Study On Several Dominating Problems Of The Emulsion Polymerization Of Vinyl Acetate

Since the emulsion polymerization of polyvinyl acetate(PVAc) latex usually uses polyvinyl alcohol (PVA) as protective colloid, so the action mechanisms of PVA in PVAc latex and the viscosity and rheology of PVAc latex influenced by PVA were researched in this paper. Moreover, the mechanisms of emulsion and microemulsion polymerization of PVAc is very illegible, and they were also investigated primarily in this paper.There are three action mechanisms of PVA in the emulsion polymerization of vinyl acetate. They are free PVA, adsorbed PVA, grafted PVA. Ultracentrifugation and two-step selective solubilization procedure are applied to measure the fraction of each form of PVA in the latex. And it can be concluded as below: When the hydrolysis degree increases, the fraction of free PVA decreases and adsorbed PVA increases and grafted PVA increases slightly; And when the concentration of PVA increases, the fraction of free PVA increases slowly then decreases sharply and adsorbed PVA increases gradually and grafted PVA decreases then increases.Study on rheological behaviour and apparent viscosity of PVAc latex affected by the properties of PVA such as degree of hydrolysis, degree of polymerization and hydrophobic modification had been presented. Experimental results indicated that the behavior of PVAc latexes using PVA1788 or PVA1799 as protective agent is more like that of a pseudo-plastic fluid, and both of them show critical shear rate points within the range of measurement (from 0 to 2000 s-1). When the shear rate surpasses the critical point, shear stress will drop sharply, and the latex structure is going to be unstable. But the behavior of polyvinyl acetate latex using hydrophobic modified PVA as protective colloid is different, it behaves more like a stable non-Newton fluid with an index of about 0.70, also there is no critical shear rate point within the range of measurement (from 0 to 2000 s-1).Study on zeta potential and partical size distribution of PVAc latex affected by the polymeric condition had been presented. Experimental results indicated that: It was very difficult to prepare stable latex in strongly acidic solution. The latex prepared in weakly acidic solution showed that there were two opposite zeta potentials, the size of the latex was smaller and the size distribution was wider. The latex prepared in neutral solution showed that there were also two opposite zeta potentials, the size of the latex was bigger and the size distribution was narrower. The latex prepared in alkaline solution showed that there was only one zeta potential, but the size of the latex was the biggest and the size distribution was the narrowest.Study on microemulsion of PVAc latex affected by different initiation systems had been presented. Experimental results indicated that: The reaction was very drastic when using zaodiisobutyronitrile as initiator. Otherwise, it was gentle when using hydrogen peroxide-ascorbic acid as initiator. And the degree of using ammonium persulfate-sodium acid carbonate as initiator was between the formers. There were two stages of molecular-weight distributions when using the initiators respectively. In the part of higher stage of molecular-weight distribution, the system using hydrogen peroxide-ascorbic acid as initiator had the biggest value. In the part of lower stage of molecular-weight distribution, the values were similar. The size of latex was smaller, and the distribution was narrower when using zaodiisobutyronitrile as initiator. In contrary, the size of latex was bigger, and the distribution was wider when using ammonium persulfate-sodium acid carbonate as initiator. And the degree of using hydrogen peroxide-ascorbic acid as initiator was between the formers.