Abstract: In-situ microfibrillar reinforced composites based on blends of polypropylene (PP), poly(ethylene terephthalate) (PET), and compatibilizer propylene-g-glycidyl methacrylate (PP-g-GMA) were prepared via slit-extrusion, hot-stretching, and quenching. The effect of PP-g-GMA on the morphology of dispersed phase before stretching and microfibrils after stretching, mechanical properties, and crystallization behavior were studied using SEM, DSC, and mechanical testers. The addition of compatibilizer reduced and homogenized the sizes of dispersed phase before stretching, however，the aspect ratio of PET microfibrils was decreased. The compatibility was improved distinctly and thus improved mechanical properties. The PET microfibrils in the blends caused heterogeneous nucleation for PP, resulting in higher crystallization temperature and crystallization rate.

Key words: Polypropylene, Poly(ethylene terephthalate), in-situ microfibrillar blend, slit-extrusion-hot-stretching-quenching process, propylene-g-glycidyl methacrylate