A morphological study on the plasticization of poly(vinyl chloride) by diethylhexyl succinate and Dibutyl Phthalate

The effects of different plasticizers on the structural features of PVC were investigated. Particular emphasis was on the fine structure as denoted by small-angle X-ray scattering (SAXS). The influence of plasticizer content on the mechanical response was followed by dynamic mechanical spectroscopy. The particular plasticizers investigated principally were diethylhexyl succinate and dibutyl phthalate, although other phthalate plasticizers were investigated including dibutyl succinate and dibutyl sebacate. It was noted that structural features at the 100– to 200–å level were systematically influenced by the type and amount of plasticizer and in particular by its solubility parameter. To account for the observed behavior, a model was proposed which speculates that the absorption of plasticizer is nonuniform within the system and in particular within the local regions where crystallites exist. The level of swelling of plasticizer into the amorphous regions at some distance from the crystallites is different (and greater) than that in disordered regions near the crystallites. This degree of difference in swelling, however, is dependent upon the solubility parameter of the plasticizer. This model, which is in general support of an earlier model, also helps to account for the large difference in temperature-dependent dynamic mechanical behavior introduced by the different plasticizer species.