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Aligned Natural Fibres and Textiles for Use in Structural Composite Applications

Periodic Report Summary 2 - NATEX (Aligned natural fibres and textiles for use in structural composite applications)

Project context and objectives:

NATEX is focussed on the development of aligned textiles from natural fibres suitable for use as high strength reinforcing fabrics to produce structural composite parts using bio and oil based thermoplastic and thermoset resins. This includes the use of orientated woven natural fibres in bio-derived thermoplastics and thermosets, to produce high-tech products with high added value from entirely renewable resources.

The main innovations in NATEX project are:

1. modification of the fibre surface to obtain the desired interface properties when combined with the polymer matrix
2. new spinning process to reduce the yarns' twisting during the textile manufacturing process, increasing the fibre volume fraction and the wetting of the fibres. This is going to increase the mechanical properties of the yarns.
3. new weaving techniques are being developed to improve impregnation and to obtain innovative three-dimensional (3D) textiles
4. new commingling and film stacking is being developed for thermoplastic composites, for improving the permeability of the composite and to obtain well mingled yarns.

Besides, a large range of resin processing methods will be adapted to suit them to the characteristics of the modified fibres, such as vacuum bagging, vacuum consolidation, compression moulding, continuous compression moulding, infusion and resin transfer moulding.

Basic research on joining technologies as hot welding over natural fibre composites will be also performed.

Project results:

Since the beginning of the project, an important effort has been focussed in 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 good potential for better compatibility with hydrophobic polymers.

For the development of natural fibre based textile performs 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 characterised with good results. 2D and 3D fabrics from natural fibres and blends of thermoplastic and natural fibres have also been successfully prepared and characterised.

Regarding the adaptation of thermoplastic and thermoset polymers to improve their compatibility with natural fibres, 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 performance closed 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 focussed 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.

Potential impact:

With respect 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 currently work is focussed 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.

The expected final results are that aligned natural fibres with improved properties will be combined with thermoplastics and thermosets, increasing the mechanical properties of biocomposites and introducing them in structural applications in different sectors such as transport, energy, agricultural machinery and shipbuilding.

Considering the importance of the final application sectors, the versatility of use of the fabrics in conventional processes, and the nowadays limitations on the use of natural fibres in composites, an important replacement of the currently used traditional textiles and non-textiles by natural textiles is expected in the composites sector since these natural reinforcements are kept at competitive costs. The numerous advantages of the manufactured composites with natural fibres is significantly contributing to the growth that is expected in textile production and will accelerate the predicted growth ratio for the next 10 years period near 5 %.

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