Recycling C/PPS laminates into long fibre thermoplastic composites by low shear mixing

The increasing interest in continuous fibre reinforced thermoplastic composites has resulted in a rise of industrial waste. The recycling of the waste is topic of this study, aiming at high mechanical properties by retaining both a long fibre length and the matrix material. Consolidated continuous carbon fibres reinforced PPS laminate waste was collected, shredded to flakes of 20 mm on average and processed by a small scale and low-cost mixing machine at different volume fractions. The benefit of this machine resides in a low shear mixing phase that prevents fibre breakage but heats and mixes the material well. By a piston the charge was transferred into a compression mould for forming and consolidation of plates. Samples were cut and analysed by flexural bending tests. Cross-sectional microscopy was used to further analyse the composite quality and structure. Micro mechanical models of Tandon Weng and Kelly Tyson were used to predict the stiffness and strength depending on fibre orientation, fibre length and fibre content. Properties of the recycled material were compared to the predictions, to samples made of the virgin continues fibre material and to samples made of commercially available 3mm long pellets. Experimental values of the recycled material increase with fibre fraction at a sample rate, but slightly lower compared to theoretical values. At higher fibre content the properties limit out, not reaching continuous fibre laminates. Strength values show a trend similar to the one predicted by the random 2D Kelly-Tyson model. Microscopic images display a disentanglement of the woven structure from the input material. No significant difficulties were found during processing underlining the robustness of the studied process.