Antioxidant effects in PVC plasticized with DIDA

Abstract

SynOPSiSAntioxidants such as bisphenol A (BPA) have long been recommended for retention of physical properties on oven-aging of PVC plasticized with certain plasticiaers. We have shown how BPA inhibits oxidative fragmentation of plasticizers such as diisodecyl adipate (DIDA) and thus decreases apparent volatility, and how it improves retention of modulus, elongation, and low temperature flexibility. Low concentrations are more beneficial than either zero or high concentrations, especially on longer aging. A t higher concentrations, although the plasticizer is retained in the PVC, it becomes less efficient a t low temperature, and low-temperature flex is impaired while elongation is preserved. DIDA exudes during oven-aging unless oxidation occurs to prevent it. When BPA is present, exudation is worst a t the most efficient concentrations of antioxidant. This appears to be the normal incompatibility of DIDA a t 105OC which is permitted by the antioxidant. On oxidation, the dielectric constant of DIDA rises into the 4-8 range, signifying compatibility with PVC, and the DIDA does not exude. LNTRODUCTIONAntioxidants have frequently been added to plasticized poly(viny1 chloride) (PVC) for improved retention of physical properties on oyenaging, especially since Fischer and Vanderbilt' reported their value with plasticizers prepared from 0x0-alcohols. The ASTM test method D 2288-64T2 recommends use of 0.1% bisphenol A (BPA) in case of weight gain instead of a weight loss during volatility testing of plasticizers per se. Yet, there are problems that have remained unanswered. Our observ% tions of PVC plasticized with diisodecyl adipate (DIDA) and of the plasticizer per se-with and without bisphenol A-have helped clarify a number of phenomena connected with the use of antioxidants. Among these are improved retention of elongation and low-temperature flex, reduced apparent volatility, but a reduction in apparent compatibility.Plasticizers such as DIDA or diisodecyl phthalate with many methyl branches in the alcohol moieties have numerous tertiary hydrogens as points of attack for oxidation. The adipates to some extent, and the azelates and sebacates even more so, may also be oxidized in the acid portion of the molecule, probably on the beta carbon atoms.a Antioxidants such as BPA inhibit this oxidation, protect the plasticizer and resin from deterioration, and help in the retention of physical properties of the plasti-

The Effect of Di-2-ethylhexyl Phthalate on the Thermo-oxidative Ageing of Poly(vinyl chloride)/Epoxidized Natural Rubber Blends

“…Threshold effects of DOP plasticizer concentration have also been noted for rigid PVC. 31 The improvement in the degradation properties of PVC/ENR with DOP incorporation implies that the presence of DOP is effective in altering the epoxide/ heavy metal salt balance. According to the gel theory of plasticization, the plasticizer breaks the loose attachments in PVC and masks the centres of force, conse- quently reducing the number of attachments in the dynamic equilibrium of solvation and des~lvation.~' This action is known to confer stability to PVC formulations and thus the incidence of release of HCI is reduced.…”

Plasticizers

“…However, upon extensive heating in air this oxidation-susceptible plasticizer builds up peroxides, undergoes chain scission and weight loss, and changes in compatibility. As shown in Table I, if the oxidation phenomenon is negated in per se DIDA by the presence of an antioxidant, bisphenol A, the plasticizer remains unchanged in dielectric constant and predictably would be incompatible (20).…”

“…Other types such as phosphates and epoxies have special chemical effects that can be synergistical ly beneficial. A small amount of phosphate plasticizer used with a phthalate frequently adds a measure of light stability and fungus resistance (50)(51)(52). Epoxy compounds varying from inefficient epoxy resin plasticizers (e.g., bisphenol A diglycidyl ether) to the moderately flexibilizing epoxidized vegetable oils (e.g., ESO, epoxidized soya oil) and to the very efficient octyl epoxystearates and tallates are all used for their excellent heat-stabilizing ability.…”

Dynamic Heat Stability of Expandable Semi-Rigid PV C

“…The mechanism of the thermal degradation of PVC is not yet resolved, but a free radical mechanism has been proposed by some authors (4). For these reasons, we have investigated The antioxidant 2,2'-bis (4-hydroxyphenyl) propane, BPA, is widely used in plasticized PVC to inhibit thermal oxidative degradation of plasticizers (5). However, BPA was found to interact with azodicarbonamide to form color in foam.…”