Study on Graft Copolymerization of Polyacrylate with Vinyl Monomers and Its Modifying Polyvinyl Chloride
|School||Hebei University of Technology|
|Keywords||polyvinyl chloride polyacrylate graft vinyl chloride seeded sequential emulsion copolymerization core-shell morphological structure ACR composite resin suspension graft copolymerization modified polyvinyl chloride|
In this dissertation, the project focused on improving the toughness of polyvinyl chloride (PVC) with the goal of extending the range of use. Blending modification and graft copolymerization modification of polyvinyl chloride (PVC) with polyacrylate (ACR) were investigated.In the first approach to blending modification, polybutyl acrylate (PBA)/ polymethyl methacrylate (PMMA) core/shell ACR with different mean diameters were prepared by seed sequential emulsion copolymerization or micro-suspension copolymerization. The ACR particles were blended with PVC resin to prepare PVC/ACR composite materials. The relationship between ACR and its glass-transition temperature and the morphological structure of latex particles were investigated through differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) or transmission electron microscope (TEM). The effects of the core/shell ratio, crosslinking agent, initiator content, the average molecular weight of PMMA and the mean diameter of ACR on the toughness of PVC/ACR blends were studied in detail. The results showed that the proper core/shell ratio is at the range of 60/40 to 70/30, and the better crosslinking agents are allyl methacrylate (AMA) and trimethylolpropane trimethacrylate (TMPTMA). It was demonstrated that the proper crosslinking agent content in the core of the ACR latex is less than 2wt%, and that in the shell of the ACR latex is less than 1wt%. The proper initiator content is 0.25wt% according to the monomer weight. Ensure ACRs to have core/shell structure, the better toughness of the PVC/ACR blends were obtained from the lower average molecular weight of the ACR shell polymer PMMA. The results showed that the mean diameters of the ACR disperse phase particle in the PVC matrix at the range of 300nm to 500nm will be better to improving the notched impact strength of the blends.The rheological experimental results showed that the plasticization time of the blends is shorter than pure PVC resin. The vicat softening temperature points (VSP) of the blends are common to the pure PVC materials. The thermal decomposition temperatures of the blends increased with the increasing of the ACR content.In the second approach, graft copolymerization process was adopted for chemical modification of PVC. Three kinds of acrylate monomers n-butyl acrylate (BA), ethyl acrylate (EA), 2-ethylhexyl acrylate (2-EHA), ethyl acrylate (EA) were used to synthesis polyacrylate (ACR) latices through different emulsion copolymerization processes, and then the ACR latices were graft copolymerized with vinyl chloride monomer (VCM) through suspension graft copolymerization to produce high performance ACR-graft-PVC composite resins of significant commercial utility.The suspension graft copolymerization results showed that the ACR latex can accelerate the reaction of VCM. The mechanical properties, dynamic mechanical property, thermal properties, rheological behavior, morphological structure and the broken profile of the ACR-g-PVC composite materials, were determined and characterized. When the ACR latices were prepared by two-step copolymerization and seed sequential copolymerization, the ACR-g-PVC composite materials would have the better toughness. The notched impact strength of the ACR-g-PVC composite materials increased 20 times that of PVC, when the ACR content is up to 6wt%. The proper ACR content in the ACR-g-PVC composite resins is at the range of 5wt% to 10wt%. While the content of ACR is equal, the better dispersion of the ACR in the PVC matrix could be obtained with greater fraction of the ACR-g-PVC copolymer and the lower Tg of the ACR phase. And the proper dispersion phase domain diameter range is 300nm to 600nm. The rheological behaviors of the ACR-g-PVC composite resins were better than that of PVC. TEM showed that the ACR phase is much uniformly dispersed in PVC matrix, and the distance between the ACR particles is about 300nm to 500nm. SEM showed that the fracture surfaces of the tensile samples and the notched impact samples have good toughness.Finally, soap-free emulsion copolymerization was exploited in the third part on ACR-g-PVC graft composite resins (chapter 5) to prepare the ACR latex. BA was copolymerized with N-vinyl pyrrolidone (NVP), a water-soluble monomer, or copolymerized with sodium vinyl sulfonate (SVS), a surface-active monomer. Another monomer di(octyl maleate) dibutyl stannum (DOMDBS) was employed to the soap-free emulsion copolymerization to improve the thermal consistance of the result graft composite resins. The results showed that BA and NVP can form steady ACR latex, BA and SVS can’t form steady ACR latex. Whereas the thermal consistance of the ACR-g-PVC composite resin with NVP/BA copolymer is worse off. When the DOMDBS was employed to prepare ACR latex, the thermal consistance of the result ACR-g-PVC composite resin is much better than that of PVC. Mechanical and rheological properties of ACR-g-PVC composite materials were investigated, and the results showed similar rules that of ACR-g-PVC composite material in which the ACR was prepare through emulsion copolymerization.