A NEW APPROACH TO PVC-PLASTICIZER INTERACTION BY USING A T-G CONCENTRATION POWER EQUATION

The concentration power equation recommended by Brekner, Schneider and Cantow for adapting the compositional dependence of the glass tempera ture, T-g, of compatible binary polymer blends has been used to correl ate the experimental T-g data obtained for PVC-plasticizer systems. It is demonstrated that the T-g VS composition data for such systems can be adapted with the condition that two different concentration power equations are applied separately to the two branches of the curves sep arated by the cusp typical for these systems. Accordingly, different v alues are obtained for the parameters of the concentration power equat ion for the two branches of the T-g VS composition curves. A certain s ignificance is attributed to the cusp, characterized by a critical com position of the system. Below the critical composition the plasticizer will be fixed by energetic driven hetero-interaction preferentially i n the 'interdomains' within the amorphous PVC matrix, causing a stiffe ning of the blend. Above the critical concentration the plasticizer wi ll still penetrate these domains, but this time due to plasticizer-pla sticizer homocontacts which thus contribute to an increase of the mobi lity and consequently of the entropy of the blend. This different beha viour is characterized by means of the different parameters of the con centration power equations for the two branches of the T-g vs composit ion curves. Additionally it is shown that the parameters can be correl ated with the usual compatibility criteria of the plasticizer ranking. (C) 1997 Elsevier Science Ltd.