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Polypropylene-graft-maleic anhydride (PP-g-MAH) ionically modified with zinc(II) (PP-g-MAHZn) in varying amounts of ionic associations were prepared via melt reaction. Absorption bands in FTIR-ATR and shifted binding energy in X-ray photoelectron spectroscopy showed the formation of zinc carboxylates in PP-g-MAHZn. Decreased crystallinity, gradually increased viscosities, and storage modulus with the increment of zinc carboxylates in the PP-g-MAHZn were investigated by thermal and rheological analysis, which were attributed to the restriction of chain mobility via ionic interactions between polymer chains and aggregations of ionic domains. Furthermore, PP-g-MAHZn was introduced to polypropylene as an additive to promote foamability, and the PP/PP-g-MAHZn blends displayed higher viscosities and storage modulus compared with pristine PP in rheological measurements. In addition, the PP/PP-g-MAHZn blends were foamed by supercritical CO2 and cryogenically fractured surfaces were observed by scanning electron microscope. PP/PP-g-MAHZn foams presented high closed-cell content, uniformity of cells, and increasing cell density owing to the combined effects of rheological properties, while maintaining the cell structures and good dispersion of the PP-g-MAHZn as nucleating sites. These results reveal that PP-g-MAHZn is a suitable additive to produce high melt strength PP for foam production.

Maleic anhydride grafted onto atactic polypropylene (aPP-g-MAH) using a solution grafting reaction with e-caprolactam promoter was investigated in this study. FTIR-ATR and elemental analysis (EA) measurements showed that the optimal degree of grafting (DG) of aPP-g-MAH could be achieved at a 5.03 wt% when e-caprolactam was added as the radical protecting agent. aPP-g-MAH was then introduced to PP and PP/Nylon 6 (PP/Ny6) as a nucleation and compatibility agent, respectively. The DSC curve of the PP/aPP-g-MAH blend showed that the crystallization temperature of the blend was increased to 115.3 °C, higher than that of pristine PP. In addition, POM observations demonstrated that the size of the spherulites present in pristine PP shrank obviously. Moreover, the dynamic temperature variations in the POM observations revealed that the initial crystallization temperature of PP/aPP-g-MAH was much higher than that of pristine PP. The results indicate that the aPP-g-MAH additive was an excellent nucleating agent for the PP materials. When aPP-g-MAH was added as a compatibility agent for PP/Ny6 blending, the cryogenically fractured surface of the PP/Ny6/aPP-g-MAH (5 wt%) blend presented good compatibility between PP and the Ny6 domains. The crystallization temperatures of PP/Ny6 blends with 10–50 wt% Ny6 were higher than that of pure PP, and the blends with aPP-g-MAH had much higher of that. These findings reveal that aPP-g-MAH is a good nucleation and compatibility agent in PP/Ny6 blends.