Study on thermal degradation of polyvinyl chloride by ultraviolet spectroscopy and Congo Red method

The authors prepared a nontoxic composite thermal stabilizer for polyvinyl chloride (PVC) by compounding pentaerythritol and sorbitol with Ca/Zn stabilizer. The Congo Red method was adopted to determine the stabilizing time of the composite material and to study the interaction and stabilization mechanism between the polyhydric alcohols and Ca/Zn stabilizer. The results indicate that a good synergism exists between the polyhydric alcohols and Ca/Zn, which is beneficial to effectively bating the phenomenon of 'zinc burning'. The thermal stabilizing effect on PVC of sorbitol is superior to pentaerythritol. The analysis by ultraviolet spectrometry reveals the formation mechanism of conjugated polyenes with different chain lengths during the thermal degradation process of PVC. The quantity of the short chain conjugated polyenes (conjugated chain length less than 6) dramatically increases with degradation time. However, the growth rate in quantity of the long chain conjugated polyenes (conjugated chain length equal to or higher than 6) is much lower than its short chain counterpart.