| Aiming at industrial development of poly(vinyl chloride) resin for rigid pipe with great diameter, a particle formation approach of this special-use PVC resin was proposed based on the well-known particle formation mechanism of vinyl chloride suspension polymerization. The basic research on systhesis laws was carried out in a 5 liter autoclave and pilot research was carried in a 100 liter autoclave using the optimized recipe and technology. PVC resin with regular particle shape, high bulk density, good powder flowability and gelation property was prepared.PVC resin with high bulk density is the main direction for producing the special PVC for pipe with great diameter, spherical PVC hasn't ever been produced wholesale. Some PVC samples and standards of domestic and international companies have been collected and analyzed, it was found that pipe grade PVC with excellent quality often show plump-like particle shape, narrow particle-size distribution, few fine particles and few closed sell inside particles. A particle formation course of pipe grade PVC resin was designed as: using specific dispersant system, specific dispersant injection mode and specific agitation mode.Agitation for the 5L autoclave has been improved and an agitator with good agitation effect has been developed. Many dispersant system and dispersant injection modes were applied in the polymerization. It was observed that injection of Na gas to the polymerization system could decrease the amount of dispersant agent to level comparable to that of industrial production by restraining the monomer flow back. Injection of part of dispersant agent continuously during the polymerization could perfect particle shape effectively, increase bulk density, improve power flowability. The principle of perfecting particle shape was analyzed theoretically and it is proposed that the draw-force of perfecting particle shape is the additional pressure produced by interfacial tension, the additional pressure on particles with different diameter are different, which would lead to different in porosity. The porosity inside and outside particles was calculated from bulk density and cold plasticizer absorption and could be used to characterize the accumulative density and to reflect the quality of PVC. The continuous injection mode was studied indetail, and factors affecting the stability of polymerization and particle features of resin,such as the ratio of initial added dispersant agent(s) to the total amount dispersant agentsand the addition rate of dispersant agents, were optimized. PVC resin with bulk density ≥0.55g/ml, cold plasticizer absorption ≥20% were prepared, using the optimized recipeand technology.The internal particle morphology, special area and the processability of PVC wereinvestigated in detail, it was found that the aggregation degree of parimary particles in theoptimized PVC resins was lower and special area was relatively greater. A combinationof high bulk density and good flowability was obtained by using PVC with a narrowparticle-size distribution. The gelation course of PVC compound was analyzed and it wasproposed that particle's shape was an important factor influencing the gelation of PVC.The gelation property of PVC resin with excessively round and slick particle shape whouldbe bad. It was also proposed that properties of PVC compound were the final determinantsof the extrusion speed.The agitation features of the 100L autoclave were analyzed and the agitator wasoptimized. The usage of dispersant agents and the technology of continuous injection ofdispersant agents were optimized through polymerizations carried on the 100L autoclave.PVC resin with regular particle shape, higher bulk density and excellent powderflowability and gelation properties were obtained and used in the industrial production ofpipe. The extrusion speed increased as special-use PVC resin prepared by this work wasused.Key words: Polyvinyl chloride, suspension polymerization, rigid pipe with great di...
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