Lubricants are very important for PVC processing due to their properties to facilitate the process by means of reducing friction. For example, rigid PVC processing is impossible without lubricants. Typical lubricants belong to the following chemical families; hydrocarbon waxes, metal stearates, fatty acid esters, ester waxes and amide waxes. Lubricants can be classified into three main sub-groups as external, internal and combined lubricants. This grouping is according to their lubrication and are called combined lubricants.
Internal lubricants reduce friction between molecules by weakening the strength between polymer molecules. Thus, they increase production by decreasing viscosity of the polymers. Most of the internal lubricants reduce the glass transition temperature (Tg) and some other properties of PVC. Under normal conditions they do not exudate nor have negative effects on corner weld strength, printability and bonding.
External lubricants are incompatible with PVC compounds (They do not dissolve in PVC or disperse homogeneously) at processing temperatures. They act as an interface between the PVC compounds and the metal surfaces of the processing equipment and prevent the molten PVC from adhering to the processing equipment. The behavior of PVC within the processing equipment depends on the composition of the external lubricant. In addition, these materials reduce the friction between the polymer particles during the plasticizing process, thereby preventing temperature increase.