Effects of a compatibilizing agent on the morphology, interface and mechanical behaviour of polypropylene/poly(ethylene terephthalate) blends

Three maleic anhydride-grafted-polypropylene (PP) derivatives [N, N-dihydroxyethyl monomaleic amide (C-2A), octodecyl monomaleate (C-3), and 2-(N, N-dihydroxyethylamino)ethyl monomaleate (C-4)] were prepared by melt grafting and utilized to compatibilize polypropylene/poly(ethylene terephthalate) (PP/PET) blends. The resulting blends were characterized by means of scanning electron microscopy, thermal analysis and testing of mechanical properties. The results show the compatibilizing effects of the three PP grafts are very different and strongly dependent on the functional groups present. Compatibilizer C-4 produced the finest dispersed phase morphology, whereas C-3 showed little compatibilizing effect. Substitution of 40 wt.% of C-2A with a tert-butyl phenolic resin further improved the compatibilizing effect and resulted in much finer domains of the dispersed phase. Modulated-temperature differential scanning calorimetry (M-TDSC) determination revealed that the glass transition (T-g), crystalline temperature (T-c), melting temperature (T-m), and enthalpy of crystallization (Delta H-c) of the PET component all declined to some extent by comparison with neat PET. The increment of heat capacity at the glass transition, Delta C-p, was found to be changed by the compatibilizers and displayed a trend in Very good agreement with that of the morphology, as well as with the mechanical properties. The decrease in the Delta C-p value may be used as a new parameter for quantitative estimation of the extent of compatibilization, as the decrease in Delta C-p is related to the increase of interface content. (C) 1999 Elsevier Science Ltd. All rights reserved.