Lubricants

Abstract

Lubricants are essentially processing additives: their primary role is to influence some aspects of behaviour of PVC compositions under the heat and shear experienced in the processing machinery, so that the processing is made easier, whilst certain factors promoting thermal degradation of the polymer are counteracted (see below). For example, in the extrusion of a rigid PVC composition effective lubrication can increase output for a given heat and power consumption, or reduce the heating and mechanical power required for a given output rate. As constituents of a PVC composition, lubricants can also influence some material properties, for example the thermal stability (either directly, or through interaction with other components of the formulation; see below), impact strength of some uPVC compositions, surface finish and printability (which may be impaired by the presence of a lubricant). The lubricating action and effects may be divided into external and internal, but the lubricants themselves cannot be so classified with complete accuracy, since many can combine both functions in varying degrees, depending on the proportion used and the particular processing conditions. Moreover, other components of a PVC formulation can have lubricant effects, and influence the performance of, or requirements for, the lubricant proper.