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Extrusion Foaming of Semi‐Crystalline PLA and PLA/Thermoplastic Starch Blends
Author(s) -
Mihai Mihaela,
Huneault Michel A.,
Favis Basil D.,
Li Hongbo
Publication year - 2007
Publication title -
macromolecular bioscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.924
H-Index - 105
eISSN - 1616-5195
pISSN - 1616-5187
DOI - 10.1002/mabi.200700080
Subject(s) - crystallinity , polylactic acid , extrusion , crystallization , materials science , thermoplastic , composite material , crazing , plasticizer , starch , blowing agent , chemical engineering , polymer chemistry , chemistry , polymer , polyurethane , biochemistry , engineering
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.