Special Additives for the Improvement of Workability and Performance

Here we will mention leftovers-lubricants that diminish the friction between polymer particles (internal) or with the walls of the fabricating machines (external). An internal lubricant affects mainly a reduction of viscosity while an external one affects the surface layer and augments the output (provided no slip occurs). Many lubricants serve simultaneously as internal and external agents, as a borderline is not that sharp. The polymer most demanding of lubrication is PVC for improving workability and elimination of degradation. However, other polymers are lubricated as well, like polystyrene, polyester and polyolefins. Among the common lubricants are fatty acids and their salts, paraffins, and low MW fractions of polyethylene. Only a small concentration should be used in order not to affect the ultimate properties. In the case of broadly distributed PE, self lubrication occurs. 

Let us now survey the compoimding process itself. As mentioned, some components already appear in the polymer, being introduced by the resin manufacturer (mainly heat stabilizers and antioxidants) but one should always check to see if their concentration is sufficient and whether the compound fits specific requirements. The use of a master batch has been described, wherein the fabricator has to vmdertake an accurate diluting process. 

A theoretical analysis of solid mixing is rather complicated. Statistical units are used based on the variance of concentration in different zones of the compound, leading to a parameter, termed the intensity of dispersion. Other parameters based on the dimension of length are coimected to the real location of the dispersed particle. 

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