Interfacial cylindrite of poly(lactic acid) induced by pulling a single glass fiber

The shear-induced interfacial crystallization structure and morphology of poly(lactic acid) (PLA) was investigated by pulling a single glass fiber (GF) at different velocities and over different durations at 120 degrees C. The hierarchical cylindrites with two layers were found when the GF pulling speed or pulling time arrived at a critical value according to the polarized optical microscopy (POM) results. Beyond the critical value, the cylindrite thickness of the inner layer sharply increased and finally reached saturation at 18.5 mu m along the radial direction. The POM results were consistent with the value of the shear affected range assessed by the thermo-mechanical model (Monasse, 1992). The relative degree of crystallinity (A(922)/A(956)), based on polarized Fourier transform infrared spectroscopy (FTIR), increased with fiber pulling speed, and then reached a plateau at 1.68, corresponding to the critical speed. The spatial competitiveness at the fiber surface is the main factor responsible for the formation mechanism of the cylindrite, especially the hierarchical cylindrite.