A key question facing the composites industry 鈥� What happens to manufacturing waste and end-of-life parts? 鈥� has been silently swept under the rug for years as companies resigned themselves to paying for landfill disposal while metals suppliers touted recyclability to industry. But at least three marketplace realities have converged to drive the growth of composites material recycling, particularly reclamation of carbon fiber:
- First, the European Union鈥檚 end-of-life-vehicle (ELV) directive聽requires聽that 85%, by weight, of the materials used in a car or light truck must be reusable or recyclable.
- Second, carbon fiber鈥檚 high manufacturing cost and high performance, even in chopped form, make it an attractive recycling target, which is creating market pull for recycled fiber products, most notably, from automotive.
- Finally, the newest generations of consumers were raised on environmental awareness, actively support recycling activities and closed-loop manufacturing, and seek out goods with recycled content.
础濒迟丑辞耻驳丑听CW鈥檚 coverage of composites recycling dates back over a decade, informal statistics still show that only ~2% of composites-related companies are active recyclers. That said, three years since our most recent feature on the subject, there is demonstrably greater interest and activity, and real applications of recycled fiber are growing. This blog summarizes the upcoming article which will appear in print in the July issue of CompositesWorld magazine.
The technologies: different approaches
One reason aluminum and steel remain formidable competitors to composites is their suppliers鈥� long track records in recycling, which has helped reduce their overall material production costs, says Ed Pilpel, senior technical advisor at Polyone Advanced Composites (Englewood, CO, US) and the current recycling committee chairman at the American Composites Manufacturers Assn. (ACMA, Arlington, VA, US). 鈥淏ut it took those industries 30-50 years to achieve their current success rate at recycling, which for aluminum is upward of 80%. The composites industry is much younger, and we have years to go,鈥� he admits, 鈥渂ut we鈥檝e got to jump into the deep end of the pool and get going.鈥�
Those who聽have聽jumped in are employing several recycling strategies, separately or in combination. Most initial efforts have focused on reclamation and reuse of high-quality carbon fiber material waste streams, typically from aerospace manufacturing, because they are relatively easy to work with聽and聽yield high-quality carbon fibers with properties virtually undiminished, albeit in chopped form (continuous fiber can also be recovered, discussed below). Waste sources include off-spec material, cutting/trimming/kitting scraps (dry and prepreg) and bobbin ends, including thermoset and thermoplastic materials.
Current commercial methods for eliminating the resin from the carbon fibers are聽pyrolysis聽(thermal treatment) and聽solvolysis聽(chemical treatment). Although pyrolysis requires thermal energy to burn off the resin, and can cause fibers to char, the energy of pyrolysis represents only a fraction of the embodied energy of virgin carbon fiber. Some sources say solvolysis requires even more energy than thermal treatment, but it enables recovery of fiber聽and聽resin. In both processes, the recovered fibers transfer well to nonwoven mats or thermoplastic pellets for injection molding, and are a natural fit for automotive part applications.
More difficult is recycling of end-of-life (EOL) cured parts to complete a true 鈥渃losed-loop鈥� situation, where materials are recovered from scrapped products and reused in new iterations of those products. Pyrolysis and solvolysis can be applied to cured parts, as can mechanical crushing, typically used for fiberglass parts; the resulting crushed glass/resin material is either reused as a resin filler, burned for energy (waste to energy plants) or co-processed in cement kilns.
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