Enhanced Compatibility of Starch with Poly(lactic Acid) and Poly(ɛ-caprolactone) by Incorporation of POSS Nanoparticles: Study on Thermal Properties

In this work, we explore the ability of polyhedral oligomeric silsesquioxane (POSS) nanoparticles to increase the compatibility of hydrophilic starch with hydrophobic poly(lactic acid) (PLA) and poly(ɛ-caprolactone) (PCL). Morphological analysis demonstrated that lower contents of POSS (0.5 and 1 wt%) enhances the compatibility of the system. However, higher inclusion of POSS results in the formation of aggregates and thus a lower level of compatibility. Transmission electron microscopy revealed that PCL acts as an intermediate between PLA and starch, and that POSS is primarily localized within the PLA and PCL phases. Based on differential scanning calorimetry, PLA's crystallinity increases from 22.9% to 31.6% upon adding a very low content of POSS (0.5 wt%). However, the PCL's crystallinity is slightly hampered due to formation of these PLA crystallites. In contrast with the crystallization behavior and based on the thermal degradation kinetics, we found the composite's thermal stability is greatly increased when moderate to high contents (3 and 5 wt%) of POSS are utilized. Dynamic mechanical analysis results also confirmed good POSS dispersion within the matrix, especially at lower contents. In conclusion, POSS serves as an efficient compatibilizer for PLA/starch/PCL systems with improved thermal properties.