Kajornprai Todsapol, Suttiruengwong Supakij, Sirisinha Kalyanee
Department of Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
Department of Materials Science and Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Sanamchandra Palace Campus, Nakhon Pathom 73000, Thailand.
Polymers (Basel). 2021 Sep 10;13(18):3066. doi: 10.3390/polym13183066.
Crystalline morphology and phase structure play a decisive role in determining the properties of polymer blends. In this research, biodegradable blends of poly(l-lactic acid) (PLLA) and poly(butylene succinate) (PBS) have been prepared by melt-extrusion and molded into specimens with rapid cooling. The crystalline morphology (e.g., crystallinity, crystal type and perfection) is manipulated by annealing the molded products from solid-state within a short time. This work emphasizes on the effects of annealing conditions on crystallization and properties of the blends, especially impact toughness and thermal stability. Phase-separation morphology with PBS dispersed particles smaller than 1 μm is created in the blends. The blend properties are successfully dictated by controlling the crystalline morphology. Increasing crystallinity alone does not ensure the enhancement of impact toughness. A great improvement of impact strength and heat resistance is achieved when the PLLA/PBS (80/20) blends are plasticized with 5% medium molecular-weight poly(ethylene glycol), and simultaneously heat-treated at a temperature close to the cold-crystallization of PLLA. The plasticized blend annealed at 92 °C for only 10 min exhibits ten-fold impact strength over the starting PLLA and slightly higher heat distortion temperature. The microscopic study demonstrates the fracture mechanism changes from crazing to shear yielding in this annealed sample.
结晶形态和相结构在决定聚合物共混物的性能方面起着决定性作用。在本研究中，通过熔融挤出制备了聚（L-乳酸）（PLLA）和聚丁二酸丁二醇酯（PBS）的可生物降解共混物，并通过快速冷却将其模塑成试样。通过在短时间内对模塑产品进行固态退火来控制结晶形态（例如，结晶度、晶体类型和完善程度）。这项工作重点研究了退火条件对共混物结晶和性能的影响，特别是冲击韧性和热稳定性。在共混物中形成了PBS分散颗粒小于1μm的相分离形态。通过控制结晶形态成功地决定了共混物的性能。仅增加结晶度并不能确保冲击韧性的提高。当PLLA/PBS（80/20）共混物用5%的中分子量聚乙二醇增塑，并同时在接近PLLA冷结晶的温度下进行热处理时，冲击强度和耐热性有了很大提高。在92℃下仅退火10分钟的增塑共混物的冲击强度比起始PLLA高十倍，热变形温度略高。微观研究表明，在该退火样品中，断裂机制从银纹转变为剪切屈服。
