Suspension Polymerization of Hydroxypropyl Methylcellulose in PVC
Using Hydroxypropyl Methylcellulose as separating agents, the products obtained have structured and loose particles, suitable apparent density and excellent processing performance. However, the use of Hydroxypropyl Methylcellulose alone can contribute to good invariance of resin though. The overall performance of resin is poor. The compound use of hydroxypropyl methylcellulose and several different alcoholysis degree of PVA (polyvinyl alcohol) can make the performance of the products better, the quality easy to control and at the same time can reduce the cost.
The dispersing agent is the main factor that influences the particle shape of PVC(polyvinyl chloride)resin. The smaller the surface tension of the aqueous solution of general dispersing agents and the interfacial tension with VCM (Vinyl chloride monomer) are, the finer the VCM droplets can be dispersed. And thus the particle diameter of PVC resin will be smaller. The stronger the protection ability of the dispersing agent is, the closer the obtained PVC resin particles will be and the smaller the porosity will be. And intergranular coalescence is also more difficult, so it is easy to form “single-cell” (sub-particle) resins.
In order to make the PVC resin with well-proportioned evacuation of particles, narrow particle size distribution and suitable apparent density, a single dispersant system is difficult to meet the above requirements, so two or more kinds of compound dispersion systems are commonly used, and even a small amount of surfactant can be added as auxiliary dispersing agents.
For example, in the compound dispersion system of PVA and HPC, the higher the alcoholysis degree of PVA is, the greater the surface tension of the aqueous solution will be and the stronger the protection ability will be, while a certain concentration of hydroxypropyl methylcellulose has a good dispersing effect.
Therefore, using PVA with high alcoholysis degree (75-80%) as the primary dispersing agent, and compounding a certain amount of hydroxypropyl methylcellulose as the dispersing agent for suspension polymerization, it is easier to prepare the PVC resin that can meet the requirements of particle morphology.