The polymerizer should be descaled after being used many times.
Emulsion polymerization is a method to produce paste resin, which usually uses a water-soluble initiator, vinyl chloride monomer, water, emulsifier, and nonionic surfactant.
The emulsion is made of water, vinyl chloride monomers, the emulsifiers with surfactants such as sodium alkyl sulfonate.
The initiator can use water-soluble potassium persulfate or ammonium persulfate. The "redox" initiation system can also be used.
Polyvinyl alcohol is also added 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 polymerization product is latex, and the particle size of the emulsion is 0.05 ~ 2 μ m, which can be directly applied or spray dried into powdered resin.
The polymerization period of emulsion polymerization is short and easy to control. The obtained resin has a high molecular weight and a uniform degree of polymerization, which is suitable for polyvinyl chloride paste, artificial leather, and impregnated products.
The formula of emulsion polymerization is complex and the impurity content of the product is high.
The relative molecular weight of PVC resin prepared by emulsion polymerization is 12500 to 125000, which is a white powder with fine particles (generally 0.1 ~ 1 μ m). It is loose, odorless, non-toxic, stable to acids, bases, and salts at room temperature, and has good plasticizing properties. It can be mixed with plasticizers and other auxiliaries to form a paste, and the thickening viscosity does not exceed 20% for 24 hours at room temperature.
The disadvantages are poor electrical insulation, poor transparency, and high product cost.
5.2.3 Bulk polymerization:
5.2.3.1 Advantage
This method has the advantages of a simple production process, good product quality, and low production cost.
(1)This method doesn't use water as the medium, nor need any auxiliary such as dispersants. The only materials needed are vinyl chloride and initiators, so the production process is very simple.
(2)The performance of bulk PVC resin is better than that of suspension PVC resin.
The resin contains few impurities, the monomer content is less than 1mg/kg, and the particle size distribution is concentrated.
(3)The structure is regular, the porosity is high and uniform, the amount of adsorbed plasticizer is large and fast, and the plasticized resin mixture is the same as the dry powder, which is easy to store and transport.
(4)It is also easy to process without a plasticizer.
(5)The products have good transparency, thermal stability, and electrical insulation.
5.2.3.2 Produce equipment

The polymerization device is special and is mainly composed of a vertical prepolymerizer reactor and a horizontal polymerizer reactor with a frame agitator.
Because the particle characteristics of bulk PVC are similar to those of suspension resin, which is loose, but without skin film and more crystalline. In addition to heat dissipation and anti-sticking, bulk polymerization also needs to solve the problem of maintaining the loose structure of particles, which is guaranteed by two-stage polymerization.
(1) The first stage is pre-polymerization, which is carried out in a vertical kettle.
A small part of vinyl chloride and a limited amount of highly active initiators (such as ethyl peroxide sulfonate) are added to the kettle and prepolymerized to 7%-11% conversion at 50-70 °C to become dead-end polymerization, to prevent excessive conversion.
Stir quickly to form a loose particle skeleton.
The conversion rate is estimated by the heat taken away by jackets and condensers.
(2)The prepolymer, more monomers, and another part of the initiator are added to another low-speed stirring (30r/min) kettle. The monomers continue to polymerize on the pre-formed particle skeleton to make the particles grow and keep the morphology unchanged.
The polymerization is ended when reaches 70% to 90% conversion,
The residual monomer is discharged, and the finished product is obtained by crushing and sieving.
The prepolymerization only takes 1 ~ 2 h, but the polymerization takes 5 ~ 9 h.
One prepolymerizer can be equipped with several polymerizers.
The particle size and shape of the resin are controlled by stirring speed, and the reaction heat is taken out by monomer reflux condensation.
5.2.4 Micro-suspension method.
The micro-suspension method has high production efficiency and stable product quality.
The particle size of the obtained resin is between suspension and emulsion polymerization resin, which can replace paste resin.
The dosage of plasticizer absorbed is big, and the product transparency is good.
5.2.5 Comparison of three polymerization processes:
Items |
Suspension polymerization |
Bulk polymerization |
Emulsion polymerization |
Micro-suspension method |
Formula composition |
Monomer, initiator, dispersant, water |
Monomer, initiator |
Monomer, initiator, emulsifier, water |
Monomers, initiators |
Polymerization location |
Monomer droplet |
Inside the body |
Micelle and latex particles |
In solution |
Temperature control |
Easy |
Hard |
Easy |
Easy |
Polymerization speed |
Larger |
Medium |
High |
Low |
Molecular weight control |
Medium difficult |
Difficult |
Easy |
Easy |
Production characteristics |
Batch |
Batch |
Continuous |
Continuous |
Main characteristics and uses |
Suitable for injection molding or extrusion resin |
Pure and rigid injection molded products of polymer |
Paints, adhesives |
Paints, adhesives |
5.3 Basis for Process Plan Selection.

5.3.1 Technological process.
(1)The bulk polymerization process is simple, the occupation area is small, and there is no waste discharge, the exhaust can reach the lowest degree, the environmental pollution is less, the product quality is good and the purity is high, especially suitable for transparent packaging materials and cable lines.
(2) The suspension process is a relatively mature process, which occupies an absolute share of PVC production in the world at present, with a high product conversion rate, the largest variety of products, and ease of adapting to the market.
(3) The emulsion method is a method to produce paste resin with a complex process, high cost, and poor resin quality.
(4)Micro-suspension method has the problem of monomer pollution in solvent recovery and residual use, and the high cost is only used for special purposes.
5.3.2 Economic aspects.
Bulk polymerization is the most economical scheme, but the viscosity of the system in the later stage of polymerization is very high, which can only be effectively implemented when there are engineering solutions for stirring and heat transfer in the polymerization reactor.
If the later processes such as refining, recovery, and drying are included, the economy of each polymerization process decreases in the following order:
suspension polymerization > bulk polymerization > Micro-suspension polymerization > emulsion polymerization.
VI, New material - modified Plastics.
At present, the total annual demand for modified plastics is about 50 million tons.
Modified plastics are an important part of the field of new chemical materials.
Because 1 kg plastic can replace heavier materials such as 2-3 kg steel, fuel consumption can be reduced by 6% -8% for every 10% weight reduction in the car.
Therefore, the more modified plastics are applied in the automobile, the more energy-saving can be achieved.

6.1 Replacing Steel with plastic material of PVC
The application of using internal plasticizing process and additive formula can ensure the mechanical and electrical properties, and improve the flame retardancy of PVC plastic steel. The product can have the advantages of high strength, corrosion resistance, non-flammability, good insulation, lightweight, convenient construction, and so on. This material can replace steel pipe in the electrical wiring system.
6.2 Replacing Wood with plastic material PVC
PVC wood-plastic composite is a new type of composite prepared by a hot pressing process using waste wood fiber and plastics as the main raw materials and appropriate processing aids.
This product fully meets the concept of recycling renewable resources and petroleum products and is of great significance in alleviating the current shortage of wood and oil resources, serious environmental pollution, and other problems.
VII, Recycling.
Polyvinyl chloride (PVC) is recyclable and its resin identification code is "3".
