Optimization of the sieving process as applied to mechanical recycling of glass fibre reinforced composites

With rapid composites development, immense quantities of fibreglass waste will accumulate in the environment. Mechanical recycling has been shown to be an adequate method to tackle this problem, while Fused Filament Fabrication (FFF) could serve as a high-value application of recyclate. In this lab-scale study, the important sieving step in mechanical recycling was optimized using a coupled Taguchi and Grey Relational Analysis approach to improve the yield percent of useable fine recyclate and its yield rate while minimizing the content of oversized fibres. Shredded and ground fibreglass composite was sieved in a 200 mm diameter shaker while the input mass, sieving duration, anticaking additive content, and sieving aid content were varied according to the Taguchi arrays. A 35 % yield and a 2.0 g/min or 120 g/h yield rate of fine recyclate were achieved, while a range of 0.4–8.6 % oversized fibre content was observed. Using Grey Relational Analysis, the best operating condition was achieved with 30 wt % of sieve input, 20 min of sieving time, and 100 % sieving aid coverage on the 600, 425, 250, and 150 μm sieves. Fibre length distributions were mostly similar between the runs. Overall, percentage yield and yield rate behaved in competition, where optimizing for one reduced the other. Sieving aids benefited both performance metrics simultaneously. Use of fumed silica, a finely powdered anticaking additive used by industry to reduce agglomeration, was found to be detrimental during Grey Relational Analysis, while maximal sieving aid content was preferred.