Influences of some polymerization conditions on particle properties of suspension poly(vinyl chloride) resin

Abstract

Effects of polymerization temperature, conversions, and nonionic surfactant on the particle properties of suspension poly(vinyl chloride) (PVC) resins were investigated. It was shown that polymerization temperature has no significant influences on the mean particle size of PVC resin, and that the cold plasticiser absorption (CPA) of resin decreases linearly with the increase of polymerization temperature. Agglomeration of VCM droplets finishes before 20% conversion, and the mean particle size keeps almost constant at later stages of the polymerization process, but the CPA continues decreasing with the increase of conversion. Scanning Electron Microscopy (SEM) micrographs show that the degree of agglomeration of primary particles increases with polymerization temperature and conversion. Addition of nonionic surfactant to the VCM suspension system, as a secondary suspending agent, has a great influence on the particle properties of PVC resin. The particle size and CPA increase as the concentration of nonionic surfactant increases. The nonionic surfactant with a greater HLB value is more effective in raising the mean particle size, but is less effective in raising the CPA. It is considered that the added nonionic surfactant would be absorbed faster on the VCM/water interface than the poly(vinyl alcohol) (PVA), which was used as the primary suspending agent. Because the colloid protection ability of the nonionic surfactant is less than that of PVA, droplets become less resistant to coalescence, and the mean particle size of the final PVC resin increases consequently. The increase of porosity is caused by the combined effects of increased coalescence of VCM droplets and the nonionic surfactant's steric effect inside the droplets.

Suspension Polymerization Processes

“…The addition of a secondary stabilizer can also effect the particle size distribution of the polymer particles [16]. PVC porosity can also be increased by using non-ionic surfactants as secondary stabilizers [17]. PVA can become grafted onto polymer that is formed inside the drops so that a "skin" forms on the final particle surface [18,19].…”

Free‐Radical Polymerization: Suspension

“…The precipitating polymer aggregates to form unstable microdomains, which aggregate further to give domains. Some components of the drop stabilizers are chosen because they are miscible with the monomer and they can influence the agglomeration of primary particles [82]. The primary particles grow by polymerization within them and by buildup of microdomains or domains on their surfaces.…”

“…When nonionic surfactants, such as Span85, Span60 and Span20, are used as SSAs, with PVA as the main stabilizer, the mean particle size of PVC resins increases quickly as the concentration of nonionic surfactant increases [82]. The degree of agglomeration of primary particles increases with polymerization temperature and with conversion.…”

“…Thus, the colloid protective ability of the composite suspending agent would decrease because the nonionic surfactants with a low molecular weight have a lower colloid protective ability than that of PVA. High conversions of VCM are not always desirable because the porosity of PVC particles usually decreases linearly with monomer conversion, as shown in Figure 5.7 [60,82]. Zerfa and Brooks [60] showed that, at low monomer conversion, PVC porosity increases if a high monomer reflux rate is used.…”

“…Here, increased porosity may be the result of incomplete drop coalescence creating voids at the sites where droplets are not well contacted [82]. Here, increased porosity may be the result of incomplete drop coalescence creating voids at the sites where droplets are not well contacted [82].…”