Polyvinyl chloride is formed by free radical polymerization of vinyl chloride.

There are suspension polymerization method, emulsion polymerization method and bulk polymerization method. Suspension polymerization method is the main method, which accounts for about 80% of the total output of PVC.

Sources of monomers: ethylene method, petroleum method and calcium carbide method.

Our country's method: mainly the calcium carbide method.

The quality of the resin is characterized by particle size and particle size distribution, molecular weight and molecular weight distribution, apparent density, porosity, fisheye, thermal stability, color, impurity content, and powder free flow properties.

(1) Suspension polymerization method makes the monomer suspended and dispersed in the water phase in the form of droplets, and the selected oil-soluble initiator is dissolved in the monomer, and the polymerization reaction proceeds in these droplets, and the heat of the polymerization reaction is absorbed by the water in time In order to ensure that these droplets are dispersed in water as beads, suspension stabilizers such as gelatin, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, etc. need to be added. Initiators mostly use organic peroxides and azo compounds, such as diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, diethylhexyl peroxydicarbonate, and azobisisoheptonitrile, azo Diisobutyronitrile and so on. The polymerization is carried out in a polymerization vessel equipped with a stirrer. After polymerization, the material flows into the monomer recovery tank or stripper to recover the monomer. Then it flows into the mixing kettle, washed with water, dewatered by centrifugation, and dried to obtain the finished resin product.

(2) Emulsion polymerization method One of the earliest industrial production methods of PVC. In emulsion polymerization, in addition to water and vinyl chloride monomers, surfactants such as sodium alkyl sulfonate are also added as emulsifiers to disperse the monomers in the water phase to form an emulsion, using water-soluble potassium persulfate or Ammonium persulfate is the initiator, and "oxidation-reduction" initiation system can also be used, and the polymerization process and suspension method are different. There are also added polyvinyl alcohol as an emulsion stabilizer, dodecyl mercaptan as a regulator, and sodium bicarbonate as a buffer. There are three polymerization methods: batch method, semi-continuous method and continuous method. The polymerized product is in the form of latex, the particle size of the emulsion is 0.05-2μm, and it can be directly applied or spray-dried into a powdered resin. The emulsion polymerization method has a short polymerization period and is easier to control. The obtained resin has a high molecular weight and a relatively uniform polymerization degree. It is suitable for making polyvinyl chloride paste, making artificial leather or impregnating products.

(3) Bulk polymerization method The polymerization device is relatively special, mainly composed of a vertical pre-polymerization tank and a horizontal polymerization tank with a frame-type agitator. The polymerization is carried out in two stages. The monomer and initiator are pre-polymerized in the pre-polymerization kettle for 1 hour to generate seed particles, and the conversion rate is 8%-10%. Then they flow into the second-stage polymerization vessel and add the same amount of monomer as the pre-polymer. , Continue to aggregate. When the conversion rate reaches 85% to 90%, the residual monomers are discharged, and then the finished product is obtained by crushing and sieving. The particle size and shape of the resin are controlled by the stirring speed, and the reaction heat is taken out by the monomer reflux and condensation. The production process of this method is simple, the product quality is good, and the production cost is low.

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