Particle polyvinyl chloride latex

The influence of the type of initiators (sodium persulfate versus 2,2 -azobisisobutyronitrUe) on the particle nucleation mechanisms and kinetics involved in the styrene miniemulsion polymerizations has also been studied [39]. As expected, the oil-soluble 2,2 -azobisisobutyronitrile promotes nucleation in the homogenized monomer droplets. On the other hand, formation of particle nuclei in the continuous aqueous phase becomes more important when water-soluble sodium persulfate is used. This result is consistent with the vinyl chloride work of Saethre et al. [44]. The number of polyvinyl chloride latex particles generated by mechanisms other than monomer droplet... 

FIGURE 12.16 Shear thickening found by Hoffman [47] for 1.25 pm diameter polyvinyl chloride (PVC) latex particles in di-2-ethylhexyl phtiialate with the discontinuous dependence of viscosity on shear rate. Redrawn fi m Hofhnan [49]. 

The adsorption isoterms of SDS on polyvinyl chloride (PVC) latex particles in the presence of various concentrations of sodium ions in the bulk solution, have been determined by Bibeau and Matijevic (2 ). In the latices which were examined by us, the surface concentration of emulsifier was confined to the region well below the saturation level. Under these circumstances only a negligible fraction of the total amount of emulsifier will be dissolved in the aqueous phase. 

Emulsion Polymerization Emulsions have particles of 0.05- to 5.0-pm diameter. The product is a stable latex, rather than a filterable suspension. Some latexes are usable directly, as in paints, or they may be coagulated by various means to produce very nigh-molecular-weight polymers. Examples are polyvinyl chloride and butadiene-styrene rubber. 

Water based latex emulsions consist of fine particles of high molecular weight copolymers of polyvinyl chloride, or polyvinyl acetate, acrylic esters, styrene-butadiene, or other resins combined with pigments, plasticizers, UV stabilizers, and other ingredients. A variety of thickeners, coalescing aids, and other additives are present in the water phase. 

Latex adhesives consist of particles of polymers with diameters of the order of 1 pm suspended in an aqueous medium. Surfactant molecules such as anionic soaps, which are adsorbed on the surfaces of the particles, maintain the particles in solution and thereby stabilize the latex. Stabilization can also be gained by the presence of a soluble polymer in the aqueous phase. The volume fraction of the phases is about 50%. Current adhesives include the latices of natural rubber, styrene-butadiene random copolymer, polyvinyl acetate and its copolymers with ethylene and vinyl chloride. For any further information on polymer latices the reader is directed to the three volumes of Blackley (1997). 

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