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TIP. Revista especializada en ciencias químico-biológicas
Print version ISSN 1405-888X
TIP vol.9 n.1 Ciudad de México Jun. 2006
Artículos originales
Mechanism of radiation-chemical and pyrolytic transformations in lexan ®
Mecanismo químico de transformaciones radiolíticas y pirolíticas en lexan ®
1Instituto de Ciencias Nucleares, UNAM. E-mail: aliev@nucleares.unam.mx.
2Laboratory of Plasma Chemistry and Planetary Studies. Ciudad Universitaria, Apdo. Postal 70-543, СР. 04510, México, D.F. Instituto de Ciencias Nucleares, UNAM.
We report here a new approach to study the mechanism of radiation-chemical transformations in polymeric materials based on the combined analysis of radiolytic gases, and pyrolytic products from preirradiated polymers by flash pyrolysis coupled to gas chromatography -Fourier transformed infrared spectroscopy- mass spectrometry with electron impact mode (GC-FTIR-MS). Lexan® (bisphenol-A polycarbonate) was studied in the dose range from 0.125 to 1.0 MGy. Lexan irradiation was accompanied by the preferential release of carbon monoxide followed by minor production of hydrogen, carbon dioxide and methane. Pyrolyzed Lexan releases mainly carbon dioxide, methane, benzene, toluene, phenol and 4-methyl-phenol. On the basis of these results we suggest two main pathways of Lexan radiation-induced scission with equal probabilities: (a) carbonate bond and (b) aliphatic-aromatic bond ruptures.
Key Words: Lexan; radiolysis; flash pyrolysis; GC-FTIR-MS; mechanism of degradation
Reportamos una nueva metodología para estudiar el mecanismo de transformaciones por radiación en materiales poliméricos basada en el análisis combinado de los gases de origen radiolítico, y los productos pirolíticos, generados mediante la pirólisis rápida de polímeros pre-irradiados, acoplado a la cromatografía de gases -espectroscopia de infrarrojo con transformada de Fourier- espectrometría de masas por impacto electrónico. El Lexan® (policarbonato de bisfenol-A) fue estudiado en el rango de dosis de 0.125 a 1.0 MGy. La irradiación del Lexan estuvo acompañada por la liberación preferencial del monóxido de carbono seguida de una producción menor de hidrógeno, dióxido de carbono y metano. El Lexan pirolizado liberó principalmente dióxido de carbono, metano, benceno, tolueno y 4-metilfenol. Con base en los resultados obtenidos sugerimos dos vías principales para la incisión del Lexan por radiación con igual probabilidad: (a) ruptura del enlace carbonato y (b) ruptura del enlace alifático-aromático.
Palabras Clave: Lexan; radiólisis; pirólisis instantánea; CG-IRTF-EM; mecanismo de degradación
Acknowledgements
The authors thank Francisco Garcia from ICN-UNAM for sample irradiation. We are indebted to Dr. Jay LaVerne from the Radiation Laboratory of the University of Notre Dame in Indiana for useful discussion of this work. Financial support from the UNAM project INI 01903 and the CONACyT project 46137 are gratefully acknowledged.
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Received: February 13, 2006; Accepted: June 19, 2006
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