A PPA processing aid is a fluoropolymer additive that lets polyolefins run faster through a die without surface defects. Added at only 50–800 ppm, it coats the die wall, removes sharkskin melt fracture, lowers head pressure and cuts die build-up, without changing the mechanical, sealing or printing properties of the film. As a formulation development partner, SYCHEM TECH helps film, pipe and cable processors choose the grade and dosage and set up the masterbatch.
This guide explains why melt fracture happens, how a PPA works at the die wall, typical loadings by application, which additives interfere with it, how to choose a grade, and what to check when a PPA is not working.
What is a PPA processing aid?
Polymer processing aids (PPAs) are fluoropolymers, most often fluoroelastomers based on vinylidene fluoride and hexafluoropropylene. Some grades also contain an interfacial agent, such as polyethylene glycol, that helps the fluoropolymer reach the die wall. PPAs do not mix with polyethylene: they stay dispersed in the melt as small droplets. That incompatibility is exactly what makes them work.
PPAs are used mainly in polyolefin extrusion: LLDPE and mLLDPE blown and cast film, HDPE pipe and blow moulding, wire and cable insulation, raffia and masterbatch. Selected grades also work in PP and in some engineering plastics.
Why melt fracture happens
Inside the die, the melt next to the steel wall is held almost still while the core moves fast. At the die exit that surface layer suddenly has to speed up, and above a critical wall shear stress it tears. Depending on the output, you see one of three defects:
- Sharkskin (surface melt fracture): fine ridges across the flow direction that make film hazy and matte. This is the defect a PPA is designed to remove.
- Stick-slip: alternating smooth and rough bands, as the melt periodically sticks to the wall and then slips at higher output.
- Gross melt fracture: severe, irregular distortion at very high output, caused by flow instability at the die entry. A PPA does not fix this one.
Narrow molecular-weight-distribution resins such as metallocene LLDPE, low melt-index grades, narrow die gaps and high output all raise the wall shear stress and make sharkskin more likely. Running hotter or opening the die gap can hide the defect, but both cost film properties or output. A PPA removes it at the source.
How a PPA processing aid works at the die wall
The dispersed fluoropolymer droplets move to the metal surfaces of the extruder and die and gradually build a thin coating there. The melt then no longer sticks to bare steel; it slips over the low-energy fluoropolymer layer. Slip at the wall lowers the shear stress at the die exit, so the output at which sharkskin starts moves higher, head pressure drops, and degraded material has less chance to collect at the die lips.
The coating is dynamic: the melt keeps wearing it away and fresh PPA keeps rebuilding it. That has three practical consequences:
- Conditioning time. On a clean die the layer typically takes 20–60 minutes to form. Melt fracture clears gradually, often as smooth bands that spread across the film.
- Continuous feed. If the PPA feed stops, the coating wears off and the defect returns.
- Purges remove it. Abrasive purge compounds and die cleaning strip the layer, so the line has to be reconditioned afterwards.
Benefits of a PPA processing aid
| Benefit | What changes on the line |
|---|---|
| Melt fracture eliminated | Glossy, clear film and smooth pipe and cable surfaces at the same output. |
| Higher output | Line speed can often be raised, typically by 10–30% at equal head pressure, before sharkskin returns. |
| Lower head pressure and torque | Less motor load and energy per kg. Some lines can run a lower melt-index resin they could not process before. |
| Less die build-up | Longer runs between die cleaning, and fewer streaks and gels from degraded deposits at the die lips. |
| Lower melt temperature | No need to run hot just to suppress melt fracture, which helps film properties and cooling capacity. |
| Better masterbatch | Better pigment wetting and higher pigment loadings in black and colour masterbatch. |
Typical PPA loading by application
| Application | Resin | Typical active PPA |
|---|---|---|
| Blown film | LLDPE | 200–400 ppm |
| High-speed film | mLLDPE | 300–600 ppm |
| Agricultural film | LLDPE / LDPE / EVA | 200–500 ppm |
| Pipe | HDPE / HMW-HDPE | 300–500 ppm |
| Raffia and film | PP / PP copolymer | 400–800 ppm |
| Wire and cable insulation | PE / silane XLPE | 300–600 ppm |
| Black masterbatch | PE carrier | 2–3% of a PPA masterbatch |
These are starting points. Formulas with antiblock, pigments or fillers need more, as explained below. The ranges match the grade guide on our polymer processing aid page.
How to dose a PPA processing aid
- Make a masterbatch first. PPA powder is 100% active, far too concentrated to dose directly. Compound a 2–3% PPA masterbatch on a twin-screw extruder, in a carrier with a melt index close to the production resin. Good dispersion is the biggest single factor in PPA performance.
- Let it down to the target. For example, a 2% PPA masterbatch added at 2% gives 400 ppm of active PPA in the film.
- Condition the die. On a clean line, many processors run two to three times the target dose for the first hour so the coating forms faster, then drop to the steady-state level.
- Keep it running. Feed the PPA continuously, and recondition after any purge or die cleaning.
Additives that interfere with PPA
A PPA has to reach the die wall and stay there, so anything that adsorbs it or scrubs the coating off reduces its effect:
| Additive | Effect on the PPA | What to do |
|---|---|---|
| Antiblock (talc, silica, diatomaceous earth) | High surface area adsorbs PPA, and abrasive particles wear the die coating. | Raise the PPA dose, add antiblock and PPA in separate masterbatches, and compare antiblock types. |
| TiO₂ and other pigments | Adsorb PPA and abrade the coating. | Use a higher dose and check the pigment’s surface treatment. |
| Mineral fillers (CaCO₃, talc) in compounds | Same mechanism, at much higher loadings. | Choose a grade intended for filled systems and trial the dose. |
| Some HALS and slip agents | Polar additives that compete for the metal surface. | Trial the PPA with the full additive package, not in neat resin. |
If your film also carries UV stabilizers, our HALS UV stabilizer guide covers how to choose them, and our antioxidants and HALS range lists the grades we supply.
How to choose a PPA processing aid
- Resin and process. Grades are tuned for a resin family and a process, such as mLLDPE film, HDPE pipe or PP raffia.
- The rest of the formula. Antiblock, pigments and fillers call for a higher dose or a grade intended for filled systems.
- Melt temperature. Polyolefin film runs well within any grade’s range. For engineering plastics and high melt temperatures, confirm the grade’s temperature rating on its TDS.
- Food contact. Mainstream grades are declared to FDA 21 CFR 177.1520. Ask for the producer’s compliance statement with the TDS.
- Physical form. Most grades are powders for masterbatch production. A granular grade (PPA 2800S) is easier to dose directly.
| Resin and process | Suggested SYCHEM PPA grades |
|---|---|
| mLLDPE / LLDPE blown and cast film | PPA 2200, 2200B, 2800, 9000E |
| LDPE and agricultural film | PPA 2100, 2300, 2800 |
| HDPE pipe, sheet and blow moulding | PPA 2800, 2815, 9000H |
| PP raffia and film | PPA 2800S, 2815, 9000P |
| EVA, wire and cable | PPA 2200, 2300, 2613 |
| Engineering plastics (PA, PET, PC, PMMA, ABS) | PPA 2800S, 2815 |
Grade data sheets and samples are sent on request. Tell us your resin, line and the defect you want to fix, and we will email the TDS for the grades that fit.
Troubleshooting a PPA that is not working
| Symptom | Likely cause | Fix |
|---|---|---|
| Sharkskin has not cleared after an hour | Dose too low, poor dispersion, or antiblock and pigment taking up the PPA | Raise the dose or run a conditioning dose, check the masterbatch dispersion, and separate the antiblock and PPA masterbatches. |
| Melt fracture returns after a purge or die clean | The coating was stripped off | Recondition the die with a higher dose for the first hour. |
| Melt fracture in only part of the die | Uneven die temperature or uneven coating | Check the die heater zones and allow more conditioning time. |
| Gels or specks in the film | Poorly dispersed PPA, or a masterbatch carrier with the wrong melt index | Re-compound the masterbatch on a twin-screw and match the carrier melt index to the resin. |
| Severe distortion at very high output | Gross melt fracture, which starts at the die entry | A PPA cannot fix this: lower the output, raise the melt temperature or change the die. |
| Head pressure has not dropped | Coating not yet formed, or dose too low for the formula | Allow full conditioning time, then raise the dose. |
Frequently asked questions
What is the shelf life of a PPA processing aid?
Our PPA grades have a 24-month shelf life when stored below 30 °C in a cool, dry place out of direct sunlight. Keep opened bags sealed.
Can a PPA be used with recycled polyethylene?
Yes. Recycled PE often contains fillers, pigments and degraded material that take up PPA, so expect to need a higher dose than for virgin resin, and confirm it with a trial.
Does a PPA change the film’s mechanical, sealing or printing properties?
At normal ppm loadings, a PPA is not expected to change tensile or impact strength, heat sealing or printing. If the film goes into demanding lamination or printing work, confirm it on your own line.
Is a PPA the same as a slip agent or EBS wax?
No. Slip agents such as erucamide lower film-to-film friction after extrusion, and EBS wax is an internal and external lubricant used mainly in PVC, ABS and compounds. Neither removes melt fracture. If you need lubrication or slip rather than die-wall release, see our EBS wax and silicone masterbatch.
Are PPAs affected by PFAS regulations?
Most PPAs are fluoropolymers, which fall within the broad PFAS definitions used in the EU restriction proposal and in some brand-owner specifications. The rules are still developing and differ by market, so check the current requirements for your end use, and ask us for the producer’s regulatory statement on a specific grade.
Get a PPA recommendation
Tell us your resin grade, process, line output and the defect you want to fix. We will suggest a PPA grade, a masterbatch route and a starting dose, and email you the TDS and arrange samples. Contact our technical team or write to info@sychemtech.com.
Related products: our polymer processing aid (PPA) range of 13 application-tuned grades, the lubricants hub, EBS wax, silicone masterbatch and PE resin.
