Investigation on the reuse of recycled carbon fibers in various non-wovens for HP-RTM and WCM processes

Abstract

Nowadays increased efficiency is demanded more and more often and becomes a crucial part of technology and development. A possible solution is the reduction of moving masses, which is often realized by substituting materials with carbon fiber reinforced plastics (CFRP). On the contrary, the production of carbon fiber reinforced plastics often creates great amounts of fiber waste. Furthermore the recycling of end-of-life parts will further increase the quantities of carbon fiber waste. This waste material is only used as a short fiber reinforcement in sheet molding compound (SMC) or bulk molding compound (BMC). An alternative is the production of non-woven fabrics. In this study non-woven fabrics from recycled carbon fibers are successfully infiltrated with a fast curing epoxy system in high pressure resin transfer molding process (HP-RTM) and wet compression molding process (WCM) and their mechanical properties are determined. Needle punched ’airlay’ and ’carding’ type non-wovens with area densities from 300-900 g/m2, and initial fiber lengths of 60-110mm are used. Some non-wovens are further reinforced with the ’maliwatt’ technology. It is possible to find process parameters for successful infiltration of non-wovens with an average carbon fiber volume fraction of 20-40% in the composite using a plate geometry. Tensile, flexure and compression testing are conducted and reveal that ’carding’ type materials, and ’airlay’ type materials with 110mm initial fiber length, have an anisotropic behavior. ’Airlay’type materials with initial fiber lengths of 60-90mm show an isotropic behavior. Large deviations of the fiber volume fractions and area densities of up to 25% from the expected mean value are discovered for some types of non-wovens. SEM scans of fracture surfaces reveal fiber bundles indicating a need for further improvement of the non-woven production process. Finally, no significant difference of the infusion processes on the tested materials properties are recognizable.