Dehydrochlorination of PVC Compositions During Thermal Degradation

The polyvinylchloride (PVC) differs from other polymer materials by low thermostability. The process of dehydrochlorination takes place even at low temperatures. The purpose of this investigation was to determine the influence of different PVC additives on formation of hydrogen chloride (HCl) from thermal degradation in different gaseous fluids. It has been established that the HCl formation takes place more in nitrogen as a medium than in air medium at a given temperature, especially for the high temperature region. Dibutyl phthalate (as a plasticizer) in 25 mass % w.r.t. PVC, reduces the mass loss due to HCl formation by about 5%, which is the result of two interaction processes - between HCl and plastifier degradation products. It has been found that the addition of 5 mass % of stabilizer in PVC slows down the process of dehydrochlorination and as a result the loss of mass is 2-5% less, compared to non-stabilized samples. Calcium carbonate as a filler was found to be active above 400-500 °C and reduction in mass loss was found to be up to 15% at a temperature range of 800-900 °C. Calculation of kinetic parameters shows that the rate of dehydrochlorination depends on the composition of PVC. The activation energy of formation of HCl in air, in a temperature range of 400-600 °C has been found to be 12.7, 13.3, 16.1 kJ/mol for pure, plasticized and stabilized PVC, respectively. The results reported here shall be useful for development of methods for waste utilization and their influence on the environment