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Physical extruder foaming of poly(lactic acid)—processing and foam properties
Author(s) -
Larsen Åge,
Neldin Christoffer
Publication year - 2013
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.23341
Subject(s) - materials science , blowing agent , extrusion , crystallinity , composite material , supercritical fluid , nucleation , foaming agent , plastics extrusion , cushioning , lactic acid , supercritical carbon dioxide , rheology , blow molding , porosity , polyurethane , mold , chemistry , organic chemistry , biology , bacteria , genetics
The article describes extrusion foaming of poly(lactic acid) (PLA) using carbon dioxide in the supercritical state as foaming agent emphasizing the steps required to establish a stable extrusion process. Low melt strength of PLA plays a role in optimizing processing conditions. The tests included PLA grades of different viscosity in addition to a chain extender. Processing at low temperature is possible due to the plasticizing effect of the CO 2 on the PLA melt and a sufficiently low melt temperature is also a prerequisite in production of stable foams due to improved melt strength. Foams were characterized by density, cell structure, crystallinity, and mechanical properties in compression. Low density, microcellular foams with density down to 20–30 kg/m 3 were obtained for three different PLA grades. Varying die temperature and pressure drop rate we can explain observed abrupt drops in density with increasing CO 2 content by the interplay between cell nucleation and gas diffusivity at given temperatures. An effect on melt strength similar to using a chain extender is achieved by lowering the melt temperature at the die. Observed variations in sample crystallinity do not correlate with foam density. The PLA foams have good energy absorption capability. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers