Stearic acid can also be used as an internal lubricant (making the plastic body easy to be molded) and an external lubricant (plastic body easy to fall off from the grinding tool, also called release agent), but this is relative, because an auxiliary agent called zinc stearate is added into the PVC pipe, which can be used as a stabilizer or a lubricant, and their specific gravity also determines which is the internal lubricant and which is the external lubricant.

Stearic acid 180 1 is widely used. It can be used as a lubricant, but it cannot be said to be an internal lubricant. It is more used as a release agent, that is, an external lubricant!