Ethylene-vinyl acetate copolymer impact modifier for polypropylene

Abstract

The study of utilization of ethylene-vinyl acetate copolymer (EVA) having 28% by weight of vinylacetate (VA) content as an impact modifier for isotaetic polypropylene (PP) was carried out as well as the study of a possibility to use polypropylene grafted maleic anhydride (PP-g-MA) as a compatibilizer. Effect of screw speed of a twin screw extruder, amount of dicumyl peroxide and maleic anhydride (MA) on percentage of MA grafting onto PP and melt flow index of the resulting PP-g-MA were studied. The optimum condition for the preparation of PP-g-MA was found, the screw speed should be of 90 rpm, dicumyl peroxide of 4 phr, and MA of 6.3 phr. The properties of resulting PP-g-MA were 0.7% grafting, and melt flow index (load 2.16 kg/230๐C) of 25 g/10min. This PP-g-MA was employed as the compatibilizer for PP/EVA blend which EVA in the polyblend were in the range of 0-50% and PP-g-MA of 0-10 phr. EVA having 28% VA content was better impact modifier than that having lower VA content. Usage of 2 phr PP-g-MA slightly improved the impact strength properly. Morphology of the polyblend composed of EVA droplet dispersed in the matrix of PP. When compared with other elastomers, EVA was the better modifier than the others, except styrene-ethylene-butadiene-styrene (SEBS) at 20%. Tensile strength at yield and hardness of polyblend decreased with the increase of EVA amount and the usage of PP-g-MA did not affect on that properties. Elongation at break of polyblend increased with the increase of EVA content in polyblend from 5 to 40%. If the amount was over than 40%, this property was poorer. The usage PP-g-MA slightly decreased the elongation at break when the EVA content in polyblend was 5-30%. The large decrease of this property was when the EVA content in the polyblend was upto 40-50%, especially, when the amount of PP-g-MA used was 6 and 10 phr. The miscibility of polyblend found that EVA could be only miscible with the amorphous region of PP.