Superior Performance of Fully Biobased Poly(lactide) via Stereocomplexation-Induced Phase Separation: Structure versus Property
2015
Ma, Piming | Shen, Tianfeng | Xu, Pengwu | Dong, Weifu | Lemstra, Piet J. | Chen, Mingqing
Superior properties such as high strength, toughness and transparency of fully biobased poly(lactide) (PLA) were achieved simultaneously without any external modifiers. The improvement in properties is well explained by a structural/morphological study. Stereocomplex PLA (SC-PLA) was obtained by melt compounding asymmetric poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends at 200 °C and confirmed by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) analyses. The SC-PLA domains (d = 950–1200 nm) lead to a physical cross-link network in the PLLA matrix. Rheology and Molau experiment reveal two different microstructures as a function of SC-PLA content, i.e., the connection of SC-PLA domains varied from chain entanglement to direct molecular bridging when the SC-PLA content increased from 10% to 23%. The SC-PLA crystals and the cross-link network reinforced the PLLA matrix, resulting in increases in melt viscosity, modulus and yield strength. Surprisingly, the elongation at break of the PLLA/PDLA blends was increased concomitantly from 11% to 200% with the SC-PLA content up to 10%. The brittle-to-ductile transition is ascribed to the cross-link network and easy deformation/cavitation of the SC-PLA domains. In addition, the asymmetric PLLA/PDLA blends exhibit an average visible light transmittance as high as 70% and the blends showed excellent heat-resistance after a short annealing at 100 °C.
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