Rheological, mechanical and morphological behavior of polylactide/nano-sized calcium carbonate composites

Semicrystalline polylactide (PLA) is a promising material to replace petroleum-based plastics since it can be synthesized from renewable resources. PLA exhibits high tensile strength and modulus, but very low strain-at-break and toughness. In this study, the effects of the nano-sized calcium carbonate (nCaCO₃) on the rheological, mechanical and morphological properties of polylactide are evaluated. The PLA/nCaCO₃ composites with different filler compositions, as well as neat PLA (used as reference) were prepared by melt mixing in a twin-screw extruder. The results show that the presence of 7.0 wt% of nCaCO₃ in the composite not only produced an ultimate strain improvement, but also better overall toughness balance in comparison to the other compositions. MEV micrographs showed the presence of microvoids with composition containing 7.0 wt% nCaCO₃, which explains the mentioned mechanical behavior. This composition also showed more viscous behavior in relation to neat PLA and 5.0 wt% nCaCO₃ composite. Composite with 3 wt% of nanofiller presented the highest viscous behavior in relation to neat PLA and other composites. Both mechanical data and Cole–Cole plots indicated the overall absence of higher filler aggregates in the composites analyzed, corroborating the MEV micrographs.