Improving Stiffness, Strength, and Toughness of Poly(omega-pentadecalactone) Fibers through in Situ Reinforcement with a Vanillic Acid-Based Thermotropic Liquid Crystalline Polyester

We report on the morphology and performance of melt drawn poly(omega-pentadecalactone) (PPDL) fibers reinforced with a vanillic acid-based thermotropic liquid crystalline polyester (LCP). The in situ reinforced PPDL/LCP fibers developed in this work are considered to be renewable in nature, given the fact that the feedstock for both polymers can be obtained from natural resources. To prepare these fibers, the polymers were mixed in a small scale twin-screw extruder, followed by melt-drawing of the extrudate. It is demonstrated that the tensile modulus and tensile strength of the fibers increase with increasing LCP orientation and concentration. Despite the brittle nature of the pure LCP component, melt-spun PPDL/LCP fibers maintain their ductile deformation for fibers containing up to 30 wt % LCP. The improved stiffness and strength of these PPDL/LCP fibers in combination with their ductile nature ensure improved energy absorption during deformation and effectively increases their toughness compared to the pure PPDL material. A further increase of the LCP content to 40 wt % and higher results in a poor control over the blend morphology, and brittle failure of the fibers is observed after the application of 2-3% strain. Small angle X-ray scattering data indicate that after processing, transcrystallization of PPDL occurs on the surface of the oriented LCP phase. According to DSC analysis, this transcrystallization on the oriented LCP fibrils is accompanied by an increase in the crystallization temperature. These findings have been confirmed through morphological analysis using transmission electron microscopy. It is anticipated that this interfacial crystallization strengthens the PPDL/LCP interface and allows delocalization of stress during deformation