The simplest classification of lubricants classifies them as being Internal and External, based on their relative compatibility with PVC primary particles. Many lubricant molecules have a polar head and a non-polar tail, with very different attractions for each end, as in the case of surfactants. Polar headed waxes such as fatty alcohols, fatty acids (Stearic Acids) fatty esters and fatty amides have moderate compatibility in PVC and are characterised as internal lubricants. Non-polar waxes like paraffin and polyethylene are incompatible with PVC and are called external lubricants.

Internal lubricants reduce the frictional forces occurring between the PVC molecule chains, thus reducing melt viscosity. They are polar and thus are highly compatible with PVC. They help achieve excellent transparency even at high dosages and do not tend to exudate, which helps optimizing welding, gluing, and printing properties of the final product.

External lubricants reduce the adhesion between PVC and metal surfaces. They are mostly non-polar such as paraffin and polyethylene waxes. The external lubrication effect is largely determined by the length of the hydrocarbon chain, its branching and its functional group. At high dosages they can lead to cloudiness and exudation

Non-polar, Polar and film forming are the three main classifications of lubricants for PVC based on their modes of operations.

PVC lubricants can also be categorised according to their origins, principally four – petroleum, synthetic hydrocarbon, mineral and some natural vegetable based triglycerides.

Petroleum waxes consist of two types. First, Paraffin waxes (which are macro crystalline, containing primarily linear alkanes in the C20 to C40 range and are hard and brittle with melting range of 45 – 70 deg C. Second types are Microcrystalline waxes which contain significant quantities of cyclic and branched chain alkanes in the C30 to C80 range, and are soft, tough and have high affinity for oil. They melt in the range of 45 to 70 deg C. Petroleum waxes for PVC also include waxy petroleum oils that work as excellent external lubricants.

Synthetic Hydrocarbon waxes used in PVC are basically of three fundamental types. They include Polyethylene wax, Oxidised Polyethylene wax and synthetic Paraffin wax also known as Fischer-Tropsch wax. The most popular and effective Polyethylene waxes have a melting range of 98 – 115 deg C. Their oxidation results in chain scission at their branch points resulting in the formation of a wide array of oxygenated products including acids, alcohols, esters, aldehydes, ketones and hydroperixides. The resulting Oxidised PE waxes are much more polar, more compatible with PVC and act as film formers in PVC melts. Fischer-Tropsch waxes are microcrystalline, water white, oil free, hard and with high melting points. They are often blended with natural paraffins to raise their melting points. Due the better dielectric constant, electrical resistance and electrical breakdown strength of FT waxes compared to other petroleum waxes, they are preferred for production of cables and wires.

Mineral waxes are principally derived from Montan Wax which is a fossilised vegetable wax. Over past several years, Montanic acid and its esters and soaps have found wide use in PVC for high tech plastic lubricant applications. Their combination of high molecular weight, film forming properties and plate out resistance is unequalled by alternate lubricants. Ethylene glycol montanate and partially saponified 1,3 butanediol montanate are excellent examples.

PVC lubricants produced from naturally occurring triglycerides can be considered to be derivatives of 1-Octadecanoic acid, commonly called Stearic Acid, a linear saturated carboxylic acid having 18 carbon atoms. Stearic Acid can be converted into a wide variety of lubricants. In many instances, there are more variety of complex ester lubricants on the market than there are discernable advantages.

Polar lubricants are hydrocarbon compounds containing polar functional groups such as alcohols, esters and amides. They orient in PVC melts with polar head attracted to PVC. Examples are Stearyl Alcohol, Glycerol Monostearate, Stearyl Stearate, Montan ester, etc. When interchanging polar-headed lubricants, considerations should be based upon functional groups, molecular weights, melt viscosities, volatility and melting points.


                                                                          

For flexible PVC compounds, one type of lubricant, a film former, is generally sufficient for most lubricant applications, because the presence of ester based plasticizer acts as a polar headed lubricant. Occasionally, however, a speciality purpose polar-headed lubricant, such as GMS, is beneficial for imparting a special ancilliary property such as fog resistance to a flexible vinyl film.

For rigid PVC applications, as a general principal, PVC lubricant systems of a single class are not as effective. Often, all three classes, namely polar, non-polar and film formers are required to achieve optimal results. Balub class of lubricants work on this principal to give the best results.