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

In this study, the outcome of operating conditions of extrusion assisted by supercritical CO2 for the manufacture of poly(lactic acid) foams was investigated. It was found that the temperature before and inside the die was the most prominent parameter to tune the foam properties. Foam porosity as high as 96% could be obtained (for die temperature between 109 and 112 degrees C), representing a total expansion exceeding 30. In this temperature range, low crystallinity (approximate to 6%) was induced giving foams with high radial expansion i.e., large diameters and open porosity. At 112 degrees C, the CO2 was able to greatly expand the foams, providing 73% of its potential blowing effect. On the other hand, a low die temperature (below a die temperature of 107 degrees C) induces a significantly higher level of crystallinity resulting in foams with closed-porosity and a large longitudinal expansion due to higher strength of the polymer melt. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45067.