Degradation thermally induced

Another problem occurs when some fire retardant formulations ate exposed to elevated temperatures (eg, when used as roof tmsses or as roof sheathing) thermal-induced strength reductions can occur in-service. The thermo-chemical factors were discussed by LeVan and Winandy (26), and a kinetic degrade model was developed (27). The treater should be consulted to obtain appropriate in-service modifications for specific fire retardant treatments. 

A high percentage 01 water remains after the sublimation process, present as adsorbed water, water of hydration or dissolved in the diy amorphous solid this is difficult to remove. Usually, shelf-temperature is increased to 25 to 40°C and chamber pressure is lowered as far as possible. This stiU does not result in complete diying, however, which can be achieved only by using even higher temperatures, at which point thermally induced product degradation can occur. 

Measurements of thermal analysis are conducted for the purpose of evaluating the physical and chemical changes, which may take place as a result of thermally induced reactions in the sample. This requires that the operator subsequently interpret the events observed in a thermogram in terms of plausible thermal reaction processes. The reactions normally monitored can be endothermic (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, chemical degradation, etc.) or exothermic (crystallization, oxidative decomposition, etc.) in nature. 

Heat. In the solid state, thermal degradation starts as a slow process at around 150 °C.2 Cyclics and siloxanes (Si-O-Si characteristic IR stretch at 1,100 cm-1) are formed and the polydispersity increases.292 In solution, thermally induced degradation is slower (23 h, 190 °C for complete degradation). The rate of degradation increases with increase in temperature. 

We have previously synthesized a number of titanium polyethers of the following general structure (3,4). A variety of aromatic and aliphatic diols were successfully incorporated as the fundamental backbone units of the polyethers. These materials are insoluble and do not soften prior to thermal-induced degradation. 

Curacins (345-348) are a small family of bioactive compounds with a unique thiazoline-containing lipid bearing a cyclopropane unit. From the cyanobacterium Lingbya majuscula, Gerwick reported the isolation of curacin A (345) in 1994 [265], curacins B (346) and C (347) one year later [266] and, finally, curacin D (348) in 1998 [267]. The structures of these compounds were determined by detailed spectroscopic analysis. The previous absolute configuration proposed for 345 by chemical degradation [268] was confirmed by several total syntheses [269, 270]. The absolute configuration of 346 was deduced by its thermally induced interconversion with 345 [266]. 

Thermal Degradation and Sintering. Thermally induced deactivation of catalysts may result from redispersion, ie, loss of catalytic surface area because of crystal growth in the catalyst phase (21,24,33) or from sintering, ie, loss of catalyst-support area because of support collapse (18). Sintering processes generally take... 

Some oxidation of the cellulose chains also seems to take place, suggested by the rise in HAS matter during exposure and by the initially rapid rate of change that occurred upon subsequent thermal degradation of the exposed papers. This represents the "potentially harmful" effect of exposure, leading to loss in degree of polymerization through thermally-induced reactions. These concepts are not new but the authors trust that a clear demonstration of the effects has been useful. 

Peptides formed enzymically or by mineral acid hydrolysis or thermal degradation of higher molecular veight protein can also serve as flavor precursors in thermally induced reactions. The reactivity of peptides is evidenced by their behavior during pyrolysis/GC (9), heating in air (10), reactions vith mono- (11), and dicarbonyl (12, 13) compounds and reactions in hot acetic acid (1A). The types of reactions observed for peptides include side-chain thermolysis, fragmentation into amino acids, DKP formation and Halliard reaction vith ambient carbohydrates. 

Overall, this paper provides a basis for water-mediated retro-aldol degradation chemistry contributing to thermally-induced volatile flavors. Although lipids provide the principle starting materials for the generation of alpha/beta unsaturated carbonyls in... 

Steam distillation is the most common process for the extraction of essential oils from plants (1-3). It provides a fast and simple way to obtain aromatic components which bear the characteristic odor of that species. However, "still notes" or "burnt notes" are frequently found in freshly distilled oil. The off-flavor results in most cases from thermally induced hydrolytic or degradative reactions (4). 

Figure 5 shows the thermally induced hydrolytic degradation of citral (geranial and neral) into 2-methyl-2-hepten-6-one and acetaldehyde. It is similar to the reaction mechanism as proposed by Josephson and Lindsay (22, 23). The relatively higher amount of 2-methyl-2-hepten-6-one and the concomitant lower amount of geranial and neral in steam distilled oil confirmed again a previous report (24). 

Figure 5. Thermally induced hydrolytic degradation of citral (geranial and citral) into 2-methyl-2-hepten-6-one and acetaldehyde.

Thermal treatment, such as steam distillation during sample preparation, will cause considerable degradative reaction to both volatile and nonvolatile compounds of ginger. To the contrary, however, preparation under low temperature, such as liquid carbon dioxide extraction, can effectively eliminate thermally induced degradative reactions. 

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