Physical extruder foaming of poly(lactic acid)—processing and foam properties

Abstract

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 CO2 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/m3 were obtained for three different PLA grades. Varying die temperature and pressure drop rate we can explain observed abrupt drops in density with increasing CO2 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

Mastering the structure of PLA foams made with extrusion assisted by supercritical CO2

“…They are listed in Table . In this study, T 2 and T 3 were fixed at 180 °C to ensure a molten polymer in the barrel before and after the CO 2 injection . T 5 and T 6 were first set up at 160 °C before injecting the CO 2 .…”

Foaming of Polylactide in the Presence of Chain Extender

“…where DHm (J/g) is the melting enthalpy, DHc (J/g) is the cold crystallization enthalpy and DHm°is the melting enthalpy of a 100 % crystalline PLA reported to be equal to 93 J/g [16].…”

“…They concluded that the increase in crystallinity can be a way to overcome the problems of dimensional stability, provided that it can omit the processing difficulties associated with crystalline polymers. Larsen and Neldin [16] have studied qualitative differences between PLA 2002D, 3251D and 8052D at foaming. It was shown that the material density decreased abruptly or gradually as a function of the blowing agent (CO 2 ) solubility.…”

Chain Extension and Foaming Behavior of Poly(lactic acid) by Functionalized Multiwalled Carbon Nanotubes and Chain Extender

“…[7][8][9][10][11][12] Matuana and Diaz added the nanoclay as the nucleating agent in the PLA during the foaming process through a continuous-extrusion system and studied the heterogeneous nucleation effect of nanoclay on the cellular morphology of PLA foam. [7][8][9][10][11][12] Matuana and Diaz added the nanoclay as the nucleating agent in the PLA during the foaming process through a continuous-extrusion system and studied the heterogeneous nucleation effect of nanoclay on the cellular morphology of PLA foam.…”

“…9 Kohlhoff and Ohshima reported a kind of microcellular foam with an open porous structure prepared by PLA blended with polystyrene or poly(methyl methacrylate). 11 To produce PLA with high melt viscosity and elasticity for foaming, 1,4-butanediol and 1,4-butane diisocyanate as low-molecular-weight chain extenders were added into PLA in a Haake melt mixer. The important finding was that the addition of chain extender could introduce inhomogeneities in the PLA matrix.…”