Thermal degradation pathways

The breaking of chemical bonds under the influence of heat is the result of overcoming the bond dissociation energies. Organic polymers are highly thermally sensitive due to the 

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Scheme 12 The influence of steric congestion on thermal degradation pathway.

Figure 8.5 Oxidation and thermal degradation pathway leading to the formation of the characteristic compounds present in pine pitch...

Figure 5.1 Probable thermal degradation pathways for hemicelluloses, according to Fengel and Wegener (1989).

Barontini F. Cozzani V, Cussola A, et al. 2001. Investigation ofhexabromocyclododene thermal degradation pathways by gas chromatography/mass spectrometry. Rapid Commun Mass Spectrom 15(9) 690-698. 

These polymers may be compared with the more detailed discussion of thermal degradation pathways for phenol-formaldehyde resins described in Section 2.3.3 earlier, which explains the... 

Thermal Degradation Pathways of Some Polymers and Their Clay Nanocomposites and Resulting Reduction of Peak HRR... 

The Control of Thermal Degradation Pathways in Poly(vinyl chloride) by Heat-Stabilizing Additives... 

Thermal degradation pathway products of the oxazolidinone antibiotic Zyvox . In a study of the degradation chemistry of the drug Zyvox, the first member of a new class of oxazolidinone antibiotics, Hadden et al. utilized long-range GHMBC data to... 

Conventional organie systems are based on the acid catalysed dehydration of carbonifics sueh as dipentaerythritol. Metal oxides also have a use as catalytic flame retardants. For example, both antimony and tin have been used to impart flame retardancy to cellulosics without any assistanee from halogen eompounds. They appear to alter the condensed phase thermal degradation pathways in such a way that more non-volatile ehar and less flammable gases are generated. It has been found that low levels of potassium biearbonate significantly modify the pyrolysis kinetics of a cellulose to yield more ehar. 

Poly(phenylene oxide) (PPO) is a thermoplastic, linear, noncrystalline polyether commercially produced by the oxidative polymerization of 2,6-dimethylphenol in the presence of a copper-amine catalyst. PPO has become one of the most important engineering plastics widely used for a broad range of applications due to its unique combination of mechanical properties, low moisture absorption, excellent electrical insulation property, dimension stability and inherent flame resistance. This chapter describes the recent development of this polymer, particularly on the production, application, compounding, properties of its alloys and their general process conditions. The polymerization mechanism and thermal degradation pathways are reviewed and new potential applications driven by the increasing environmental concerns in battery industry, gas permeability and proton-conducting membranes are discussed. 

The thermal degradation pathway of pure PS involves chain scission followed by depolymerization. The resulting products are styrene monomer, dimer, and trimer through an intrachain reaction. However, the presence of clay causes changes in the degradation pathway of polystyrene. In the thermal decomposition of PS nanocomposites, the presence of products from interchain reactions is significant, because the radicals have more opportunity for transfer [20] (Figure 3.3). 

In an effort to fashion a unified mechanism for clay nanocomposites, Wilkie et al. have studied the effect that clay has on the thermal degradation behavior of more than 11 different polymers. This work also attempts to correlate the thermal analysis data with flammability properties measured in a cone calorimeter. " In this work TGA degradation products were cryogenically trapped and analyzed using gas chromatography/mass spectroscopy (GC-MS) the thermal degradation pathways of the polymers with and without clay were investigated. Wilkie... 

Thermally-assisted hydrolysis and methylation (THM) using organic alkaline reagents is widely utilised for reliable and informative characterisation of various condensation-type polymers that are often intractable for the conventional pyrolysis techniques [619]. Wang [618] has extended the derivatisation concept and distinguishes pre-pyrolysis and post-pyrolysis (i.e. pre-column ) derivatisation reactions. The purpose of pre-pyrolysis derivatisation is to secure a favourable thermal degradation pathway during pyrolysis. 

It is important to understand the thermal degradation pathways of polymers and the effect of additives on this degradation in order to either accelerate or retard the degradative process. In some cases, such as a landfill, it is advantageous to accelerate degradation while in other applications, such as in processing or reducing flammability, it would be desirable to retard it. 

According to predictions based on the above measured and analyzed results, an expected overall thermal degradation pathway of PHB is illustrated in Scheme 9.7 [76]. 

Scheme 9.7 Expected overall thermal degradation pathway of PHB.

Another recent development in derivatisation technology is of the prepyrolysis type. The purpose of this type of derivatisation is to convert the functional group in the polymer in a design way to obtain a favorable thermal degradation pathway during pyrolysis. These favourable pathways normally utilise a major monomer or monomer-related fragment to allow for easier qualitative and quantitative analysis. The major difference between the prepyrolysis derivatisation and postpyrolysis derivatisation is that the polymer backbone should be stable enough to resist the attack from the... 

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