Effect of Stereocomplexation on High-temperature Microcellular Foaming Behaviour, Compressive Property and Heat Resistance of Branched Poly(l-lactide)/poly(d-lactide)

In our study, in order to prepare PLA microcellular foam at high temperature, linear polylactic acid (L-lactone) (PLLA) was mixed with epoxy resin chain extender, and then blended with polylactic acid (D-lactone) (PDLA) to prepare bPLLA/PDLA mixture. The bPLLA/PDLA mixture produces stereocomplex (SC) crystals. The addition of SC crystal as a melt enhancer resulted in a significant enhancement of the melt strength of bPLLA, with an increase of 10⁴. Furthermore, the nucleation effect increased the overall crystallinity (X_C) of the bPLLA/PDLA blends from 5.29 to 23.21%, thereby enhancing the heat resistance of the bPLLA/PDLA blends. The hot deformation temperature was increased from 55.5 °C to 62.4 °C. During the foaming process, SC crystals acted as nucleating agents for bubbles, reducing the cell diameter from 30.59 μm to 3.09 μm, increasing the cell density by 10², and improving cell uniformity. In addition, an increase in PDLA content resulted in a notable enhancement in the compressive strength of bPLLA foam, from 0.44 MPa to 0.72 MPa. After heat treatment at 150 °C, the dimensional deformation was found to decrease from 42.59 to 13.13%, accompanied by an improvement in heat resistance. This study presents a simple method for the preparation of PLA microporous foam at high temperatures, resulting in the production of high-performance PLA foam, which is of great significance for the development of batch foaming towards industrial continuous foaming production.