Final Report Summary - NANOSTAB-GB (Novel Nano-Stabilisation for Green Bioplastic Nanocomposites) There is currently a large demand for green biopolymer-clay nanocomposites, e.g. biopolymers reinforced with naturally occurring nano-clay fillers (which have been organically modified), as these fillers are low cost eco-sustainable raw materials that impart much improved properties to the polymer matrix, e.g. increased barrier properties. However, these biopolymer-clay nanocomposites cannot compete with fossil fuel-derived polymers-clay nanocomposites because of their low thermal stability and mechanical performance. The problem of stability is related critically to the thermal instability of organic compounds used to modify nanoparticles under production conditions; this gives rise to the formation of acidic sites, free radicals and other initiating species (via Hoffman elimination) that are responsible for accelerating the thermoxidative degradation of polymer nanocomposites. Some of the main technical challenges for biopolymer-based (bPNC) and fossil fuel-based (PNC) nanocomposites include: low thermal stability at processing temperatures and limited thermo- and photo- oxidative stability in service; morphology and distribution of the nanoparticles (NP) in the polymer matrix; environmental impact at end-of-life (for PNC only); health and safety issues associated with nanoscopic particles. So far, only limited stabilisation of both bPNC- and synthetic PNC- based nanocomposite materials have been achieved through the application of conventional industrial stabilisation systems; there is overwhelming evidence which shows that the stability of such materials are extremely low compared to that of analogously prepared unfilled polymers. The main aim of NANOSTAB-BG was, therefore, to address the issues of stabilisation of these materials by managing their thermoxidative degradation and achieving maximum performance properties. Overview of results: The main results of the NANOSTAB-BG project was the successful production of bNPC with enhanced thermal stability and long-term durability; the key results achieved are:• Successful synthesis and characterisation of novel clay-organic modifiers containing a grafted phenolic antioxidant (g-AO) function which is based on a quaternary ammonium salt. The new organo-modifier (gAO-OM) was then used to modify the natural montmorillonite clay (MMT), to give (gAO-OM-MMT), through cation-exchange reactions;• Attempted synthesis and characterization of novel clay-organic modifiers containing an in-built hindered amine stabilizer (HAS) function which is a based on quaternary ammonium salt. The synthesis was very challenging with inconclusive results due to time constraints. However, the available data obtained so far would suggest that the HAS has reacted with the quaternary ammonium salt to give an organo-modifier (HAS-OM) which was then used to modify the natural montmorillonite clay, to give (HAS-OM-MMT), through cation-exchange reactions;• Production and performance of novel biopolymer-based MMT-nanocomposites whereby the newly prepared gAO-OM-MMT and HAS-OM-MMT clays were incorporated in different biopolymers, e.g. polyamide (PA11) and polylactic acid (PLA), by melt mixing, and the thermo-oxidative and photo-oxidative resistance of the nanocomposites produced were examined and compared with similarly prepared nanocomposites but containing commercially modified clay (OM-MMT) having the same organo-modifier used to synthesise the new gAO-OM. Results have shown that the nanocomposites containing the new gAO-OM-MMT give rise to higher stability (less thermo-oxidative degradation) at high temperatures of the polymer’s processing, compared to similarly produced nanocomposites based on the same polymers but containing the commercial OM-MMT-clay. The comparison was done with, and without, blend mixing of an equivalent amount of a similar but non-reactive commercial hindered phenol stabiliser. In addition, the novel nanocomposites containing the new gAO-OM-MMT caused a lower extent of photo-oxidative degradation during accelerated UV exposure, compared to that of simple nanocomposites containing the commercial OM-MMT-clay, with and without, the physically mixed (of equivalent amount) commercial photostabiliser; • Successful synthesis of a new layered double hydroxides (LDH) nanoparticles containing effective phenolic antioxidant, AO (AO-LDH), and hindered amine stabilizer, HAS (HAS-LDH), through anion-exchange reactions and characterization through advanced spectroscopic techniques, x-ray diffraction and thermo-gravimetric analysis; and,• Production and performance of novel biopolymer-based LDH-nanocomposites whereby the newly prepared AO-LDH and HAS-LDH nanofillers were incorporated in two different polymeric matrices, PA11 and PLA, by melt mixing and the thermo- and photo- oxidative resistance of the produced nanocomposites were examined and compared with similarly prepared nanocomposites but containing commercially unmodified LDH in presence and absence of a blended mixture (of an equivalent amount) of a similar stabilisers. The novel nanocomposites containing the new AO-LDH and HAS-LDH nanofillers gave rise to lower thermo-oxidative stability at high temperatures but they resulted in better photo-oxidative stability monitored during accelerated weathering test.The overall aim of NANOSTAB-GB was, therefore, accomplished and has resulted in two outstanding achievements. First, the successful preparation of a new graft-AO-containing clay organic modifier, and its subsequent use for the stabilisation of biopolymer-based clay-nanocomposites where it becomes possible for the stabilisation reaction to take place locally at the interface between the matrix and the filler particles, an area that is critical for controlling the degradation process, thus giving rise to an improved overall long-term thermal stability and in-service durability compared to the commercial clay-nanocomposites. Throughout this work, advanced techniques, e.g. high-performance multinuclear-NMR, Fourier Transform Infrared (FTIR) Spectroscopy and Gas Chromatography–Mass Spectrometry were used for the characterisation of the novel organo-modifiers in order to investigate the chemical immobilization of the stabilising molecules within the organo-modifiers. Similarly, advanced techniques were used for the characterization of the prepared biopolymer nanocomposites; this includes rheological analysis to monitor the thermal degradation during processing, x-ray diffraction analysis, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to determine the nanoparticle morphology (intercalated/exfoliated), and differential scanning calorimetry (DSC) to determinate the sample crystallinity. To evaluate the long-term thermo-oxidative stability and photo-oxidative durability, all nanocomposite samples were subjected to thermal ageing and accelerated weathering; the progress of the degradation was followed by monitoring the oxygen-containing species as a function of the exposure times using Fourier Transform Infrared (FTIR) analysis.Second, the novel “smart” stabilisation and reinforcement approach for clay-based biopolymer nanocomposites was implemented: the clay-organic modifier was modified so that it contains a grafted antioxidant (gAO) or an effective hindered amine stabilizer (HAS) function. The innovative modified nano-fillers were shown to act as both nano-fillers and carrier for stabilising molecules. In this way, the stabilisation reaction would take place at the interface area between the matrix and the nano-fillers giving rise to enhanced overall long-term stability. Therefore, the new stabilisation approach, whereby the stabilising molecules become both bound (immobilized) onto the organic modifier as well as embedded into the interlayer galleries of nanoparticles, is a “smart” way of stabilising polymer nanocomposites. In this way, the stabiliser becomes “available-on-demand” as it is present, at the molecular level, close to the oxidation sites which have to be deactivated or inhibited, in order to achieve the performance targets for a safe, stable and durable biopolymer nanocomposites.Conclusions: The NANOSTAB-GB project will result in 3 peer-reviewed papers (1 is ready to be submitted for publication, 2 are in preparation), and have resulted in further 5 papers/posters published in conference proceeding and 2 seminar lectures. The academic impact relates to synthetic approaches and characterisation methodologies that have led to the development of: • New types of organo-modifiers containing stabilising agents/functions;• New types of multifunctional nano-fillers with in-built reinforcing and stabilising action/capability; and• New types of PNC and bPNC with enhanced thermo-oxidative resistance at normal polymer processing temperatures, and thermo- and photo- oxidative resistance at long ageing and exposure times.Impact on the career development: During the research and training periods at Aston’s “Polymer Processing and Performance” Research Group (AU-PPP), Birmingham, UK, National Research Council at the Institute of Organometallic Chemistry (NRC-ICCOM), Pisa, Italy, and Laviosa Chimica Mineraria srl, Livorno, Italy, the Research Fellow (Dr. Nadka Tzankova Dintcheva) has:• Gained theoretical and experimental experience in synthesis of reactive stabilising molecules and their immobilisation onto clay-organo-modifiers and chemical and material characterisation techniques; • Gained experimental experience in ion-exchange reactions to modify both natural montmorillonite clays and layered double hydroxides fillers and advanced structural characterization methods; • Acquired new skills and know-how in processing and spectroscopic analysis of the new nano-fillers;• Acquired competence in project management and learned about the process for research commercialization;• Built an extensive network of academic and industrial collaborators indicative of an advanced independent investigator; and• Organised and managed joint seminars on advanced nanocomposites with visiting researchers and the staff members of the NRC-ICCOM and Laviosa srl.As a result, of the Marie Curie IEF (“NANOSTAB-GB” 300302) project, Dr. Dintcheva was able to achieve a career step-change: she will be awarded an Associate Professorship at her home institution, University of Palermo. Impact on European excellence and competitiveness: NANOSTAB-GB project contributes to both European excellence and competitiveness: by training and developing further the skills of an active researcher to become a leader in nanocomposites technology; by delivering the scientific objectives of the programme as a result of achieving the technical milestones outlined in the project and by addressing some key issues concerning the sustainable development of highly stable in-service, and yet biodegradable at end-of-life, biopolymer-nanocomposite materials.Socio-economic impact of the project: The project contributes to the EU nanocomposites technology community through the implementation of a novel “smart” stabilising approach, and to the chemical industry through the production of low-cost multifunctional advanced nano-fillers. The scientific excellence of the project (training and results) contributes to the transition of Europe to a knowledge-based society in this area, driving the transformation of industry towards higher added value sustainable development as set out in NANOSTAB-GB strategic objectives.Societal impact: The project will have impact on society through the possibility of bringing to market new novel nano-fillers containing in-built stabilisation functionalities for the production of advanced safe and stable biopolymer-based nanocomposites. The project results will help to widen the application fields of biopolymer based nanocomposites with the introduction of ‘intelligent/smart-active’ materials for packaging, automotive, biomedical, and other novel applications.Environmental impact: The proposed novel “smart” stabilizing approach opens new horizons in the quest for new, safe, stable and durable biopolymer-based materials with limited environmental impact and controlled end-of-life.
