Preparation And Properties Of Toughened Poly (Vinyl Chloride) Blends

Unplasticized polyvinyl chloride (U-PVC) exhibits good chemical-resistance, flame-retandance and higher tensile strength, but it is easy to get brittle fracture under stress due to its low impact strength. PVC product with high toughness can be obtained by incorporating of impact modifier into PVC by melting blending or chemical grafting copolymerization. In this thesis, chlorinated polyethylene (CPE) and ethylene-vinyl acetate copolymers (EVA) were selected to toughen PVC by melting blending and grafting copolymerization methods. Influences of CPE and EVA structure, content on the structures and properties of modifier PVC resins or alloys were investigated.Although CPE-g-VC resins with higher impact strengths can be prepared by vinyl chloride (VC) suspension grafting polymerization in the presence of low content of CPE (i.e,10%), the obtained resins showed bomodel size distributions, affecting its dry after polymerization. Thus, a new policy was proposed to prepare toughened PVC by blending PVC with CPE-g-VC resins with high CPE contents, which were synthesized by swelling grafting polymerization. It was found that CPE could be well dispersed in the water phase by adding anion surfactant or using wet CPE directly in grafting copolymerization. The prepared CPE-g-VC resins with high CPE contents exhibited greaterr average size than CPE raw materials, and the particl size distributions were narrow. The fusioin properties of PVC were almost same by blending with CPE or CPE-g-VC resin, while blending of PVC with CPE-g-VC resin showed better toughening effect than blending of PVC with CPE. Thus, the usage of CPE could be reduced to achieve same impact strength, and the decrease of tensile strength would be small, by using the approach of blending PVC with CPE-g-VC resin with high CPE content. The uniformity of chloride distribution in CPE chains had a significant effect on the toughening effect of CPE to PVC. Due to the relative lower uniformity of chloride distributin in CPE supplied by the corporated factory, its toughening effect was poored than two other CPEs.In order to choose EVA with good toughening effect on PVC, melting blending of PVC with EVA with different vinyl acetate (VAc) contents was firstly carried out, and the influences of EVA contents on mechanical properties were investigated. For EVA with lower VAc content (i.e,15wt%), the impact strengths of PVC/EVA alloys were increased with the increase content of EVA and then levelled off, while an optimized EVA content was existed to achieve the highest impact strength when EVA with high VAc content (i.e, 25wt%) was used to modify PVC. EVAs with VAc contents of 15% and 25% were selected to be graft copolymrized with VC. The modified PVC resins exhibited closed particles sizes to that of common PVC resin, while the internal porosity of resin was decreased and aggregalate degree of primary particles was increased as EVA added. Impact strength as higher as 45kJ/m2 was achieved for EVA-g-VC copolymers with about 8% EVA1 (15% VAc) and EVA3 (25% VAc), indicating the better toughening effect of EVA by grafting copolymerization method.