From the principle of action, internal lubrication is to weaken the intermolecular forces between polymer molecular chains by means of lubricant molecules penetrating into the molecular chains of polymers, so that the molecular chains slide more smoothly. Thus, the melt viscosity is reduced. External lubrication, on the other hand, forms an isolation film between the plastic and the metal surface of the processing equipment, as if a layer of lubricating oil is applied between the machine equipment and the plastic, reducing the friction between the two.
In terms of compatibility with polymers, internal lubricants have a certain compatibility with polymers and can play a role by integrating into the molecular chains; external lubricants, on the other hand, have poor compatibility with polymers and mainly play an isolating role on the surface.
The effects of internal and external lubrication are also different. Internal lubrication mainly improves the fluidity of the plastic melt, reduces processing energy consumption, and reduces product defects caused by insufficient fluidity, such as flow marks and bubbles. External lubrication, on the other hand, focuses on preventing the plastic from adhering to the equipment, helping the product to be easily demolded, reducing deformation caused by demolding stress, and improving the surface finish and dimensional accuracy of the product.
In terms of applicable scenarios, internal lubrication plays a prominent role in injection molding, blow molding, and other processes that require high melt fluidity; external lubrication, on the other hand, is indispensable in extrusion, thermoforming, and other processes where adhesion is prone to occur. Understanding these differences can help in accurately selecting the appropriate lubrication method during plastic processing, thereby enhancing product quality and production efficiency.
