Around the 1970s, HPMC began to be used alone or in combination with other dispersants as a protective colloid for the polymerization of synthetic resins. The resulting polymer had more uniform particle shape, low bulk density, better fluidity, thermal stability and processability. Vinyl chloride polymerization, butadiene, acrylonitrile and styrene copolymerization, HPMC or composite system can be used as dispersant, glue retention agent,
Suspending agent, can achieve good results.
The particle characteristics of suspension method polyvinyl chloride resin include: average particle size, particle size distribution, particle morphology, particle internal structure, etc. These parameters directly affect the absorption speed of small molecule plasticizers and stabilizers, as well as the processing speed and processing speed of products. In order to prevent the coalescence between droplets in the early stage of the reaction and between the polymer particles in the middle and late stages of the reaction, dispersants and stabilizers are often added to the system. Dispersant, stabilizer and stirring speed are important factors affecting the average particle size, particle size distribution, particle morphology and internal structure of suspended polymers.
Suspension polymerization dispersants can be divided into: water-soluble organic polymers, such as gelatin, polyvinyl alcohol (PVA), HPMC; water-insoluble inorganic powders, such as calcium phosphate. The current development direction is to use a composite dispersion system, that is, a composite of two or more organic dispersants, or a composite of organic and inorganic dispersants, and sometimes anionic surfactants are added. Using HPMC as dispersant, the obtained product has regular particle size, looseness, suitable apparent density and excellent processing performance, which basically replaces PVA. However, although HPMC is used alone, although the resin has good stability, the overall performance of the resin is poor. When used in combination with several PVA with different degrees of alcoholysis, the product performance is better, the quality is easy to control, and the cost can be reduced.
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