Research Of Low-Temperature Crack Resistance Of Polypropylene Random Copolymer Materials

Polypropylene random copolymer(PPR) has been widely used in industry field in recent years because of its excellent comprehensive properties, especially in the field of indoor and outdoor pipes. Due to its high brittleness at low temperatures, it is easy to produce stress induced cracking, which affect the process of production, storage, transportation, installation and the use of PPR pipes. Therefore, it is a key technology to improve the low temperature crack resistance of PPR materials. At present, the impact toughness of PPR can be improved by the addition of high impact elastomers. However, most of the researches mainly focused on the improvement of impact toughness of PPR at room temperature and 0℃. The study on low temperatures(-10℃~0℃) and ultra low temperatures(-30℃~-10℃) were not deep enough.In this study, POE/HDPE and TPR elastomers were blended with the matrix to get PPR composites, and then modified by annealing to improve the low temperature crack resistance of the materials. The effects of different toughening modifiers and annealing process on the mechanical properties and crystallization behaviors were studied. Main research contents were:(1) By blending PPR with POE/HDPE and three kinds of TPR elastomers, the finest modification agent which had better toughening effect on PPR under low temperatures and ultra low temperatures were selected;(2) Several groups of PPR composites and annealing technologies were investigated by the orthogonal experiment, the best toughening system and annealing process were selected;(3) Then parallel experiments were carried out to analyze the effect of annealing on crystallization behaviors of PPR composites;(4) Through practical extrusion of PPR pipes, the effect of preferred modifers and annealing process on the toughening of PPR pipes in actual production application were observed. The following conclusions are obtained:(1) POE/HDPE and TPR(2088A) modifiers significantly increased the impact toughness of PPR materials at room temperature and low temperatures. PPR/POE/HDPE obtained good toughness at-10℃~23℃, PPR/TPR(2088A) obtained good toughness at-30℃~-10℃;(2) The finest annealing process of PPR composites was 120℃ and 6 h, the crystallization temperature, crystallinity and lamellar thickness of PPR/POE/HDPE and PPR/TPR(2088A) were significantly increased through annealing and the crystal transition from α to β induced in the materials have been observed. The strength and toughness of annealed PPR/POE/HDPE and PPR/TPR(2088A) composites have been further improved;(3) The impact toughness of PPR pipes at room temperature(23℃) and low temperatures(-30℃~0℃) were significantly improved by blending with POE/HDPE and TPR(2088A) modifiers and annealing. The synergistic toughening effect is obvious, with almost no loss of longitudinal reversion and hydrostatic performance;(4) Adding toughening modifiers and annealing has synergetic effect on strengthening and toughening PPR. This provided a good reference for the further application of PPR materials.