Influence of pigments on degradation of polymers. IV.

Thermal degradation of polystyrene, polymethylmethacrylate and acrylonitrile-styrene copolymer.

Abstract

Authors investigated the effect of pigments affecting on thermal decomposition of polystyrene, polymethacrylate and styrene-acrylonitrile resins being marketed at present, purposing at their mold-processing, by the measurement of change in weight, change of viscosity and by the change of resin structure.
1. STYRENE RESIN. In accordance with proceeding of thermal decomposition of the styrene resin, much quantities of the monomer were regenerated, decreasing the molecular weight with increase in the carbonyl radical and double bond in parallel. It was made clear that some additives such as, pigments and others, according to the kind of the additives, greatly affected on the decomposition. As for the kind of pigments, for instance, red iron oxide and cadmium red etc. had promoting effect and on the other hand cobalt blue and cyanine blue etc. had suppressing effect. This cause was reduced, from investigation on the effect of each metallic salts, as that it came from a catalytic action of iron or cadmium etc., as metal, onto the decomposition of polymer. For activation energy of the decomposition, it was measured as 23.4 kcal for blank and as 22 kcal for the mixing of red iron oxide.
In case thermal decomposition in vacuo, the effect of additives was scarcely recognized. As for the effect on concentration of the additives, an increasing tendency was recognized in proportion with increase in the concentration, within range of 2 percent approximately, whereas the effect was recognized as comparatively smaller at more than that concentration.
2. METHACRYLATE RESIN. Thermal decomposition of this resin also proceeds while it decreases the weight and as the viscosity lowers, however, an effect different from the case of styrene resin was made clear wherein the thermal decomposition of the resin at constant temperature was decreased for the change after a certain interval of time from the commencement of decomposition, reaching to a limited step without going further, and it was also made clear that the pigments affected onto the degree of the step. Such pigments as cadmium yellow and red iron oxide etc. effected as promoter for the decomposition, and similar tendencies were also recognized for oxides, carbonates and sulfates containing the same type of metals under consideration. Such effects were scarcely recognized in case in vacuo.
3. ACRYLONITRILE-STYRENE COPOLYMER. In case decomposition of this copolymer, the. effect of pigments could obtain from similar means under the same principle, and which made clear the effect of the pigments, being comparatively decreased, and the promotion effect was confirmed for red iron oxide and for cadmium red etc. containing iron and cadmium as metal. Difference was not recognized in that carried out in vacuo. Effect on pH with the pigments was not recognized.
In summary when compared the effect of pigments onto various type resins being marketed, the. authors believe there exists minor problem in the practice as for the three kinds of resin reported in this paper, as compared with the kind of resins previously reported for polypropylene, polyacetal and. polycarbonate which were more affected.