Plasticization and anti-plasticization effects caused by poly(lactide-ran-caprolactone) addition to double crystalline poly(L-lactide)/poly(ε-caprolactone) blends

The effect of adding poly(lactide-ran-caprolactone), P(LA-ran-CL), random copolymers to melt mixed poly(lactide)(PLA)/poly(epsilon-caprolactone)(PCL) 80/20 blends is investigated. The concentration of P(LA-ran-CL) copolymer added to the blends was 2 wt% and two different types of P(LA-ran-CL) copolymers were employed. They varied in composition and molecular weight. Compression molded sheets were evaluated by SEM (Scanning Electron Microscopy), PLOM (Polarized Light Optical Microscopy), DSC (Differential Scanning Calorimetry) and tensile tests. SEM micrographs show that 80/20 PLA/PCL blends exhibit the typical sea-island morphology characteristic of immiscible blends with PCL finely dispersed in droplets on a PLA matrix. The PLA phase crystallizes during cooling from the melt only in blends containing P(LA-ran-CL) copolymers. The copolymer with the higher amount of epsilon-caprolactone, and with a lower T-g, produces a larger plasticization effect in comparison with the other copolymer used (characterized by a higher amount of PLA) and can significantly increase the crystallization rate of PLA up to an order of magnitude. On the other hand, part of the P(LA-ran-CL) chains is dissolved in the PCL phase of the blends and induces an antiplasticizing effect that reduces the crystallization rate of the PCL dispersed phase.