SynopsisThe stability of poly(viny1 chloride), as measured by thermogravimetric analysis, is significantly different from that of other thermoplastics. It is shown that the onset of weight loss can be correlated with the development of color in a processed resin. It is further shown that the ingredients within a rigid polyvinyl chloride compound drastically alter its thermal behavior. The effect of lubricant and stabilizer on the degradation of poly(viny1 chloride) is stressed.The processing of thermoplastic materials usually requires reasonably high temperature stability (up to 300°C.) of polymers. It is apparent that all resins do not behave similarly ( Fig. 1) and, since this is also true of single resins from different sources or of different batches of a resin from the same source, it is necessary to be able to distinguish or determine the differences in thermal stability. Thermogravimetric analysis (TGA) affords an excellent method by which this may be accomplished. Most of the common resins (e.g. , polyethylene and polystyrene) have a single weight-loss mechanism or reaction. This is not true, however, of resins such as polyvinyl chloride (PVC). PVC is especially vulnerable to changes in thermal conditions due to the chlorine groupings, and thus its weight-loss process is somewhat different (see Fig. 1).The thermal instability of PVC can be followed by a three-step weightloss thermogram on the TGA. This degradation procedure is identified as follows (Fig. 2): A is the region of dehydrochlorination (weight loss of 50-60y0), B is the evolution of simple hydrocarbons formed by cyclization and chain scission (weight loss of 15-3oyO), and C is a gradual evolution of the more complex degradation compounds.'r2The initial formation of conjugated bonds (caused by the evolution of HCl) imparts a coloring to the PVC compound that is quite unfavorable to the processer. Since PVC compounds are mixtures of PVC resin and additives such as lubricants, stabilizers, and modifiers, it is necessary to understand the influence of these additives 011 the stability of the material. It is the purpose of this paper to demonstrate the use of the TGA technique *
