Coupled pyrolysis, degradation analysis

Coupled pyrolysis techniques find three distinct areas of application. Polymers which degrade cleanly to relatively few volatile products, such as PMMA, polyisobutene, and many step-reaction polymers, are often amenable to detailed product analysis and to kinetic analysis of the formation of individual products (12,43). 

Coupled Pyrolysis Techniques. Perhaps the most powerful techniques currently available are those in which the pol3mier is pyrolyzed for a short time in a pyrolysis system directly coupled to a modem anal3dical instrument capable of analysis of the volatile products. Although direct pyrolysis coupled with ftir is available, the most common techniques have been gas chromatography, mass spectroscopy, and combinations of the two. In contrast to tga, these techniques provide no real information on the onset temperature of degradation or on the number of distinct stages, but they can give very detailed information about the products of reaction. 

These features coupled with inherent sensitivity and broad detection ranges of modern GC/MS (hydrogen to oHgomers) make pyrolysis GC/MS perhaps the most versatile and potentially useful single technique for the in-depth analytical degradative analysis of complex silicone elastomers. 

The characterization of relatively complex polymers is usually carried out by means of coupled techniques because sometimes a single technique is not enough to elucidate their structures. Pyrolysis of polymers is an old technique used many years ago to identify materials by their vaporized decomposition products. The coupling of this simple method with a powerful identification technique, such as infrared (IR) spectroscopy or, often, mass spectrometry (MS), has demonstrated its utility for the analysis of polymeric materials and, mainly, for the characterization of their degradation products. 

The combination of polymer analysis and evolved gas analysis certainly provides considerable and complementary information about the degradation process, but in many cases pyrolysis-evolved gas - FTIR analysis alone is very useful, and generally simpler. This technique was pioneered by Griffiths (10) but developed to a high level by Lephardt and Fenner (11-13) we have found it to be very useful for characterisation work. In recent years it has been coupled with TGA (TGA-FTIR) but this does not yet appear to be widely used. The manufacturers data so far suggest that the pyrolysis chamber/gas cell relationship has not yet been optimised. 

Further notable developments include renewed interest in the use of laser source pyrolysis, particularly in combination with time-of-flight mass spectrometry, which offers the possibility of targeting particular chemical bonds for degradation, and the coupling of analytical pyrolysis and tandem mass spectrometry, to induce the fragmentation of specific pyrolysate ions. The latter has culminated in the construction of a number of novel instruments, including a pyrolysis ion trap mass spectrometer capable of MS analysis. 

H. Sato, T. Kituchi, N. Koide, and K. Furuya, Thermal degradation and combustion process of liquid crystalline polyesters studied by directly coupled thermal analysis—mass spectrometry. Journal of Analytical and Applied Pyrolysis, 37, 173 (1996). 

Thermal evolution analysis is an excellent tool for polymer studies complementary to other thermal techniques such as DTA, TG and pyrolysis. Its applications include thermal degradation studies, determination of additives and contaminants, polymer composition and structure identifications. With small variations, the apparatus can also be used for vapour pressure measurements, and for determination of odorous materials in polymer systems. Coupling of TEA to GC for the identification of effluents is practicable and useful. TEA-CT-GC was used for the analysis of volatiles from ABS 10 ppb of styrene but negligible acrylonitrile was detected in the headspace of a typical ABS resin [42]. 

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