High Performance Discontinuous Fibre Composites - a sustainable route to the next generation of composites

Continuous carbon fibre composites are capable of competing directly with advanced metals in terms of structural performance. The advantages of composites come from the ability to manufacture complex shapes, generally in relatively low volume production, in weight saving and corrosion resistance. However, continuous fibre composites are difficulties to manufacture, leading to both high costs and to the potential for generation of a range of defects impacting strongly on performance. In addition, continuous fibre composites cannot be directly recycled as there is no way of reusing the fibres that can be extracted in long, but not continuous and topologically ordered form. From an examination of the current status of the composites industry two big challenges can be identified. The first is to increase defect-free production volumes by at least an order of magnitude - leading directly to the need to simplify and automate the manufacturing processes [12]. The second is the requirement to generate more sustainable composites solutions by moving towards a circular economy based model [13] via the development of recycling processes able to retain the material's mechanical properties and economic value. In principle, there is nothing new in this analysis of the challenges, however, a great deal of research activity has been expended in these areas in the last two decades without achieving a step-change in capability. The central thesis of this proposal is that the principal difficulties in both achieving low cost, reliable, high volume production and readily recyclable advanced composites arise from a single source: the fact that the fibres are continuous and that both problem areas can be directly tackled by adopting highly Aligned Discontinuous Fibre Reinforced Composites (ADFRCs).
Our vision is to generate a fundamental step-change in the composite industry by further developing and applying the HiPerDiF (High Performance Discontinuous Fibre) technology to produce high performance ADFRCs. This new, high volume manufacturing method was invented at the University of Bristol in the EPSRC funded HiPerDuCT (High Performance Ductile Composite Technology) programme (EP/I02946X/1). The basic concept is that if discontinuous fibres are accurately aligned and their length is significantly longer than the critical fibre length, the tensile modulus, strength and failure strain of the obtained composites are comparable to those of continuous fibre composites. This technique, developed in the HiPerDuCT programme has also shown the potential to tailor mechanical behaviour of composite materials, delivering pseudo-ductility via hybridisation and fibre pull-out mechanisms. The HiPerDiF technology offers the opportunity to realise the potential of aligned discontinuous fibre composites and produce a significant industrial and societal impact.
Changing the fibre reinforcement geometry from continuous to discontinuous, without compromising the mechanical properties, will have a wide impact on the composite industry. The fibre discontinuity will allow an increase in the productivity of automated manufacturing processes and the formability of complex geometries, reducing the manufacturing generated defects. The use of ADFRC will increase the tailorability of composite materials by leading to truly multifunctional composite materials, able to respond to multiple design requirements. ADFRC will open the way for the adoption of a circular economy model in the composite sector by allowing the remanufacturing of reclaimed carbon fibres in high performance and high value feedstock and by producing more readily recyclable materials.

The development, manufacturing and use of polymer composites have been highlighted at the highest levels in Government as a key aspect of the UK's current and future industrial strategy. This has been underpinned by the publication of the UK composites strategy and major infrastructural investment in the form of a National Composites Centre (NCC), led by UoB and industry. The development of novel reinforcement types and the associated manufacturing processes and equipment offers very significant opportunities to expand and develop the UK composites industry. Shifting towards ADFRC will significantly widen the application of composites materials and will generate an expansion into new applications and markets. A wide range of industries involved in the production of raw materials and automated manufacturing solutions for composites will benefit from the development of novel ADFRCs. Fibre reclamation industries and natural fibres growers/processors will be able to widen their market, generating employment opportunities in the composite and ancillary sectors. Recyclable thermoset plastics producers, which are struggling to find suitable applications despite the potential of their products, will have new applications potential to explore.
The development of intrinsically recyclable composites would open up the possibility for the application of a circular economy model in the composite sector, making it more resilient to fluctuations in the international raw materials markets, less reliant on imports, and helping it to reduce its carbon footprint. Therefore, the HiPerDiF process, offering a route to a circular economy UK composite industry, will make it more resilient, independent and environmentally conscious; helping the UK to retain its world-leading role. Moreover, the adoption of this model and the improvement in the automated manufacturing will have lasting beneficial effects on the labour market, generating jobs across the composite industries.
New design and manufacturing approaches will allow the application of composites into new research fields and markets. The National Composites Centre in Bristol is the UK's principal investment in the development of composites manufacturing processes and will work closely with this project to ensure that the commercial impact of the project is maximised. The new fundamental knowledge that will be generated during the project will not only be made available to the industrial and academic world but also to a wider public with the aim of stimulating a debate about the composite materials recycling and sourcing policies and new and less conventional applications of composite materials.