured glasses due to their low viscosity. After complete evaporation of the ethanol solvent, the resulting solid material becomes colourless and forms strong adhesive bonds to the inner glass surfaces. This is probably due to the high number of hydroxyl groups present in the oligomer. After an even longer time period, the TEA may be removed by further hydrolysis under ambient conditions and moderate RH. Then, the material should be transformed to an amorphous hydrated aluminium hydroxide still adhering to the glass surface and exhibiting the advantages of inorganic materials, i. e. mechanical and light stability and, due to its refractive index, an optical appearance very similar to glass. Further ion migration into the filled microfissures may even lead to a glass-like composition (glass-in-glass consolidation).
Different activities were performed to follow two main objectives: a better understanding and controlling of the degradation via hydrolysis after application and the improvement of the penetration properties. Based on the formulation of A18 different modifications of the synthesis and formulation had been tested in the laboratory.
• Modifications of the synthetic process (by variation of pH or introduction of silica sols) to influence the network forming process of the compound after application didn’t result in better performances. For this reason further investigations were performed with A18 (original formulation).
• Ellipsometric porosity was performed on specifically treated samples to determine the theoretical pore size of the “porous” inorganic network: most micropores are less than 1 nm in diameter, a very promising result.
• The viscosity of different dilutions were investigated. The viscosity of the 1 % dilution is nearly comparable to pure ethanol (1,5 mm2/s). The results up to a 10% dilution rise slightly and are only little higher than for the 1 % dilution. Test applications on deteriorated model glasses confirms that this would be the most suitable dilution in conservation practice.
• Whereas the coating properties / flow are better with lower dilution the wetting properties are similar for the 1 % to 10 % dilutions. Since A18 is not a coating material the coating properties are not relevant in conservation practice but give an indication on the overall material properties. Moreover the addition of surfactants or wetting agents (polysiloxanes or polyacrylates) to improve the penetration properties was not successful. The version without surfactant showed the best flow and wetting properties.
• In the initial formulation of A18 the solvent to dissolve the intermediate A18 powder is ethanol. The solution can be further diluted with different solvents (toluene, acetone, methyl ethyl ketone, water). Other solvents for the dilution of the intermediate powder were tested. In order to reduce the flammability of the final product, solvents with a higher flash point than ethanol were preferred. The best alternative to ethanol seemed to be diacetone alcohol (higher flash point, very good flow characteristics and wetting properties of the sol). To provide a product whose adhesion to glass is also good at elevated humidity (at least at 70 % RH) the optimization focused on the variation and examination of the complexation process as well as the hydrolysis process:
• the amount of complexing agent was modified compared to the original recipe. The resulting materials were examined in the state of powder material, as sols and finally by using bending tests (gluing of overlapping microscopic slides) to get approximate values of adhesion properties. It was found that a reduction of complexing agent is suitable (1:0.8).
• The second parameter to be observed was the hydrolysis process. By changing the parameters (amount of the water and time) for hydrolysis, the process was not improved.
• Finally, the problem of unsatisfactory stability of A18 at high relative humidity was solved at this point by the modification of the degree of complexation to obtain a higher degree of condensation. Samples prepared with the new modification show better results when exposed to high relative humidity (72% to 77 % RH) than samples made with the original formulation. Another bending force test was performed in comparison to other consolidants for glass conservation (Paraloid B72 and Ormocer-G). Weathering was carried out at 85 % relative humidity and at 85 °C. After storage at these conditions samples made with A18 (50 %) obtained similar results as for the commercial product Paraloid B72, very commonly used in conservation. To meet even higher mechanical stability requirements under high RH exposure, as it may be the case for stained glass windows in a cathedral in humid climates or at certain seasonal conditions, the A18 sol can be further modified by adding an epoxysilane (GPTMS, 10%) and seal the treated glass by applying a transparent hybrid polymer coating on top to avoid any degradation of adhesion (A18-G, ORMOCER®-G).
The development of a suitable pilot product for glass consolidation made the modification of the original A18 (as prototyped in EU project CONSTGLASS) necessary. The new product A18 was synthetized with only 0.8 mol complexing agent to 1 mol aluminium alkoxide to improve the adhesion performance on glass.
The final production of alkoxides was 1 kg of A18 for glass treatment, according to the amounts needed for the activities to be performed to test their efficiency.
Regarding the glass consolidant, the synthesis of A18 consists of four steps: complexation of aluminium alkoxide with TEA, hydrolysis by continuous addition of water, distillation to remove the solvent to get a dry compact material, dissolution of the powder (which have to be stored excluding humidity). To get the final A18-sol, the powder can be solved in alcohol on demand. The sol is a clear liquid and can be stored at room temperature but humidity has to be kept away.
The original A18 sol has a storage stability of at least two years. No negative impact on the viscosity and adhesion parameters could be determined within this period of time. The material also stayed clear over the whole time of observation. The new modification of A18 (internal labeling A18) was produced in amounts of up to 1 kg s. Further up-scaling was performed within WP5 to achieve relevant amounts for industrial production.
In the initial idea, biocide should have been added to the metal-alkoxides solution with the aim to obtain a carbonate matrix with immobilized biocide additives. as pointed out by the one of the advisor of the project (Prof. Dr. Joris Van Acker), expert on wood conservation, if the two products are mixed, the resulting solution become consequently a new biocide formulation which requires a new evaluation procedure to be approved for its use in the European Union. Such procedure couldn’t be carried out within the framework of NANOMATCH whose main focus is to develop innovative consolidants, with biocide properties if doped with appropriate biocide molecules, not new biocide molecules. In addition, many commercial biocides are formulated in aqueous solution, while the calcium alkoxide consolidants cannot be in contact with water during their application.
Consequently, it was decided to apply the biocide and the consolidant products separately and that the biocides chosen had already been approved for use in the EU Annex I or IA of the European Biocidal Product Directive 98/8/EC, or at least already be included in the list of active substances to be examined under the review program (Annex II of Commission Regulation 1451/2007).
Another important criteria used for the choice of the biocide is its harmlessness towards cultural heritage materials, in particular the most sensitive ones like wall paintings, so it was decided to choose biocide that have already been thoroughly tested on heritage materials and that have a proven record of harmlessness.
Finally, the choice of biocides to apply also depends on the micro-organisms growth to prevent. It has been decided to focus on algae for stone substrates and on fungi for stone-like substrates, as they are the main responsible of biodeterioration on site. Consequently, for both stone and stone-like substrates, two commercial biocides have been chosen for testing: Biotin T (CTS, Paris) which contains didecyldimethylammonium chloride (large spectrum biocide efficient against all micro-organisms) and 2-octyl-4-isothiazolin-3-one (fungicide) and Proxymousse (Société PCD Peintures, Caudry, France) which contains benzododecinium chloride (large spectrum biocide).
Concerning the work on wood it was decided to focus on wood deteriorated by fungi. In fact fungi degraded wood samples are more reproducible and can be made in a matter of months, compatible with the NANOMATCH project timeframe. Therefore the biocides chosen are fungicides and the two commercial biocide products are: Odeon 4 (DTS Oabe) which contains Tebuconazole as an active ingredient (fungicide for wood and formulated in nonaqueous solvent) and a small amount of Permethrin, and Bardap 26 (Lonza) which contains as active substance N,N-Didecyl-N-methylpoly(oxyethyl) ammonium propionate (large spectrum biocide efficient against all types of micro-organisms).
The WP3 focused on the scientific evaluation in the laboratory of the performance of the products developed during the NANOMATCH project and their comparison with commercially available ones. Tests were carried out to evaluate on four substrates (stone, wood, glass, and wall painting) three main characteristics of the products: their compatibility with the substrate, the efficiency of the product effect (consolidating effect for stone, wall painting and glass, pH-neutralisation effect for wood, biocide effect for the combination product-biocide) and their durability/long-term performance (via artificial aging for example).
For stone substrate, three lithotypes with very different total porosity and water absorption characteristics were selected for laboratory testing: Carrara marble, Savonnières limestone and Maastricht limestone. All Carrara marble samples were heated 1 hour at 600°C to artificially increase the stone porosity and water absorption coefficient through thermal deterioration, and thus allowing some consolidant penetration. The stone samples then received either a NANOMATCH treatment: Ca(OTHF)2 (calcium tetrahydrofurfuryloxide) or Ca(OEt)2 (calcium ethoxide); or a commercial treatment: KSE 300 HV (a silicic acid ester) or CaLoSiL (calcium hydroxide nanoparticles). In addition some samples were left untreated.
The compatibility of the products with the substrate was evaluated both in term of aesthetic compatibility, via colour measurements before and after treatment, and in term of physical compatibility, via measurements of water absorption and drying properties of the treated stone. Regardless of lithotype, the treatment which modified the stone colour the least was Ca(OTHF)2. KSE 300 HV treatment induced a greater, but still limited colour change. On the other hand, Ca(OEt)2, and even more significantly CaLoSiL, induced much greater colour change on the samples, essentially towards a lighter, whiter colour. Regarding the water transport properties, the specimens treated with NANOMATCH products or CaLoSiL showed both an absorption and a drying behaviour not significantly different from that of the untreated samples, these three treatments are thus physically compatible with the lithotypes studied. On the other hand, most samples treated with KSE 300 HV show a different water absorption behaviour, with a slower water absorption rate and even, for the Maastricht samples, a significantly lower total weight gain, due to both the significant quantity of KSE 300 HV solution absorbed by specimens and its high product deposit rate, decreasing excessively the substrate porosity, and thus can be considered incompatible with it.
The efficiency of consolidation effect of the treatments, that is their performance, was assessed via the evaluation of the treatment depth of penetration and of its consolidating effect using ultrasonic velocity measurements, drilling resistance measuring system and dynamic modulus of elasticity calculations. The tests showed that KSE 300 HV is the treatment with both the highest penetration depth (up to 5 cm in the very porous Maastricht limestone) and largest consolidating effect. Ca(OTHF)2 penetration is around half of that of the ethyl silicate and its consolidating effect is also smaller. Finally, if both Ca(OEt)2 and CaLoSiL show the smallest (and similar) penetration depth, the NANOMATCH product impart a larger consolidating effect to the stone than CaLoSiL. A microscopy study also enabled to finely examine the interaction of the products and the stone substrate at the porous network level.
Finally the treatment durability, i.e. their long-term behaviour, was evaluated using three artificial accelerated weathering tests in an attempt to simulate natural weathering. Samples treated with Ca(OTHF)2, CaLoSiL or left untreated were submitted, after pre-conditioning, to three separate environmental cycling protocols to test their resistance to salt crystallization (solutions of 5% wt Na2SO4 or 10% wt NaCl), frost and thermal shock. Ca(OTHF)2 treatment improves the resistance of the samples to salt crystallization but less than CaLoSiL, treatment which most reduces material loss. On the other hand, for both the frost resistance test and the thermal shock resistance test, Ca(OTHF)2 treatment is more effective than CaLoSiL in, respectively, reducing material loss and limiting the decrease of the Young’s elasticity modulus.
For the wood substrate, four different species, three hardwood ones (oak, linden and poplar) and one softwood (pine) were selected for laboratory testing. Most wood samples were first submitted to fungal degradation by white rot fungus (Coriolus versicolor) for the hardwood species and by brown rot fungus (Coniophora puteana) for the softwood species. The wood samples then received either a NANOMATCH treatment (Ca(OTHF)2 or Ca(OEt)2) or a commercial treatment (Paraloid B72). In addition, some samples previously deteriorated by fungus and some sound samples were left untreated.
Aesthetical compatibility of the treatments with the substrate was assessed by measuring colour and gloss change. The most severe colour change after treatment was with the 6% Ca(OEt)2 solution for all wood species (pine, poplar and linden). On the three wood species, all treatments also caused a darkening, most obvious on the light-coloured linden and poplar samples, seen as a yellower colouration on treated samples than on non-treated ones for both Paraloid B72 and alkoxide treatments. Changes in gloss caused by the treatments are relatively small and barely visible.
Water vapour uptake from the air and dynamic water vapour release rate (drying) were determined by measuring the weight change of the samples placed at 20˚C at different relative humidities. The equilibrium water uptake of the different wood species and treatments increased slightly upon treatment. As the changes are marginal, this behaviour is not believed to be of importance for any further degradation by fungi. Anyhow, the dynamic vapour release of the samples was slightly increased after treatment. Thus, overall, the risk for microbial activity due to the presence of water is not increased as the treated wood does not stay humid any longer than the untreated one.
Abrasion (wear) resistance was determined by a so-called Taber test, adapted to the smaller sample size (4 samples are hold at once). The number of cycles (only 200, considerably lower than commonly used) was determined empirically to insure that the sample thickness is reduced by not more than half after the test. For the pine samples, the standard deviation was too high to allow for any meaningful conclusion. For poplar and linden samples, treatment increased the wear index, indicating an increased rate of weight loss caused by the grinding. This could be due to: the previously measured slight increase in water retention; a weakening of the sample surface due to a too high alkalinisation for the alkoxide treated-samples; and for the Paraloid B72 treated-samples, a poor adherence of the polymer resin to the rotted wood tissue, which, as it becomes detached, acts as a grinding aid.
Alkoxide-treated samples have been examined by SEM-EDAX. Calcium carbonate formation was observed on the surface. Uneven penetration was found down to 2 mm as was incorporation in and on wood cell-walls. Calcium containing crystals was also found on fungal hyphae. The crystal structure suggests calcium oxalate.
The surface pH was measured on the wood samples after the grinding test, around 2 months after treatment. The top 1-2 mm surface material was grinded and deionised water added to the wood powder. After one night, the pH of the filtered water phase was measured. Surface pH measurements show a clear neutralisation effect of the two alkoxide treatments on the acidified wood samples. A pH increase between 1.5 to 3.5 pH units was observed. In some cases, this increase might be so much as to exceed the original wood pH which can be between 5 and 6. As expected, the Paraloid B72 treatment did not increase the pH.
Infrared spectra of the treated and non-treated surface of brown rot degraded pine were obtained by the ATR method. It appears that the samples treated by Ca-alkoxide solution give more or less similar spectra, lacking the typical absorption bands from the degraded pine, but shows typical absorption bands from carbonate, calcite and vaterite.
To conclude, Ca(OTHF)2 is the preferred alkoxide for the wood treatment as it induces less whitening than Ca(OEt)2. No consolidation is obtained by application of the NANOMATCH products but both products have shown to have a potential pH-neutralizing effect on the acidified wood surface (1-2 mm). On the other hand, samples treated with commercial Paraloid B72 showed neither significant consolidation nor any pH-neutralizing effect after treatment.
The assessment of glass substrates treated with the newly developed modified A 18 NANOMATCH product was carried out. Several types of samples were used to evaluate the compatibility, performance and durability of the A 18 glass consolidant: plated microscopic slides and microscope slides with cover slides. A 18 was used at 10% or 50% concentration in ethanol and the product was compared to two commercially available glass conservation products: ORMOCER-G (polysiloxane / polyacrylate mixture, 10% concentration) and Paraloid B72 (polyacrylate, 10% concentration).
Bending tests on plated microscopic slides were carried out to evaluate adhesive strength. The tested products were applied between two overlapped glass slides and let dry to allow for solvent evaporation. At a 50 % concentration, A 18 exhibits high adhesion strength but is not applicable on micro-fissured glass samples. At a 10% concentration, its adhesion strength is similar to that of the commercial adhesives: Paraloid B72 and ORMOCER-G. However, with a 10% A 18 solution, the glass surface is not fully covered, so the data are not really comparable with the commercial products exhibiting full coverage. It can be assumed that the A 18 applied at a 10% concentration will accumulate within the micro-fissures and, after evaporation of the solvent, strong adhesive bonds will indeed form.
To evaluate the transparency of the newly developed product, UV-Vis spectra were taken of a 50 % solution of A 18 applied between a glass microscope slide and its cover slide to simulate a micro-cavity. The A 18 consolidant showed a very high transparency as testified by the absence of absorption bands in the visible range (c. 400-800 nm) in the spectrum.
Artificial weathering experiments in climate chambers were carried out to study the durability of the A 18 treatment. In the first artificial weathering test, the samples were exposed at 30°C and 50% RH, either in the dark or under simulated sunlight conditions. No change was observed in the UV-Vis spectra taken before and after weathering, which means that no change of colour of the A 18 could be detected. Similarly, no change in the A18 ATR-IR spectra after weathering was observed, which means that no chemical changes could be detected, demonstration of the chemical stability of the product.
In the second artificial weathering test carried out, plated microscopic slides were exposed at room temperature either in a “dry” environment (32% RH) or in a “humid” environment (75% RH). They were then submitted to a bending test after 2 weeks, one month, six months and a year. The results demonstrate the high adhesion strength to glass surfaces exhibited by the 50 % concentration A 18, which seems to be influenced by moisture and also depends on the length of exposure. But, taking the standard deviation into account the adhesion strength of A 18 onto glass always remains at least comparable to commercial glass consolidants (Paraloid B72 and ORMOCER-G), which due to their hydrophobic nature seem to be less sensitive to higher humidity levels.
To exclude any potential failure of A 18 at higher humidity levels, it was decided to offer an extra solution for applications in higher humidity situations by adding an epoxy silane (GPTMS) to the original formulation and seal the treated original glasses by applying a coating of ORMOCER-G. This holistic approach will be valuable for all historical glasses exhibiting severe damage, which cannot be secured by applying A 18 alone.
For polychromy, investigations to evaluate the compatibility and efficiency of the two NANOMATCH products were carried out first on pigments alone and then on painted, stone-like model samples. The first study focused on six powdered pigments (blue smalt, green malachite, green earth, raw Sienna, orange minium, and carbon black) and their behaviour when mixed with a NANOMATCH consolidant (Ca(OTHF)2 or Ca(OEt)2), as well as with two salts commonly found in historic buildings: halite (NaCl) and thenardite (Na2SO4). These consolidant/pigment/salt systems were characterized using colorimetry on powder, X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). The study aimed at determining if the hygroscopic salts, which are one of the main degradation agents of wall paintings, led to a transformation of the consolidant / pigment pair and, more broadly, at studying the compatibility between consolidant and pigment without having to take into account a possible binder. This study shows that the behaviour of some pigments in presence of Ca(OEt)2 or Ca(OTHF)2 depends on the salt content. If there is no hygroscopic salt present, nothing seems to occur, showing that the NANOMATCH consolidants themselves do not induce an alteration of the pigments. If NaCl or Na2SO4 are present, malachite, green earth and Sienna earth pigments show modification. The most important one is the malachite darkening that is not yet explained. These results highlight the importance of applying the NANOMATCH consolidants directly on the painted layer only if no hygroscopic salts are present and thus underline the importance to carry out substrate desalination prior to treatment when necessary.
The second set of experiments used model lime-based wall painting replicas painted using three different painting techniques (affresco, with an egg binder or with an oil binder) and 12 different pigments. In addition, some samples are left unpainted. The wall painting samples are treated with either a NANOMATCH consolidant (Ca(OTHF)2 or Ca(OEt)2), or commercial consolidant (CaLoSiL or Primal E330S) or a NANOMATCH consolidant-commercial biocide (Proxymousse or Biotin T) combination to check that the biocides have no adverse effect on the polychromy. In addition, some samples are left untreated.
A colorimetric study was first carried out to evaluate the aesthetical compatibility of the consolidants with the substrate. The overall colour change after treatment depends: on the pigment, pigments creating more saturated colour tend to show greater change; on the painting technique (regardless of pigment and treatment), with the general tendency of a greater change for fresco than for oil binder, than for egg binder technique. For a given pigment, the colour change induced by the different treatments depend on the painting technique. When the pigments are applied affresco or with an oil binder, CaLoSiL treatment induces the largest colour change, followed NANOMATCH consolidant treatment, and finally Primal E330 S treatment which induces the smallest colour change. When pigments are applied with an egg binder, Ca(OTHF)2 treatment induces the largest colour change, followed by CaLoSiL, then Ca(OEt)2, then Primal E330 S. Finally, in most cases, the application of a biocide after a NANOMATCH consolidant increases colour change, sometimes significantly.
The second study focused on the efficiency of the consolidant treatment, that is, on the assessment of the surface strengthening effect induced by the consolidant. Evaluation was carried out using an impact testing device that creates impact holes on the sample surface and then by measuring their volume using a rugosimeter. Smaller the impact crater, harder is the surface of the material, thus more efficient the consolidant is. The surface strengthening results show that, as for the colorimetric study, the different consolidants behave differently depending on the sample painting technique. For the egg binder samples, Ca(OEt)2 is the better consolidant followed by Ca(OTHF)2, while CaLoSiL is the worst one. For the fresco painting technique, Ca(OTHF)2 gives better results, followed closely by CaLoSiL and Primal E 330S; for the oil binder techniques, CaLoSiL gives better results followed by Primal E 330S and Ca(OTHF)2; in both cases, Ca(OEt)2 gives the worst result.
Regardless of painting technique, one of the two NANOMATCH consolidants is always among the best treatments, but one of them is not universally better than the other, and the performance of each depends on the painting technique of the wall painting support. With an egg binder painting, Ca(OEt)2 is the better performer both in terms of aesthetical compatibility and efficiency (consolidating effect), and it is better than CaLoSiL. With a fresco or oil binder painting, Ca(OTHF)2 is the better performer both in terms of aesthetical compatibility (better than CaLoSiL) and consolidating effect (better than CaLoSiL for fresco). The widely used acrylic consolidant, Primal E330S, does not perform significantly better than the other consolidants, as one of them always provides a better surface strengthening effect than Primal. Finally, CaLoSiL seems to be the better consolidant for oil binder samples, but is the worst performing treatments in term of surface strengthening for egg binder samples.
Biocides performance assessment was carried out on three different materials: stone, stone-like substrate (model wall painting) and wood to evaluate the effectiveness of commercial biocides when used in combination with NANOMATCH consolidants and to understand the interaction between them.
For stone substrate, Savonnières and Maastricht limestone samples were treated with only a NANOMATCH consolidant (Ca(OTHF)2); only a commercial quaternary ammonium biocide (Biotin T or Proxymousse); a combination of commercial biocide and NANOMATCH consolidant; or are left untreated. The samples were then submitted to accelerated colonization by a filamentous green algae (Klebsormidium flaccidum) over three weeks.
For stone-like substrate, lime-based wall painting replicas with an egg binder paint layer of four separate pure pigment areas (blue smalt, carbon black, green malachite and orange minium) were used. The same consolidant and biocide treatments applied on the stone specimens are used on the wall painting samples. After treatment, the samples were submitted to accelerated colonization by a melanin fungus (Cladosporium sp.) over two weeks.
For both stone and wall painting samples, the evaluation of biocide effectiveness was based on the assessment of the colonization kinetics. The extent and speed of colonization were evaluated by visual examination of the sample surface coupled with image analysis using the Image J FIJI software and by metabolic activity measurement by Adenosine Tri Phosphate (ATP) assay.
Stone samples treated only with Ca(OTHF)2 show the same general colonization tendency than untreated samples with a rapid increase in the first two weeks 2 weeks, and then, after 3 weeks, either a small decrease of the percentage of surface colonized (Savonnières samples) or a continuous increase (Maastricht samples). Samples treated only with a biocide show no colonization throughout the 3-week period. Importantly, a total absence of colonization is also observed for samples treated first with the consolidant and then with a biocide. This shows that the NANOMATCH consolidant does not alter the biocidal action of the biocides when it is applied before the biocide. On the contrary, when a biocide is applied before consolidant, colonization is detected immediately on the Maastricht samples or after 2 weeks on the Savonnières samples. This shows that when the consolidant is applied after a biocide, it reduces considerably its biocidal action. Visual examination and ATP assay show the same colonization trend.
Like the stone samples, wall painting samples treated only with Ca(OTHF)2 show similar surface colonization than untreated samples, while biocide-treated samples show no colonization. However, for biocide-consolidant combination treatment, the product application order on wall painting has the opposite effect than the one observed on stone. On the model wall painting samples, a very low level of colonization is observed on samples treated first with a biocide, then with the consolidant; while the greatest amount of colonization is seen on samples treated first with a consolidant and then with a biocide. Thus the biocide action of Biotin T or Proxymousse is much reduced when they are applied after the consolidant. This could be due to an interaction between some pigment components and the two quaternary ammoniums inhibiting their biocidal action.
For the wood substrates, one softwood species (pine) and two hardwood species (linden and poplar) were selected. Before treatment, half of the wood samples were partially degraded by either a brown rot fungi (Coniophora puteana) for the softwood species or by a white rot fungi (Coriolus versicolor) for the hardwood species, enabling to obtain fragile specimens that need consolidation. All samples, both sound and degraded, were then treated with a combination of a commercial biocide (Odeon 4) and a NANOMATCH consolidant (Ca(OTHF)2 or Ca(OEt)2) or were left untreated.
The protective effectiveness of the biocides against wood destroying Basidiomycetes was evaluated using a modified version of the EN 113:1996 standard. The main modifications are smaller sample size, and thus shorter degradation time, and initial sample condition: some samples undergo an initial fungal degradation prior to treatment, others do not. After treatment, the samples were submitted to fungal degradation and their weight loss measured at the end of a given period to evaluate the biocidal efficiency of the different biocide-NANOMATCH product combinations.
The poplar samples results were discarded as the weight loss of untreated sound samples after fungal degradation was only 5%, less than the 20% required by the standard. This is probably due to the contamination of the experiment vessels by another fungi. For linden samples, both biocide-consolidant combinations were efficient on sound samples (weight loss below 3%) but insufficient on samples deteriorated before treatment as their weight loss was of the same order of magnitude than untreated deteriorated samples. So for deteriorated samples, the treatments do not provide any additional protection against the fungi action. For the pine samples, both biocide-consolidant combinations brought efficient protection against the Basidiomycetes action on both the deteriorated and sound samples (maximum weight loss of 2%), while untreated samples, both deteriorated and sound, showed very significant weight loss (respectively 40.3% and 60.1%). So for the pine samples, application of any of the NANOMATCH consolidants after the biocide does not affect its efficiency.
The WP4 focused on the scientific evaluation in the field of the performance of the NANOMATCH products.
Model and historical substrates of the 4 materials studied within the project - natural stone and stone like materials, wood, glass – were exposed in the 4 selected European sites (S. Croce Basilica in Florence (Italy), Cologne Cathedral (Germany), Stavropoleos Monastery in Bucharest (Romania), Oviedo Cathedral (Spain)). The samples were left untreated, treated with Nanomatch products or conventional consolidants, and exposed around 11 months.
Climatic and microclimatic data (rain, wind, solar radiation, relative humidity, air and surface temperature) were collected outdoors (shelter and unsheltered positions) and indoors, analysed, and their temporal evolution during the experimental campaigns was studied. The risks for the most important physical damage processes for the materials investigated (i.e. condensation, freeze-thaw cycles, salts crystallization etc.) were evaluated, as well as other potentially damage phenomena related to the climatic and microclimatic conditions (i.e. surface heating, thermo-hygrometric cycles, etc.). Analyses performed on model and historical samples allowed to evaluate the performance of the new products also in comparison with conventional restoration treatments.
The thermal behaviour of the stone substrates treated with Ca(OTHF)2 was generally similar to the one of the samples untreated and treated with CaLoSiL.
The risk for condensation was less than 15% of total monitoring time in all the sites, following the scale Florence>Oviedo>Bucharest>Cologne. The percentage of total time of condensation for the samples treated with Ca(OTHF)2 resulted similar or lower compared to the untreated samples, except for Bucharest, where the situation was opposite. Concerning the comparison between the two treatments, in Cologne and Bucharest the risk for condensation was higher for the sample treated Ca(OTHF)2, but only on the latter site the difference was significant.
The crystallisation risk was evaluated for sodium chloride and sulphate, the former very common, the latter very damaging. Results showed that the risk was of low extent in all the sites, with no significant difference between the two salts.
The number of freeze-thaw cycles and the number of wet-frost days were calculated as indices of potential frost damage process. Results showed that the conditions for the occurrence of these events have quite never been satisfied in none of the sites, hence no significant difference between the treated and untreated substrates, and between the different treatments.
The selected lithotype model samples (Carrara marble, Laspra dolostone, Savonnières and Albeşti limestone) were analysed with colorimetry, Scotch Tape Test, optical microscopy (OM), Scanning Electron Microscopy (SEM), Mercury Intrusion Porosimetry (MIP), Ion Chromatography (IC) and capillary water absorption for the evaluation of compatibility, efficiency, and durability in terms of aesthetic compatibility, surface cohesive effect, porosity and pore size distribution, penetration and distribution of the consolidant.
In terms of aesthetic compatibility, spectrophotometric data (colorimetry) indicated that Nanomatch product can be considered suitable as consolidant for the selected lithotypes as it does not affect the stone appearance when appropriately applied. Regardless of lithotype, Ca(OTHF)2 induced a much smaller colour change than CaLoSiL. For both products, the colour was essentially due to an increase in lightness value (L*) and a decrease in b* value (towards blue, away from yellow).
Scotch Tape Test showed a good surface cohesive effect achievable in a short time after the application of Nanomatch treatment, due to the fast reactions of alkoxides with atmospheric H2O and CO2. On the contrary, CaLoSiL treatment seemed to be ineffective in reducing the detachment of the surface as the quantity of incoherent material removed before and after treatment was comparable. Moreover, greater cohesion of the surface was detected after the exposure period, even though Nanomatch product was almost absent on the stone surface, as confirmed by OM and SEM observations.
After the application of the Nanomatch product, OM and SEM investigations showed that it led to the formation of microcrystalline aggregates on porous limestones surfaces, some-where penetrating the stone matrix; whereas on stones characterized by low porosity or microporosity (as Carrara Marble), it formed a discontinuous microcrystalline surface layer. Application of the conventional CaLoSiL also resulted in the formation of a layer on the sample surface but significantly thicker than the one created by Ca(OTHF)2 and very limited evidence of penetration of CaLoSiL was observed.
After exposure, morphological observations on stone surfaces and sections of samples treated with Ca(OTHF)2 and CaLoSiL, demonstrated that the calcium carbonate coating deriving from Ca(OTHF)2 was barely observable over the surface and randomly distributed on wider pores and cracks below the stone surfaces, while the consolidant obtained from carbonation of CaLoSiL was exclusively located on the outmost surface and affected by fissures, as the substrate itself, due to outdoor weathering.
Comparing and combining the different results, it is possible to argue that the calcium carbonate deriving from the calcium alkoxide derives from a partial dissolution, penetration and recrystallization of the product within the porous matrix as a consequence of the exposure, that is, the presence of liquid water. This behaviour is in agreement with the kinetic processes that takes place during calcium carbonate’s formation: first step is assumed to create amorphous calcium carbonate (ACC) which exhibits a higher solubility in comparison to the other CaCO3 polymorphs. Further re-arrangements of the ACC in aqueous solutions lead to calcite which has the lowest solubility among all calcium carbonates. These processes might be responsible of the calcite’s permanency over the stone surfaces for those materials treated with the CaLoSiL, whereas ACC from Ca(OTHF)2 is dissolved and then re-precipitates as calcite within the pores under the stone surfaces.
Moreover, SEM observations carried out on treated samples after exposure highlighted a rough and pitted surface identifiable as a deterioration phenomenon linked to the impact of acid rain. Results concerning cumulative amounts of rainfall during the monitoring campaigns together with acidifying agents concentrations, registered by the local agencies for the air monitoring, contribute to attribute to the acid rain action the responsibility of the partial dissolution of the consolidating treatments and of the pitted effect shown on Carrara marble sample by SEM micrographs.
On the basis of the available data on climate change impact on cultural heritage it has to be underlined that surface recession and phenomenon of dissolution and recrystallization of surface layers due to the impact of precipitation is likely to increase in the future because of the foreseen increase in precipitation amount , including events of heavy rain – strong events, and increase of CO2 concentration in the atmosphere.
Capillary water absorption tests have shown that both Ca(OTHF)2 and CaLoSiL are compatible with the lithotypes studied, while both treatments induce a decrease of the macro-porosity (pores greater than 10 µm) of the samples.
The microscopic analysis on the historical samples demonstrated that the application of Ca(OTHF)2 and CaLoSiL resulted in the formation of a more or less thin layer on the stone surface. In some lythotypes, as Laspra dolostone and Albeşti limestone, also a clear deposition of the consolidant treatments in the pores was detected, resulting in a very slight decrease of porosity and pore size distribution of the stone, as measured by MIP.
After exposure, the treatments were still present as micro-crystalline layers on the sample surface of Laspra dolostone and Albeşti limestone and, in minor amount, on Savonnières limestone. On Carrara marble no presence of the treatment was detected anymore after exposure, most probably due to the high level of decohesion of these Carrara samples, and the consequent possible loss of the surface layer during exposure on site. In general a decrease in the amount of most soluble ions was measured after exposure, due to both cleaning of the stone samples before treatment and wash out due to rain during exposure. Only the amount of acetate ion, denoting biological activity, increased after exposure. No significant differences were detected between porosity and pore size distribution of the stones before and after exposure.
Two types of model wall painting samples were exposed on site in the same rack of the stone samples, but in sheltered positions: unpainted mortar and mortar with an egg-binder paint layer with 4 pigments applied (blue smalt, carbon black, green malachite and orange minium). Both painted and unpainted samples received one of four treatments: Ca(OTHF)2, Ca(OEt)2, CaLoSiL or no treatment.
The thermal behaviour of the stone-like substrate treated with Ca(OTHF)2 was generally similar to the one untreated at each site.
The risk for condensation was negligible in Florence and Oviedo, while in Cologne and Bucharest it was between 8-11% of total monitoring time. Moreover, in Cologne it was slightly higher for the treated sample than the untreated one, whilst in Bucharest the situation was opposite.
As for stone samples, the only site in which the percentage of freeze-thaw cycles was different from zero was Bucharest, nevertheless it was extremely low (0.2% of total time) for both the treated and untreated substrates.
The microclimatic conditions for the crystallisation-dissolution cycles of sodium chloride and sulphate occurred rarely at each site (percentage of risk lower than 2%), following the scale Florence≈Oviedo≥Cologne>Bucharest.
For the unpainted model samples, regardless of treatment, it was impossible to distinguish any change of colour. The efficiency of the different treatments also depended on the pigment considered thus general conclusions are difficult to be drawn.
The surface hardness, obtained indirectly by the volume of the hole made with an impact testing device, showed that the effect of the treatments was different on the painted and unpainted samples, similarly to the results obtained in the laboratory on non-exposed samples.
Comparing results from the different sites, no overall trend emerged linking these results to field exposure locations, either in term of colour change or in term of surface hardness. With both types of measurement, there were no samples exposed at a given site which showed more limited colour change or higher surface hardness after exposure for all types of substrates and treatments than samples at the other sites. Differences between samples exposed at the different sites could be explained by differences in environmental factors present at each site. However, the influence of several deterioration factors, such as freeze-thaw cycling or conditions favourable to crystallisation-dissolution cycles of sodium chloride and sulphate, was extremely limited at all the sites. The presence of pollutants could also explain differences in weathering, however the protection offered to the samples by the rack design strongly limited such effect. The more limited daily variations in temperature and relative humidity observed in Bucharest and the more important risk of condensation observed in Cologne and Bucharest, did not translate either in significant differences between the samples exposed at the different sites. The model wall painting samples, unlike stone samples, were sheltered from rain and quite protected. Such absence of water conjugated with relatively short exposition time and a very mild 2013-2014 winter in Europe, could explain the limited differences in deterioration between the samples of the different sites.
Three original stone-like substrates were selected for treatment: a detached wall painting fragment in Florence, pieces of archaeological mortar from the Old cathedral flooring in Cologne, and a sheltered in situ fresco section in Bucharest.
The colour measurements confirmed the visual observations, i.e. the application of Nanomatch products as well as of CaLoSiL, caused in some cases (Florence and Cologne) a more or less significant whitening of the sample surface. For the only original painted substrate in Bucharest, no significant whitening could be detected, indicating that others factors such as the proper adaptation of the solution concentration to each specific substrate, the skills of the operator applying the treatment, or the presence of previous surface conservation treatment hindering the consolidation penetration, might have to be taken into account.
The Scotch tape test carried out in Florence showed that the cohesion of the surface treated with Ca(OTHF)2 was slightly higher than the untreated surface.
Four wood species, artificially deteriorated by fungal attack, were exposed in the field. The type of rot decay depended on the species: white rot for hardwood species (linden, poplar, oak); brown rot for softwood species (pine). The samples were treated first with the biocide product Odeon 4 applied by brushing with 150 ml/m2. After drying a second treatment was done by brushing two times with 6% Ca(OTHF)2 in 2-propanol.
As humidity plays the most important role in the risk assessment for wood conservation, for each site the distribution of high relative humidity (RH) values was calculated. In Florence and Cologne RH was always lower than 80%, and was 70% respectively for 11% and 36% of total monitoring time. In Oviedo RH was higher than 80% for 23% of the time and never reached 90%. In Bucharest the environment was extremely humid throughout the year, due to the exposure location, in fact RH was higher than 95% for 92% of the total time.
The measurements on wood model samples included visual changes, colour changes, sample mass variations, surface pH, mould resistance, SEM observations.
Spectrophotometer tests on sound and aged samples were performed on defined spots before and after alkoxide treatment. On all four wood types the treatment caused slight visible darkening and yellowing, indicated by a decrease of L* value and an increase of b* value.
In terms of visual changes induced by exposure, only the model samples exposed in Bucharest showed significant visible alterations (as general mould growth) due to the very high environmental RH at this location. No other samples, either original or model samples, developed any mould. The other visible changes observed on these samples after exposure were darkening by sunlight of Cologne samples caused by photo-oxidation (sunlight exposure) and the grey hue seen on Ca(OTHF)2-treated dark brown-rotted pine samples on all sites.
Similarly, the only significant weight change was seen on the samples exposed in Bucharest that exhibited very significant weight loss due to fungal degradation favoured by extreme humidity conditions. Additional tests with induced mould growth showed no difference between treated and untreated samples of all wood types. Neither alkoxide nor Odeon 4 fungicide inhibited the mould growth. These results showed that Ca(OTHF)2 plus Odeon 4 fungicide treatments when applied only on one face of the samples are not enough to protect against mould growth under severe humidity conditions. The samples should be fully impregnated, or at least treated on all sides, to be really efficient against physical deterioration by fungi. On the other three sites the weight changes and wood mass loss were limited, as rotting fungi only are active at RH higher than 95% for prolonged periods of time.
The surface pH neutralisation effect induced by the Nanomatch treatment was also maintained after exposure. All Ca(OTHF)2-treated wood samples, regardless of species, maintained a higher pH (up to a few pH units) than untreated samples at all sites. The increased alkalinity was though less pronounced after 10 months, which could be an effect of slow carbonisation.
As a general conclusion, the Ca(OTHF)2 treatment can be applied to increase the pH of fungal degraded and acidified wood. By using a reduced alkoxide concentration (3%) can also reduce visual darkening of wood and reduce formation of white precipitate on the wood surface.
The historical samples selected for treatment were: half of the oak stake in Bucharest; half of one side of the seat from the choir (poplar wood) in Florence; one of the oak strips and one of the two fir strips in Cologne; half of the not covered back-side of the walnut altarpiece frame in Oviedo.
Similarly to model samples, Ca(OTHF)2 application on different historical wood types (poplar, oak, fir and walnut), damaged by wood rot and insect, resulted in a pH increase of about 1-3.5 pH unit. This positive effect was still measured after 10 months exposure on site.
Visual observations revealed white deposit at the surface on some of the treated samples. In the case of the Oviedo walnut sample, this effect might have been enhanced by the absence of cleaning of the wood before treatment application.
The SEM-EDX observations on oak and fir samples from Cologne after 10 months exposure showed the presence of the treatment (in the form of Ca precipitate) both at the surface and in depth, sign of its durability.
Deteriorated model glasses and microscopic slides were exposed at all sites on the front side of the original windows.
The percentage of total time when glass samples were exposed to RH>75 % was calculated, being humidity levels critical for the adhesive bonds of A18 onto glass. Results showed that at each site this percentage was between 8-11%, except for Bucharest where these conditions never occurred. Moreover, there was no risk of condensation in none of the sites for the samples exposed indoors.
The durability of the A18 treatment was assessed by evaluating the visual, chemical and physical changes of the product induced by exposure, also in comparison to the commercial consolidants, Ormocer®-G and Paraloid® B72.
In terms of visual changes, no indication of yellowing of the exposed A18-treated samples were observed in contrast with samples treated with conventional glass consolidants.
In terms of physical and chemical changes, UV-Vis spectroscopy showed that the transparency of A18 deposited between two microscopic slides remained high even after long-term exposure under outdoor conditions. Raman spectroscopy showed that A18 reacted very slowly under low RH ambient conditions. Whereas in higher RH environment, glass corrosion induced by weathering as well as atmospheric deposits and potential transformation products of A18 into an inorganic amorphous solid material made the spectra difficult to interpret.
The durability of the adhesive properties of the treatment was also assessed. The field tests on model samples demonstrated the high stability of the A18 consolidant exposed under indoor ambient conditions at medium RH. Under higher humidity levels inside historic buildings, A18 moisture sensitivity led to a decrease of adhesive force after exposure. Indeed, despite the high initial adhesive strength of A18, its moisture sensitivity is more pronounced than that of the organic (Paraloid® B72) or hybrid (Ormocer®-G) polymers, which do not undergo a transformation process under the influence of water. Consequently, the best application procedure could be to seal the A18 precursor molecules after its infiltration into the deteriorated glass to protect them from high humidity levels and to ensure a very slow transformation process almost without degradation of the adhesion behaviour.
The historical samples selected for the treatment with A18 came from stained glass windows of Cologne Cathedral in Germany (Jesus-Sirach-Window, 1870) and the Fontfroide Abbey in France (1914-25).
After exposure, the treated historic glass sample from Cologne Cathedral visually showed a slight increase of detectable micro-fissures, whereas the “wet-effect” of the treated surface was reduced and the flaky parts of the fissured surface were again more visible. These changes are in line with the consolidation process starting with the release of solvent (ethanol), drying and formation of a hybrid solid (A18 complex) and its consecutive slow transformation to an inorganic solid (gelatinous aluminium hydroxide), which may last fairly long, especially after sealing the treated microfissured glass sample with an Ormocer®–G top coat. The latter slows down the hydrolysis and release of triethanolamine, preserving the high adhesive force of the A18 complex. The filling of the microfissures and sealing of the glass surface by a hydrophobic coating to exclude moisture, should stop the ongoing selective ion leaching processes and contribute to a long-term stabilization of the glass.
WP5 “Towards market” is a WP mainly devoted to develop the plans to market the metal-alkoxides developed in WP2 and evaluated in WP3 and WP4. In this WP the impact of the use of the metal-alkoxides have been assessed on human health and environment and the best processing parameters for industrial production has been defined. Additionally, a cost/benefit analysis of the new products has been made, as well as a business plan followed by a market risk assessment.
The work on the risk assessment of health and environmental effects for stone and wood alkoxides has been defined in detail. The study has been broken down in seven distinctive steps covering respectively a literature review, occupational exposure and characterisation of nanoparticles released during this exposure, environmental exposure and characterisation of nanoparticles released in an outdoor scenario.
Nanoparticles applied for restoration purposes were estimated, mimicking the outdoor ageing due to rainwater and seasonal temperature turnover. For glass frits the released Ca concentration is comparable for all tested restoring solutions (Calosil, Ca(OTHF)2, Ca(OEt)2) and it ranges from 25 to 31 μg/mL. Conversely Ca concentration is negligible for marble specimens due to the high Ca background in the matrix; therefore it can be supposed that in real exposure scenarios the Ca contribution from these products is negligible. The characterization of leached solutions from nanoparticles released in outdoor scenario tests has confirmed the full missing of such nanoparticles, and the most reasonable explanation is that acidic conditions (rain) will favour their dissolution in water.
Dermal and eye contact during application have the highest exposure concern, but the adoption of adequate skin protection cloths and glasses would prevent exposure.
The main risks for the operator health are skin and eye contact. However, the condition of work and the adoption of adequate personal eye and skin protections are reducing the health risk to extremely low levels.
The final document covers guidelines and MSDS sheets on the related risks.
With regard to the glass consolidant, risks and hazards were identified regarding the health, physical and environmental aspects. For each of the precursors, complexing agent, solvent and finished product risks were individually assessed based on the available information (e.g. MSDS data sheets) and the experience. Safe handling rules and personnel protection gear were identified. Also the fire protection measures were defined given that products like ethanol are highly flammable. MSDS data sheets were made for the different finished products of the A18 product range.
Regarding the industrial up-scaling, the synthesis process was first defined at lab scale. Several processes were considered and finally the ammonia method has been selected since this method gave the best results in terms of solubility of the alkoxides. Small quantities (from mg till some grams) were first produced in the glove box. Then the first productions outside of the glove box were made again at the level of some grams. As NANOTEGO was not able to scale up the process, it was necessary to look for alternative toll processors to produce larger quantities. The original process was adapted to fit the equipment of these toll processors and first test batches of 10 grams were produced at the selected toll processor ABCR. Then the production of larger batches in the range of 200–400 grams has been made for the two alkoxides. The resulting material was used for the lab tests and field tests of respectively WP3 and WP4.
In a section phase, discussions were held with the toll processor to solve the remaining problems (the residual ammonia in the second alkoxide had to be evacuated, the ammonium stripping step at the end of the synthesis had be lengthened and the applied vacuum needed to be increased) and to produce larger quantities of the alkoxides.
Regarding the evacuation of the residual ammonia in the second alkoxide, the ammonium stripping step at the end of the synthesis needs to be lengthened and the applied vacuum needs to be increased.
In addition, to produce industrial quantities, it was recommended to include an ammonium recuperation step with adapted equipment to reduce the raw material costs of the product further.
In summary, the process and the most important process parameters have been defined to support an industrial process. It will hence be possible to produce the required quantities defined.
Regarding the prototyping of aluminium alkoxide product (molecularly dispersed aluminium alkoxide complex) for glass consolidation, the main objective was to advance the prototype A18 to a pilot material, which should be transferred into market. The best processing parameters for industrial production had to be defined.
The synthesis route as well as the strategy for the A18 material application was altered since the last report due to new knowledge and results of testing on site.
The favourite version now is a two component system named CLOISIL A18, consisting of an A-component CLOISIL A18, meaning the aluminium alkoxide complex and a B-component Accelerator A18 (an epoxy-functional component for accelerated and thorough curing). The penetration ability respectively the filling performance can be controlled by adoption of the solid content.
For this solution, 100 litre batch sizes have been made reproducible. The synthesis route is therefore fixed and can be called on demand.
The product for glass consolidation can be manufactured in amounts of about 100 kg applicable material. The synthesis route could be specified, the material properties verified.
Resulting on the property demands on a glass consolidation product, the recipe is available either as a one- or a two-component-system, depending on the demands in relation of either a temporary fixing model or a durable bonding of historical glass substrates.
Calculation of precursor costs for small scale amounts production have been established:
• Calcium ethoxyde for stone and wood conservation
The calculation refers to the synthesis of about 1 kg of Ca(OEt)2 with a solid content of approximately 12.5 % w/W, which is adequate for penetration and filling small fissures on deteriorated stone and woods. The cost of production of 1 pure kg of Ca(OEt)2 is about of 334.0€. taking into account that this alkoxide is obtained as suspension in 8l of solvent, the cost of 1l of suspension of Ca(OEt)2 at 12.5% in i-PrOH is therefore about 41.7€.
• Calcium tetrahydrofurfuryloxide for stone and wood conservation
The calculation refers to the synthesis of about 1 kg of Ca(OTHF)2 solid. The product has to be adequately solubilized in appropriate solvents to be suitable as conservation product for stone and wood. The cost of production of 1pure kg of Ca(OTHF)2 is about of 171.26€. considering that the alkoxide is used as suspension, the cost of 1l of suspension of Ca(OTHF)2 at 10% w/W in i-PrOH is about of 17.2€. If different solvents are used, the corresponding costs need to be calculated accordingly.
• A18 for glass treatment
The calculation of precursor costs for small scale amounts refers to the synthesis of about 1 kg A18 sol with a solid content of approximately 10 % which is adequate for penetration and filling of nanosized scratches of corroded glass. The precursor costs for approx. 86 to 90 g A18-powder are about 20 to 22 €, which means that the precursor costs of the corresponding amount of about 1 kilo 10 % A18-sol are approximately 30 to 35 €.
With respect to the cost/benefit analysis, two different calculations have been done, based on the inputs of WP2 and WP3: for the consolidant developed for its application in stone, stone-like materials and wood and for the consolidant developed for its application in glass. Additionally, the impact of the economies of scale has been included. The calculation has been done for the first stage of production in the worst case scenario.
In the case of the consolidant for stone, the production costs (personnel, utilities used, capital depreciation costs, production margin) were obtained from the toll processor quote for three different yearly volumes. For calcium tetrahydrofurfuryl alkoxide the costs are: 120 kg/year (6 x 20kg units) @ 253,10 EUR/kg; 600 kg/year (10 x 60 kg units) @ 237,30 EUR/kg; 1200 kg/ year (20 x 60kg units) @ 163,70 EUR/kg. For the calcium etoxide emulsion, the costs are: 565 liters (113 x 5 liter units) : 60,70 EUR/liter, 2.625 liters (105 x 25 liter units): 50,10 EUR/liter, 5.600 liters (56 x 100 liter units): 50,10 EUR/liter.
The raw material costs for the powder of CLOISIL A18 can reach about 30 € per kg.
Therefore, the 1-component system, readily mixed as a 10 % mixture, will come to final costs of about 115 € per kg. Production costs for 100 kg CLOISIL A18 (one production/year) may rise up to 160 €/kg, depending on several factors regarding the composition of material; meaning solid content and requirements for either 1- or 2-component-system.
The benefits of the products developed in Nanomatch are that they fill an important gap in the range of consolidant products for stone, wood and glass. For stone there do not exist inorganic based consolidants with such a high level of solubility. A patent request has been filed as consequence.
A first important parameter to be obtained for the development of a business plan and the subsequent exploitation plan is the potential volume of the European market.
In order to estimate this number a series of questionnaires were launched in November 2013 in France, Italy, Spain and Romania and were addressed to different kinds of stakeholders: applicators and contractors, owners, restoration architects and subsidisers. These questionnaires were launched in November 2013 in France, Italy, Spain and Rumania.
The total outcome of the market volume for Europe was defined at 20.000 litres, taking only into account the market for stone consolidation in cultural heritage buildings.
Due to the limited market volumes estimated, internet sales based marketing and sales approach was selected and cost calculations done in the case of consolidant developed for its application in stone.
The commercial costs have been defined during the discussions on the business model.
For glass, the new material CLOISIL A18 is a product with promising future prospects. However, investigations on the glass consolidation market revealed, that only small volumes can be disposed, now and in future. It is a very restricted niche market with little growing capacities.
The potential customers of product CLOISIL A18 are conservators/restorers of glass material, association of restorers, administration of cultural heritages and museums / archaeological institutes (conservation scientists/research centres).
At present a clear growth of the market around antique glasses, hole glasses, generally regarding glass consolidation or glass fixing or even glass bonding shows no trend towards a market growth. It is a very restricted, limited area with no potential growing ability.
The potential market is spread over Europe. The centres of archeologically interesting areas are: France, Spain, Italy, Great Britain and Germany.
With the previous information, the financial statements have been projected for 10 years and the benefits have been quantified. And sensitivity analysis has been developed to know how changes in the assumptions of model affect the profitability.
The final exploitation plan shows an attractive business opportunity for an SME that already has business synergies in the defined market and/or in similar type of chemistry.
The market risk assessment is dependent on the potential volume of the European market and the final results of WP3 “Workability and application of metal alkoxides” in order to establish the efficiency in terms of workability and shelf-life. Along this period these parameters has been defined and the market risk assessment has been determined.
The assessment of market risks is a process of identification of potential threats that significantly influence the establishment in the market of a newly-developed product as well as the maintenance of an existing product in the market. These threats can arise from a different nature, source or discipline.
In the case of applications for stone an important risk detected is that the shelf-life of the consolidant in liquid form is very limited. This means that powder and solvent have to be supplied as separate component and mixed on-site.
As volume for the Cultural Heritage market in Europe which is only a fraction of the initial expectations as laid down in the DoW for the NANOMATCH project, one the more important risk detected is that the business could not be interesting for SME’s.
In this context, it is important to mention the huge market potential to restore historic renders of hydraulic calcium mortars where today is no solution, particularly the historic no classified privately owned buildings with such renders in Central Europe (mid to southern Germany as an example) could mean an explosion for this product shifting it from a niche market to a commodity market application.
The business could be more interesting if the market is not limited to the cultural heritage niche, looking for new markets or new applications.
Alkaline earth and semi-metal alkoxides precursors have been synthesized tuning their properties on the basis of the stone, wood and glass substrate characteristics and the specific functionality to be addressed. This resulted in a new generation of nano-structured materials, suitable for the treatment of historic substrates in a compatible way, as a real alternative in the conservation market with respect to the widespread use of inappropriate commercial products, designed for completely other purposes and that, in the recent years, have shown detrimental effects due to their fast deterioration. Indeed, the new NANOMATCH consolidants have either the same composition or a major chemical affinity and compatibility with the historic substrates and are inherently lasting longer than today’s solutions available in the market. The promising technical performances held by the products result also from the high interest of the restorers raised in the occasion of the different workshops organized during the project and the enthusiasm from the restorer partners within the consortium.
In economic terms, thanks to the long durability of the products and thus to the reduction of retreatability needs, the frequency and extent of application will be lower, reducing also the maintenance costs. Cost estimates for production and application, are pointing towards well affordable total ownership costs. Last but not least, applications beyond the Cultural Heritage Conservation may be pursued to increase the business.
Input on development status of Ca alkoxides for stone/wood conservation and future exploitation plan
The objective of this write up is to review the product development status of the consolidants for stone and wood, to comment the business model developed in work package 5 of the project, to summarize the outstanding issues and to outline the exploitation path and planning upon Nanomatch project completion.
Product development status
The products developed within Nanomatch project are very promising nanotechnology based consolidants for the consolidation of stone. They are first of all of inorganic nature whilst most of the other products in the market are of organic nature making exception for the products CaLoSiL and Nanorestore.
The reactivity of the products is excellent as proven in the lab and field tests during the project. The solubility is superior to the other nanotechnology based products of inorganic nature. This means that the consolidation performance of these products is excellent meeting amply the research objectives of the project. During the different workshops in Nanomatch project, restorers attending these events have confirmed their strong interests in these products as they fill an important gap.
After preliminary investigations sufficient ground was found to support a patent application request which has meanwhile been filed by CNR – IENI, the partner responsible for the development of the product and the synthesis process.
The above mentioned facts are an excellent basis to exploit this product in the market but there are unfortunately some remaining problems to be resolved. The main problem to tackle is the storage stability of the product. When applied fresh, the product delivers all of its consolidation potential but when aged, the nano-particles have somewhat coagulated in the emulsion. By ultrasonic treatment of the emulsion before application in the field, this phenomenon can be partly reversed and the problem remedied. Such a treatment is also recommended for the CaLoSiL product. However, it would be highly desirable to find solutions to avoid this coagulation under storage in order to exploit the maximum potential of the product and to avoid shelf life management in the production planning and storage, complexity and costs during application. The enclosed ammonia, remaining in one of the products and causing odor and discoloring during application, needs to be removed during the production process but this is a rather simple problem to solve.
Business model development
One of the main problems was to identify the potential in the market for cultural heritage conservation. This market is extremely fragmented and difficult to access with respect to suppliers of the products, the restorers, the conservation architects and the monument owners.
Three different levels of volume have been assumed in the business model development to cope with this uncertainty. Anyway, even the largest projected volumes are still rather small, a toll processing route for the manufacturing of the product and a low cost distribution and sales model via internet sales and a part-time product manager has been defined as realistic exploitation path. The actual toll-processor/distributor has expressed interest in the product.
The business model financials project a moderate profit and a pay-back of 4-5 years which is not bad as an additional product line for a toll processor/distributor who disposes already over the infrastructure and organization to exploit.
The main outstanding issues are the product stability after ageing and the rather moderate market volumes.
Resolving the first problem requires further research on the product during ageing and the generation of solutions like the addition of anti-coagulation agents.
The second issue requires increased market research in the conservation market and beyond to raise the market potential and to find additional applications. The render of historic buildings in Southern Germany for instance do not have a solution for consolidation and this product could be the answer.
A research project was proposed under the NMP-21 call of Horizon 2020 where this work was part of the proposal. The proposal didn’t pass the first stage evaluation. Meanwhile the scientists working on the product formulation and the product process have left the CNR-IENI organization, creating an additional issue of finding valid replacements to tackle efficiently the first problem mentioned above.
Exploitation path and planning
The exploitation path needs to resolve first the product ageing problems, then work out the market potential further and find other applications to finally refine the distribution/sales plan.
This work is best done by creating a multidisciplinary group composed of the scientific research institute who has created the product and is owning the patent if granted; an experienced restoring company which could be the Romanian partner of Nanomatch covering the application aspects in field; a toll processor to optimize the production process, reduce the costs and manufacture the products for the market; a sales/distribution company championing the product and its application in the market.
ABCR could be this toll processor since they have already experience with the product and process during Nanomatch and they have expressed interest by participating to the NMP-21 proposal. Their distribution and sales arm could collaborate with RED in the development and implementation of the sales and distribution plan.
A restorers association within the EU could be an additional asset in the definition of the market and in the dissemination/promotion of the products amongst their members.
Obviously, such a collaboration needs to be governed by a consortium agreement managing the intellectual property rights and the sharing of the financial returns of this initiative.
Another problem is the financing of such an initiative. The fast track to innovation instrument in Horizon 2020 would be an excellent instrument to finance this additional work and bring the product to the verge of a market launch in the European market.
Given the composition and experience of the staff of RED, this SME could take the lead in this collaborative work, coordinate the efforts between the partners and participate in the sales/distribution and technical assistance by providing a product manager when the product is launched in the market.
Input on exploitation plan of Al alkoxides for glass conservation
The new material CLOISIL A18 is a product with promising future prospects. The CLOISIL A18 provides very good penetration features and also accelerated curing (as a 2-component-system). The cured material is non-sticky and adequately cross-linked. The stability against humidity could be improved significantly.
However, investigations on the glass consolidation market revealed, that only small volumes can be disposed, now and in future. The potential customers of product CLOISIL A18 are conservators/restorers of glass material, association of restorers, administration of cultural heritages and museums / archaeological institutes (conservation scientists/research centres). At present a clear growth of the market around antique glasses, hole glasses, generally regarding glass consolidation or glass fixing or even glass bonding shows no trend towards a market growth. It is a very restricted, limited area with no potential growing ability.
Other possible sectors for the material CLOISIL A18 may form a larger volume for dispatch, thus larger sales units and higher selling quantities could reduce the production costs and can lead to a durably profitable expansion.
Plans for future development by T_O_P Oberflächen GmbH may include additional ideas and technologies to be created for treatment of historical and archaeological subjects, glass and other porous materials, such as wood, plaster, ivory and others.
First steps into this direction involved applications on wooden material at Tecnalia, Spain and T_O_P. The studies corresponded by the sector describing the penetration on wood. Another factor to be taken into account was the intensification of colour when finishing wood with the CLOISIL A18 material.
Based on these results, Fraunhofer ISC will further explore the suitability of the consolidant for other purposes. The aluminium alkoxide complex can also be further modified by common means of nanotechnology to qualify it for different applications, e.g. through functionalization and condensation with sol-gel based precursors. These research opportunities will be followed within other regional, national, or European projects.
Since the beginning of the project, different activities concerning dissemination were planned and carried out, in order to make the broad field of conservation professionals, industry and owners aware of the project results. Also SMEs in research, production and marketing of innovative products for the conservation of built heritage were involved in the knowledge transfer campaign. NANOMATCH website was present on the internet at a very early stage of the project and it was continuously updated and enhanced. Moreover, leaflets, brochures and posters were produced and distributed within the national networks of the consortium partners and at national and international conferences, workshops and fairs all over Europe and beyond. Three newsletter was designed to bring the most recent news about the project results; they were distributed via the project website and through the scientific networks of the consortium members, contributing to the regional and national awareness and fostering dissemination of the project targets and results achieved. The continuous discussion of the results within consortium meetings and the 4 organized training workshops, as well as the questionnaires delivered to conservators, potential end-users, and other stakeholders, led to best practice operational guidance, occupational safety, and minimized risk for the treatment of original substrates. Finally, at the end of the project an international conference was organized and a DVD produced.
Five out of the thirteen consortium partners are SMEs: this large presence of companies guaranteed that the results of this project clearly benefit SMEs and create a favorable economic impact on the sector concerned, contributing to enhance the competitiveness of European industry, particularly SMEs, in different sectors such as restoration, conservation, materials, etc.
The societal implications of the project are as follows:
Direct creation of new, mostly highly qualified and attractive jobs in the field of innovative material production and high added value services on historic material consolidation;
Involvement of young scientists, providing a further opportunity to involve and train new young and female scientists.
Indirect creation of jobs mostly linked to cultural tourism, by promoting social dynamism and conservation of historic urban areas;
Improving the quality of life of the citizens living in historic cities. Built heritage deterioration and subsequent inadequate conservation, causes insecurity to people living/visiting the affected cities and increases social degradation in these cities.
List of Websites:
Project public website:
Coordinator contact details:
Dr. Adriana Bernardi
National Research Council (CNR)
Institute of Atmospheric Sciences and Climate (ISAC) - Unit of Padova
Corso Stati Uniti 4
35127 Padova, Italy
Tel. +39 049 8295906
Fax. +39 049 8295619
Grant agreement ID: 283182
1 November 2011
31 October 2014
€ 3 082 933,62
€ 2 522 698,46
CONSIGLIO NAZIONALE DELLE RICERCHE
This project is featured in...
Deliverables not available
Grant agreement ID: 283182
1 November 2011
31 October 2014
€ 3 082 933,62
€ 2 522 698,46
CONSIGLIO NAZIONALE DELLE RICERCHE
This project is featured in...
Grant agreement ID: 283182
1 November 2011
31 October 2014
€ 3 082 933,62
€ 2 522 698,46
CONSIGLIO NAZIONALE DELLE RICERCHE