High temperature thermal degradation

Toschi, T.G., A. Cosat, and G. Lercker. 1997. Gas chromatographic study on high-temperature thermal degradation products of methyl hnoleate hydroperoxides. Joum o jhe AmencanOU Cherms 387-91. 

Phenolic networks are well known for their excellent thermal and thermo-oxidative stabilities. The mechanisms for high-temperature phenolic degradation include dehydration, thermal crosslinking, and oxidation, which eventually lead to char. 

The transition from crystalline to melt state, which is normal for crystalline polymers, is not observed with cellulose under normal conditions. It appears that the secondary bonds giving rise to the crystalline state are too strong and too numerous to be broken by a rise in temperature. Thermal degradation (beginning at ca. 180 °C) precedes melting under atmospheric pressure conditions. Nevertheless, a plastic deformation interpreted as melting has recently been reported for cellulose fibers exposed to laser radiation in a highly confined (pressurized) space [43]. The fracture surface of a thermoplastically deformed cellulose disc is shown in e Fig. 10. 

There are two mechanisms by which the high-temperature fluids degrade, i.e., 1) thermal degradation and 2) oxidative degradation. 

PTFE is a highly crystalline polymer that is devoid of crosslinks and branching. PTFE undergoes nearly 100% conversion to monomer at elevated temperatures. Thermal degradation by chain depolymerization at the chain ends probably starts at low temperatures (250-350 °C), while random-scission cleavage likely becomes more pronounced at higher temperatures. Although PTFE is the most stable of... 

Blister Raised or layered zone on the surface of the part Plastic material temperature may be too high, causing thermal degradation of the plastic... 

The conduction heating process has been used almost exclusively for ceramic substrate because these materials do not degrade when exposed to the high platen temperatures. Thermal degradation would be more likely for organic laminates. Best results are realized when this process is used with relatively thin substrates (<1.0 mm). 

Polymer extrusion and injection molding are conducted mainly in the viscous state. For these processes, mechanical degradation can be observed to decrease with increasing temperature for comparisons at either constant shear rate or shear stress. The coefficient is larger for comparison at constant shear rate since viscosity decreases with temperature. Thermal degradation, however, can prevail in these experiments, consistent with the relatively high temperatures at which extrusion and injection processes are performed [18, 64-72]. Mechanical forces may be directly involved or may contribute to a temperature increase. 

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