The molecular formula of PVC is (ch2-chc1) n, which is synthesized from acetylene and hydrogen chloride (calcium carbide route), ethylene and chlorine (petrochemical route) into vinyl chloride monomer, and then polymerized to form Pvc Resin. According to the polymerization process, it can be divided into bulk, suspension, lotion, solution and other polymerization products, of which more than 80% are suspension polymerization products, and about 10% are lotion polymerization resins, which are mainly used for paste materials. The production, preparation and types of PVC are as follows.
1、 Production and preparation process
1. Bulk PVC
The properties of bulk PVC Resin are better than those of suspension PVC. The Resin contains less impurities, the monomer content is less than 1mg/kg, and the particle size distribution is concentrated. The structure is regular, the porosity is high and uniform, the amount of Plasticizer adsorbed is large and the speed is fast. The plasticized resin mixture is as easy to store and transport as the dry powder. It is easy to process without plasticizer. The product has good transparency, thermal stability and electrical insulation.
2. Micro suspension method
Micro suspension method has high production efficiency and stable product quality. The particle size of the resin obtained is between suspension and lotion polymerization resin, which can replace paste resin. Large amount of resin plasticization, good transparency of products.
3. Lotion method
The relative molecular weight of lotion polymerized PVC resin is 12500~125000, and the particles are fine (generally 0.1~1 μ m) The white powder is loose, odorless and non-toxic. It is stable to acids, alkalis and salts at room temperature. It has good plasticizing performance. It can be mixed with plasticizers and other additives to form a paste. It can be used at room temperature for 24h. The thickening viscosity is not more than 20%, and there is no precipitation. The disadvantages are poor electrical insulation, poor transparency and high product cost. See table 2-17 for technical indexes of lotion PVC.
2、 Category
Suspension polymer resins in China are divided into seven categories according to their relative molecular weight, and each category is divided into compact and loose types according to their particle shape. Resin particle size is about 100~150 μ m. They consist of numerous 0.1 μ The particles with the size of M are agglomerated. The entire surface of some particles is covered by a layer of "film". The film is relatively firm and difficult to damage. This is a compact resin with poor penetration ability of plasticizer. The "film" of the loose resin is very thin and not fully covered, which is conducive to the penetration of plasticizer into the particles. Its molecules are arranged in a random structure, with a crystallinity of up to 5%~10% (including a small amount of syndiotactic structure with a crystallinity of 20%). The weight average molecular weight is 50000 ~ 120000, and the relative molecular weight is closely related to melt viscosity, processing temperature, product performance and application.
PVC is white powder or bead, which is transparent after plasticization and easy to color. Unplasticized products are tough, and the hardness and mechanical properties can be freely adjusted by adding plasticizers. Flame retardant, self extinguishing and good electrical insulation. Good water resistance, chemical stability, ACID and alkali resistance, but soluble in most solvents. The thermal stability of the resin is poor, but it can be overcome by adding heating stabilizer.
