The effect of different compatibilizers agents on the nucleation and crystallization behaviour of poly(lactide)/poly(ɛ-caprolactone) blends

In this work the effect of adding different kind of compatibilizers to poly(lactide)(PLA)/poly(ε-caprolactone)(PCL) 80/20 blends has been investigated, evaluating the results by SEM (Scanning Electron Microscopy), PLOM (Polarized Light Optical Microscopy), DSC (Differential Scanning Calorimetry) and tensile tests. The addition of poly(lactide-ran-caprolactone), P(LA-ran-CL) to PLA/PCL blends does not improve the compatibility between PLA and PCL, however a plasticization effect, that increases the crystallization ability of the PLA phase, is induced. Such plasticization effect can increase the spherulitic growth rate of PLA up to two or three fold as compared to neat PLA, depending on the Tg of the random copolymer employed. At the same time copolymer incorporation in the blends leads to an anti-plasticization effect of the PCL droplets, reducing their crystallization rate. Poly(L-lactide-block-carbonate) diblock copolymers P(LA-b-C) are effective in improving the miscibility between PLA and PCL. However, the acceleration of the cold crystallization kinetics of PLA upon blending with PCL, often reported in the literature, is not connected with the miscibility between PLA and PCL phases, as it is also present in the uncompatibilizated PLA/PCL blend, but is due to a nucleation effect induced by PCL crystals on glassy PLA. Such nuclei only become effective upon heating to PLA cold crystallization temperatures, at which PCL is already molten. The addition of poly(ε-caprolactone)-poly(carbonate) (PCL-co-PC) based copolymers does not cause an increase in miscibility in PLA-PCL phases, however copolymers addition causes a reduction of molecular weight in melt mixed blends. As result, PLA phase within the blends containing PCL-PC based copolymers shows a higher tendency to crystallize during both isothermal and non-isothermal DSC experiments. The increased crystallization of PLA phase is attributed to an increase in spherulitic growth kinetics determined by PLOM analysis.