Enhanced polylactide stereocomplexes by aluminum oxide particles for reliable thermal conductivity at elevated temperature

Stereocomplex-type polylactide (sc-PLA) with high heat resistance provides great promise for renewable and environmentally friendly PLA as alternative engineering plastics. However, due to the weak melt memory of stereocomplex (sc) crystallites, that is, its poor ability to reform sc crystallites after melting, sc-PLA cannot be processed by conventional melting methods, and its lack of functional properties limits its practical applications. In this work, the interchain interactions between PLLA and PDLA chains are found to be well kept in equimolar PLLA/PDLA blends via the incorporation of Al2O3 particles for the first time, which effectively overcomes these drawbacks. The composites show good melt memory for sc crystallization, and exclusive sc crystallites form during cooling after eliminating the thermal history when the content of Al2O3 is higher than 3 vol%. Moreover, exclusive sc crystallites still can be formed in the composites with high Al2O3 contents of 40 vol%. The interchain interactions between PLLA and PDLA chains are well kept in the melt of the composites, endowing the composites with the capability to overcome the kinetic barrier and form sc crystallites rapidly during cooling. Benefiting from the high thermal conductivity of Al2O3, and enhanced sc crystallites with high heat resistance, the sc-PLA composite with 40 vol% Al2O3 shows a thermal conductivity of 1 Wm(-1)K(-1), and the thermal conductivity can be maintained at elevated temperatures (25-180 degrees C). The synchronously enhanced sc formation and reliable thermal conductivity at elevated temperatures enabled by Al2O3 provide a new design approach for PLA as an alternative engineering plastic.