Materials Novel
Materials Novel Bio-Composites for Structural Applications by Miguel Angel Sibila, Chemical Laboratory Department Sergio Fita, Composites Department Inma Roig, Composites Department all Technological Institute of Plastics (AIMPLAS) Paterna (Valencia), Spain (a) (b) (c) www.natex.eu www.aimplas.es Composite plate made of PLA reinforced with flax fibre: (a) Image of the surface, (b) microscopy image of the surface, (c) micrograph from the cross-sectional area. Bio-composites manufactured from natural materials such as fibres and bio-derived polymers offer a sustainable alternative to traditional ones, but at present they are still not available for their use in structural applications. Researchers at the Technological Institute of Plastics (AIMPLAS), Spain, in close collaboration with several Technological Institutes, Associations, and SMEs from eight different European countries, are currently developing aligned textiles from natural fibres that are suitable for their use as highstrength reinforcing fabrics to produce structural composite materials. This includes the incorporation of orientated woven natural fibres in both bioderived thermoplastics and thermoset resins, to produce high-tech products from renewable resources. The European Research Project, entitled Natural Aligned Fibres and Textiles for Use in Structural Composites Applications (NATEX), is funded by the European Commission 1 . The partners involved in this project are: • NETCOMPOSITES LTD (United Kingdom) • EUROPEAN PLASTIC CONVERTERS ASSOCIATION (Belgium) • AGCO (France) • FORMAX UK, Ltd. (United Kingdom) • EKOTEX (Poland) • TECHNICAL UNIVERSITY OF DENMARK (Denmark) • CHEMOWERK GmbH (Germany) • INSTITUT FÜR VERBUNDWEKSTOFFE GmbH (Germany) • ASFIBE (Spain) • PIEL,S.A. (Spain) • TRANSFURANS CHEMICALS (Belgium) • AALTO-KORKEAKOULUSÄÄTIÖ (Finland) • INSTYTUT WLOKIEN NATURALNYCH I ROSLIN ZIELARSKICH (Poland) • ABENSI ENERGÍA (Spain) • BAFA BADISCHE NATURFASERAUTBEREITUNG, GmbH (Germany) • VTT TECHNICAL RESEARCH CENTRE OF FINLAND (Finland) The innovation of the NATEX project has been focused on four main aspects: • Modification of the fibre surface in order to obtain the desired interface properties when combined with the polymer matrix. • New spinning processes to reduce the yarns’ twisting during the textile manufacturing process, increasing the fibre volume fraction and the wetting of the fibres, potentially leading to better mechanical properties of natural fibre-reinforced composites. • New weaving techniques to improve impregnation and to obtain innovative 3D textiles. • New commingling and film stacking methods for thermoplastic composites, in order to improve the permeability of the composite and to obtain well mingled yarns. 12 bioplastics MAGAZINE [04/11] Vol. 6
Materials • Adaptation of diverse resin processing methods (Vacuum bagging, Compression moulding, Infusion and Resin Transfer Moulding) in order to fulfil the characteristics of the modified fibres The mechanical properties of bio-composites are being enhanced by means of the improvement of the aligned natural fibres properties: good impregnation, improved interface area between fibres and matrix, most of the fibres oriented in the axis in which stress is applied, reduction of moisture uptake, high and homogeneous quality fibres, reduced twist and linear density of the yarn, suitable fibre architecture minimizing the nesting. The final aim of the project consists of the incorporation of these bio-materials in applications with high mechanical requirements in different sectors: transport, energy, agricultural machinery and shipbuilding. As an example, a panel system structure, which will be used in photovoltaic solar systems and thermal solar systems, is being designed and developed in order to obtain a part by using new biocomposites to replace current metallic materials. With these new biomaterials, the corrosion drawbacks experienced by traditional panel system structures and components based on metallic materials is expected to be overcome, whilst obtaining other benefits such as reduced weight or increased sustainability at a competitive cost. The behaviour and durability of these materials under high temperature conditions will be assessed in order to satisfy the requirements for such structures. However, the impact of NATEX will mainly affect the European Textile sector, which mostly consists of small and medium-sized companies, by increasing market competitiveness through the creation of high added value customized materials as reinforcement for structural parts made of composites. Additionally, the project will also provide benefits to the other sectors involved in the new material supply chain: agriculture (fibre growers), renewable and synthetic resin producers and end users (transport systems, energy systems, agricultural machinery and shipbuilding). Besides, in general terms, the project could also be potentially applied to other sectors where structural parts are required: furniture, sports and leisure, aircraft, building, etc. Since the beginning of the project, an important effort has been focused on the development and modification of natural fibres. As a result, the relationship between fibre processing, fibre defects and fibre properties has been determined. Additionally, the modification of surface properties of natural fibres in order to improve interfacial characteristics with both thermoplastic and thermosetting polymers has been performed, showing a good potential for better compatibility with hydrophobic polymers. For the development of natural fibre based textile preforms suitable for biocomposites, diverse configurations by using the most suitable spinning systems have been obtained leading to different twisting angles and mechanical properties of the yarns. Moreover, blends of natural fibres with both petroleum-based and bio-based thermoplastic fibres have been developed and characterized with good results. 2D and 3D fabrics from natural fibres and blends of thermoplastic and natural fibres have also been successfully prepared and characterized. Regarding polymers, sheets obtained from modified petroleum-based and bio-based thermoplastic resins with different additives have featured better extrusion processability, leading to higher dimensional stability, less defects, better aesthetics and higher outputs. Moreover, better mechanical properties and adhesion to natural fabrics have been observed compared to raw polymers. In the case of thermosetting resins, the addition of suitable additives have shown improved adhesion of unsaturated polyester resins to natural fabrics, leading to higher mechanical properties. The processing of unsaturated polyester resins and natural fabrics by different methods such as resin transfer moulding (RTM) and infusion has been carried out with good impregnation properties and surface finishing. Renewable thermosetting furan resins have shown a comparative performance to that of phenolic resins. Furthermore, a specific furan resin has been found ideal for prepreg applications. From all the developed materials, an important effort has been focused in the modification and adaptation of suitable processing techniques for both thermoplastic and thermoset biocomposites production. Thermoplastic biocomposites have been successfully processed by defined manufacturing techniques such as compression moulding, leading to good mechanical properties and surface finishing. Considering thermosetting biocomposites, parts with good mechanical properties and surface appearance have been processed by RTM and methods. Prepregs from furan resins and natural fibres have been processed by compression moulding leading to good mechanical properties and finishing. With regard to the final applications of the project, different case studies have been selected to be developed from natural fabrics and both thermoplastic and thermosetting resins. Requirements for these parts have been established and current work is focused on the development of first prototypes. Good preliminary results have been obtained from the shipbuilding and transport system case studies showing a good prospect for the development of biocomposites from polymers reinforced with natural fibres. 1: Acknowledgement: NATEX project has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) NMP area (Nanosciences, nanotechnologies, Materials and new Production Technologies) under grant agreement N o 214467. The information above reflects only the NATEX beneficiaries’ views and the Community is not liable for any use that may be made of the information contained therein. bioplastics MAGAZINE [04/11] Vol. 6 13
