Polypropylene Grafted With Multi-monomers By Solid Phase Grafting And Its Application In Polypropylene/talc Composites

The isotactic polypropylene (PP) was modified by solid phase graft copolymerization with glycidyl methylacrylate (GMA) and styrene (St), using benzoyl peroxide (BPO) as the initiator and xylene as the interfacial agent. The influence factors including the reaction time, the concentration of initiator and monomer and monomer ratio were systematically investigated. The degree of grafting (DG) was measured by chemical titration. FTIR spectra, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) were employed to characterize the structure, thermal properties as well as the molecular weight distribution of the grafted polymer. The results indicated that the degree of grafting could be controlled by the reaction condition. Compared with pristine PP, the melting temperature (T_m) and the degree of crystallinities (X_c) increased duo to the introducing of polar monomer GMA. Meanwhile, the crystallization rate and temperature (T_c) of the grafted polypropylene were higher than those of the pristine PP because the grafted side chain acted as a nucleating agent, and enhanced the heterogeneous nucleation. Compared with the graft polymerization by single monomer, the glycidyl methylacrylate and styrene grafted polypropylene (PP-g-GMA-St) has higher grafting degree, molecular weight and more narrow molecular weight distribution. PP/talc composites compatibilized by PP-g-GMA-St were preapred by melt extrusion, followed by injection molding. The effects of talc and PP-g-GMA-St on their morphology, mechanical properties as well as the melting and crystallization behaviors were systematically investigated. The results indicated that the addition of talc destroyed the chain package of PP macromolecules, decreased the melting temperature, and increased the crystallization temperature of PP due to its heterogeneous nucleation. Moreover, the incorporation of PP-g-GMA-St further decreased the melting temperature, and increased the crystallization temperature of PP due to its effective compatibilization to PP/talc composites. During the processing of PP/talc composites, the shearing force delaminated the talc layers, and enhanced the dispersion of talc in PP matrix. These factors led to the high flexural modulus and impact strength of PP/talc composites. It was noted that the incorporation of PP-g-GMA-St increased the viscosity of PP/talc composite melts and made PP-g-GMA-St easily intercalate into the gallery of tals layers. These factors were useful for talc to be further delaminated. At the same time, the addition of PP-g-GMA-St enhanced the interfacial adhesion between talc and PP matrix. The results led to the higher impact strength of PP/talc composites. When the contents of talc and PP-g-GMA-St are 20 wt.% and 2.5 wt.%, the mechanical properties of PP/talc composites are optimized.