Effect of needle-punching on the internal morphology and mechanical properties of recycled non-woven carbon fiber reinforced thermoplastics with tailored anisotropic ratio

The ongoing environmental crisis and growing demand for sustainability pose significant challenges to the widespread adoption of carbon fiber composites. Regulations aimed at reducing carbon emissions emphasize the importance of incorporating recycled carbon fiber (rCF). This study investigates the internal morphology and mechanical behavior of needle-punched non-woven carbon fiber reinforced thermoplastics (NW-CFRTP) using rCF as reinforcing substrate and polyamide-6 as base matrix. NW-CFRTP offer a promising alternative to continuous composites as they enable tailoring of mechanical performance by anisotropic ratio. Needle-punching is a widely employed process to improve material handling, property stabilization, and flow deterrence – key considerations for large-scale production. However, there are concerns regarding its potential adverse effects on the high in-plane mechanical properties. The NW-CFRTP in this study utilized orientation tailored rCF to enhance directional mechanical properties, making it more suitable for structural members in automotive applications. Internal morphology was analyzed through X-ray micro-computed tomography scanning to evaluate tensorial anisotropy and flow behavior. Mechanical properties were experimentally assessed and further analyzed through multi-scale modelling approach to estimate engineering constants. Results indicate that needle-punching effectively mitigates turbulent flow while preserving fiber orientation and planarity, with minimal compromise in mechanical performance. The tailored NW-CFRTP in this study, to the best of the author's knowledge, achieved the highest reported performance for recycled discontinuous CFRTP with fiber volume fraction below 30 %, demonstrating exceptional fiber utilization efficiency. Finally, the theoretical properties derived through multi-scale modelling provide a solid foundation for finite element analysis to support adoption of the material on a larger scale.