Gelation of suspension PVC with small amount of plasticizer compounds

The course of gelation of suspension PVC-S (K values 58, 61 or 67) plastified with small amounts (0.5-4 phr) of dioctyl phthalate (DOP) was investigated in Brabender plastometer chamber. Rotational speed of rotors was 28 min(-1). On the basis of torque changes and the measurements of real temperature of gelating compound versus process time the curves of torque change versus this temperature were prepared for various plasticizer contents. It was found the higher DOP content the lower temperature corresponding to maximum torque, characterizing the gelation process. The dependence of real temperature of a compound in equilibrium state (TE) on DOP content shows that gelation occurs when chamber temperature reaches 170 degrees C and plasticizer content is equal DOPmin = 2.5 phr. Effects of these parameters on the torque measured at equilibrium state are similar. Addition of 2.5 phr of DOP caused rapid increase in gelation degree (G) during processing of all the types of PVC tested, at temp. 175 degrees C.