TABLE OF CONTENTS Lubricants classically function in two ways: (1) externally to reduce friction between the polymer melt and hot metal surfaces during processing; and (2) internally to reduce frictional forces within the polymer matrix and, in so doing, lower the effective viscosity. External lubricants, by definition, have poor compatibility with PVC and migrate to the surface to create metal release. Internal lubricants are more compatible, have high polarity, and are therefore more soluble in PVC. Both types are essential for processing of PVC-U formulations, particularly taking account of the differing shear conditions resulting from extrusion, calendering, or injection moulding. In practice, most lubricants have both external and internal characteristics, but vary in the ratio of one to the other in the way they perform. However, the correct balance and type of internal to external and addition level are crucial due to the influence on gelation level, plate-out of incompatible materials in the die and calibration equipment, and physical properties.
The main chemical classes that make up lubricants are all waxes or soaps and are as follows:
Amide wax ethylene bisstearamide (EBS) has a balance of internal and external behaviour.
Hydrocarbons, which can be split up as:
Paraffin waxes linear alkanes with chain lengths varying from C 20 to C 50 which are very external in nature. The lower molecular weights show some internal character.
Polyethylenes (PE) with molecular weights ranging from 500 to 1000 (C 35 C 70) with linear or...
