Single and hybrid organoclay-filled PLA nanocomposites: Mechanical properties, viscoelastic behavior and fracture toughening mechanism

摘要

Poly (lactic acid) (PLA) nanocomposites based on single and hybrid organic-modified montmorillonites were previously studied in terms of their morphological, thermal and fire performance. As surfactants of the organoclays influenced the compatibility between the nanofillers and PLA with different degrees of clay platelets dispersion, the present work investigated the effect of these features in the mechanical properties of PLA nanocomposites. PLA nanocomposites specimens were analyzed by dynamic-mechanical-thermal analysis, which pointed out changes in the viscoelastic behavior of the materials by the incorporation of the organoclays, namely the increase of the storage modulus due to polymer chains movements restriction and reinforcement effects associated with the dispersion of the nanofillers. Flexural and impact testing showed that hybrid organomontmorillonites containing ester ammonium and ethoxylated amine improved PLA's ductility, toughness and impact resistance. This behavior was explained by the high level of compatibility and interaction between the surfactants and PLA chains due to the polar groups in their structures. These organoclays caused a transition on PLA's fracture from brittle to ductile in a way that the toughening mechanism was explained by crazing and multi-shear banding induced by the plasticized interfacial region around these organoclays.