Lubricants
Additives > Lubricants
Lubricants | ||
They are used mainly in rigid materials, facilitating the process in obtaining pipes, bottles, film, sheets, etc. One of the most important aspects in polymer technology is lubrication, as it is very linked to stabilization, especially in the processing of rigid ones, where degradation during transformation is critical. | ||
There is internal lubrication, which is obtained with metallic stearates and fatty acid esters, esters of montana wax, glyceryl esters, such as those of stearic and oleic acids; long chain alcohols, et cetera. The function of these additives is to decrease the friction of the polymer molecules with each other, so as to improve the flow of the material. In general, the internal lubricants are chemically similar to the external ones, with the exception that they have greater compatibility with the polymer and do not easily migrate to the surface. External lubrication, which is obtained through the use of paraffinic oils, paraffin waxes and low molecular weight polyethylenes. The purpose of external lubricants is to reduce and control the adhesion between the polymer and the metal parts of the transformation equipment. They have low solubility in the polymer, especially at the processing temperatures, but they must have sufficient polarity so that they have affinity for both the polymer and the metal surfaces. This is achieved with molecules that have a polar and a non-polar zone. | ||
The internal lubricants contribute to lower the viscosities of the fusion and to reduce the friction between the molecules. The external lubricants work essentially migrating towards the surface, where they reduce the friction of the molten plastic and the metal walls of the extruder, calender, etc. This particularity is also used to impart final properties to the product, such as anti-adherence (antiblocking) or non-stickiness (antitacking). Among all lubricants, stearic acid is by far the most used. The migration speed of the lubricants to the interface depends on their molecular weight. | ||