Lubricants and Processing Aids — Internal, External and Fluoropolymer

Direct answer

Internal and external lubricants solve opposite problems and are routinely confused. An internal lubricant is compatible with the polymer, lowers melt viscosity and internal friction, and reduces torque and frictional heat — it changes how the melt flows. An external lubricant is deliberately incompatible, migrates to the metal interface, and controls sticking, die build-up and release — it changes how the melt meets the tool. Too much internal lubricant gives you a soft, under-fused extrudate; too much external gives you plate-out, poor weld lines and print failures. A fluoropolymer processing aid is a third category: it coats the die land to eliminate melt fracture (sharkskin) in polyolefin film and pipe at low addition levels.

Selecting against the defect you actually have

• Sharkskin or matte streaking on LLDPE film or pipe. Fluoropolymer processing aid, typically a few hundred ppm as a masterbatch. Raising melt temperature to hide it costs output.
• Die build-up or drool at the exit. External lubricant, or an aid dosed to clear the die land; also check filler surface treatment before adding more lubricant.
• High torque, high melt temperature, motor limit reached. Internal lubricant, usually with the fusion behaviour of the compound reviewed at the same time.
• Poor filler dispersion at high loading. Coated filler plus an internal lubricant; adding external lubricant here makes dispersion worse.
• Rigid PVC fusion control. A balanced internal and external package, designed together with the stabilizer — never chosen in isolation.

Interactions you must check before dosing

Lubricants are not neutral. External lubricants and some waxes migrate to the surface and destroy printability, paint adhesion and heat sealing. Stearates interact with the stabilizer system in PVC and can shift fusion time in either direction. Over-lubrication reduces mechanical strength at weld lines because the two flow fronts no longer knit. And in highly filled compounds, the lubricant demand is set largely by the filler's surface treatment — a coated calcium carbonate at 40 % needs a different package from an uncoated one.

What to specify on your enquiry

1. Polymer and compound, including filler type and loading.
2. Process — extrusion, injection, calendering, blow moulding.
3. Defect being solved and where it appears on the line.
4. Current additive package and dose.
5. Downstream operation — print, paint, seal, weld.
6. Regulatory frame — food contact, potable water, toy safety.
7. Annual volume.

Related knowledge

• Antioxidants when the symptom is degradation rather than friction.
• Compatibilizers when the issue is phase separation in a blend.
• Mould care where plate-out is appearing on the tool.