Thermomechanical degradation

The use of extruder with large screw lengths (large value of L/D) and initiators with short tq.s values is not reasonable because of the weak influence of the melt residence time in the extmder upon the grafting efficiency and probable thermomechanical degradation of the grafted product. 

Odell JA, Keller A, Muller AJ (1992) Thermomechanical degradation of macromolecules. Colloid Polym Sci 270 307-324... 

La Mantia [37] studied the relationship between the mechanical properties of recycled PA 6 and the recycling conditions used. Samples were recycled up to five times. It was found that the addition of an antioxidant between each extrusion reduced the effects of hydrolj ic and thermomechanical degradation on polymer molecular weight, and thus on viscosity and mechanical properties. 

Although the degradation behavior is common to all polymeric materials, the effects of photooxidative and thermomechanical degradation on PP are dramatic because of the tertiary carbon present in the chain of this polymer. 

In the following, the influence of the degradation on structure and properties of the polymeric materials will be reviewed, considering in particular the thermomechanical degradation. As for the blends, the basic concepts regarding the behavior of polyphasic systems and compatibilization will be presented. 

In most cases, the effect of the thermal factor cannot be ignored and the polymer in the fluid state suffers thermomechanical degradation. 

TABLE 2 Activation energies of thermal and thermomechanical degradation... 

PP is more sensitive to thermomechanical degradation. The molecular weight of PP decreases drastically with the number of reprocessing steps, with a concomitant reduction in mechanical properties, in particular of elongation at break. 

Previous thermogravimetric analysis had established that under such processing conditions no appreciable thermomechanical degradative effects were detected. To perform tensile and fracture tests the sheets were successively cut by a mill. 

Thermomechanical degradation of refractories can be largely elassified into three... 

Figure 10.10. Example of thermomechanical degradation. Magnesite-chrome brick lining of a metallurgical reactor in vacuum...

La Mantia, F. P. and Mongiovi, C.,Thermomechanical degradation of compati-bihzed and uncompatibilized nylon 6/polypropylene blends, Polym. Degrad. Stabil., 66,337-342 (1999). 

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