Polyvinyl Chloride (PVC) Resin

I. Overview
Polyvinyl chloride (PVC) is a polymer formed by the polymerization of vinyl chloride monomer (VCM) in the presence of initiators such as peroxides and azo compounds or under the action of light or heat according to the free radical polymerization mechanism. Vinyl chloride homopolymers and vinyl chloride copolymers are collectively referred to as polyvinyl chloride resin.

Ⅱ.Production Method

1) Suspension Polymerization Method
The suspension polymerization method makes the monomer suspended and dispersed in the water phase in the form of droplets. The selected oil-soluble initiator is dissolved in the monomer. The polymerization reaction is carried out in these droplets. The heat of the polymerization reaction is absorbed by the water in time. In order to ensure that these droplets are dispersed in the water in the form of beads, it is necessary to add the suspension stabilizer, such as gelatin, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, etc. Initiators are mostly organic peroxides and azo compounds, such as diethylhexyl peroxydicarbonate, azobisisoheptonitrile, azobisisobutyronitrile, etc. The polymerization is carried out in a polymerization kettle with an agitator. After polymerization, the material flows into a monomer recovery tank or a stripping tower to recover the monomer. Then it flows into a mixing kettle, washed, centrifuged and dehydrated, and dried to obtain the finished resin product.

2) Emulsion Polymerization Method
Emulsion polymerization is one of the earliest methods for industrial production of PVC. In emulsion polymerization, in addition to water and vinyl chloride monomer, surfactants such as sodium alkyl sulfonate are added as emulsifiers to disperse the monomers in the water phase to form an emulsion. Water-soluble potassium persulfate or ammonium persulfate is used as an initiator. The “oxidation-reduction” initiation system can also be used. The polymerization process is different from the suspension method. Polyvinyl alcohol is also added as an emulsifier stabilizer, dodecyl mercaptan as a regulator, and sodium bicarbonate as a buffer. There are three polymerization methods: intermittent method, semi-continuous method and continuous method. The polymerization product is latex-like, with an emulsion particle size of 0.05 to 2μm, which can be directly used or spray-dried into a powdered resin. The polymerization cycle of the emulsion polymerization method is short and easier to control. The resulting resin has a high molecular weight and a relatively uniform degree of polymerization. It is suitable for making polyvinyl chloride paste, artificial leather or impregnated products.

3)Bulk Polymerization Method
The polymerization device of bulk polymerization method is special, mainly composed of a vertical prepolymerization kettle and a horizontal polymerization kettle with a frame stirrer. The polymerization is carried out in two stages. The monomer and initiator are first prepolymerized in the prepolymerization kettle for 1 hour to generate seed particles. The conversion rate reaches 8% to 10%, and then flow into the second stage polymerization kettle, and the same amount of monomer as the prepolymer is added to continue polymerization. When the conversion rate reaches 85% to 90%, the residual monomer is 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 reflux condensation of the monomer. This method has the simple production process, good product quality, and low production cost.

Ⅲ.Usage
Polyvinyl chloride is one of the most widely used general-purpose plastics. PVC has good water-proof and flame retardant properties. Polyvinyl chloride is widely used in: water supply pipes, household pipes, house wallboard, commercial machine housings, electronic product packaging, medical equipment, food packaging, etc.

IV. Summary
Polyvinyl chloride was once the world’s largest-volume general-purpose plastic with a wide range of applications. Based on existing technologies, Tianli will increase its R&D investment in polyvinyl chloride production, continuously innovates processes, and improves the efficiency, energy saving and stability of production equipment to meet the needs of high-quality processes in the polyvinyl chloride industry.