Development of recycled carbon fibre moulding compounds - Preparation of waste composites

Critical to the recovery of high value fibres from any recycling processes is the preparation of waste material for input to the processes. Higher fibre lengths have greater intrinsic value further down the carbon fibre lifecycle due to their ability to achieve higher mechanical properties in moulded parts. The fluidised bed process under investigation is more effective at processing shorter fibre lengths and thus, ideally, a narrow range of intermediate length fibres is desired from any comminution process. The granulating process is investigated here for the comminution of fibres from scrap prepreg. Various granulator screens are investigated for three woven and three non-crimp prepreg forms. The resulting material is sieved to provide an indication of mass fraction at various fibre lengths. Fibre: resin mass fractions are given at the various sieved sizes and an optical method is presented for analysis of the true size of the prepreg pieces. Results show that the materials tested behave in a predictable manner and fibre lengths are within the range sought for the recovery process. Optical analysis shows that the sieving measures the minor axis dimension of the pieces and thus with knowledge of the mean aspect ratio the sieving process can be calibrated to provide a rapid and accurate assessment of particle size.