Fibre length distribution of shredded thermoplastic composite scrap

Shredding is a crucial step when recycling thermoplastic composite waste. The outcome of this step can be in the form of flakes or particles of various size, which strongly depend on the chosen shredding solution and the material type. It was shown that the mechanical properties of a part manufactured with these flakes are influenced by the fibre length of those. Characterising the length of fibres in the flakes is therefore important to link it with mechanical properties [1]–[4]. Literature on characterising FLD in the case of large (a few centimetres) and multi-layered flakes is scarce. However, recycling solutions for these flake sizes exist [5], confirming the interest for this topic. In order to fill this gap, this paper firstly develops a method to determine the FLD of a batch of flakes and secondly investigates the effect of both process parameters and waste size on the FLD. The newly developed method is based on the image processing of flakes. Besides, the sampling process that is linked to the image processing method was found to be both repeatable and reproducible at a high precision, showing that batch-process recycling is robust with respect to the influence of sampling . Following that, ways to tailor the FLD were explored. It seems that the scrap size does not influence the FLD but blade width and screen size of the shredding machine largely govern this FLD.