Enhanced thermal, rheological, mechanical, and morphological properties of reactive recycled PET/recycled PP blends: influence of long-chain branching

Recycled polyethylene terephthalate (rPET) was blended with 25-75 wt% of recycled polypropylene (rPP) by reactive blending in an internal mixer. Pyromellitic dianhydride (PMDA) was used as a chain extender for PET to modify the blends and improve their performance. Effects of the long-chain branched (LCB) structure of PMDA and nucleation effects of rPP on rPET were investigated quantitatively by studying morphology, rheological behavior, crystallization, thermal, and mechanical properties of the blends. Rheological behavior showed that modified rPET/rPP blends achieved significantly high storage moduli and complex viscosities after branching. Both X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results showed that increasing the content of rPP in the blends led to an increase in crystallinity, suggesting that the rPP phase acts as a nucleating agent for the crystallization of rPET. A further finding was that PMDA decreased the degree of crystallinity because of the effect of LCB structure on crystallinity. In comparison to unmodified rPET/rPP blends, modified blends showed improved impact resistance. Nanomechanical mapping showed interfacial broadening between the rPET matrix and rPP dispersed phase, confirming the LCB’s effect. Moreover, SEM images showed an irregular surface at the grain boundary between rPET and rPP in modified blends, confirming enhanced interaction at the interface.