Non-isothermal crystallization behavior of compatibilized polypropylene/recycled polyethylene terephthalate blends

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A binary blend of polypropylene (PP)/recycled polyethylene terephthalate (rPET) and ternary blends of PP/rPET (80/20 w/w) compatibilized with different amounts (5 and 15 mass%, respectively) of a new compatibilizer, PP grafted with maleic anhydride in presence of diallyl phthalate (PP-g-MAH/DAP), are prepared using a twin-screw extruder. The non-isothermal crystallization kinetics and the crystallization morphologies are investigated by differential scanning calorimetry and polarized optical microscopy (POM), respectively. The crystallization temperature and rate of the binary blend increase during the non-isothermal crystallization process, indicating that rPET phase has nucleation ability for crystallization of the PP matrix. However, the crystallization temperatures and rates of the ternary blends slightly decrease because of the chemical reaction between MAH and the rPET terminal groups. Applying the equations proposed by Jeziorny, Ozawa, and Mo to analyze the non-isothermal crystallization kinetics of pure PP and PP in the binary and ternary PP/rPET blends, agreement is found between the experimental results and Mo method. The crystallization activation energy increases in the binary PP/rPET blend, which is ascribed to the confinement effect on the motion of the PP chains by large rPET particles, and this confinement effect is mitigated with the inclusion of PP-g-MAH/DAP. POM observation confirms the heterogeneous nucleation of rPET on PP and the restriction of crystallization of PP by the incorporation of PP-g-MAH/DAP.