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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-

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1 he rapid growth of plasticized vinyl compositions has necessitated the installation of additional equipment and the utilization of such equipment at the highest efficiencies. The Banbury mixer is the main compounding unit for fluxing vinyl compounds. Plasticizers are added to vinyl resins not only for the desirable properties they impart but also for improving processability. This article discusses the effect of different plasticizers, fillers, and lubricants on vinyl compounding in the Banbury mixer.Plasticizers exert a considerable effect on the fusion time of a vinyl compound. The plasticizers studied are