Thermal degradation, effect

In such a process an additive or solvent of low volatility is introduced in the separation of mixtures of low relative volatilities or for concentrating a mixture beyond the azeotropic point. From an extractive distillation tower, the overhead is a finished product and the bottoms is an extract which is separated down the line into a product and the additive for recycle. The key property of the additive is that it enhance the relative volatilities of the substances to be separated. From a practical point of view, the additive should be stable, of low cost, require moderate reboiler temperatures particularly for mixtures subject to polymerization or thermal degradation, effective in low to moderate concentrations, and easily recoverable from the extract. Some common additives have boiling points 50-100°C higher than those of the products. 

Volatile ginger oil obtained from steam distillation has been the subject of many research studies (5-12). However, the thermal degradative effects of steam distillation upon volatile and nonvolatile components of ginger were seldom discussed. Recently, Moyler (1) compared the advantages of liquid carbon dioxide extraction over conventional methods such as solvent extraction or steam distillation by showing reconstructed GC chromatograms which clearly displayed the differences. However,quantitative results showing the differences were not mentioned. 

In the present report, the amount of most monoterpene alcohols and sesquiterpene alcohols in distilled oil was higher than those extracted by liquid carbon dioxide. It is possible that the differences were due to the thermal degradative effect of steam distillation upon the nonvolatile glycosides of monoterpene alcohols and/or sesquiterpene alcohol, as in the case of tomato. 

The compression-molded part, by definition, does not have flow-induced orientation. Comparison of compression-molded part properties with those of an injection-molded part can show the effect of melt temperature on properties. In the compression-molded article without flow-induced orientation, the impact strength remains constant until a certain melt temperature is surpassed and then decreases. This thermal degradation effect can be attributed to the polybutadiene component, which acts as an initiation site for oxidative degradation of the matrices. 

Table 7.5 The symptoms and reasons for the thermal degradation effect of high temperature on ethylene formal disulphide polymers ...

Other also standardized methods generate special influences for irreversible changes that sometimes do not match the interaction of effective influences under actual service conditions. Thermal degradation effects achieved by rolling or kneading may generally not be used to evaluate resistance they describe only the resistance to special processing conditions. 

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