Effect of stereocomplexation on the microcellular foaming behaviour at high temperature, compressive property and heat resistance of branched poly(L-lactide)/poly(D-lactide)

To improve the melt strength and crystallisation property of polylactic acid (PLA) for achieving a good foaming performance at high temperatures, linear poly(l-lactide) (PLLA) was mixed with an epoxy chain extender to obtain branched PLLA (bPLLA), which was then blended with poly(d-lactide) (PDLA) to prepare a bPLLA/PDLA blend. The bPLLA/PDLA blend produced stereocomplex (SC) crystals, which increased the melt strength and viscosity of the blend. The synergistic effect of the SC crystals and the branched structure endowed bPLLA/PDLA with high melt strength and processability. In contrast, the nucleation effect of the SC crystals on bPLLA reduced the cell size, resulting in excellent microcellular foamability at the melting temperature. The formation of SC crystals in the blending process increased the crystallinity and enhanced the cell structure. As a result, the compressive strength of bPLLA/PDLA is increased from 0.44 MPa to 0.72 MPa. At 150°C, the dimensional deformation rate decreased from 42.59–13.13%, whereas the heat resistance increased by > 300%. This research provides a facile method for preparing PLA microcellular foams with high performance at high temperatures, which is essential for practical applications.