The role of hydroxypropyl methylcellulose in VCM polymerization is in VCM suspension polymerization. To avoid the convergence between early polymer droplets and middle and late polymerization particles. It is necessary to participate in loose protective agents into the VCM suspension polymerization system. In the case of fixed stirring characteristics, the type. Nature and dosage of loose agent become the key factors in controlling the characteristics of PVC particles. The commonly use loose system was multiple PVA system and hydroxypropyl methylcellulose + multiple PVA, and the latter was mostly used in China at that time.
- (1) Hydroxypropyl methylcellulose polymerization temperature: the average molecular mass of PVC is selecte on the polymerization temperature base. The loose agent has no effect on the molecular mass base, but in order to ensure the loose glue retention effect of the loose agent on the polymer. The temperature of the loose agent gel is generally higher than the polymerization temperature.
- (2) Particle characteristics: particle diameter, shape, porosity and particle distribution. As the important policy of SPVC quality, are related to the mixer / reactor planning, polymerization water-oil ratio. Loose system and VCM end conversion rate, during which the loose system is particularly important.
- (3) Hydroxypropymethylcellulose stirring: the same as the loose system has a great impact on the quality of SPVC. Because the end particles depends on the standard of VCM droplets in water, the stirring speed is accelerated. The droplet standard decreases; when the mixing speed is too large, the droplets will attack and merge.
- (4) Loose protection system: the protection system protects the VCM droplets in the early stage of the reaction to avoid annexation. And once the generated PVC accumulates in the VCM droplets. The loose system protects the condensation of the controlled particles, and then obtains the finished SPVC particles. Loose system is into main loose system and auxiliary loose system. The main loose agent have high alcohol solution PVA, hydroxypropyl methyl cellulose. Which affect the full function of SPVC; assist the loose system is to advance some characteristics of SPVC particles. In general, large reactors can use loose system.
- (5) Main loose system of hydroxypropyl methylcellulose. They are water-soluble and stabilize the VCM droplets by reducing the interface tension between the VCM and the water. Loose agent is necessary to be below the gel temperature. And the viscosity of the main loose agent solution should not be too high.
- (6) Auxiliary se system of hydroxypropyl methylcellulose: they are with the main loose system. Can advance porosity and dispatch particle distribution. In contrast to the water solubility of the main loose agent, they have the proper solubility with the VCM. In general, the amount of main loose agent can be slightly after participating in the loose agent.