Different thermo-oxidative degradation routes in poly(vinyl chloride)

PVC and mixtures. with calcium stearate (CaSt(2)) or zinc stearate (ZnSt(2)) were degraded at different temperatures (160, 170, 180 and 190 degreesC) in order to follow their HCl evolution. The same mixtures were degraded in similar conditions but at convenient time intervals to have samples to characterise and follow such curves by many other techniques. Yellowing index (YI) and visible reflectance spectroscopy were used to study colour changes, Carbonyl index by FTIR (CI) and fluorescence spectroscopy to follow oxidation and chromophoric species and molecular weight and gel percentage to detect crosslinking and chain scission. Temperature does not affect the amount of HCl evolved, only the rate and YI does not represent the release of acid for PVC and PVC+CaSt(2) only for PVC+ZnSt(2). On the other hand, visible reflectance always shows the colour trends observed by eye. Crosslinking is favoured by high temperature for the first two mixtures, but where the Zn soap is added chain scission plays an important role. (C) 2001 Elsevier Science Ltd. All rights reserved.