Nitrogen-Assisted Foam Injection Molding of Polylactide with Carbon Fibers and PTFE Nanofibrils

Abstract Polylactide (PLA)-based foams are viable sustainable alternatives to traditional petroleum-derived foams owing to their intrinsic biodegradability, superior biocompatibility, light weight, and high specific strength, with potential applications in packaging, insulation, and biomedical fields. However, their inherently low melt strength and slow crystallization kinetics hinder the development of high-performance PLA foams. A reinforcement strategy combining in situ fibrillated polytetrafluoroethylene (PTFE) and carbon fibers (CFs) is applied to enhance the morphological, rheological, thermal, mechanical, and foaming behavior of PLA foams fabricated using nitrogen-assisted foam injection molding (FIM). The combined PTFE/CF reinforcement resulted in uniform cell nucleation and a refined microcellular foam structure. Rheological analysis showed a higher complex viscosity and storage modulus, indicating the formation of a percolated fibrillar network. Notably, extensional viscosity measurements showed that the incorporation of only 0.5 wt % CF induced pronounced strong strain hardening, leading to improved melt strength and foamability. The foam density of composites lowered 15% compared with pure PLA foam. The compressive strength and flexural stiffness improved significantly as compared to pure PLA foams by more than 11% and 20.5%, respectively. Furthermore, the thermal conductivity of the composite foam decreased by 21% with the addition of carbon fiber (CF), indicating improved thermal insulation. These findings demonstrate a promising strategy for developing PLA-based nanocomposite foams for lightweight structural and thermal-insulation applications.