COOPERATION BETWEEN CHEMICAL AND PHYSICAL NETWORKS IN CROSS-LINKED AND PLASTICIZED PVC

The effect of crosslinking of plasticized PVC on the mechanical properties has been investigated. Crosslinking was performed by using a dithioltriazine, and penetration as a function of temperature was used to follow the changes in mechanical properties. Changes in the melting behavior were detected by differential scanning calorimetry. Even rather low levels of gel content gave a substantial reduction in penetration in the interval 60–110°C, while a more complete reaction prevented major penetration up to at least 200°C. The penetration curve of heavily crosslinked materials showed several plateaus and the transitions could be related to melting of different crystallites formed by annealing at different temperatures. The physical network formed by the crystallites constitutes an important complement to the chemical network in plasticized PVC crosslinked by dithioltriazine. Both the amount and the melting temperature of the crystallites increased after annealing. The introduction of the chemical network further improved the heat resistance of the crystallites. The presence of the two networks will therefore show a synergistic effect with respect to the mechanical properties at increased temperatures. Copyright © 1991 John Wiley & Sons, Inc.