Polyfvinyl chloride stability

Akutin (52) performed an exhaustive study on the influence of processing conditions and the nitrile rubber/poly(vinyl chloride) ratio on the mechanical characteristic of the product. The experiments were carried out in a Brabender Plastograph at 160-180° C and rotor speed of 10-50 rpm. The polyfvinyl chloride) molecular weight was 83500. A resin with an epoxy group content of 20.75% was added to the blend as plasticizer and stabilizer. Figure 29 shows that the... 

Investigation of the kinetics of the reaction of 4-chloro-2-pentene, an allylic chloride model for the unstable moiety of polyfvinyl chloride), with several thermal stabilizers for the polymer has led to a better understanding of the stabilization mechanism. One general feature of the mechanism is complexing of the labile chlorine atom by the metal atom of the stabilizer. A second general feature is substitution of the complexed chlorine atom by a ligand (either carboxylate or mercaptide) bound to the metal. Stabilization requires that the new allylic substituent (ester or sulfide) be more thermally stable than the allylic chlorine. The isolation of products from stabilizer-model compound reactions supports the substitution hypothesis of poly(vinyl chloride) stabilization. 

The use of a soluble metal-chelating agent such as tetrasodium ethylenediamine tetraacetate effectively stabilizes an anaerobic formulation against small amounts of metal contamination [173]. The wide variety of appUcations of anaerobic adhesives and sealants is made possible by the modifications which make the viscosity appropriate to the application. An application which requires penetration into close fitting parts should have very low viscosity while a product used with large, loose fitting parts should have a high viscosity. Polymethacrylates, cellulose esters, butadiene-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, polyfvinyl chloride), copolymers of vinyl chloride and vinyl acetate, polyfvinyl acetate), cellulose ethers, polyesters, polyurethanes, and other thermoplastic resins have been used to control the flow characteristics of anaerobic sealants [174]. 

Acid scavengers are an important type of stabilizers used in the stabilization of polyfvinyl chloride), although they are used in other types of polymers as well. Therefore, this class of substances deserves a separate chapter. 

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