Thermal dehydrochlorination of pure PVC polymer: Part I—thermal degradation kinetics by thermogravimetric analysis

• Published in: Journal of applied polymer science 2021-07, Vol.138 (25), p.n/a
• Main Authors: Cruz, Patrick Pimenta R., Silva, Leonardo Cerqueira, Fiuza‐Jr, Raildo A., Polli, Humberto
• Format: Article
• Language: English
• Subjects: Catalysts; Chlorine; Conversion; Dehydrochlorination; Hydrochloric acid; kinetic analysis; Kinetics; Materials science; Molecular structure; Nucleation; Polymers; PVC; Sequences; Suspension polymerization; Syndiotacticity; Tacticity; Thermal degradation; Thermogravimetric analysis
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.50598

Thermal degradation of PVC occurs in two stages, with each stage subdivided into two substages. The first refers to the dehydrochlorination, where hydrochloric acid is formed, and giving polyene structures. Hitherto, the degradation mechanism and action of hydrochloric acid as a catalyst during the dehydrochlorination stage are poorly known. Recently, the importance of the tacticity has gained attention for its influence on the dehydrochlorination mechanism. The present work focused on the dehydrochlorination stage, studying the molecular structure by FTIR analysis and the kinetic parameters by TGA analysis in Nitrogen atmosphere, based on three mathematical methods: Friedman, Kissinger, and Flynn‐Wall‐Ozawa. The sample was a pure homopolymer obtained by suspension polymerization. The dehydrochlorination kinetics follows a first order reaction model and occurs by nucleation and growth. The dehydrochlorination begins with the loss of very labile chlorine atoms present in defective and isotactic molecular segments. The formed HCl acts as a catalyst in the degradation. Following 40% conversion, a drop in Ea is observed. After that, chlorine atoms present in syndiotactic and atactic sequences, are released and, added to the large number of polyene chain sequences, and an increase in Ea is observed up to 60% conversion, where the dehydrochlorination stage is concluded. The thermal degradation of PVC occurs in two stages, the first being dehydrochlorination, where the elimination of HCl occurs from the loss of labile chlorine atoms, present in defective parts of the polymer chain, but also present in isotactic molecular segments, resulting in formation of polyene structures. Dehydrochlorination represents the loss of about 60% of the original PVC mass