Lubricants and Flow Promoters

The term lubricant or lubricating agent is often encountered to describe certain additives incorporated into plastics materials. There are, however, various types 

The choice of lubricant for a particular composition and process can be quite critical but beyond stating that such materials will normally be fluid at processing temperature and should have a solubility parameter at least 3 MPa different from the polymer, little further fundamental guidance can be given and selection is normally made by an empirical trial and error basis. 

It has been seen that internal lubricants are essentially low molecular weight flow promoters which, unlike plasticisers, have little effect on the 

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Additives which alter physical properties either during processing or in the final plastic include plasticizers, fillers, lubricants and flow promoters, impact modifiers and foaming agents. 

Uses Plasticizer, processing aid for extrusion of PVC, urethanes lubricant and processing aid for filled PS, PC reactive diluent and flow promoter for epoxy powd. coatings... 

Lubricants have been classified as either internal or external. Typically, internal lubricants have meant materials that are compatible with PVC that promote flow. The difference between internal lubricants and plasticiser is that the internal lubricant is only soluble at high temperature whereas the plasticiser is soluble and functional at room temperature. External lubricants on the other hand, are said to be incompatible and come to the surface and create metal release. It is reported that there are two distinct types of external lubricants. Internal lubricant efficiency can be readily predicted by simple mathematical formula and that partial substitution of esters for paraffin allows the reduction of modifier or increased filler levels to achieve savings without loss of any physical properties. 

Lubricants and process aids can be either (a) internal, whereby they act in the resin phase to increase melt flow and throughput, prevent shear burning, and resist melt fracture (by reducing viscosity at high shear rate), or (b) external, whereby they act at the interface between resin and other materials to improve release of the composite, promote dispersion of fillers, resist melt fi"acture, and/or reduce friction between resin and process equipment. 

Internal lubricants are low molecular weight materials which promote flow of the polymer in the melt. Unlike external lubricants, compatibility between lubricant and polymer is essential. Waxes and stearates are typically used. 

Compounds of adipates, palmitates. sebacates. and stearates are used as lubricants and plasticizers for many types of plastics, including PVC and engineering plastics. Cetyl palmitate can be used in place of natural wax and can act as a lubricant for engineering plastics. Octyl and iso-octyl palmitate are clear oily liquids with anti-blocking properties and additional heat stability that are also used as plasticizers for PVC and as a viscosity modifier for plastisols. The stearates are used, broadly, as viscosity stabilizers in PVC and lubricant/flow promoters in PS and ABS, particularly where low-temperature properties are required. Cetyl stearate is used as a lubricant for engineering plastics. 

Description Cetyl stearate heavy, rich, non-greasy used in place of natural wax lubricant for engineering plastics. Iso-cetyl stearate, iso-stearyl stearate comparable with natural waxes but low freezing point makes them liquid at low temperatures viscosity stabilizers for PVC and plastisols lubricant/flow promoters for PS and ABS, pigment dispersion aids ... 

Description Butyl stearate, iso-butyl stearate, iso-octyl stearate oily colourless liquids, insoluble in water, readily soluble in vegetable and mineral oils, acetone and ether lubricant/flow promoters for PS and ABS, pigment dispersion aids octyl (2-ethyl hexyl) stearate is also a viscosity stabilizer for PVC and piastisols ... 

Processing stabilizer Also called a flow promoter. In thermoplastics they act in the same manner as internal lubricants where they plasticize the outer surfaces of the plastic particles and ease their fusion, but can be used in greater concentrations (about 5 pph). With TS plastics they are not reactive normally and therefore reduces the rate of interactions of reactive groupings by a dilution effect. Thus easier processing may be derived mainly from the reduction in the rate at which the melt viscosity increases. At the same time the overall cross-linking density is reduced. 

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