Thermal degradation modeling mechanism

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. 

Photochemistry of Model Compounds. Preliminary photochemical studies have been carried out on l,3-diphenoxy-2-propanol (3)8 as a model compound for bisphenol A-epichloro-hydrin condensates 1. The utilization of 3 as a model compound for thermal degradation of 1 has been reported. Irradiation (254 nm) of 3 in acetonitrile (N2 purge) provides two major volatile products, which have been identified as phenol and phenoxyacetone (4), by comparison of retention times (gas chromatography) with known samples. A possible mechanism for... 

Further developments of the work include a more accurate study of the mechanisms of desulfurization processes using instrumental improvements. This will enable an easy quantitation of gas yield and a thermochemical approach of elemental processes. We also have been using model polymers to better study the interactions of pyrite and sulfur with the organic matrix during coal pyrolysis, oxidation and combustion (34 and to examine more accurately the specific role of organic sulfur in thermal degradation processes. 

What are the principal fundamental mechanisms by which thermal degradation, sintering and redispersion of supported metals occur What factors determine which of these mechanisms predominates or controls the sintering process What do we leam from model catalyst studies regarding these mechanisms ... 

Mechanistic Interpretation - Although the nature of the interactions between the polymers and the catalysts is not exactly known, the products that are formed and the changes that occur when an acid catalyst is used as compared to thermal degradation are consistent with a carbenium ion mechanism commonly used to account for products observed for conversion of small hydrocarbons over acid catalysts. Recent work suggests that the actual species on the surface of the catalyst is an alkoxide, but carbenium ion chemistry can still be used as a model of the transformations that occur. ... 

The time-to-failure of a structure or its components is an important issue for structural safety considerations in fire. On the basis of the strength degradation models for FRP materials under elevated and high temperatures developed in Chapter 5, the time-to-failure is predicted for GFRP tubes and laminates under both thermal and mechanical loading in compression. Temperature responses were again calculated using the thermal response model presented in Chapter 6. 

An experimental investigation directly on polymers in order to find out the degradation products is difficult to realize. However, both the study of degradation of model compounds like butylene dibenzoate [5-7], and the general mechanism of thermo-oxidation of organic molecules (scheme 2), can be very helpful to propose a specific mechanism for the thermo-oxidative degradation of PBT (scheme 6). In order to simplify the discussion, the contribution of thermal degradation has not been considered. 

Yashitake and Furukawa investigated the thermal degradation mechanism of a.y-diphenyl alkyl allophanates and carbanilates as model compounds for crosslinking sites in polyurethane networks by pyrolysis-high-resolution GC/ FTIR (Py-HR GC/FTIR). Pyrolysis was performed at 250°C, 350°C, 450°C, and 500°C. 

Yashitahe,N. Furufcawa,M. Thermal degradation mechanism of a, y-diphenyl alkyl allophanate as a model polyurethane by pyrolysis-high-resolution gas chromatography/FT-IR. J. Anal. Appl. Pyrol. 1995, 33, 269. 

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