Synthesising Of Low Polymerization Degree, Porous, And Skin-less PVC Resin

Poly(vinyl chloride) (PVC) resin with low polymerization degree ,high porosity and less skin exhibits: low aggregation degree of primary particles, easy diffusion for micromolecule and easy processing. It was widely used in chlorinating PVC resin field and so on. Aiming at decreasing polymerization degree as well as increasing porosity and basing on the well-known particle formation mechanism of vinyl chloride suspension polymerization, synthesis recipe of PVC resin with low polymerization degree, high porosity and less skin was designed. Effects of different dispersants and surfactants on the interface tension of VC-H₂O, the ability of dispersion and colloid-protection of different dispersion systems were investigated. The research on synthesis laws was carried out in a 5L autoclave. Effects of dispersants, surfactants, mercpatoethanol, pH buffering agent and agitation power on the particle features of PVC resin were studied, providing instruction for industrial development of PVC resin with low polymerization degree ,high porosity and less skin .Using trichloroethylene (TCE) to simulate vinyl chloride (VC), effects of concentrations as well as composition of dispersants, species as well as concentrations of surfactants and mercpatoethanol on the interface intension of VC-H₂O , dispersion and colloid-protection ability of dispersion system were studied. Basing on Gibbs adsorption equation and R-value theory, a competitive adsorption model of composite surfactants was established. Since non-ionic surfactants were more easily adsorbed by the interface of VC-H₂O than macromolecule dispersants. The competitive adsorptions between non-ionic surfactants and macromolecule dispersants would occur. As a result, the interface tension of VC-H₂O as well as colloid-protection ability was reduced. The competitive adsorptions between mercpatoethanol and macromolecule dispersants would also occur, and the interface tension of VC-H₂O as well as colloid-protection ability was reduced.The research on synthesis laws was carried out in a 5L autoclave. Effects of theconcentrations and composition of dispersants, type and concentrations of surfactants, mercpatoethanol and pH buffering agent on particle features were investigated. The effect laws of these factors were explained basing on their effects on the interface tension of VC-H2O and colloid-protection ability. The results showed that reducing concentration of dispersant systems could not only improve the skin feature of particle, but also increase apparent density and CPA. However, if concentration of dispersant system was too low, particles could aggregate to form blocks, and the apparent density would also be reduced. Among the four kinds of non-ionic surfactants(Span2(h Span4(k Span60 and Span80),the ability of improving cold plasticizer absorption in order of : Span60> >Span20>Span80>Span40,and the ability of narrowing particle size distribution of PVC resin in order of : Span80>Span60>Span40> Span20. So Span60 was the most suitable surfactant for aiding surfactant for synthesizing PVC resin, which could obtain higher porosity as well as narrower particle size distribution. When concentration of Span60 arrived at 0.16%, the porosity inside PVC particle as well as the skin outside PVC particle would be improved largely. Mercpatoethanol can reduce polymerization degree largely, but also influences particle features of PVC resin The skin feature as well as particle features could be improved when pH buffering agent was used. Effect of agitating intensity on particle features was also studied .It was found that PVC resin with higher porosity and apparent density as well as narrower particle size distribution could be obtained when the agitation speed was higher at the early stage of polymerization and was rapidly reduced to the critical agitating speed when the conversion arrived at 15²0%.