Crystallization behaviour of poly(lactide) in immiscible blend with poly(ε-caprolactone), comparison with solution and melt-mixed blends

Poly(ε-caprolactone)-poly(carbonate) based copolymers, both block and random, were synthetized and characterized by 1H-NMR spectroscopy. The copolymers have been tested as compatibilizers in 80/20 (w/w%) PLA/PCL blends prepared both by melt and solution mixing. The concentration of PCL-PC based copolymer added to the blends was 2 wt%. Compression moulded sheets and solvent cast films were evaluated by GPC (Gel Permeation Chromatography), TGA (Thermogravimetric Analysis), SEM (Scanning Electron Microscopy), PLOM (Polarized Light Optical Microscopy), DSC (Differential Scanning Calorimetry). The addition of the copolymers does not cause an increased miscibility in PLA-PCL phases since a reduction of PCL particles size is not detected in SEM micrographs. At the same time, upon copolymers addition PLA’s Tg value does not decrease in both melt and solution mixed blends. Copolymers addition causes a reduction of molecular weight in melt mixed blends. In particular, the random copolymer (PCL-ran-PC) causes the highest reduction molecular weight in melt mixed blend, since it is characterized by the lower thermal stability as shown in TGA analysis. As result, PLA phase within melt mixed 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. Upon molecular weight reduction in melt mixed blends containing copolymers, PLA chains have a higher mobility resulting in an improved motion towards the growing crystal front.