Thermal degradation kinetics

There have been many studies on the thermal and thermo-oxidative degradation of PMMA.23 24 It is well established that the polymer formed by radical polymerization can be substantially less stable than predicted by consideration of the idealized structure and that the kinetics of polymer degradation are dependent on the conditions used for its preparation. There is still some controversy surrounding the details of thermal degradation mechanisms and, in particular, the initiation of degradation.31... 

Extensive research has been conducted to determine the thermal-decomposition properties of polymers, the products of their degradation, and the kinetics involved in their reaction during pyrolysis (Ml). Complete comprehension of the mechanism involved in thermal degradation requires, among other facts, knowledge of these three fundamental aspects ... 

Polymers have inherently high hydrocarbon ratios, making liquefaction of waste plastics into liquid fuel feedstocks a potentially viable commercial process. The objective is to characterise the thermal degradation of polymers during hydrogenation. LDPE is studied due to its simple strueture. Isothermal and non-isothermal TGA were used to obtain degradation kinetics. Systems of homopolymer, polymer mixtures, and solvent-swollen polymer are studied. The significant variables for... 

Rios, A.O., Borsarelli, C.D., and Mercadante, A.Z., Thermal degradation kinetics of bixin in an aqneons model system, J. Agric. Food Chem., 53, 2307, 2005. 

Scotter, M.J., Castle, L., and Appleton, G.P., Kinetics and yields for the formation of colonred and aromatic thermal degradation products of annatto in foods, Food Chem., 74, 365, 2001. 

The thermal degradation of anthocyanins, both in extracts and model systems, was reported to follow first-order reaction kinetics in all studies. The stability of anthocyanins and all pigments found in foods decreased with increases in temperature. 

Kanasawud and Crouzet have studied the mechanism for formation of volatile compounds by thermal degradation of p-carotene and lycopene in aqueous medium (Kanasawud and Crouzet 1990a,b). Such a model system is considered by the authors to be representative of the conditions found during the treatment of vegetable products. In the case of lycopene, two of the compounds identified, 2-methyl-2-hepten-6-one and citral, have already been found in the volatile fraction of tomato and tomato products. New compounds have been identified 5-hexen-2-one, hexane-2,5-dione, and 6-methyl-3,5-heptadien-2-one, possibly formed from transient pseudoionone and geranyl acetate. According to the kinetics of their formation, the authors concluded that most of these products are formed mainly from all-(E) -lycopene and not (Z)-isomers of lycopene, which are also found as minor products in the reaction mixture. 

Dhuique-Mayer, C. et al. (2007). Thermal degradation of antioxidant micronutrients in citrus juice Kinetics and newly formed compounds. J. Agric. Food Chem. 55(10) 4209 -216. 

FIGURE 12.2 Mono exponential (dashed lines) and bi-exponential fitting (solid lines) of the kinetic HPLC data for the thermal degradation of bixin in a 20% ethanolic solution at 98°C ( ) Bixin (O) sum of di-cw bixin peaks ( ) all-frans-bixin ( ) oxidation compound (C17). (From Rios, A.O. et al., J. Agric. Food Chem., 53, 2307, 2005. With permission.)... 

The degradation kinetics of total carotenoid contents and visual color of papaya puree were investigated at temperatures between 70°C and 105°C (Ahmed et al. 2002). The thermal degradation of total carotenoids and color change parameters (Hunter, axb values) followed first-order reaction... 

Ahmed, J., U. S. Shivhare, and K. S. Sandhu. 2002. Thermal degradation kinetics of carotenoids and visual color of papaya puree. J. Food Sci. 67 2692-2695. 

Dutta, D., A. Dutta, U. Raychaudhuri et al. 2006. Rheological characteristics and thermal degradation kinetics of beta-carotene in pumpkin puree. J. Food Eng. 76 538-546. 

Zepka, L. Q., C. D. Borsarelli, M. A. A. R da Silva et al. 2009. Thermal degradation kinetics of carotenoids in a cashew apple juice model and its impact on the system color. J. Agric. Food Chem. in press, doi 10. 1021/jf900558a. 

Recently, several reports of the flame-retardant properties of boron-containing bisphenol-A resins have appeared from Gao and Liu.89 The synthesis of a boron-containing bisphenol-A formaldehyde resin (64 and 65) (Fig. 42) from a mixture of bisphenol-A, formaldehyde, and boric acid, in the mole ratio 1 2.4 0.5, has been reported.893 The kinetics of the thermal degradation and thermal stability of the resins were determined by thermal analysis. The analysis revealed that the resin had higher heat resistance and oxidative resistance than most common phenol-formaldehyde resins. 

A kinetic study of the thermal degradation of cetyl-trimethylammonium bromide inside the mesoporous SBA-3 molecular sieve... 

A model for the SSP of PET under typical industrial processing conditions has been developed by Ravindrath and Mashelkar [15]. Their calculations are also based on experimental data reported in the literature. The results allow the rough conclusion that the reaction rate decreases by a factor of 6 for the temperature range between 285 and 220 °C, accompanied by a decrease of the thermal degradation by a factor of 40. The fact that suitable SSP conditions can be found to warrant a fast reaction rate and minimal degradation makes this process industrially important. These same authors also state that at an early stage of the reaction the kinetics have a predominant influence, whereas diffusivity plays a major part at a later stage of the reaction. 

Table 13.5 Reaction rate constant0 and activation energy data for the thermal degradation of PET [29b, 29c, 39]. From Thermal degradation of PET. A kinetic analysis of gravimetric data , Covney, J. D., Day, M. and Wiles, D. M., J. Appl. Polym. Sci., 28, 2887 (1983), copyright (1983 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

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