In-situ microfibrillated Poly(ε-caprolactone)/ Poly(lactic acid) composites with enhanced rheological properties, crystallization kinetics and foaming ability

Abstract

The present study aims at investigation on the morphology, rheology, isothermal crystallization and foaming behavior of the fibrillated PCL/PLA composites. The samples containing 5, 10 and 20 wt% PLA were melt-blended with PCL using a twin-screw extruder, following hot-stretching. The SEM morphology results revealed that the samples before stretching demonstrated spherical PLA domains; however, after stretching the spherical particles transformed to fibrillar structures and developed a 3D-network of entangled PLA fibers. Melt rheological properties of the samples before stretching suggested that the viscosity and storage modulus of the composites were increased with increasing the amount of PLA particles. This effect became more noticeable when the PLA domains were fibrillar. Moreover, rheological results unveiled that the fibrillated PCL/PLA composites showed a solid-like behavior which was evidenced with a plateau of storage modulus at low frequency region. Isothermal crystallization kinetics of the composites indicated that the PLA nanofibrils acting as heterogeneous nucleation, remarkably accelerated the crystallization at various crystallization temperature. Moreover, under high PLA nanofirbrils, the interaction between a large amout of induced PCL crystal nuclei and increased viscosity hinder motion of PCL molecules, which resulted in a higher isothermal crystallization activation energy. A close examination of batch foaming data suggested that the fibrillated samples induced further open-cell foams in comparison with that of the pure PCL and undrawn PCL/PLA samples.