Thermal degradation definition

At very high temperatures, the chemical nature of the catalytic agents may be altered so that the catalytic activity is definitely lost. This type of thermal degradation is called solid-state transformation and can be seen as an extreme form of sintering, which leads to the transformation one crystalline phase into a different one. Phase transformations in the bulk washcoat and incorporation of an active metal into the washcoat may take place during solid-state transformation. 

Another set of definitions with which one should be aware is the difference between thermal degradation and thermal decomposition, because they are not exactly the same thing. Thermal degradation means that under heat exposure, some property of the material has degraded or become less than what it was before exposure to heat. 

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. 

Photo/thermal Degradation. Although transmission or ATR IR spectra gave no Indication of a photo- or thermally-induced alteration In the POP microstructure, the uv-lrradlated or heated films showed a definite darkening or blackening. As may be seen from Table II, the rates for photolnduced blackening In etched and... 

The preceding discussion shows that, despite the large number of experiments that have been performed to elucidate the mechanism of the thermal degradation of polystyrene, many aspects of the problem are not definitively resolved. 

Definition Starch etherified with propylene oxide, rendering it more resist, to thermal degradation and bacterial attack... 

The thermal stability of polymers prepared from bis(8-hydroxy-5-quinolyl) derivatives has been of continuing interest to the workers in this field. A recent series of papers (27-29) represents the definitive work on this property. Some decomposition temperatures obtained by thermogravimetry in vacuum are shown in Fig. Vll.l for three series of polymers. The trend in thermal stability for the Ni > Cu < Zn polymers is unmistakable, and is in agreement with other bis(8-hydroxyquinoline) coordination polymers containing these metals (31). By studying the volatile products arising as a result of the thermal degradation... 

A number of conclusion can be drawn from the above studies. Firstly some physical properties such as glass transition temperature and thermal degradation are independent of macromolecular architecture but are dependent on the nature of the chain ends. Other physical properties such as solubility, chemical reactivity, viscosity, etc. are dependent on macromolecular architecture and definite differences are observed between linear, hyperbranched and dendritic macromolecules based on the same building block. 

The formation of activated species during mechanoehemieal degradation is, in general, not sufficiently documented both experimentally and with respect to the proposed mechanisms to give a definite proof of their existence. In the dilute state, the rate of energy transfer is high and it is reasonable to assume that any activated species, if present, will be thermalized well before the occurrence of a chemical reaction. 

---