| Polypropylene (PP) is one of the most commonly used plastics because of its good properties, wide applicability, and low cost. However, PP is limited in its application in several technologically important fields, because of its low surface energy, lack of reactive sites, difficulty to dye, extremely poor hygroscopicity, low impact strength, and poor compatibility with synthetic polar polymers. So modification of polymeric materials, especially polyolefin with polar monomers, has been extensively studied due to the discovery of newer routes such as surface modification and alloying for obtaining speciality products. Modification of PP through solid-phase grafting was reported first in 1989 by Rengarajan et al. Compared with other techniques, this technique has many advantages such as lower solvent requirement, low temperature, low cost and low pressure process, and the process also leads to a higher percentage of grafting.The solid-phase grafting polymerizations of styrene onto two kinds of spherical polyolefin granules (copolymer (PPR) and homopolymer (PP)) were studied in detail. Effects of various reaction parameters on the grafting reactions in both materials were investigated. The reaction in copolymer (PPR) resulted in higher graft percentage (Gp%) and graft efficiency(Ge%) than that of homopolymer(PP), and graft products from copolymer (PPR) which have the same graft percentage (Gp%) also had lower melting points (Tm) and melting enthalpy (â–³ Hm) than that from the homopolymer (PP). The results showed that the chain structure of the matrix directly affects the reaction behaviors and the product properties. The co-monomer existing in materials could raise the graft efficiency, and also affect the distributing of branching chain.Effects of various reaction parameters, such as prepolymerization time, monomer concentration, initiator concentration, reaction temperature, reaction time on the amount of the grafted PS in the PP, graft efficiency, and the molecular weight of the product were investigated. The results showed that the graft level increases with increase in prepolymerization time. As the reaction temperature, monomer concentration, initiator concentration and reaction time increase, both Gp% and Ge% increase to a maximum and then decrease. When annealed PP was used in the grafting polymerizations, Ge% become lower, and molecular weight become higher than the product obtained from unannealed PP.Gels were formed in many grafting products, and the gel content in the PP/PP-g-PS alloys greatly increased with increasing styrene concentration and initiator concentration. FT-1R analysis of the gel showed that PS segments extensively participated in the cross-linking reaction.The structure and phase morphology of the produced PP/PP-g-PS alloy were characterized by infrared (FT-1R), 13C-NMR, differential scanning calorimetry (DSC), GPC, viscometry, polarized light microscope (PLM) and SEM. The results showed that styrene was grafted onto the PP backbone, and solid phase graft polymerization in PP granule produced the graft polymer, PP-g-PS.The final product is still in the form of regular spherical granules, which is beneficial to the industrial process. The size of PP spherulites and the crystallinity was greatly reduced after grafting PS on PP. Long branching chains and gels could inhibit the growth of spherulites of PP. Under the studied conditions, there were different degree of PP chain degradation in the graft reaction.The rheological behaviors of PP materials and PP/PP-g-PS alloys were investigated. The relationship between the viscosity and the shear rate was studied using melt indexer and THERMOHAAKE capillarity rheometer. The results showed that with the increasing of St/PP and TBPB/PP, melt index increased first, then became lower after reaching a maximum. All PP materials and PP/PP-g-PS alloys showed shear-thinning behavior. Most of the PP/PP-g-PS alloy samples showed the similar rheological behaviors as the PP materials.
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