Structural transformation, thermal endurance, and identification of evolved gases during heat treatment processes of carbon fiber polymer precursors focusing on the stereoregularity

• Published in: Journal of thermal analysis and calorimetry 2017-08, Vol.129 (2), p.821-832
• Main Authors: Santhana Krishnan, G., Murali, N., Jafar Ahamed, A.
• Format: Article
• Language: English
• Subjects: Ammonia; Analytical Chemistry; Atacticity; Chemical reactions; Chemistry; Chemistry and Materials Science; Chromatography; Cleavage; Copolymers; Cyanides; Degradation; Endurance; Evolution; Fragmentation; Gas analysis; Gas chromatography; Gases; Gravimetric analysis; Heat treatment; Homology; Hydrogen; Hydrogen cyanide; Infrared analysis; Infrared spectroscopy; Inorganic Chemistry; Ions; Isotacticity; Mass spectrometry; Measurement Science and Instrumentation; Nitriles; Physical Chemistry; Polymer industry; Polymer Sciences; Prepolymers; Pyrolysis; Scientific imaging; Spectrometry; Spectroscopy; Thermal analysis; Thermal resistance; Transformations
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-017-6190-y

Structural transformations of polyacrylonitrile microstructure with varying degrees of stereoregularity during the thermal-oxidative degradation and pyrolysis reactions were investigated employing coupled thermal techniques namely pyrolysis–gas chromatography–mass spectrometry, evolved gas analysis–mass spectrometry, and thermal gravimetric analyzer-FT infrared spectrometry (TG-FTIR) in the temperature range of 200–600 °C. More number of intense peaks with large ionic abundances in the thermal curves and pyrograms indicate that atactic-rich polyacrylonitrile copolymers undergo thermal cleavage, fragmentation and cyclization reactions more readily than isotactic polyacrylonitrile. The mass loss accompanying the thermal reactions was accounted for the evolution of hydrogen cyanide, ammonia, and homologous of alkyl nitrile having molar mass between 47 and 224  m / z ; their most probable structures were identified. Thermal analysis results confirm that nitrile cyclization reactions proceed preferentially at isotactic triads leading to a steady and stable thermal-oxidative degradation reactions as compared to atactic-rich polyacrylonitrile. The simultaneous TG-FTIR results of evolved gas analysis also validate the pyrolysis experiments.