Effects of steam on the thermal dehydrochlorination of poly(vinyl chloride) resin and flexible poly(vinyl chloride) under atmospheric pressure

A steam-based treatment for the dehydrochlorination of poly(vinyl chloride) (PVC) at atmospheric pressure was evaluated. Temperatures ranging from 170 to 250 °C and steam concentrations of up to 75 vol% were applied to PVC resin and flexible PVC. Overall, the addition of steam increased the dehydrochlorination ratios for both sample types, regardless of temperature. PVC resin reached a maximum dehydrochlorination ratio of 76% after 1 h of treating at 250 °C and at a steam concentration of 50 vol%; this compares favorably to the 61% achieved under nitrogen. Higher steam concentrations reduced the maximum dehydrochlorination ratio for PVC resin; this was shown to be the result of a shielding effect due to rapid, superficial dehydrochlorination. This effect was not observed for flexible PVC, which reached a maximum dehydrochlorination ratio of 69% after 1 h of treating at 250 °C and at a steam concentration of 75 vol%; again, this is a significant improvement over the 51% value obtained under nitrogen. Moreover, the loss of plasticizer was shown to account for the majority of the flexible PVC weight loss. The reaction kinetics was also investigated. The proposed treatment is of special interest for the treatment of PVC medical equipment, since it could fulfill the needs for both sterilization and dehydrochlorination which the disposal of this waste requires.