Colloidal stability of PVC primary particles in vinyl chloride

Abstract

Abstract:The electrostatic contribution to the colloidal stability of PVC primary particles (R = 0.15 ~) dispersed in vinyl chloride, was calculated using models based on the Coulombic interactions and the DLVO theory. The calculations were based on: a) the particle charge as obtained from literature data on the electrophoretic mobility of PVC primary particles in VCM and b) on estimates of the Debye length as obtained from measurements of the electrical conductivity of VCM and of solutions of Bu4NBF 4 in VCM.The calculations showed that particle stability would decrease with particle size (experimentally-observed behaviour), only if the particle charge increased with size at a lower rate than in proportion to particle radius.The calculations also suggest that particle growth may be governed by a competitive growth mechanism of electrostatic origin. Particle growth is assumed to occur by absorption of many small, weakly charged basic particles from the monomer phase. According to the calculations, the electrostatic interaction between primary and basic particles may be such that the growth of the smaller primary particles is favoured over that of the larger ones.

Electrostatic and steric stabilization of PVC primary particles

“…The results of Figures [10][11] are in qualitative agreement with the experimental observations of Tornell and Uustalu,21 who found that, as the molecular weight or/and the amount of PMMA increased, the formation of primary particle aggregates was delayed. Note that longer stabilization periods will not necessarily lead to an increase of the primary particle size, since particle growth is mainly controlled by particle coalescence.…”

“…Primary radicals, formed by initiator CCC 0021-8995/93/030445- 15 decomposition, rapidly react with the monomer to produce PVC macromolecules that are insoluble in the monomer phase. These closely spaced polymer chains combine together to form unstable polymer microdomains, which have a radius of about [10][11][12][13][14][15][16][17][18][19][20] nm. However, the microdomains (or basic particles) have a limited stability and agglomerate rapidly to generate the primary particle nuclei, also called domains.…”

Aggregation phenomena in the suspension polymerization of VCM

“…This consideration is in agreement with a similar consideration suggested in the fiterature that was based on the examination of the maximum energy barrier [15]. For cp = 0, Eq.…”

“…For the system PVC/VCM the value of the Hamaker's constant was taken as 5 x 10 -2' J [13]. The energy of repulsion can be calculated from the DLVO theory, or for particles smaller than the Debye length by a modified Coulomb's law [15]. In order to minimize the effect of the variation of the reciprocal Debye length, the repulsion energy in this work was considered to be given by a simple Coulomb's law Qo.…”

“…These chloride ions may be the product of either PVC dehydrochlorination or the decomposition of VCM peroxide formed during the reaction of VCM with the residual oxygen. On the contrary, other investigators [8,15] have indicated that a constant charge approach leads to a situation where the aggregation of a basic particle with a large primary particle is favored over its aggregation with a small primary particle. They based those considerations on the theoretical calculations of the maximum energy barrier that had to be overcome, so that two particles collided.…”