Plastic Lubricants in PVC Processing: Internal vs External

PVC does not melt like most thermoplastics — it gels and fuses through primary particles. Without adequate lubrication, it sticks to metal surfaces or fails to develop sufficient melt strength.

Internal Lubricants

Internal lubricants are compatible with PVC at processing temperatures; they reduce intermolecular friction within the melt.

Stearic acid: Classic internal lubricant; promotes rapid fusion; risk of plate-out at excessive levels. Glyceryl monostearate (GMS): Good internal lubricant with mild external effect; FDA-compliant. Calcium stearate: Dual function as lubricant and acid scavenger.

Typical loading (rigid PVC pipe): 0.3–0.8 phr total internal lubricant.

External Lubricants

External lubricants are incompatible with PVC; they migrate to the melt-metal interface as a release layer.

Polyethylene wax (PE wax): Standard external lubricant for rigid PVC pipe and profiles. Typical loading: 0.3–0.5 phr.

Paraffin wax: Lower cost; limited to low-temperature applications due to high volatility.

Fusion Profile and Lubricant Balance

Formulation problem	Diagnosis	Adjustment
Slow fusion, melt fracture	Insufficient internal lubricant	Increase stearic acid or GMS
Plate-out, die deposits	Insufficient external lubricant	Increase PE wax
Poor surface gloss	Insufficient external lubricant	Increase PE wax or add OA wax

HMEChem supplies both internal and external PVC lubricants including stearic acid, PE wax, OA wax, and specialty lubricant blends.