Lubricant masterbatch is the quiet workhorse of the plastics compounding industry. It rarely appears on a datasheet as a headline property, yet it decides whether a highly filled polypropylene compound runs at 900 kg/h or stalls at 600 kg/h, whether a rigid PVC profile line survives eighteen months on the same screw set or needs re-flighting after nine, and whether a blown film die produces twelve hours of clean output or a bead of degraded drool every ninety minutes. In 2026, as compounders push filler loadings higher, migrate to recycled feedstocks with unpredictable rheology, and squeeze specific energy consumption to meet energy-cost and carbon targets, the humble lubricant package has moved from an afterthought to a first-order formulation variable.
This guide is written for compounders, masterbatch producers, extrusion process engineers and technical buyers who need to understand what a lubricant masterbatch actually does inside the barrel, how to choose between wax, amide, stearate, silicone and fluoropolymer chemistries, how much to dose in parts per hundred resin, and how to manufacture the masterbatch itself on a co-rotating twin-screw extruder without destroying the very additive you are trying to deliver. Kerke, a Wanplas factory specialising in parallel co-rotating twin-screw compounding extruders, has supplied KTE-series lines to masterbatch producers in more than 70 countries, and the process windows described here reflect that field experience across colour, filler, additive and cable compounding applications.
By the end of this article you will be able to specify a lubricant masterbatch by function rather than by trade name, predict the effect of a dosage change on torque and coefficient of friction, design a screw configuration that disperses a wax package without shearing it into vapour, and diagnose the five most common field failures — screw slippage, plate-out, die drool, blooming and lost seal strength — from their symptoms.
What Is Lubricant Masterbatch and Why Compounders Rely On It
A lubricant masterbatch is a concentrated, pelletised carrier of friction-modifying additives, typically containing 5 to 30 percent active lubricant dispersed in a polymer carrier, designed to be let down into a base resin at 1 to 5 percent to deliver a controlled dose of slip, release and viscosity reduction. It exists because pure lubricants are almost impossible to meter accurately and safely in their raw form: waxes arrive as fine powders or flakes that bridge in hoppers, fatty amides are electrostatic and dusty, metal stearates are respiratory irritants, and fluoropolymer processing aids are supplied at concentrations so low that direct addition would require dosing accuracy beyond the reach of most gravimetric feeders.
Encapsulating these actives in a pellet solves four problems at once. First, it converts a dusty powder into a free-flowing pellet with a bulk density in the 480 to 560 kg/m³ range that behaves like the base resin in the hopper. Second, it pre-disperses the additive so that the downstream converter’s single-screw extruder — which has far less mixing capability than a twin-screw compounder — only needs to distribute an already-broken-down additive rather than disperse an agglomerate. Third, it protects the operator from inhalation exposure to stearate and amide dusts. Fourth, it allows precise, repeatable dosing at let-down ratios that a volumetric or loss-in-weight feeder can hold to within plus or minus 0.5 percent.
The three functional jobs of a lubricant package
Practitioners often lump all friction modifiers together, but a well-designed lubricant masterbatch performs three distinct jobs, and the ratio between them is what differentiates a generic product from an engineered one.
- Viscosity reduction (internal function). The lubricant partially dissolves in the melt, increasing free volume between polymer chains and reducing the entanglement density. The result is lower apparent shear viscosity at a given shear rate, lower specific energy input in kWh/kg, and lower melt temperature. This is the function that unlocks throughput on torque-limited machines.
- Metal release (external function). The lubricant is thermodynamically incompatible with the matrix, so it phase-separates and migrates to the highest-energy interface, which is the steel of the barrel, screw and die. A boundary film only a few hundred nanometres thick prevents polymer adhesion, controls plate-out, and eliminates the stagnation zones that generate degraded black specks.
- Surface slip and abrasion resistance (in-service function). After the part is made, residual lubricant blooming to the surface lowers the static and kinetic coefficient of friction, easing bag opening, improving conveying, reducing scuffing on automotive interior parts, and improving mar and scratch resistance on textured surfaces.
These three jobs frequently conflict. A lubricant that is excellent at reducing melt viscosity is, by definition, compatible with the matrix and therefore poor at forming a metal-release film. A lubricant that blooms strongly to the surface to give a low in-service coefficient of friction will also bloom during storage and can destroy printability. The formulation art lies in blending two or three chemistries so that the combined package covers all three functions without any single one dominating.
Where lubricant masterbatch matters most
Not every compound needs a lubricant package. Unfilled polyethylene film grades typically do not. The applications where a lubricant masterbatch shifts the economics decisively are those where friction is high, shear is intense, or the polymer has poor intrinsic slip:
- Highly filled polyolefin compounds with 50 to 80 percent calcium carbonate, talc or barium sulphate, where filler-to-metal and filler-to-filler friction dominates the torque signature.
- Rigid PVC, which has no melt strength margin and degrades rapidly if local shear heating pushes the melt above roughly 205 °C. PVC formulation is essentially an exercise in lubricant balancing.
- Engineering thermoplastics such as PA6, PA66, PC, PBT and POM, where high melt viscosity and high processing temperatures create severe adhesion and sticking on hot tooling.
- Glass-fibre reinforced compounds, where the abrasive fibre ends scour barrel liners and lubricant films are the primary defence for screw element life.
- Recycled polyolefins and mixed post-consumer streams, where contamination, degraded chain ends and inconsistent melt flow index make processing windows narrow and unstable.
- Wood-plastic composites, where cellulose fibre absorbs lubricant and the required dose can be several times that of a mineral-filled compound.
Across these segments the pattern is consistent: correctly dosed lubricant masterbatch buys throughput, reduces melt temperature by 8 to 20 °C, lowers motor load by 8 to 25 percent, and extends tooling intervals — all without changing the base resin. Very few additives offer that combination of leverage at a Low to Medium relative cost contribution to the formulation.
Internal Versus External Lubrication: The Mechanism Explained
The internal-external distinction is the single most useful mental model in lubricant technology, and it rests on one variable: the compatibility of the lubricant with the polymer matrix, expressed practically through solubility parameter matching and molecular polarity. Internal lubricants are partially soluble and act inside the melt; external lubricants are insoluble and act at the melt-metal boundary. Almost every processing problem attributed to “wrong lubricant” is in reality a wrong internal-to-external ratio.
How internal lubrication works at the molecular level
An internal lubricant has a molecular structure similar enough to the host polymer that it dissolves into the amorphous phase. In a polyolefin, that means a long aliphatic hydrocarbon chain; in PVC, it means a moderately polar ester group attached to a fatty chain. Once dissolved, the lubricant molecules occupy space between polymer chains, increasing free volume and reducing the number of physical entanglements per chain. The macroscopic consequence is a drop in zero-shear viscosity and a flatter viscosity-shear rate curve.
The practical signature of good internal lubrication in a compounding line is unmistakable. Motor amperage falls. Melt temperature at the die falls, sometimes dramatically, because a large fraction of melt heating in a twin-screw extruder is viscous dissipation rather than conduction from the barrel heaters. Specific energy consumption, measured in kWh per kilogram of output, typically drops from a baseline of 0.20 to 0.28 kWh/kg on a filled polyolefin down to 0.16 to 0.22 kWh/kg. Because dissipative heating scales with viscosity times shear rate squared, even a 15 percent viscosity reduction produces a disproportionate thermal benefit at high screw speeds.
The limitation of internal lubricants is equally clear. Because they are soluble, they stay in the bulk and do not build a boundary film on the metal. A compound lubricated exclusively with internal chemistry will run cool and easily but will still stick to the die land, still generate drool, and still show plate-out on calender rolls.
How external lubrication works at the interface
An external lubricant is chosen precisely because it is incompatible. During melting and conveying, the incompatible species is driven out of the bulk by thermodynamic exclusion and by the shear gradient, which sweeps low-viscosity minor phases towards the wall. Within a few L/D of melting, a thin, continuous film of lubricant coats the barrel and screw surfaces. Because this film has a much lower viscosity than the bulk melt, it introduces wall slip: the melt no longer obeys the no-slip boundary condition, and a measurable slip velocity develops at the interface.
Wall slip is a double-edged tool. It reduces drag on the screw, reduces frictional heat generation at the barrel wall, delays the onset of sharkskin melt fracture at the die exit, and prevents adhesion in stagnation zones. But excessive wall slip destroys conveying efficiency. In a single-screw extruder, output depends on drag flow, which depends on the melt sticking to the barrel and slipping on the screw; if the melt slips on both, output collapses and the machine surges. This is the physical origin of the classic overdose symptom: an operator adds more lubricant to fix a torque problem, and the extruder begins to surge and lose throughput.
The balance point and why it is formulation-specific
Rigid PVC illustrates the balance most clearly because the entire formulation is designed around it. Calcium stearate acts primarily as an internal lubricant with strong co-stabilising and fusion-promoting behaviour. Paraffin wax acts almost purely externally, delaying fusion and providing metal release. Oxidised polyethylene wax and low-molecular-weight PE wax sit in between, with the degree of oxidation setting polarity and therefore the internal-external ratio. A rigid PVC pipe formulation that fuses too early scorches and yellows; one that fuses too late leaves unfused primary particles, producing brittle pipe that fails the drop-impact test. The lubricant package sets the fusion time, and fusion time is measured directly on a torque rheometer.
| Characteristic | Internal Lubricant | External Lubricant |
|---|---|---|
| Compatibility with matrix | Partially soluble; matched solubility parameter | Insoluble; mismatched polarity by design |
| Primary site of action | Bulk melt, between polymer chains | Melt-to-metal interface, boundary film |
| Effect on melt viscosity | Reduces significantly, 10–30 percent typical | Little change in bulk viscosity |
| Effect on wall slip | Minimal | Strong; introduces measurable slip velocity |
| Effect on fusion time (PVC) | Shortens fusion, promotes gelation | Delays fusion, reduces early shear |
| Effect on melt temperature | Lowers by 8–20 °C via reduced dissipation | Lowers modestly, 3–8 °C, via reduced wall friction |
| Risk of overdose | Loss of mechanical strength, plasticising effect | Screw slippage, surging, plate-out, blooming |
| Typical chemistries | Glycerol monostearate, fatty acid esters, calcium stearate, low-MW PE wax | Paraffin wax, oxidised PE wax, EBS, metal soaps, silicone, fluoropolymer PPA |
| Effect on printability and sealing | Generally neutral | Can degrade markedly if migratory |
Lubricant Chemistries Compared: Waxes, Amides, Stearates, Silicone and PPA
There are roughly six chemistry families that account for the overwhelming majority of lubricant masterbatch actives, and each occupies a distinct position on the internal-external axis, the thermal stability axis, and the migration axis. Choosing correctly requires matching all three to the base polymer, the processing temperature and the end-use requirements.
Polyethylene waxes and oxidised PE waxes
Low-molecular-weight polyethylene waxes, with number-average molecular weight typically between 1,000 and 5,000 g/mol and drop melting points from 100 to 130 °C, are the most widely used general-purpose lubricants in polyolefin and filled compounds. Unmodified PE wax is non-polar and behaves largely as an external lubricant in polar systems such as PVC and engineering resins, but as an internal lubricant in polyolefins, where it is compatible. Oxidised PE wax carries carboxyl and carbonyl functionality with acid values commonly in the 15 to 30 mg KOH/g range, which raises polarity, improves pigment and filler wetting, and shifts the balance towards internal lubrication in PVC.
PE wax is particularly valuable in filler masterbatch production. A calcium carbonate masterbatch at 75 to 80 percent loading cannot be compounded at reasonable throughput without a wax package that coats the mineral surface, lowers the effective viscosity of the highly filled melt, and prevents filler-metal abrasion. Typical wax addition in a filler masterbatch is 1 to 3 percent of the total masterbatch weight, sometimes higher for very fine grades with high specific surface area.
Fatty acid amides: erucamide, oleamide, stearamide and EBS
Fatty acid amides are the dominant slip agents in film applications. Erucamide, a C22 monounsaturated amide with a melting point around 78 to 82 °C, is the workhorse for polyethylene film because its long chain gives slow, controlled migration and a persistent low coefficient of friction. Oleamide, the C18 analogue, migrates faster and gives a quicker COF drop but is more volatile and more prone to blooming excess. Stearamide is saturated and more thermally stable but less effective as a slip agent.
Ethylene bis-stearamide, universally abbreviated EBS, is chemically distinct and functionally the most versatile amide in the family. With a melting point of 140 to 145 °C and thermal stability comfortably above 300 °C, EBS is stable enough for polyamide, polycarbonate and PBT processing. Crucially, EBS is essentially non-migrating at ambient temperature, so it does not bloom, does not degrade corona treatment, and does not compromise heat seal strength. It provides mould release, metal release, pigment dispersion assistance and a modest internal lubrication effect. For engineering-resin compounders, EBS at 0.2 to 0.8 phr is often the default choice.
Metal stearates: calcium, zinc, magnesium and barium
Metal soaps combine lubrication with secondary functions that make them indispensable in specific systems. Calcium stearate is the most common: it acts as an internal lubricant, an acid scavenger neutralising catalyst residues in polyolefins, and a co-stabiliser in PVC. Zinc stearate is more strongly external and is widely used as a mould release and anti-blocking aid, but in PVC it must be used cautiously because zinc chloride formed during degradation is a powerful catalyst for zinc burning — a runaway darkening reaction. Magnesium stearate offers similar lubrication with better colour stability. Barium and lead soaps have largely been displaced by calcium-zinc and organotin systems in response to RoHS, REACH and regional heavy-metal restrictions.
Metal stearates in masterbatch form typically run at 10 to 25 percent active loading. Because stearate powders have very low bulk density, often below 200 kg/m³, they cannot be fed reliably through a standard gravimetric feeder into a twin-screw main port; side stuffing with a twin-screw crammer feeder is the standard solution, and Kerke’s crammer feeder and side-feeder options exist precisely for this class of low-bulk-density powder.
Silicone: fluids, gums and silicone masterbatch
Ultra-high-molecular-weight polydimethylsiloxane, supplied as a 40 to 50 percent masterbatch on a polyolefin or engineering carrier, occupies a unique niche. Unlike a silicone fluid, which migrates readily and creates contamination problems in painting and printing operations, high-molecular-weight silicone gum stays largely bound in the matrix while still delivering dramatic reductions in surface coefficient of friction, typically from 0.50 down to 0.15 or lower, plus outstanding abrasion resistance, mar resistance and scratch resistance.
Silicone masterbatch is the preferred lubricant for automotive interior components, cable jacketing that must pull easily through conduit, wear-critical POM and PA gears and bushings, and medical tubing that requires low insertion force. It also improves the flow of highly filled and glass-reinforced compounds, and can reduce injection pressure by 10 to 20 percent at 2 to 4 percent masterbatch let-down. Its relative cost is High to Premium, so it is deployed where performance justifies it rather than as a general-purpose flow aid.
Fluoropolymer processing aids (PPA)
PPA is a special case that deserves separate treatment because it is not a lubricant in the conventional sense. A fluoropolymer processing aid, typically a fluoroelastomer such as a vinylidene fluoride-hexafluoropropylene copolymer supplied at 2 to 5 percent on a polyolefin carrier, works by coating the die land with a dynamic fluoropolymer layer. Because polyethylene has extremely poor adhesion to fluoropolymer, the melt slips at the die wall rather than undergoing the stick-slip oscillation that produces sharkskin melt fracture.
PPA does not measurably change bulk melt viscosity, does not reduce motor torque, and does not lubricate the screw. What it does is allow a linear low-density polyethylene film line to run at 2 to 3 times higher shear rate before melt fracture appears, eliminate die build-up, reduce die-line defects, and shorten colour change times. The effective concentration is remarkably low: 300 to 800 ppm of active fluoropolymer in the final resin, which corresponds to roughly 1 to 2 percent let-down of a 4 percent masterbatch. Conditioning time — the period during which the fluoropolymer coats the die — typically takes 30 to 90 minutes on start-up. Note that certain fluoropolymer chemistries face increasing regulatory scrutiny under REACH and various national per- and polyfluoroalkyl substance initiatives, and several suppliers now offer non-fluorinated polymer processing aids based on polyethylene glycol chemistry or acrylate block copolymers as alternatives.
| Lubricant Type | Melting Point / Stability | Internal / External Balance | Typical Dose (phr) | Best Suited To | Relative Cost |
|---|---|---|---|---|---|
| Paraffin wax | 50–70 °C; stable to ~230 °C | Strongly external | 0.2–1.0 | Rigid PVC pipe and profile, fusion delay | Low |
| PE wax (non-polar) | 100–130 °C; stable to ~280 °C | External in PVC, internal in polyolefin | 0.3–2.0 | Filler masterbatch, colour masterbatch, PVC | Low |
| Oxidised PE wax | 105–125 °C; acid value 15–30 | Balanced, leans internal in PVC | 0.2–1.5 | Pigment wetting, PVC, high-filler systems | Low–Medium |
| Erucamide (C22) | 78–82 °C; volatile above 250 °C | External, strongly migratory | 0.05–0.30 | PE and PP film slip, bag opening | Medium |
| Oleamide (C18) | 68–75 °C; volatile above 230 °C | External, fast migration | 0.05–0.25 | Fast COF development, thin film | Medium |
| EBS (bis-stearamide) | 140–145 °C; stable above 300 °C | Balanced, non-migrating | 0.2–0.8 | PA, PC, PBT, ABS, printable film | Medium |
| Calcium stearate | 145–155 °C; stable to ~300 °C | Internal, plus acid scavenging | 0.1–1.0 | PVC, polyolefin catalyst neutralisation | Low |
| Zinc stearate | 120–130 °C | External, mould release | 0.1–0.6 | Polyolefin, ABS; caution in PVC | Low |
| Silicone gum masterbatch | Stable above 300 °C | External, low migration | 1.0–4.0 (as masterbatch) | Wear parts, cable jacket, automotive interior | High |
| Fluoropolymer PPA | Stable above 300 °C | Die-interface only | 0.03–0.08 active | LLDPE and mLLDPE film, melt fracture | Premium |
| Glycerol monostearate | 58–65 °C | Internal, also antistatic | 0.3–1.5 | PVC, PS, antistatic dual function | Low–Medium |
Carrier Resin Selection and Concentration Design
The carrier resin is not inert packaging. It determines whether the masterbatch disperses in the customer’s process, whether the actives survive compounding, and whether the masterbatch introduces incompatibility defects into the final part. The governing rule is that the carrier must be either identical to, or fully miscible with, the base polymer of the end compound — and its melt flow index must be matched to the process that will let it down.
Melt flow index matching
A common field failure is a lubricant masterbatch made on a very high melt flow carrier — say a 40 g/10 min polypropylene — being let down into a 2 g/10 min pipe-grade polypropylene. The viscosity mismatch is so large that the masterbatch phase shears preferentially and never distributes evenly, producing streaks of over-lubricated and under-lubricated material. The rule of thumb is to keep the carrier MFI within a factor of roughly three to five of the base resin MFI, tested under the same ISO 1133 conditions. For injection moulding let-down, a slightly higher carrier MFI is acceptable and even helpful; for film and pipe extrusion, closer matching is essential.
Universal versus dedicated carriers
Low-density polyethylene and ethylene-vinyl acetate copolymers are widely used as semi-universal carriers because their low melting points allow additive incorporation at gentle temperatures and their broad compatibility tolerates use in PE, PP and some styrenics. However, a PE carrier in a polypropylene part reduces clarity, can create gel-like inclusions in thin film, and marginally reduces stiffness. In demanding applications, dedicated carriers are worth the inventory complexity: PP homopolymer carriers for PP compounds, PA6 carriers for polyamide, PBT for PBT, and PVC-compatible acrylic or chlorinated polyethylene carriers for rigid PVC.
For engineering plastics, carrier selection is constrained by processing temperature. A polyamide compound processed at 260 to 280 °C cannot use a PE-carried masterbatch without producing visible inclusions and reducing weld line strength. EBS on a PA6 carrier, or on a low-melting copolyamide carrier, is the correct construction.
Wax-bound and carrier-free constructions
A third approach uses the lubricant itself as the binder. High-concentration lubricant compactions at 60 to 90 percent active, held together by a small fraction of PE wax and pelletised on an under-water or air-cooled die-face system, minimise carrier contamination. These are used where any foreign polymer is unacceptable — for example in optical-grade polycarbonate or in single-polymer recyclable packaging structures. Producing them requires very careful thermal management on the compounding line because the material has almost no melt strength.
| Target Base Polymer | Recommended Carrier | Carrier MFI Guide | Preferred Active | Compounding Melt Temp |
|---|---|---|---|---|
| LDPE / LLDPE film | LDPE or LLDPE | 2–8 g/10 min | Erucamide, PPA, PE wax | 150–185 °C |
| PP homopolymer / copolymer | PP homopolymer | 8–35 g/10 min | Erucamide, EBS, Ca stearate | 180–215 °C |
| Rigid PVC | Acrylic processing aid or CPE | Not MFI rated | Paraffin, oxidised PE wax, Ca stearate | 165–185 °C |
| PA6 / PA66 | PA6 or copolyamide | Viscosity-number matched | EBS, montan ester, silicone gum | 240–270 °C |
| PC / PC-ABS | PC or SAN | Matched to base | Pentaerythritol tetrastearate, EBS | 250–275 °C |
| POM | POM copolymer | Matched to base | Silicone gum, PTFE micropowder | 185–200 °C |
| TPU / TPE cable jacket | TPU or EVA | Shore-matched | Silicone gum, EBS, montan wax | 175–200 °C |
| Wood-plastic composite | HDPE or PP | 0.5–4 g/10 min | Zinc stearate plus oxidised PE wax blend | 160–185 °C |
Dosage Windows in phr and the Coefficient of Friction Target
Dosage is where most lubricant masterbatch programmes succeed or fail, and the correct answer is always expressed in phr of active lubricant, never in percent of masterbatch. Working in phr forces the formulator to account for masterbatch concentration and prevents the classic error of switching from a 10 percent to a 20 percent concentrate while keeping the same let-down ratio, thereby doubling the dose.
Reading the coefficient of friction curve
Coefficient of friction is measured by the sled method described in ASTM D1894 and its ISO equivalent, reporting both a static COF, the force required to initiate motion, and a kinetic COF, the force to sustain it. Untreated polyethylene film typically shows a static COF between 0.45 and 0.80 — high enough that bags will not open on an automatic bagging machine. Adding erucamide produces a characteristic dose-response curve: COF drops steeply between 0.05 and 0.12 phr, then flattens into a plateau around 0.15 to 0.20 phr, below which further addition delivers almost no benefit but continues to increase blooming, haze and seal degradation.
Understanding this plateau is commercially important. Many converters overdose by a factor of two because they never mapped the curve. Running a simple ladder trial at 0.04, 0.08, 0.12, 0.16 and 0.20 phr, measuring COF after 24 hours, 72 hours and 7 days of ageing at controlled temperature, identifies the knee of the curve and typically allows a 30 to 50 percent reduction in slip agent consumption with no loss of function.
Time dependence and the ageing effect
Migratory slip agents do not act immediately. The amide must diffuse from the bulk to the surface, and the rate depends on temperature, polymer crystallinity, film thickness and the presence of competing additives. Erucamide in LLDPE film typically reaches roughly 60 percent of its final COF reduction within 24 hours at 23 °C, 85 percent within 72 hours, and full equilibrium in 5 to 10 days. Higher storage temperature accelerates this; roll cores stored warm can develop excessive slip and cause telescoping. Conversely, film wound tightly and stored cold may fail an incoming COF test that it would pass a week later — a frequent source of avoidable supplier disputes.
Competition matters too. Anti-block agents such as diatomaceous earth, synthetic silica and talc adsorb amide slip agents onto their high surface area. A film formulation containing 2,000 to 5,000 ppm of natural silica anti-block will require noticeably more erucamide than an unfilled control to reach the same COF, and the adsorption is greater for high-porosity diatomaceous grades than for precipitated silica with treated surfaces.
| Application | Active Lubricant | Active Dose (phr) | Masterbatch Let-Down | Target Kinetic COF | Primary Benefit |
|---|---|---|---|---|---|
| LLDPE blown film, bagging | Erucamide | 0.08–0.15 | 1.5–3.0 % of 5 % MB | 0.15–0.25 | Bag opening, winding control |
| BOPP printable film | EBS plus low erucamide | 0.10–0.25 | 1.0–2.5 % of 10 % MB | 0.25–0.35 | Slip without ink adhesion loss |
| 80 % CaCO3 filler masterbatch | PE wax plus stearic acid | 1.0–3.0 (on filler) | Built in, not let down | Not applicable | Throughput, filler wetting |
| Rigid PVC pipe | Paraffin + oxidised PE wax + Ca stearate | 0.8–1.6 total | Dry-blend dosed | Not applicable | Fusion control, no plate-out |
| 30 % glass PA66 | EBS or montan ester | 0.3–0.7 | 1.5–3.5 % of 20 % MB | Not applicable | Mould release, screw wear |
| POM gears and bearings | Silicone gum | 0.8–2.0 active | 2.0–4.0 % of 50 % MB | 0.08–0.18 | Wear rate, noise, torque |
| mLLDPE stretch film | Fluoropolymer PPA | 0.03–0.08 | 1.0–2.0 % of 4 % MB | Unchanged | Melt fracture elimination |
| WPC decking | Zinc stearate + oxidised wax | 3.0–6.0 | 4.0–8.0 % of 60 % MB | Not applicable | Die pressure, surface finish |
Wear Reduction: Torque, Specific Energy and Screw and Barrel Life
Wear reduction is the least visible but most financially significant benefit of a correctly formulated lubricant masterbatch, because screw and barrel replacement is a capital-scale event that also costs days of lost production. The mechanism is straightforward: wear rate in a plastics extruder is a function of contact pressure, sliding velocity, temperature and the abrasiveness of the compound, and lubrication attacks three of those four variables simultaneously.
The three wear mechanisms in a compounding extruder
Abrasive wear dominates in filled and reinforced compounds. Hard particles — glass fibre ends with Mohs hardness around 6, calcined kaolin, quartz impurities in talc, titanium dioxide, and aluminium trihydroxide — are dragged across the flight lands and barrel liner under high pressure. Each pass removes a microscopic volume of metal. In a heavily glass-filled polyamide running without lubrication, flight land wear of 0.1 to 0.2 mm per 3,000 operating hours is not unusual; with a properly designed lubricant film, the same compound can run two to three times longer before radial clearance exceeds the tolerance that triggers output loss and melt quality problems.
Adhesive wear occurs when polymer sticks to metal, cures or degrades, and then is torn away carrying metal with it. This is the mechanism behind the pitting sometimes seen on PVC screws. External lubricants prevent the initial adhesion, which is why paraffin wax remains irreplaceable in rigid PVC despite decades of alternatives.
Corrosive wear comes from acidic degradation products: hydrogen chloride from PVC, acetic acid from EVA, and residual catalyst acids in polyolefins. Metal stearates that act as acid scavengers, particularly calcium stearate, reduce corrosive attack directly by neutralising the acid before it reaches the steel. Nitrided barrels resist this poorly; bimetallic liners with nickel-chromium-boron overlays resist it well, and Kerke specifies bimetallic barrel liners as standard on KTE-series machines destined for halogenated or corrosive-filler duty.
Quantifying the torque and energy benefit
Specific energy consumption is the cleanest single measure of lubricant effectiveness on a compounding line. It is calculated by taking motor power drawn in kilowatts, subtracting no-load losses, and dividing by output in kilograms per hour. A typical 70 percent calcium carbonate filler masterbatch on a KTE-series co-rotating twin-screw extruder without an optimised wax package might run at 0.24 to 0.30 kWh/kg. With an optimised package the same formulation commonly runs at 0.17 to 0.21 kWh/kg, and because the machine was torque-limited rather than heat-limited, the freed torque converts directly to 12 to 20 percent higher output at the same screw speed.
The thermal benefit compounds this. Melt temperature at the die drops, which reduces additive volatilisation, reduces polymer degradation and yellowing, reduces the cooling load on the strand bath or underwater pelletiser, and reduces the risk of strand breakage. On lines pelletising heat-sensitive compounds, a 15 °C reduction in melt temperature can be the difference between a stable eight-hour run and constant strand breaks.
| Compound Type | Abrasiveness Class | SEC Without Lubricant (kWh/kg) | SEC With Optimised Package | Recommended Barrel / Screw Metallurgy |
|---|---|---|---|---|
| Unfilled LDPE colour masterbatch | Low | 0.13–0.18 | 0.11–0.15 | Nitrided 38CrMoAlA |
| 70–80 % CaCO3 filler masterbatch | Medium-High | 0.24–0.30 | 0.17–0.21 | Bimetallic liner, powder-metallurgy screw elements |
| 30 % glass-fibre PA66 | Very High | 0.28–0.36 | 0.22–0.28 | Bimetallic liner, tungsten-carbide-faced elements |
| 65 % ATH cable compound | High | 0.26–0.33 | 0.19–0.24 | Bimetallic liner, corrosion-resistant elements |
| Rigid PVC dry blend | Medium, corrosive | 0.16–0.22 | 0.12–0.17 | Chrome-plated or Ni-Cr-B overlay, counter-rotating preferred |
| WPC 55 % wood flour | Medium, high friction | 0.22–0.29 | 0.16–0.21 | Bimetallic liner, deep-flight conveying elements |
Designing for wear from the machine side
Lubrication reduces wear but does not eliminate the need for correct machine specification. On KTE-series twin-screw extruders, Kerke addresses abrasive duty through a combination of measures: segmented barrels with replaceable bimetallic liners so that only the worn zone needs replacement; splined screw shafts allowing individual element replacement rather than whole-screw scrapping; powder-metallurgy or tool-steel elements in the high-shear kneading blocks where wear concentrates; and computer-aided screw design that spreads shear over a longer axial distance rather than concentrating it in one violent mixing block. Combined with an appropriate lubricant package, these measures typically extend the interval between major screw refurbishments substantially compared with a general-purpose nitrided configuration running the same abrasive formulation.
Melt Fracture, Die Drool and Plate-Out Control
Three surface and tooling defects — melt fracture, die drool and plate-out — account for the majority of unplanned line stoppages in extrusion, and all three are directly governed by lubricant behaviour at the polymer-metal interface. Understanding the distinct physics of each prevents the common mistake of treating them with the same additive.
Melt fracture: the stick-slip instability
Melt fracture appears first as sharkskin, a fine matte roughness on the extrudate surface, then as gross distortion at higher shear rates. It originates at the die exit, where the melt undergoes a violent rearrangement from the no-slip condition inside the die land to a free surface outside. If the tensile stress at the surface exceeds the melt’s ability to relax, the surface tears periodically. The critical wall shear stress for onset is roughly 0.10 to 0.20 MPa for most polyethylenes, and narrow molecular weight distribution metallocene grades are especially prone because they have less long-chain branching to dissipate stress.
The three practical remedies are raising melt temperature, lowering output, and adding a processing aid. The first two cost throughput or quality. A fluoropolymer PPA solves the problem at the source by coating the die land with a low-surface-energy layer so the melt slips smoothly out rather than sticking and tearing. The conditioning behaviour is important: after start-up with fresh, thoroughly cleaned tooling, expect 30 to 90 minutes before the fluoropolymer layer is established and the sharkskin clears. Pigments with high surface area, particularly titanium dioxide and carbon black, compete for the fluoropolymer and can require 1.5 to 2 times the normal PPA dose.
Die drool: the accumulation problem
Die drool, also called die build-up, die lip build-up or plate-out at the die, is the accumulation of a waxy or crusty deposit at the die exit that periodically detaches and contaminates the product. It arises from several converging causes: low-molecular-weight species exuding from the melt at the free surface, incompatible additives phase-separating and depositing, volatiles condensing, and shear-induced migration of low-viscosity components towards the wall.
Lubricant selection cuts both ways here. An overdosed migratory external lubricant is one of the most common causes of drool; erucamide overdose in film, or paraffin overdose in PVC, will build a visible bead within an hour. Conversely, the correct lubricant, particularly a fluoropolymer PPA or a well-matched oxidised wax, eliminates drool by preventing the stagnation zone from forming in the first place. Diagnosing which situation applies requires analysing the deposit: an amide-rich, soft, white deposit indicates slip-agent overdose; a hard, dark, oxidised deposit indicates a stagnation and degradation problem that a release-oriented lubricant will fix.
Plate-out on rolls, calenders and moulds
Plate-out is the deposition of a thin film of additive residue on calender rolls, embossing rolls, cooling rolls and injection mould surfaces. In PVC calendering it is a chronic problem, typically caused by incompatibility between the lubricant, the stabiliser and any filler surface treatment. Zinc stearate and calcium stearate can react with residual acidity or with each other to form insoluble species that deposit. The classic diagnostic is to change one component at a time; the classic prevention is to keep total lubricant below the solubility limit and to avoid combining strongly incompatible external lubricants at high dose.
In injection moulding, plate-out shows as a hazy film in the cavity that transfers to part surfaces and eventually blocks vents. Reducing migratory lubricant, switching to non-migrating EBS or high-molecular-weight silicone, improving venting and lowering mould temperature all help.
Practical rule: if a defect appears immediately on start-up and worsens with running time, suspect lubricant overdose or incompatibility. If a defect appears only at high output or after a shear-rate increase, suspect insufficient interfacial lubrication or missing processing aid.
Twin-Screw Compounding Parameters for Lubricant Masterbatch Production
Producing lubricant masterbatch is fundamentally different from producing colour or filler masterbatch, and the difference confounds many compounders who apply pigment-dispersion logic to a wax system. Pigment dispersion demands intense shear to break agglomerates; lubricant incorporation demands the opposite, because the actives are low-melting, thermally fragile and volatile, and because excessive shear simply drives them out of the melt and onto the barrel wall where they cause slippage rather than mixing.
The core principle: distributive mixing at low specific energy
Waxes and amides melt at 70 to 145 °C, far below the processing temperature of any carrier. They do not need to be dispersed; they need to be distributed uniformly and then locked into the pellet. Consequently the screw design objective is maximum distributive mixing with minimum dispersive shear, and the target specific energy input is unusually low — typically 0.10 to 0.16 kWh/kg for a wax or amide masterbatch, compared with 0.22 to 0.30 kWh/kg for a carbon black concentrate.
This drives several concrete design decisions on a Kerke KTE-series co-rotating twin-screw line:
- Length-to-diameter ratio of 36 to 44 L/D for amide and wax systems. Shorter than 32 L/D leaves insufficient length for gentle melting, downstream addition and devolatilisation; longer than 48 L/D increases residence time unnecessarily and raises the risk of thermal loss of volatile amides.
- Two short kneading zones rather than one long one. The first, positioned around 8 to 12 L/D, melts the carrier using 45-degree forward kneading blocks. The second, around 20 to 24 L/D, distributes the additive using narrow-disc kneading blocks or toothed mixing elements. Avoid 90-degree neutral or reverse blocks except where a melt seal is required ahead of a vacuum vent.
- Downstream side-feeding of the lubricant. Feeding waxes and amides into the main hopper causes them to melt in the solids-conveying zone, coat the pellets, and produce feeder bridging and screw slippage. Introducing them through a twin-screw side feeder at 14 to 18 L/D — after the carrier is fully molten — is the correct practice and typically raises stable throughput by 20 percent or more.
- Vacuum devolatilisation at 26 to 32 L/D at 0.06 to 0.09 MPa absolute, to remove moisture, residual free fatty acid and low-boiling fractions that would otherwise cause pellet porosity and downstream screw slippage.
- Screw speed of 200 to 400 rpm. Lower than typical masterbatch practice, because tip speed governs shear heating and there is nothing to disperse. Many wax masterbatch programmes run best at 250 to 300 rpm on a 52 to 65 mm machine.
Barrel temperature profile design
The temperature profile for lubricant masterbatch is characteristically flat and cool, often with a deliberately cooled feed section and a slight downward taper towards the die. The purpose of the cool feed zone is to prevent premature melting of the additive in the hopper throat, which is the single most common cause of feed instability on these products.
| Barrel Zone | Function | PE-Wax MB on LDPE | Erucamide Slip MB on LLDPE | EBS MB on PA6 |
|---|---|---|---|---|
| Feed throat | Solids conveying, prevent bridging | Water-cooled, 25–40 °C | Water-cooled, 20–35 °C | Water-cooled, 30–45 °C |
| Zone 1–2 (4–8 L/D) | Pre-heat, softening | 130–150 °C | 140–160 °C | 200–230 °C |
| Zone 3–4 (8–14 L/D) | Melting, first kneading block | 160–175 °C | 170–185 °C | 240–255 °C |
| Zone 5 (side feed, 14–18 L/D) | Additive introduction | 160–170 °C | 165–178 °C | 235–250 °C |
| Zone 6–7 (18–26 L/D) | Distributive mixing | 155–168 °C | 160–175 °C | 235–248 °C |
| Zone 8 (vacuum vent, 26–32 L/D) | Devolatilisation | 150–165 °C | 158–170 °C | 230–245 °C |
| Zone 9 to die (32–40 L/D) | Pressure build, strand formation | 150–162 °C | 155–168 °C | 235–250 °C |
| Target melt temperature | Measured at die adapter | 165–180 °C | 172–190 °C | 245–262 °C |
| Screw speed | Co-rotating, 52–75 mm class | 250–350 rpm | 220–320 rpm | 300–450 rpm |
| Specific energy target | kWh per kg output | 0.10–0.15 | 0.10–0.14 | 0.18–0.24 |
Pelletising choice
Pelletising a lubricant masterbatch is harder than it appears because the product has low melt strength and a tacky, slippery surface. Water-cooled strand pelletising works well for EBS and stearate concentrates on engineering carriers, where melt strength is adequate. For wax-rich, low-viscosity formulations the strand will not survive the water bath, and die-face cutting is required. Kerke’s cutting-system portfolio covers water-cooled strand, air-cooled strand, air-cooled die-face hot cutting, water-ring die-face cutting, eccentric water-mist cutting and full underwater granulation, which allows the pelletising method to be matched to the formulation rather than forcing the formulation to suit a fixed pelletiser.
For very high wax content, water-ring or eccentric water-mist die-face cutting gives the best result: the pellet is cut while still soft and is chilled by a controlled water film rather than being immersed, avoiding both strand breakage and pellet agglomeration. Downstream, a vibrating dewatering unit plus a centrifugal dryer and a short fluidised-bed cooler prevents the classic problem of warm, waxy pellets fusing into blocks in the big bag.
Machine sizing guidance
| KTE Model Class | Screw Diameter | Typical L/D | Indicative Lubricant MB Output | Typical Role |
|---|---|---|---|---|
| KTE-16 / KTE-20 lab class | 16–20 mm | 40–48 | 1–10 kg/h | Formulation trials, phr ladder studies |
| KTE-36 class | 36 mm | 36–44 | 80–180 kg/h | Pilot scale, small-batch specialty grades |
| KTE-52 class | 52 mm | 36–44 | 250–500 kg/h | Mid-volume additive masterbatch |
| KTE-65 class | 65 mm | 36–44 | 450–900 kg/h | Standard commercial slip and wax MB |
| KTE-75 / KTE-95 class | 75–95 mm | 36–48 | 900–2,500 kg/h | High-volume commodity lubricant concentrates |
| KTE-135D class | 135 mm | 40–52 | 3,000 kg/h and above | Large-scale compounding and filler lines |
Output figures are indicative and depend heavily on formulation, additive concentration, carrier melt flow and pelletising method. Kerke’s practice is to run a formulation trial on a laboratory twin-screw extruder before committing to a production screw configuration, which is why lab machines remain a core part of the KTE range alongside production lines. For formulations that cannot be handled in a single pass — for example a very high wax content requiring exceptionally low melt temperature at the pelletiser — the KTE-SE double-stage mother-baby system decouples compounding from pressure generation, letting the first-stage twin screw mix at low pressure while a second-stage single screw builds die pressure at a lower melt temperature.
Application Guide by Downstream Process
The correct lubricant masterbatch is defined as much by the customer’s converting process as by the polymer, because each process imposes a different combination of shear rate, residence time, tooling geometry and surface requirement. The following breakdown covers the main conversion routes.
Blown and cast film
Film is the most lubricant-sensitive application because the product is thin, the surface-to-volume ratio is extreme, and downstream operations — printing, laminating, sealing, bagging — all interact with surface chemistry. Requirements typically split into slip, anti-block and melt-fracture control, and it is good practice to supply these as separate masterbatches rather than a single combination product, so that each can be dialled independently. Erucamide handles slip; synthetic silica or talc handles anti-block; PPA handles melt fracture. Overdosing any one of them degrades the others, and combining all three in a fixed-ratio single concentrate removes the formulator’s ability to optimise.
Where the film will be printed or laminated, migratory amide must be capped. Many converters specify a maximum of 0.06 to 0.10 phr erucamide in printed structures, and compensate for slip using an EBS or a small silicone addition on the non-print side of a coextruded structure. Coextrusion is in fact the elegant solution: put the slip agent only in the outer sealant layer where it is needed, and keep the print layer clean.
Pipe and profile extrusion
Rigid PVC pipe and window profile production is the classical lubricant-balancing application, and the dry-blend recipe usually contains three to five separate lubricants. The key process metric is fusion level, typically targeted at 60 to 75 percent gelation for pressure pipe and validated by the methylene chloride immersion test for PVC pipe or by differential scanning calorimetry. Too much external lubricant delays fusion, leaves unfused particles and produces brittle pipe; too little causes early fusion, high shear, HCl evolution and yellowing. Because the twin-screw extruders used for PVC pipe are usually conical or parallel counter-rotating rather than co-rotating, and residence time is long, thermal stability of the lubricant package is critical.
For polyolefin pipe, the lubricant requirement is much lower, but PE-RT and PE-100 pipe compounds still benefit from a small wax addition to reduce die pressure and eliminate die lines. Within the Wanplas group, Faygo supplies the pipe and profile extrusion lines that convert these compounds, while Kerke supplies the twin-screw compounding lines that produce them — the same lubricant logic runs across both stages.
Injection moulding
In injection moulding the lubricant does three jobs: it reduces injection pressure and fill time, it improves mould release, and in wear applications it lowers the in-service coefficient of friction. Thin-wall packaging with flow lengths exceeding 200 times wall thickness benefits substantially from an internal lubricant that lowers apparent viscosity in the high-shear gate region. Glass-filled engineering parts benefit from EBS or montan ester for release and from silicone for wear.
The main caution in injection moulding is weld line strength. Excessive lubricant concentrates at the flow front and therefore at the weld line, where it acts as a release agent between the two melt fronts and can reduce weld line tensile strength by 15 to 30 percent. In structural parts with knit lines, keep total lubricant at the minimum effective dose and prefer non-migrating chemistries.
Fibre and non-woven
Polypropylene fibre spinning at draw ratios above 1:4 and take-up speeds above 3,000 m/min demands exceptional melt cleanliness and consistent rheology. Lubricant masterbatch here is used sparingly, typically as a low dose of a highly refined EBS or a metallocene wax, because any particulate contamination or unmelted additive causes filament breaks at the spin pack. Kerke’s textile masterbatch application category addresses this segment through fine filtration, high L/D screw configurations and careful vacuum devolatilisation to keep the melt free of volatiles that would otherwise create voids in the filament.
Cable and wire
Cable jacket compounds, particularly halogen-free flame-retardant grades filled to 60 percent and above with aluminium trihydroxide or magnesium dihydroxide, rely heavily on lubricants for processability. The filler loading pushes viscosity so high that without a wax and stearate package the compound cannot be extruded at commercial line speeds. Silicone gum masterbatch is additionally used to lower the jacket’s external coefficient of friction so that installers can pull long cable runs through conduit with less tension. Because these compounds must also pass flammability testing, the lubricant must be chosen so that it does not degrade limiting oxygen index or produce excessive smoke.
Quality Control, Testing and Regulatory Compliance
A lubricant masterbatch is only as good as its consistency, because the downstream converter has no practical way to compensate for batch-to-batch variation in active content. A robust quality system rests on four pillars: incoming raw material control, in-process monitoring, finished-product testing and regulatory documentation.
Incoming and in-process control
Waxes should be checked for drop melting point, penetration hardness, acid value where oxidised, and colour. Amides should be checked for melting point, free amine content, iodine value in the case of unsaturated grades, and moisture. Metal stearates should be checked for metal content, free fatty acid, moisture and loss on drying, since stearates readily absorb water that later causes pellet porosity and screw slippage.
In process, the two most useful continuous signals on a KTE-series line are motor torque as a percentage of rated torque and melt pressure at the screen changer. A drifting torque signal at constant feed rate almost always indicates an additive feeding problem or a moisture excursion. Melt temperature measured with an immersion probe rather than a flush-mounted sensor gives a truer reading and should be trended, because a slow rise indicates screw wear or a fouled vacuum system.
Finished-product tests
| Test | Method Basis | What It Detects | Typical Acceptance Approach |
|---|---|---|---|
| Melt flow rate | ISO 1133 / ASTM D1238 | Active content drift, carrier degradation | Within a narrow band around the reference batch |
| Active content assay | Solvent extraction with gravimetric or FTIR finish | Dosing accuracy, feeder calibration error | Nominal plus or minus a defined tolerance |
| Ash content | ISO 3451 | Metal stearate and inorganic filler level | Calculated from formulation |
| Moisture | Karl Fischer or loss on drying | Pellet porosity risk, downstream voids | Low ppm target for engineering carriers |
| Coefficient of friction | ASTM D1894 | Functional slip performance after ageing | Measured on a standard let-down film after fixed ageing |
| Thermogravimetric analysis | ISO 11358 | Additive loss during compounding, onset of degradation | Compared with a reference curve |
| Differential scanning calorimetry | ISO 11357 | Additive melting endotherm, confirms identity and level | Peak position and enthalpy within range |
| Filter pressure value | Screen pack pressure rise per unit mass | Unmelted additive, gels, contamination | Below a defined threshold on a fixed mesh |
| Pellet bulk density and size | ISO 60 and sieve analysis | Feeding behaviour at the customer | Consistent with reference lot |
Regulatory framework
Lubricant additives sit inside several overlapping regulatory regimes, and the masterbatch producer is generally responsible for declaring compliance. RoHS restricts lead, cadmium, mercury and hexavalent chromium, which historically appeared in lead and cadmium soaps used as PVC lubricant-stabilisers; these are now largely eliminated in favour of calcium-zinc and organotin chemistries. REACH requires registration of substances above tonnage thresholds and imposes obligations regarding substances of very high concern; several fluorinated processing aids and certain fluorosurfactant residues are under active review, which is driving interest in non-fluorinated alternatives.
Food-contact applications add another layer. Positive lists govern which lubricants may be used and at what maximum level in materials intended for food contact, and overall and specific migration limits must be verified on the finished article rather than on the masterbatch. Erucamide, oleamide, EBS, calcium stearate and most PE waxes have well-established food-contact status in major jurisdictions, but the burden of proof rests on documenting the full formulation. Chinese national standards in the GB 4806 series set the corresponding requirements for the domestic market, and GB/T methods are commonly specified for testing.
Finally, some applications carry additional constraints: medical devices require biocompatibility assessment; toys are subject to restrictions on certain substances; and automotive interiors are subject to fogging and volatile organic compound emission limits, which directly constrain the use of volatile low-molecular-weight amides and paraffin waxes. Fogging testing is a routine reason for switching from oleamide to EBS or a high-molecular-weight montan ester in automotive compounds.
Troubleshooting Guide for Lubricant Masterbatch Users
Most lubricant-related field problems fall into a small number of recognisable patterns, and correct diagnosis usually depends on noting when the symptom appears relative to a change in dose, output or temperature. The table below maps the common symptoms to their probable causes and the corrective actions that experience shows to be most effective.
| Symptom | Most Likely Cause | Diagnostic Check | Corrective Action |
|---|---|---|---|
| Output surging, unstable amperage | External lubricant overdose causing screw slippage | Reduce let-down by half and observe within one residence time | Cut external lubricant, shift balance towards internal chemistry, cool feed throat |
| White waxy bead at die lips | Amide or paraffin exceeding solubility limit | Collect deposit, run DSC for melting endotherm | Reduce migratory lubricant, switch part of the dose to EBS, polish die land |
| Hard dark deposit at die, black specks | Stagnation and thermal degradation, insufficient release | Inspect die for scratches and dead zones; check melt temperature | Add or increase PPA or oxidised wax, re-polish tooling, lower melt temperature |
| Sharkskin at high line speed | Wall shear stress above critical value | Reduce output 20 percent; if defect clears, it is melt fracture | Introduce fluoropolymer PPA at 300–800 ppm active; allow conditioning time |
| PPA not working | Antagonism from anti-block or pigment, or insufficient conditioning | Check silica anti-block and TiO2 level; verify run time since clean start | Increase PPA 1.5–2x, reduce high-surface-area anti-block, extend conditioning |
| COF too high after 24 hours | Insufficient migration time or amide adsorbed on anti-block | Re-test at 72 hours and 7 days at controlled temperature | Increase erucamide modestly, switch to faster-migrating oleamide blend, or reduce silica |
| COF drops too low, rolls telescope | Slip overdose plus warm storage | Measure COF at core, mid and outer roll positions | Reduce dose to the knee of the curve, control warehouse temperature |
| Poor ink adhesion after printing | Migratory amide lowering surface energy after corona | Dyne test immediately after treatment and again after 7 days | Cap amide below 0.10 phr, move slip to sealant layer in coextrusion, use EBS |
| Weak heat seals | Lubricant bloom acting as a release layer at the seal interface | Wipe seal area with solvent and re-test seal strength | Reduce migratory slip in sealant layer, use non-migrating chemistry |
| Plate-out on calender or embossing rolls | Incompatible lubricant-stabiliser-filler combination | Single-variable elimination trials | Rebalance internal-external ratio, avoid mixing incompatible metal soaps at high dose |
| Brittle PVC pipe, poor impact | Under-fusion from excessive external lubricant | Methylene chloride immersion test or DSC gelation level | Reduce paraffin, increase internal lubricant, raise fusion zone temperature |
| Pellet blocking in the bag | Pellets packed warm, high wax content, tacky surface | Measure pellet temperature at bagging | Add fluidised-bed cooling, extend dryer residence, consider light anti-block dusting |
| Voids and porosity in pellets | Moisture or volatile fatty acid not removed | Check vacuum level and vent port for blockage | Restore vacuum to 0.06–0.09 MPa absolute, pre-dry additives, clean vent insert |
Frequently Asked Questions
What is the difference between a lubricant masterbatch and a processing aid masterbatch?
The terms overlap but are not identical. A lubricant masterbatch delivers wax, amide, stearate or silicone chemistry that changes bulk melt viscosity, metal release and surface friction. A processing aid masterbatch usually refers specifically to a fluoropolymer or acrylic product that works only at the die interface to suppress melt fracture and die build-up, without changing bulk rheology. In practice a converter may need both, and they are dosed at very different levels: lubricants at 0.1 to 1.0 phr of active, fluoropolymer processing aids at 300 to 800 ppm.
How do I convert a supplier’s recommended percentage into phr?
Multiply the masterbatch let-down percentage by the masterbatch active concentration. A 3 percent let-down of a 10 percent concentrate delivers 0.30 percent active, which for practical purposes equals 0.30 phr in an unfilled compound. In a filled compound, phr is conventionally referenced to 100 parts of resin only, so a compound containing 60 parts filler per 100 parts resin will show a different active-on-total-compound figure. Always state the basis explicitly in specifications to prevent misunderstanding.
Will a lubricant masterbatch reduce the mechanical properties of my part?
At correct dosage the effect is small, generally within a few percent on tensile strength and modulus. At overdose the effect can be substantial: internal lubricants act as plasticisers and reduce modulus and heat deflection temperature, while migratory external lubricants concentrate at weld lines and can reduce weld line strength by 15 to 30 percent. Structural parts with knit lines should use the minimum effective dose of a non-migrating chemistry such as EBS or high-molecular-weight silicone.
Can I use the same lubricant masterbatch for polyethylene and polypropylene?
Sometimes, but it is not ideal. A polyethylene-carried masterbatch will disperse in polypropylene because both are polyolefins, but the PE phase reduces clarity, slightly lowers stiffness and can create gels in thin PP film. For transparent or thin-wall PP, use a PP-carried product. For opaque, thick-wall or non-critical PP parts, a PE-carried universal product is usually acceptable. Note also that erucamide migrates faster in PE than in the more crystalline PP, so the same phr gives different COF development kinetics.
Why does my slip masterbatch work in summer but not in winter?
Because migration is thermally activated. Amide diffusion to the film surface roughly follows an Arrhenius relationship, so a warehouse at 30 °C will develop the target coefficient of friction in a day or two, while the same film at 10 °C may take a week or more. Converters who test COF at a fixed 24-hour interval will therefore see seasonal variation that has nothing to do with the masterbatch. The fix is to standardise the ageing condition — for example 40 °C for 24 hours — rather than to change the formulation twice a year.
Do lubricants interfere with flame retardants, antistats or UV stabilisers?
They can. Migratory lubricants compete with migratory antistats such as glycerol monostearate for surface sites, so a formulation containing both may deliver neither at full effectiveness. In flame-retardant compounds, hydrocarbon waxes add fuel and can lower the limiting oxygen index by a point or more if used generously, so the dose must be optimised against the flammability rating rather than against processability alone. Hindered amine light stabilisers can interact with acidic species from oxidised waxes and certain metal soaps. Always validate the full formulation rather than testing additives in isolation.
What screw configuration change gives the biggest improvement in lubricant masterbatch quality?
Moving the lubricant from the main hopper to a downstream side feeder positioned after the melting zone. This single change eliminates the coating of solid pellets that causes feeder bridging and screw slippage, allows the carrier to melt under normal conditions, and typically increases stable throughput by 20 percent or more while improving distribution uniformity. The second most valuable change is replacing aggressive 90-degree kneading blocks with narrow-disc distributive elements or toothed mixing elements.
Is silicone masterbatch worth the higher cost compared with amide slip?
It depends on the requirement. For simple bag-opening slip in commodity film, erucamide at a fraction of the relative cost delivers the needed coefficient of friction, and silicone would be over-specification. For wear-critical parts, cable jackets that must be pulled through conduit, automotive interiors that must resist scratching, or any application where migration and surface contamination are unacceptable, silicone gum masterbatch offers a durable, non-migrating performance level that amides cannot match. The cost premium is justified where the failure mode being prevented is expensive.
How should lubricant masterbatch be stored?
In sealed moisture-barrier packaging, below 30 °C, away from direct sunlight and heat sources, and used within the supplier’s stated shelf life. Amide-containing products are the most sensitive: storage above 40 °C accelerates surface blooming inside the bag, produces a white dusty coating on the pellets, and can cause blocking. Stearate-containing products absorb atmospheric moisture readily and should be re-dried if the bag has been open. Always condition pallets to workshop temperature before opening to avoid condensation on cold pellets.
Can lubricant masterbatch help with recycled material processing?
Yes, and it is one of the fastest-growing applications. Post-consumer recyclate typically has a broadened molecular weight distribution, chain scission from previous heat histories, contamination from labels and adhesives, and cross-contamination between polymer types. The result is inconsistent melt viscosity, poor surface finish and elevated die build-up. A combined internal-external lubricant package stabilises the process window, reduces melt temperature and therefore further degradation, and suppresses the drool that contamination promotes. Within the Wanplas group, Polyretec supplies the washing and recycling front end while Kerke supplies the twin-screw pelletising lines where these lubricant packages are introduced.
Conclusion
Lubricant masterbatch rewards precision. The additive families are well understood, the mechanisms are well characterised, and the dosage windows are narrow enough that a factor-of-two error transforms a benefit into a defect. The disciplined approach is to start from the function required — viscosity reduction, metal release, or in-service slip — rather than from a product name; to select chemistry by internal-external balance and thermal stability; to match the carrier resin and its melt flow index to the base polymer; to express dosage in phr of active and to map the dose-response curve rather than accepting a supplier’s default; and to validate the full formulation for printability, sealing, weld line strength and regulatory compliance before scale-up.
On the production side, the message is equally clear. A lubricant masterbatch is not a colour concentrate, and applying pigment-dispersion screw logic to a wax system produces slippage, volatilisation and poor distribution. Low specific energy input, a flat and cool barrel profile, downstream side feeding of the additive, gentle distributive mixing elements, effective vacuum devolatilisation and a pelletising method matched to the melt strength of the formulation are the six decisions that separate a stable, high-yield line from a troublesome one.
Kerke, a Wanplas factory with over twelve years of specialisation in parallel co-rotating twin-screw compounding and more than 2,000 machines running in over 70 countries, builds the KTE-series lines that masterbatch producers use for exactly this class of work — from KTE-16 laboratory machines used to run phr ladder trials, through KTE-52 and KTE-65 production lines, to KTE-135D large-scale compounding systems and KTE-SE double-stage mother-baby configurations for heat-sensitive formulations. Backed by the Wanplas brand’s shared engineering standards, open-factory policy, annual free spare-parts allowance and global service network, Kerke supports customers from formulation trial through commissioning and long-term production optimisation. If you are developing a lubricant masterbatch programme in 2026, begin with a laboratory-scale dose-response study, define your acceptance tests before you scale, and specify the compounding line around the additive you actually need to deliver.
