Modification of polypropylene by free radical grafting

Abstract

Polypropylene (PP) market forms the second largest polymer business worldwide owing to its good mechanical properties, excellent chemical resistance and low-cost production. These attractive properties of PP are mainly dependent on its stereospecificity. Isotactic polypropylene (iPP), which can be produced by Ziegler-Natta catalysts with high isotacticity indices, has a commercial significance. However, atactic polypropylene (aPP) which has a lack of order is produced as a byproduct during iPP manufacturing. In general, aPP obtained as a byproduct has a low molecular weight, and it is essentially amorphous. Since aPP has low thermal stability and poor mechanical properties, it is considered an industrial waste, and application fields are limited. In this study, aPP was modified by free radical grafting technique to obtain value-added material from this industrial waste. Free radical grafting of functional monomers onto polyolefins is a widely practiced method for modification of polyolefins. The functionalization of polyolefins can improve their compatibility with engineering polymers. In this way, the incorporation of modified polyolefins into polymer blends and composites can be achieved. However, during free radical grafting, the desired grafting reaction competes against side reactions including homopolymerization of the monomer, chain scission and crosslinking. Within the scope of this study, grafting reactions of maleic anhydride and its derivative onto aPP were carried out in both solution and melt. The effect of reaction parameters and conditions on grafting yield and its effect on final polymer properties were investigated.