Reactive compatibilization of poly(trimethylene terephthalate)/polypropylene blends by polypropylene-graft-maleic anhydride. Part 2. Crystallization behavior

The crystallization behavior of uncompatibilized and reactive compatibilized poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends was investigated. In both blends, PTT and PP crystallization rates were accelerated by the presence of each other, especially at low concentrations. When PP content in the uncompatibilized blends was increased to 50-60 wt%, PTT showed fractionated crystallization; a small PTT crystallization exotherm appeared at similar to 135 degrees C besides the normal similar to 175 degrees C exotherm. Above 70 wt% PP, PTT crystallization exotherms disappeared. In contrast, PP in the blends showed crystallization exotherms at 113-121 degrees C for all compositions. When a maleic anhydride-grafted PP (PP-g-MAH) was added as a reactive compatibilizer, the crystallization temperatures (Tc) of PTT and PP shifted significantly to lower temperatures. The shift of PTT's Tc was larger than that of the PP, suggesting that addition of the PP-g-MAH had a larger effect on PTT's crystallization than on PP due to reaction between maleic anhydride and PTT. The nonisothermal crystallization kinetics was analyzed by a modified Avrami equation. The results confirmed that PTT's and PP's crystallization was accelerated by the presence of each other and the effect varied with blend compositions. When the PP content increased from 0 to 60 wt%, PTT's Avrami exponent n decreased from 4.35 to 3.01; nucleation changed from a thermal to an athermal mode with three-dimensional growths. In contrast, when the PTT content increased from 0 to 90 wt% in the blends, changes in PP's n values indicated that nucleation changed from a thermal (0-50 wt% PTT) to athermal (60-70 wt% PTT) mode, and then back to a thermal (80-90 wt% PTT) mode. When PP-g-MAH was added as a compatibilizer, the crystallization process shifted considerably to lower temperatures and it took a longer crystallization time to reach a given crystallinity compared to the uncompatibilized blends.