S-PVC Grain Morphology: A Review

Abstract

Among the properties required for producing PVC resin of good quality, the particle morphology (size, primary particles, agglomerates, skins, pores, etc.) plays an important role in processing and performance of products. Three main physical transitions are involved in self-structuring the grains of suspension PVC: nucleation, aggregation and growth. All of these processes are affected by many physical transitions and chemical phenomena that are inter-related and many are complex functions of polymerization conditions (i.e., agitation, temperature, stabilizers, etc.). Because of this multiscale complexity, the relationships between suspension polymerization conditions and morphology have yet to be well-understood. In spite of all these difficulties, a literature survey of the available research nevertheless provides a comprehensive and descriptive insight into mechanisms governing PVC particle formation accounting for the effect of the process variables.

The Effects of Initiators Mixture on Suspension Polymerization of Vinyl Chloride and its Comparison with other Productivity-Enhancing Procedures

“…Among works performed on the enhanced productivity of PVC through temperature-trajectory [2][3][4][5][6][7][8], in earlier work [9][10][11] we suggested the most reduction in the polymerization time up to 33%. Bijanmanesh et al [13] reported that continuous dosing of a fast initiator during suspension polymerization of vinyl chloride enhanced productivity by 40%.…”

“…By comparing these micrographs, it can be seen that the PVC grains prepared by Cok-PVC conditon are more spherical with smoother surfaces than those produced by control condition. the thick sorrounding skin as well as the uniform and large size of primary particles inside grains forming a kind of strong inner skeleton prevent the droplet from collapsing [9]. The larger primary particles in size and number at the early stage of the reaction, are more likely to collides to the inner surface of the droplets and thus strengthens the skin [10].…”

“…As, the productivity of this high demand product is still low, improving the productivity of the batch polymerization process has been always considered as a challenging issue [1][2][3][4][5]. The enhanced productivity in VCM suspension polymerization process can be effectively achieved by reducing the batch time so that predefined specifications of final product do not change remarkably.…”

“…Recently, we have successfuly implemented a variable temperature trajectory during the course of the reaction to improve productivity by reducing the polymerization time for a predefined K value [9][10][11]. In this procedure , the reaction temperature was raised to higher value than that of corresounding isothermat process at the beginning of polymerization and then decreased gradually over the process time to a lower value than that of isothermal one.…”

“…Polymer phase is changed from the aggregation of the precipitated macro-radicals to nano-domains and then domain and finally to a three-dimensional network of primary particles which are surrounded in a rigid skin. The process variables such as polymerization temperature, the type and concentration of initiator and the method of initiator addition have been found to have a significant influence on the internal structures and molecular characteristics of PVC resin [1,[8][9][10][11][12][13][14]. In other word, the final characteristics of final PVC is influenced by the conditions governed by the strategy implemented to enhanced productivity.…”