Generation on the polymer

The rapid decomposition of a peroxide in the presence of MAH results in the excitation and homopolymerization of MAH. When the latter is conducted in the presence of polypropylene, the latter undergoes degradation ( 10) while polyethylene is crosslinked under the same conditions (11). This has been attributed to the presence of excited MAH which increases the radical generation on the polymer beyond that due to the radicals from the peroxide. 

Figure 5.6. Synthesis of graft copolymers containing poly acetylene. Active catalysts for acetylene polymerization are generated on the polymer backbone, and the polyacetylene grows from the backbone.

The main difference in the method of operation between single and twin screw extruders is the way in which the material is conveyed within the machine the single screw relies on friction between the material processed and the cylinder to move the material, whereas the configuration of two screws can produce positive displacement. This means that, for example in the case of unplasticised PVC, the formulation that can be processed on a twin screw machine is not as critical as for a single screw extruder, since the quantity and type of lubricant does not affect the material feed. Furthermore, it also means that less work may need to be done (by virtue of less frictional heat being generated) on the polymer and consequently degradation may be avoided. 

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