See Reusing automotive composites production waste (Part 2)
Current issues with composites recycling
At this time there are chiefly four factors restricting the reuse and/or recycling of production wastes into composite products. First, sending waste to landfill is still by far the cheapest option for manufacturers. Second, few reuse and recycling processes are commercially viable. Third, in terms of the overall impact of recycling processes on the environment, there is likely to be not enough improvement on landfill for it to be a viable option. Fourth, there is a general unwillingness to utilise reused or recycled composites since they are perceived to be of lower quality than virgin material, and it is difficult to ensure consistency in the material performance.
The issue of cost is being resolved from two directions. Legislation being applied to landfill management will generally increase the cost of sending waste to landfill, while advances are being made in reducing the costs of recycling processes as they are scaled up, and links to the issue of a lack of commercial scale processes. For example, in the UK ELG Carbon Fibre Ltd. has scaled up its pyrolysis process to recycle 1200 tonnes of scrap per year in a continuous process, while other international recycling operators continue to do the same. But these are recycling options and large scale reuse processes within manufacturing are realistically still required (especially if using dry fibre which does not need recycling per se). Currently expanding capacities are in fact dwarfed by the increasing quantity of scrap in production (or future End of Life) being produced, but it may also make investment in capacity more readily available in the future (which drastically needs to happen to catch up with the waste produced). This is certainly true for production waste where waste locations and quality can be more adequately controlled. For costs and capacities in composites, it is also worth noting that it is far more appropriate to regard waste by volume than weight, and understand the lost value of scrap material. For example and although generalising, 1 tonne of scrap of 250gsm material is around 4000sqm, and if £25sqm equals £100k, but only costs up to £130 to dispose of (plus shipping etc.). Recapturing and reusing just 25% of such a waste volume could see significant returns depending on several factors such as material type, volume, handling requirements, suitability, and the extent of supplementary materials or processes required.
The issue of environmental impact is very interesting. Life Cycle Assessments (LCA) for landfill, pyrolysis, and incineration with energy recovery have been performed for the recycling of both glass and carbon fibre. Results suggested that for glass fibre it was more environmentally sound to send the material to landfill, while recycling of carbon fibre via pyrolysis could be environmentally beneficial if it reduced the production of virgin fibre (and it emissions). To the authors' knowledge no LCA taking in the impact of the reuse of material has been conducted, or is available at this time.
Finally, the apparent reduction in quality of reused or recycled composite is difficult to solve since the material may have inconsistent properties, and depending on the application being targeted may be simply inferior by product. There are two factors chiefly responsible for this. First, there may be a wide variation in the quality of the feedstock material due to different waste management policies within different manufacturers. Second, the reuse or recycling process may add levels of variability and costs, depending on the method(s) used (for example spinning or aligning of recovered UD tape as bundles). Certainly products available show significant variation with traditional knockdowns in properties; and this is also presently represented in the academic literature (where no consistent metric of comparison between reuse/recovery type and product exists). Generally speaking, whether reuse or recycled composite waste will return short fibre material. Due to these issues, manufacturers are unlikely to use recycled composite reinforcement in structural components in the near term. But there is a market for short fibre materials, and since this is the case, perhaps novel applications for recycled material are required instead of viewing it as a replacement for virgin material.
Reforming production waste for high value applications
To demonstrate the reforming approaches investigated at Bristol a material has been produced that can be used in high value applications. Samples have been made up into tubes and crushed in quasi-static conditions at 18mm per second, to simulate in simple set-up scenarios where energy must be absorbed. This application was chosen for two main reasons. Firstly, ultimate strength is not the primary requirement for crash structures as energy absorption performance is more important. Secondly, despite the potential for the automotive sector to grow into one of the largest consumers of composite materials, some structures will always remain metallic unless the costs of a composite equivalent can be made competitive. Similar works can be found that compare the dynamic performance of an in-date, out-of-life, and recovered fabric (infused with the same resin system) for crash structures. They showed that recovered and reused fabrics could be exploitable in this form of application, with comparable properties to virgin material, albeit reduced compared to the works of others.
Tubes were made from off-cuts of triaxial and biaxial carbon fibre NCF, with individual patch dimensions of 100×50mm. As a design feature, the thickness of the 400mm long tubes was increased down the length, and a failed tube is shown in Figure 6. Results showed the reused coupon material absorbed similar amounts of energy to continuous virgin glass fibre reinforced epoxy, and crushed in a stable and predictable manner, but absorbed more energy as the thickness of the tube increased (see Figure 7). From these initial results more recent work has focussed on understanding the failure event, identifying improvements in structural performance (to increase energy absorption in comparison to continuous carbon fibre equivalents), and exploring repeatability in mechanical performance. Since the reformed material was made from waste, the cost of buying material was technically saved. But the manufacturing time was unsatisfactory, meaning that savings on material would be outweighed by production costs. New results suggest there is scope for material performance to be improved, which would reduce this deficit, but in order for the material to be commercialised, an automated manufacturing process would need to be developed.
Evolution of design requirements
The use of reformed composite materials in both aerospace and automotive is currently restricted by generally accepted design requirements, although variation between the two sectors can be found. Aerospace design is largely driven by conservative allowables, while automotive design appears to be principally driven by process and manufacturing rate. This is likely to be due to the differences in load cases and design life of the vehicles. New aircraft have a design life of more than 35 years, whilst for automobiles it can be expected to be considerably shorter. The geometric tolerances for assembly in the automotive sector are perhaps tighter overall than for aerospace because the shape of an automobile is more design driven, while the shape of an aircraft is functionality driven. For reformed material this means restrictions in application. If it is difficult to ensure consistency in the material due to the discontinuities, both sectors are likely to be unwilling to adopt it for structural components at the present time.
Another major difference between the two sectors is the value: volume ratio. Despite product size differences, per kilogram aircraft are several times more expensive than automobiles, but the rate of production for automotive is many times higher than that of aerospace (for example, around 120 Airbus A350s per annum compared with around 20,000 BMW i3s per annum). It is said that for composite materials to make headway in automotive a more than 95% reduction in component cost, relative to aerospace, is needed and so collaborations between the sectors is beginning. Examples such as recycling are becoming available, and so convergence in design requirements (such as design for X) may be likely in the future. Such convergence suggests that a period of transition is likely to be needed in industrialising composite material use in both sectors, if they are to become widely accessible to higher volume production. The mass market automotive sector will seek to move to true composite structures (as opposed to composite clad metallic frames), whilst retaining its need for high volume: low value. Aerospace will look towards moving composite production from low volume: high value to medium volume: medium value, as the new generation of narrow body aircraft is designed. It is at this point of transition that there is an opportunity for reformed composites to demonstrate its capabilities and suitability to be used in these markets.
Future direction
The mass market automotive industry has certainly begun to move towards applying composite materials; and this includes the application of recycled materials. An example of this is the roof panel of the BMW i8, manufactured using reformed production waste carbon fibre as a random mat. As a commercial demonstrator this is excellent, but owing to costs it is likely a cheaper material could have been used due to the probable low structural loading on it. As noted previously, there is still some way to go before composites are used in the mass market automotive sector to their full potential in principal structural or sacrificial components. This is important given the Life Cycle Assessment reviews of advanced composites, examples of the performance of recycling options; and its impact on the use in the aerospace, and automotive where recycled material is suggested to be the only competitive material (although reused material will be a further benefit).
The aligned reformed material being investigated at Bristol is an example of potential progress towards this primary structure goal. Although the research is currently at a low Technology Readiness Level (TRL), it has suggested that discontinuous material performs well in energy absorbing load cases. This is hoped to be a more valuable use for reused materials than merely body panels. In order to move on from the laboratory to a commercially robust venture, a suitable manufacturing process needs to be investigated, and examples such as Patch Preforming or Part via Preform are attractive. Generally, manufacture needs to be inexpensive and as quick as possible to be competitive with manufacturing processes for other materials. But this is somewhat hindered by the nature of recovered materials having an initial cost for capture and handling; and so this will firstly need to be reduced for it to become commercially viable. One potential method to reduce this would be to include a waste collection system and a reforming station directly within the manufacturing centre of virgin material components to cut out any logistics costs (thus limiting capital risks, however to date much more emphasis has been placed on recovery processes than on collection, handling and sorting. It is certainly true that a waste management system is needed that considers the full hierarchy and the stages of the materials in terms of value, structure, and capability. If attained, then the future of composite recycling could be very promising.
Final remarks
The use of advanced composites in the early adopting industries has been steadily increasing, but risks plateauing somewhat in the near future. On the other hand, in the mass market automotive industry we are potentially on the verge of seeing a rapid and vast increase in composites use, albeit for relatively low value: high volume components (transport and associated industries may also expand into composites). A driver for this uptake is the need to reduce vehicles structural weight – electric vehicles in particular require light-weighting to account for the added mass of the storage cell(s). This uptake into the automotive sector is possible because of increasing amounts of work in reducing costs associated with design and manufacture, leading to increased material use.
Waste technology research is part of this effort, be it a reduction or reuse of the waste generated, or methods of re-applying materials back into production. Significant research effort has focussed on End of Life, but what work that has been done tends to concentrate on recovery of one product at the expense of the other, use of that recovered material in lower value structures, or employing options such as using it as low value filler. In comparison to the End of Life scene, production waste has not been looked at in any great detail; perhaps as it is seen as an element of the manufacturing process and factory system, rather than a visible waste source. Many production/manufacturing sites are implementing ISO 14000 (environmental) and ISO 9000 (quality) management status. Although not directly influencing waste management, the standards expect efficient and effective management of processes (ISO 9000) and environmental impact reductions (ISO 14000) and this may offer positive change. What work that has been done has researched scrap reduction or lower quality reuse, and not from the point of view that it may be possible to reuse it for high value applications in place of virgin materials. The work at the University of Bristol and some others is a step towards reusing material directly from production for high value use. The research is trying to turn the issue from a negative attitude of “how do we get rid of this waste” to a positive one of “how do we recover as much value out of this material as possible.”
The authors gratefully acknowledge the support of the Engineering and Physical Sciences Research Council (EPSRC), through the EPSRC Centre for Innovative Manufacturing in Composites (CIMComp)(Grant: EP/IO33513/1), and the G8-2012 Material efficiency – a first step toward sustainable manufacture(Grant: EP/K025023/1).
