Mihai Mihaela, Huneault Michel A, Favis Basil D, Li Hongbo
CREPEC, Chemical Engineering Department, Ecole Polytechnique de Montréal, P.O. Box 6079, Station Centre-Ville, Montréal, Québec, Canada, H3C 3A7.
Macromol Biosci. 2007 Jul 9;7(7):907-20. doi: 10.1002/mabi.200700080.
Low density open-cell foams were obtained from polylactic acid (PLA) and from blends of PLA with thermoplastic starch (TPS) using CO(2) as a blowing agent. Two unexpected features were found. First, a 2D cavitation process in the fractured cell walls was unveiled. Elliptical cavities with dimensions in the 100-300 nm range were aligned perpendicular to large cell cracks clearly exhibiting 2D crazing prior to macroscopic cell rupture. Secondly, a significant crystallization rate increase associated with the CO(2) foaming of PLA was discovered. While the PLA used in this study crystallized very slowly in isothermal crystallization, the PLA foams exhibited up to 15% crystallinity, providing evidence that CO(2) plasticization and the biaxial stretching upon foam expansion provided conditions that could increase the crystallization rate by several orders of magnitude.
使用二氧化碳作为发泡剂，从聚乳酸（PLA）以及PLA与热塑性淀粉（TPS）的共混物中制备出了低密度开孔泡沫材料。发现了两个意外的特征。首先，揭示了破裂泡孔壁中的二维空化过程。尺寸在100 - 300纳米范围内的椭圆形空洞垂直排列在大的泡孔裂缝处，在宏观泡孔破裂之前明显呈现出二维银纹化。其次，发现与PLA的二氧化碳发泡相关的显著结晶速率增加。虽然本研究中使用的PLA在等温结晶过程中结晶非常缓慢，但PLA泡沫材料表现出高达15%的结晶度，这证明二氧化碳增塑以及泡沫膨胀时的双轴拉伸提供了能够将结晶速率提高几个数量级的条件。
