A DMA STUDY OF THE SUPPRESSION OF THE BETA-TRANSITION IN SLIGHTLY PLASTICIZED PVC BLENDS

A new criterion for evaluating different plasticizers the ability of s uppression of the beta transition in plasticized PVC blends. According ly, the beta suppression ability is proportional to the PVC-plasticize r compatibility, expressed either by the critical solution temperature , CST, or by the interaction parameter related to the difference betwe en the solubility parameters of the blend components. The criterion is , however, valid for low plasticizer contents (<5% w/w) only, as long as the beta transitions are not overlapped by the a transitions, shift ed towards lower temperatures due to the effect of the plasticizer. Fo r higher plasticizer contents the a transition starts to overlap the b eta transition and the beta suppression ability of the plasticizer dep ends increasingly on the efficiency of the plasticizer i.e. on the dep ression of the glass transition temperature of PVC (related to the T-g of the plasticizer). Accordingly, plasticizers with both good efficie ncy (low T-g) and compatibility are more effective in the beta suppres sion than plasticizers which have only a higher compatibility but also a high T-g (i.e. reduced efficiency).