Non-isothermal crystallization, melting behavior and polymorphism of polypropylene in β-nucleated polypropylene/recycled poly(ethylene terephthalate) blends

β-Nucleated polypropylene (PP), non-compatibilized and compatibilized β-nucleated PP/recycled poly(ethylene terephthalate) (r-PET) blends were prepared on a twin-screw extruder. The compatibilizers were maleic anhydride grafted PP (PP-g-MA), glycidyl methacrylate grafted PP (PP-g-GMA), maleic anhydride grafted polyethylene-octene (POE-g-MA) and polyethylene-vinyl acetate (EVA-g-MA) elastomers. Effects of r-PET content, compatibilizer type and content, pre-melting temperature and time on the non-isothermal crystallization and melting behavior, and polymorphism of PP in the blends were investigated by differential scanning calorimeter (DSC). DSC results show that the crystallization temperature of PP crystallized predominantly in β-modification was higher than that of neat PP. In the non-compatibilized blend, PP matrix crystallized mainly in α-modification even if r-PET content was only 10 wt%. However, PP-g-MA compatibilization made PP matrix crystallize mainly in β-modification, but PP-g-GMA, POE-g-MA and EVA-g-MA did not improve the β-modification content distinctly. The α-crystal melting peak temperature of PP decreased with increasing pre-melting temperature, but r-PET content, compatibilizer type and content as well as pre-melting time had no obvious effect on the melting temperature of PP. The increase in PP-g-MA content, pre-melting temperature and time was benefit for the formation of β-modification. It is suggested that the β-nucleating agent is encapsulated or dissolved in polar r-PET in β-nucleated PP/r-PET blend, addition of PP-g-MA to the non-compatibilized blend resulted in transferring β-nucleating agent from r-PET phase into PP phase, the increase in PP-g-MA content, melting temperature and time was benefit for transferring β-nucleating agent from r-PET phase into PP phase. The non-isothermal crystallization kinetics of PP in the blends were evaluated by Mo’s method.