Lubricants are essential additives in PVC processing. For lubricants, the commonly mentioned functions in the industry can be summarized into two points. They are: it can reduce the mutual friction between particles and macromolecules in PVC melt before melting; Reduce the mutual friction between PVC melt and plastic mechanical contact surface. In today’s article, the manufacturer of Sainuo polyethylene wax will take you to analyze the internal and external lubrication of PVC lubricants from a technical perspective!

1. Internal lubrication
The internal lubrication of lubricants, in terms of PVC, can be considered the same type of substance as plasticizers, playing a plasticizing or softening role. The difference is that lubricants have lower polarity and longer carbon chains, which significantly reduces the compatibility between lubricants and polyvinyl chloride compared to plasticizers. Due to the low compatibility (and certain compatibility) between lubricants and polyvinyl chloride, only a small amount of lubricant molecules can penetrate between polymer molecular chains like plasticizers, weakening the mutual attraction between molecular chains, and causing the polymer to deform, Molecular chains are more prone to sliding and rotating with each other, while not excessively reducing the glass transition temperature of the polymer.
2. External lubrication
External lubrication refers to the interface lubrication mechanism. Lubricants adhere to the surface of molten resin or to the surface of processing machinery and molds to form a lubricant molecular layer. Due to the presence of lubricant molecular layers, a lubrication interface is formed, which reduces the friction between the resin and the processing machine. The viscosity of the lubrication interface film and its lubrication efficiency depend on the melting point and processing temperature of the lubricant. Generally speaking, lubricants with long molecular carbon chains have better lubrication effects due to their ability to keep two friction surfaces away.

3. What happens if PVC lubricant is not used well?
The phrase ‘small dosage, great effect’ describes PVC lubricants. The role of PVC lubricants in PVC processing is no less than that of stabilizers. Its use generally follows strict principles, such as internal and external sliding balance, moderate dosage, etc. If there is not enough emphasis on PVC lubricants and they deviate from the principles that should be followed when used, what will be the impact if PVC lubricants are not used well?
(1) Unbalanced internal and external lubrication
Excessive external sliding, although the extrusion speed is fast, the material is prone to growth and plasticization is not good; Excessive internal sliding, large extrusion volume, and poor material plasticization. Poor initial lubrication can cause excessive extrusion torque. Insufficient lubrication in the later stage can lead to insufficient lubrication in the homogenization section, compression section, and die section of the screw, resulting in severe material shearing and affecting the surface quality and internal performance of the extruded product. In severe cases, it can also cause decomposition.

(2) Excessive amount of lubricant used
Lubricants are not necessarily better with larger amounts. Due to the incompatibility between lubricants and PVC resin, excessive addition of lubricants can have adverse effects on the PVC blend system. The internal and external balance of lubrication mentioned is within a certain limit, as the lubricant and polyvinyl chloride blend system have adverse effects. In actual production, many processing problems and issues related to thermal stability, as well as many defects in products, may be caused by excessive lubricant usage.
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