Two failures account for a surprising share of technical complaints in film converting and metalworking. The first: a polyethylene or polypropylene film that tested fine on the extruder but refuses to open on the customer's bagging machine, because the coefficient of friction (CoF) crept back up after two days in the roll. The second: a cutting or rolling oil that lubricates well at low speed but lets the tool score the workpiece under load, because it has no boundary film to fall back on when the hydrodynamic layer squeezes out. Both problems are solved with oleochemicals — fatty amides for the film, fatty esters for the metal — and both are decided by the same trade-off between how fast the molecule migrates to a surface and how stable it is once there.
The amide mechanism: a molecule that must migrate to work
Slip agents work precisely because they are incompatible with the polymer. Blended into the melt, the fatty amide sits in the amorphous regions; after extrusion, as the film cools, its surface energy pushes it toward the surface, where it forms a monolayer with the polar amide group facing outward. That lubricating monolayer is what the film-to-metal and film-to-film contact actually slides on. Three consequences follow, and they drive all real-world dosing decisions:
- More is not better. Once a monolayer has formed, additional agent just piles up as exudation — greasy surfaces, wet blocking, interference with corona treatment and heat sealing. Industry experience: over-dosing is far more common than under-dosing.
- Migration takes time. Unsaturated amides bloom within minutes to hours; saturated ones take days. A film tested an hour after winding is not showing its final CoF.
- Everything that changes crystallinity or surface layers changes slip. Higher-crystallinity resins (HDPE, PP homopolymer) slow migration; antiblock powders, other waxes and Corona treatment all interact with the surface population.
Oleamide vs stearamide: fast bloom vs stable anti-block
| Property | Oleamide (CAS 301-02-0) | Stearamide (CAS 124-26-5) |
|---|---|---|
| Chain | C18:1 unsaturated (cis-9-octadecenamide) | C18:0 saturated (octadecanamide) |
| Melting point | ≈ 66–77 °C | ≈ 96–104 °C |
| Migration speed | Fast bloom — minutes to hours; immediate CoF drop | Slow, controlled migration over days |
| Primary role | Slip agent for LDPE/LLDPE/PP films | Anti-blocking agent; limited slip, excellent anti-cling |
| Thermal/oxidative stability | Moderate (double bond can discolour at high temperature) | Higher; less odour, less volatility at processing temperature |
| Best paired with | Silica or calcium stearate antiblock | Oleamide or erucamide (slip + anti-block pack) |
The rule of thumb used across the industry: oleamide when you need slip now, stearamide when you need the film to stop clinging for good. Stearamide's saturation makes it the better choice where processing temperatures are high, discolouration is a concern, or the application is really anti-blocking rather than slip. Many film formulations carry both — stearamide holding the layers apart, oleamide giving the immediate surface lubricity for high-speed conversion.
Working dosages: the CoF ladder
Slip performance is classified by the CoF achieved: low slip (CoF 0.5–0.8), medium slip (0.2–0.5) and high slip (0.05–0.2). In LDPE these bands correspond roughly to 100–400 ppm, 500–600 ppm and 700–1,000 ppm of oleamide. Real starting points by application:
| Application | Typical oleamide level | Target / notes |
|---|---|---|
| LDPE / LLDPE packaging film | 0.05–0.2% | Dynamic CoF well below 0.3 in laminates at ≈ 0.1% |
| BOPP for high-speed packing | ≈ 0.12% | CoF ≤ 0.2 to feed machines running 500–800 packs/min |
| CPP / blown PP film | 0.2–0.3% | CoF below 0.4; pair with silica for clarity |
| Polyolefin cable compounds | ≈ 0.05% | CoF from ≈ 0.7 down to ≈ 0.13 reported |
| Molded PP/PE, PA, styrenics | 0.01–0.5% | Release, anti-static, anti-block side benefits |
Thin films need proportionally more than thick ones (the surface population, not the bulk loading, does the work), and metallocene LLDPE — the tackiest of the polyolefins — usually sits at the top of any range. Deliver the agent as a pure slip masterbatch so the level can be trimmed line by line instead of being locked into a compound. Stearamide as an anti-block typically runs 0.1–0.5% in the same films, adjusted against the mineral antiblock it may be replacing or accompanying.
The ester side: butyl oleate and butyl stearate as boundary lubricants
Where amides solve polymer-to-polymer friction, the fatty esters solve metal-to-metal friction. Both are butyl esters of C18 fatty acids, and their polarity is the point: the ester head adsorbs onto metal surfaces and builds a boundary film that plain mineral oil cannot form.
- Butyl oleate (CAS 142-77-8) — light amber liquid, pour point below about −26 °C, kinematic viscosity ≈ 16–19 mm²/s at 40 °C with a viscosity index above 180, saponification value 164–167, iodine value 72–77. The unsaturation keeps it liquid at low temperature, which is why it shows up in rolling oils, coning and knitting oils, textile spin finishes and emulsifiable metalworking fluids — anywhere a low-pour-point, readily emulsified, biodegradable oily phase is wanted. It also plasticises PVC and rubbers and serves as a textile antistatic/softening finish.
- Butyl stearate (CAS 123-95-5) — the saturated analogue, melting at just 19–22 °C so it stays pourable at ambient temperature. The straight C18 chain gives it strong boundary lubricity and low volatility; in PVC it is a classic internal lubricant at 0.5–1 phr (transparent sheet and profile grades included), and in metalworking it serves in cutting fluids and release agents. Its oxidation resistance is markedly better than butyl oleate's — for hot, long-running metalworking circuits, the saturated ester holds viscosity and colour longer.
Choosing between them is mostly a low-temperature versus oxidative-stability trade: butyl oleate for cold-start emulsifiable systems and textile oils, butyl stearate for hot circuits and for PVC work where a low-melting internal lubricant is the job. In metalworking emulsions both are usually paired with emulsifiers (and often with extreme-pressure additives), the ester contributing the boundary layer that protects the tool between hydrodynamic films.
COA lines that separate a good lot from a problem lot
- Amide purity: ≥ 98.5% for both primary amides (C16–C18 even-numbered distribution for stearamide). Low purity means free fatty acid and unreacted feedstock — odour, colour and dosing drift.
- Acid value: ≤ 0.5–1.5 mg KOH/g (stearamide grades typically ≤ 0.5). Free acid corrodes and undermines odour-sensitive packaging.
- Iodine value: ≤ 4 g I2/100 g for stearamide (saturation check); 72–77 for butyl oleate (unsaturation consistency — a low reading signals hydrogenated or degraded feed).
- Moisture: ≤ 0.1–0.5%. Fatty amides are hygroscopic; caked beads disperse poorly and streak masterbatch.
- Melting point / colour: stearamide 96–104 °C, Gardner colour ≤ 2 — a broad or low melting range is the fingerprint of off-ratio or acid-cut material.
Selection quick answers
LDPE bag film that must open immediately after winding? Oleamide 0.05–0.15%. BOPP on a high-speed overwrapping line? Oleamide ≈ 0.12%, CoF verified ≤ 0.2 after 24 h conditioning. Film clinging in the roll even though slip looks fine? Add stearamide as anti-block or swap part of the mineral antiblock. Hot running PVC sheet sticking in the calender? Butyl stearate 0.5–1 phr as internal lubricant. Emulsifiable rolling or coning oil for a cold climate? Butyl oleate as the oily phase, emulsifier package to suit. High-temperature machining circuit needing oxidative stability? Butyl stearate, with EP additives carrying the load peaks.
Shanghai Better Chemical supplies the full oleochemical toolkit for both sides of this problem — Oleamide (CAS 301-02-0) and Stearamide (CAS 124-26-5) for slip and anti-blocking in polyolefin films, and Butyl Oleate (CAS 142-77-8) and Butyl Stearate (CAS 123-95-5) for rolling oils, coning oils, metalworking fluids and PVC lubrication. Every lot ships with a COA covering purity, acid value, iodine value, moisture and melting range, with TDS/MSDS and samples for line trials. Tell us the polymer or the metalworking circuit, the CoF or lubricity target, and we will match the grade and confirm current pricing.