Application of defoamer
Defoamer is a kind of industrial assistant with various kinds, which is widely used in various fields of national economy. However, there are various occasions to solve the defoaming problem. In order to solve the defoaming problem of many systems, a variety of defoaming dosage forms are needed. According to the source and structure of raw materials for manufacturing defoamer, it can be divided into the following three categories:
(1) products based on natural products, such as vegetable oil, mineral oil and compound, are common. Many kinds of products are still in use because of many sources and low prices;
(2) the polyether defoamer based on petrochemical products, commonly polyoxyethylene, polyoxypropylene or block copolymers of both, has become a large type of defoamer since 1960s due to the development of petrochemical industry;
(3) organosilicon defoamer with polysiloxane as the main raw material is widely used in various fields due to its excellent surface properties.

1. Application of defoamer in the preparation of dispersant
The first stage of PVC production is mainly the preparation of dispersant. When using HPMC and PVA as suspending agent, it must be prepared. The mixture should be agitated so that the solution often froth. The overflow of these bubbles and the loss of dispersant can not observe the height of the liquid level. The use of defoamer can eliminate the bubble. The block polyether defoamer can be well dispersed in the suspension system with HPMC and PVA as dispersant, which will not damage the stability of the system, and has good defoaming and antifoaming properties.

2. Application of defoamer in polymerization
In the polymerization, HPMC and PVA are used as dispersants, which have certain surface tension. With the agitation of the polymerizer, foam is formed. These bubbles can be called "wet bubbles". "Wet bubble" is generated above the liquid level of the reaction system, resulting in VCM gas-phase polymerization, making the inner wall of the kettle above the liquid level stick to the kettle, and the adhesive falls off into the kettle, which can increase the black and yellow spots of the resin. Affect the quality of resin products. In the reactor type with reflux condenser, in order to increase the cooling effect, a large number of VCM gas phase passes through the liquid layer to the condenser in the middle of the reaction, and then condenses from the condenser to the liquid, and returns to the reaction system. During this process, the volatilization of VCM vapor causes a lot of bubbles. This process often occurs in the intense period of reaction, which can be called "dry bubble". The "dry bubble" and "wet bubble" produced in the reaction system need to be eliminated by defoamer. As the suspension reaction liquid is an unstable system, the selection of defoamer will have a great influence on the whole reaction process. In addition, the addition method of defoamer should also be considered seriously. Generally, it should be added by continuous dropping 2 hours after the start of the reaction, and the defoamer should be diluted appropriately, because the addition of high concentration defoamer to the reaction system may damage the suspension system in the reactor, produce coarse particles, and affect the product quality of resin. It is a good choice to use defoamer. The product has good dilution stability, fast defoaming speed and good compatibility with suspension.