Structure property interrelationship in FDM printed polyetherimide and carbon fiber reinforced PEI composites: A comprehensive mechanical and microstructural evaluation

Polyetherimide (PEI) is a high-performance thermoplastic material suitable for advanced engineering applications due to its excellent thermal stability, chemical resistance and mechanical properties. In recent times, carbon fiber reinforcement has been explored for further enhancing stiffness and load-bearing capability. In this investigation the components were fabricated using fused deposition modeling (FDM) to examine mechanical behaviour and microstructural features of polyetherimide (PEI) and 20 wt% carbon-fiber-reinforced PEI (CF20/PEI). Mechanical tests revealed a substantial increase in elastic modulus of the composite. Although carbon fiber reinforcement increased the elastic modulus of PEI, it reduced tensile strength by 30%, elongation at break by 69%, flexural strength by 50% and ILSS by 56% because of increased porosity, fiber pull-out, and weak interfacial bonding. Field-emission scanning electron microscopy (FESEM) disclosed higher porosity, interfacial voids and inadequate fiber matrix adhesion in CF20/PEI, indicating transition toward brittle fracture and contributing observed reduction in overall performance. The results emphasise the critical role of processing induced microstructure in determining performance of high-performance thermoplastic composites manufactured by additive techniques.