Internal Mold Release Agents: 5 Chemical Classes, Dosage and Selection

Internal mold release agents are additives compounded into the plastic itself, which migrate to the part surface during molding and lower the adhesion between part and tool, so the part ejects without anything being sprayed on the mold. That makes them a formulation decision rather than a shop-floor one, so which chemistry belongs in which polymer, and at what level?

Internal release agents are one of the few plastic additives whose job is finished the moment the part leaves the tool: the additive front-loads its whole function into the seconds between mold closing and ejection, then matters again only if the surface has to be painted, printed, plated or welded.

The chemistry comes from 5 classes, metal stearates, fatty acid esters, amide waxes, polyolefin and montan waxes, and silicones; the right one depends on the polymer, the temperature and what the surface must do afterward. Dosage runs from about 0.05 wt% in PE film up to 3 parts in ABS, overdosing causes plate-out or bonding failures, and food-contact grades are checked against both EU 10/2011 and US 21 CFR, with a short list of producers, led by Baerlocher and Peter Greven, supplying most named grades.

• 5 chemical classes are used as internal mold release agents: metal stearates, fatty acid esters, amide waxes, polyolefin and montan waxes, and silicones.
• 0.5 wt% is the maximum PETS content the FDA allows in the finished resin of food-contact polycarbonate, under 21 CFR 177.1580.
• 1 wt% calcium stearate, used as a demolding agent, eliminated stuck and broken parts in injection-molded PLA (Tábi and Pölöskei, 2021).
• About 120 °C is the melting point of zinc stearate, the reason it spreads evenly across a hot mold surface.

What Is an Internal Mold Release Agent?#

An internal mold release agent is a plastics additive, not a mold coating: it is dosed into the compound or added as masterbatch, and it does its work from inside the part. It belongs to the internal branch of the release-agent taxonomy alongside metal stearates, PETS, amide waxes, montan esters and silicone masterbatch, a group that sits opposite the external, applied-to-the-tool chemistries. Internal mould release, the spelling used outside North America, describes the same additive class. External release agents, by contrast, are process chemicals rather than plastics additives on this site: they are covered only where they are used to mold plastic parts, never for concrete, bakery or die-casting release.

The hub on mold release agents for plastics and composites covers the compounded and the applied route side by side, and this page stays inside the compounded, internal half of that taxonomy.

How does an internal mold release agent work?#

An internal mold release agent works by blooming: it is deliberately formulated to sit above its solubility limit in the cooling polymer, so it diffuses out of the bulk, reaches the skin of the part and forms a thin, low-adhesion layer between the polymer and the hot steel. The rate is set by the additive's diffusion coefficient in the host resin, with molecular weight, the solubility-parameter match and loading as the main levers (Nouman and co-workers, Polymer Degradation and Stability, 2017). The physics of blooming and exudation in plastics decides how fast the layer forms.

The release layer forms in 4 steps.

1. Dissolve the additive into the melt during compounding, above its equilibrium solubility at mold temperature.
2. Contact the tool surface as the melt fills the cavity and cools against the steel.
3. Diffuse the additive toward the part-tool interface as the polymer solidifies.
4. Wet the metal with the additive's polar head, forming the low-energy film that lets the part separate cleanly.

Zinc stearate is the clearest example: it melts at about 120 °C (Baerlocher; PubChem 130 °C pure, Struktol 115 to 125 °C, Greven 118 to 122 °C), well below most thermoset mold temperatures, so it spreads and reaches the interface fast. Rabinovitch, Lacatus and Summers, Journal of Vinyl Technology, 1984, showed the polar carboxylate end of a soap such as calcium stearate wets hot metal preferentially, which is what "metal release" means; their paper argues the plain internal-versus-external label is deficient, since it describes where a substance acts, not how well it releases.

Internal vs external mold release: which one do you need?#

Internal release suits long production runs of one compound, because the release chemistry travels with the material and no operator has to spray the tool between cycles, while external release stays the better answer for short runs, frequent material changes and tools that are hard to fill. Internal release cannot be dialled back between shots: once it is compounded in, it is in every part, including the surfaces that later have to be painted, printed, plated or welded.

External types split into sacrificial systems, which are reapplied every cycle, and semi-permanent, bonded-film systems that survive several releases per application, carried in water, solvent or co-solvent bases. Silicone release emulsions and sprays sold as mixtures also carry a compliance date that internal release does not: the D4, D5 and D6 residual cyclosiloxanes they contain face the REACH Annex XVII entry 70 limit of 0.1 % by weight after 6 June 2026, which is set out in full on silicone mold release agents.

Can internal and external release agents be used together?#

Yes: many molders run a low internal level for baseline release and keep a semi-permanent external coating for the difficult areas of the tool, which is also the usual way to reduce, rather than remove, spraying. This combination is common shop-floor practice; our source library holds no quantitative study of how internal and external release perform together, so the combined effect is not established as a measured result and should be treated as a starting point for trials, not a specification.

What Are the 5 Chemical Classes of Internal Mold Release Agents?#

The 5 chemical classes used as internal mold release agents are metal stearates, fatty acid esters, amide waxes, polyolefin and montan waxes, and silicones, with metal stearates and fatty acid esters carrying most of the volume in thermoplastics.

Melting and dropping points are grade-dependent; the range given is the span across PubChem and the Struktol, Baerlocher and Greven data sheets in our source library.

1. Metal stearates (zinc, calcium and magnesium stearate)#

Metal stearates are the salts of stearic acid with zinc, calcium or magnesium, and they release because the polar carboxylate end wets hot steel while the two C18 chains stay with the polymer. They reach the market through 4 production routes, precipitation, direct conversion, the melt process and the continuous COAD process (Peter Greven).

Zinc stearate is the workhorse of SMC/BMC and polystyrene, used at a general level of about 0.5 % (Struktol); its lower melting point of about 120 °C, against 140 to 165 °C for commercial calcium stearate, makes it the preferred SMC/BMC release agent, and finer, precipitated grades release better still (Peter Greven, whose Brookfield test at 1.23 wt% showed coarser grades raise paste viscosity less while finer grades reach the same release at a lower dose, a test condition, not a dosage). Calcium stearate doubles as a polyolefin acid scavenger at 0.05 to 0.20 % and a PVC co-stabilizer; magnesium stearate, the ABS and polyamide option, runs at 0.3 to 3 parts in ABS, where it also dusts against surface adhesion.

Production routes, metal contents and the filter index for all metal stearates are compared in full on the family page, and zinc stearate carries the complete identity and regulatory record for the single most used grade in this class.

2. Fatty acid esters (PETS, GMS, EGDS, stearyl stearate and montan esters)#

Fatty acid esters are the release chemistry of choice in engineering thermoplastics, because a high-molecular-weight, low-polarity ester such as pentaerythritol tetrastearate blooms to the mold interface without clouding a transparent part. PETS, CAS 115-83-3, EC 204-110-1, C77H148O8, 1202.0 g/mol, is the flagship internal release agent for polycarbonate, cleared in the US under 21 CFR 177.1580 "for use only as a mold release agent," at not more than 0.5 percent of the finished resin, and listed in the EU under FCM 880, fatty acid (C8 to C22) esters with pentaerythritol. That 0.5 wt% figure is an FDA maximum use level, not a dosage, and 416 of 416 classification and labelling notifications for PETS report it as not classified.

Glycerol monostearate, a 40 to 45 % monoglyceride grade, melts at 58 to 60 °C and runs at 0.15 % in LDPE, 0.3 % in HDPE and 0.05 to 0.5 % in PP. Ethylene glycol distearate, CAS 627-83-8, has a dropping point of 63 to 73 °C; stearyl stearate, CAS 2778-96-3, is a waxy lubricant ester used the same way. Montan esters come from Gersthofen oxidative refining of montan wax to montanic acids, then partial esterification with ethylene glycol or 1,3-butanediol, optionally calcium-neutralized; 21 CFR 178.3770 sets a dropping point of 76 to 105 °C, and Peter Greven, holder of FCN 001963, also markets them as processing aids in PET and PBT.

The whole class of ester lubricants is compared by melting range and polarity on its family page, and pentaerythritol tetrastearate (PETS) is the reference internal release agent for polycarbonate.

3. Amide waxes (EBS, EBO, oleamide and stearamide)#

Amide waxes cross the line from slip additive to release agent at the dosage threshold: oleamide is a slip agent at about 0.05 % in film, and a mold release agent above 0.5 %. Ethylene bis stearamide, CAS 110-30-5, EC 203-755-6, 593.0 g/mol, is a bis-amide acting mainly at the melt-metal and particle interfaces, functioning as an internal and external lubricant, dispersant, release agent and antiblock agent, though not as a film slip agent. It melts at 135 to 146 °C (PubChem) or 138 to 144 °C (Baerlocher); the EBS-replacement blend Struktol TR 251 runs at 0.5 to 2.0 % in ABS, PVC and PS. EBS carries EU FCM 250, no specific migration limit, and falls under 21 CFR 178.3860 in the US, also appearing as N,N'-distearoylethylenediamine in 175.105 and 176.170/176.210.

Oleamide, CAS 301-02-0, FCM 335, is used at about 0.05 % in film as a slip agent and above 0.5 % for mold release (Struktol TR 121). It must never be described as cleared under 178.3860: that section names erucamide, oleyl palmitamide, stearyl erucamide and the saturated fatty acid amides, and oleamide appears only in 175.105 (adhesives) and 178.3910 (metallic food-contact articles). Stearamide, CAS 124-26-5, FCM 306, is a slower-migrating slip, antiblock and release agent by comparison.

Ethylene bis stearamide (EBS) is the reference amide wax for ABS and PS; the bloom rate that makes oleamide a slip agent at 0.05 % is on its substance page.

4. Polyolefin, paraffin and montan waxes#

Waxes release by forming a low-energy film at the melt-metal interface, and their molecular weight decides whether they stay in the part or wander out of it. Polyethylene wax averages up to 10,000 g/mol, while paraffin and Fischer-Tropsch waxes sit much lower, at 200 to 1,000 g/mol, and these lower grades tend to exacerbate die drool (Mhlabeni, Jamiru and Mhike, 2024); Fischer-Tropsch wax comes mainly from Sasol in South Africa. Oxidized polyethylene wax, CAS 68441-17-8, the strongest metal-release wax per phr here, runs at just 0.07 to 0.3 phr in PVC, carries EU FCM 811 (SML 60 mg/kg) and clears US 21 CFR 177.1620 (Mn at least 1,200). Montan wax, CAS 8002-53-7, a lignite extract from Amsdorf, Germany, Ione, California, and Yunnan and Jilin, China, is 62 to 68 % long-chain esters, 22 to 26 % acids and 7 to 15 % alcohols and hydrocarbons, melts at 82 to 95 °C, and carries EU FCM 529 (crude wax) and FCM 67 (esters).

Polar, oxidized waxes give the strongest metal release at the lowest dosage; non-polar paraffin does not wet the metal at all and, in PVC, works mainly by fluidising the calcium stearate layer (Rabinovitch, Lacatus and Summers, 1984).

Molecular weights and dropping points for all polymer waxes are compared on the family page, and montan wax and its Gersthofen-refined esters carry the FCM 67 and 178.3770 entries in full.

5. Silicones (PDMS and silicone masterbatch)#

Silicones give the lowest surface energy of any release chemistry, which is why polydimethylsiloxane appears both as a mold spray and as a compounded masterbatch additive. PDMS, CAS 63148-62-9, forms a low-surface-energy siloxane film at the melt-metal interface; besides external release oils, it serves as a slip and lubricant additive in masterbatch and as the basis of silicone-type, PFAS-free processing aids. EU 10/2011 lists it under FCM 575 (above 6,800 Da, viscosity at 25 °C at least 100 cSt), and 21 CFR 177.1520 clears polyoxyethylene-grafted PDMS, CAS 68937-54-2, at up to 0.3 wt% as an extrusion aid.

The restriction that matters here targets residual cyclic siloxanes, not the polymer: D4, D5 and D6 sit on the SVHC Candidate List as PBT/vPvB substances and are restricted under REACH Annex XVII entry 70, as amended by Regulation (EU) 2024/1328, at 0.1 % by weight after 6 June 2026. That limit applies to D4, D5 and D6 themselves; it does not make silicone release chemistry banned. Residual limits are set out on polydimethylsiloxane (silicone oil).

Which Internal Mold Release Agent Suits Each Polymer?#

The right internal mold release agent depends on the processing temperature, on whether the part must stay transparent and on what happens to its surface afterward: high-melting esters and bis-amides for engineering plastics, metal stearates for thermosets and styrenics, and low-melting waxes only where the melt never gets hot enough to volatilise them.

Supplier data-sheet ranges and published studies. FDA figures are legal maximum use levels, not dosages. Trials decide the final level.

Buyers who want this as a one-page reference can request quotes and download the gated Internal Mold Release Selection Chart below.

Polycarbonate and PC/ABS#

Polycarbonate is the clearest case in the whole family: pentaerythritol tetrastearate is the standard internal release agent for it, and US food-contact PC may contain no more than 0.5 percent of it. That 0.5 % figure is the limit set by 21 CFR 177.1580 for food-contact resin; it is not a technical ceiling for non-food-contact polycarbonate, which can be formulated differently. The EU route runs through FCM 880, and Peter Greven's FCN 001963 covers the saturated pentaerythritol esters used in this role.

The full PC package is covered on additives for polycarbonate.

ABS, SAN and polystyrene#

Styrenics run on metal stearates and bis-amides: magnesium stearate at 0.3 to 3 parts in ABS, zinc stearate in polystyrene and EPS, and ethylene bis stearamide wherever pigment dispersion has to improve at the same time. Baerlocher's CEASIT grades serve polyamide and SAN, its ZINCUM PS and ZINCUM TX grades serve polystyrene and EPS, and the EBS-replacement blend runs at 0.5 to 2.0 % across ABS, PVC and PS.

Dispersion and lubricant choices for styrenics are covered on additives for ABS, SAN and ASA, and magnesium stearate also serves as a dusting agent against surface adhesion in ABS.

Polyamide (nylon)#

Polyamide compounds use montan esters and metal stearates, because a release additive for nylon has to survive melt temperatures where a paraffin wax would simply boil off. Polyamide compounding draws on montan esters, calcium and magnesium stearate, EBS and special esters, and Struktol TR 063A, dosed at 0.2 to 2.0 %, reduces die bearding and drool during compounding. Montan esters keep their dropping point of 76 to 105 °C, the same specification set by 21 CFR 178.3770 that applies to their use in PVC.

Heat-stable release and lubricant choices are covered on additives for nylon (polyamide).

PET and PBT#

PET and PBT use the same pentaerythritol and montan ester chemistry as polycarbonate, mainly as processing aids that also improve release. Peter Greven markets pentaerythritol esters as processing aids in PET and PBT, and montan esters serve the same dual role. No dosage for PET or PBT release additives is established in our source library, so the chemistry is named here without a number.

Processing-aid practice for polyester is covered on additives for PET resin.

PLA and bio-based polymers#

PLA is the polymer with the clearest published number: Tábi and Pölöskei found in 2021 that 1 wt% calcium stearate as a demolding agent removed the stuck and broken parts from injection-molded PLA. The study, published in Periodica Polytechnica Mechanical Engineering by researchers at the Budapest University of Technology and Economics, gives PLA processors the one dosage in this whole family that comes from a peer-reviewed molding trial rather than a supplier data sheet.

The whole PLA package is covered on additives for PLA, and calcium stearate is also the acid scavenger of most polyolefin compounds.

Polyolefins: PP, PE and filled masterbatch#

Polyolefins rarely need a dedicated release agent, so the release function is usually carried by an additive already in the formulation: a fatty acid amide, a glycerol ester or the acid scavenger itself. Oleamide crosses from slip agent to release agent above 0.5 %, against about 0.05 % for film slip; glycerol monostearate runs at 0.15 % in LDPE, 0.3 % in HDPE and 0.05 to 0.5 % in PP. In a 60 wt% calcium carbonate LLDPE masterbatch, Radebe, Wesley-Smith, Focke and Ramjee, University of Pretoria, 2022, showed 3 wt% wax plus 1.0 wt% zinc stearate brought melt viscosity back to just above the neat polymer, against roughly 3 times higher without it. One supplier, Kisuma, reports calcium stearate in PP raffia and BOPP can impair metallization through hygroscopic calcium chloride formation, a supplier claim, not a verified result.

Where the amide is a slip agent rather than a release agent is set out on slip additives for plastic film, and most molders add internal release as a masterbatch rather than as raw powder.

Thermosets: SMC, BMC and unsaturated polyester#

Sheet and bulk molding compounds are where internal release is standard rather than optional: zinc stearate is the preferred choice, because its lower melting point lets it spread and migrate to the surface of the pressed part. Calcium stearate is also used. At the same dosage, coarser stearate grades raise paste viscosity less, while finer grades reach the same release effect at a lower dosage, the trade-off Peter Greven measured in a Brookfield viscosity test at 1.23 wt%, a test condition rather than a recommended dosage.

Fiberglass, epoxy and SMC/BMC practice is covered on mold release agents for composites.

How Much Internal Mold Release Agent Does a Compound Need?#

Internal mold release agents sit in the 0.05 to 3 percent band, with most thermoplastic compounds between 0.1 and 1 wt%, and the level is set by the surface area of the part, the draft of the tool, the processing temperature and what has to happen to the surface afterward. That 0.05 to 3 % span is the range of the named sourced values in this family, from glycerol monostearate at 0.05 % in PP up to magnesium stearate at 3 parts in ABS, not a published industry-wide figure.

• Surface area of the part governs how much release chemistry must reach the skin per unit of resin.
• Draft angle on the tool sets how much mechanical help ejection already has.
• Processing temperature decides which class survives; a paraffin wax that works in PVC would boil off in polyamide.
• Post-mold operations, painting, printing, plating or welding, push formulators toward the lowest level that still ejects cleanly.

Plastics additive dosage bands generally span ppm-level stabilizers, 0.05 to 1 % for most stabilizer packages, 1 to 10 phr for PVC stabilizers, and 10 to 70 % for plasticizers; internal release sits at the low end. A typical release masterbatch carries 40 to 65 wt% active content, let down at 1 to 5 % (25 kg per tonne of resin equals a 2.5 % let-down); wt% equals phr of the ingredient divided by total phr, times 100.

A worked example: a 20 wt% zinc stearate masterbatch let down at 2.5 % (39:1, base resin to masterbatch) delivers 0.20 times 2.5 %, or 0.5 wt% zinc stearate in the part, a calculation, not a supplier product; check it against the let-down ratio calculator. Dosage bands for every family are compared under additive dosage levels in plastics.

What Are the Side Effects of Internal Mold Release Agents?#

Internal release agents cause paint, print, plating and weld problems because the same mechanism that frees the part also puts a low-energy film exactly where those secondary operations need to bond. Every internal mold release agent works by coming to the surface, so it inevitably puts that low-adhesion film on faces that later have to accept paint, print, adhesive, plating or a weld line.

Blooming that goes wrong is driven by overdosing, poor solubility and a low-molecular-weight grade, and the fixes run the same three levers in reverse: an oligomeric or higher-molecular-weight grade, a better solubility-parameter match, or a lower loading. Plate-out in PVC comes from over-lubrication, an incompatible external lubricant, metal-soap reaction products, or pigment and filler fines, and the standard fixes are a rebalanced lubricant package, a low-plate-out one-pack formulation or an acrylic processing aid. Low-molecular-weight waxes tend to exacerbate die drool, and metallic stearates in Ziegler-Natta polyolefins are named among the contributors. In BOPP film, calcium stearate migration is reported by a supplier, Kisuma, to impair metallization; this remains a supplier claim rather than a sourced-verified result. Compounds destined for painted, printed, plated or welded parts should be trialled at the lowest release level that still ejects cleanly.

Over-lubrication and its deposits are covered under plate-out in PVC processing, and how fast an additive reaches the surface in the first place is modelled under additive migration in plastics.

How Is Internal Mold Release Performance Tested and Controlled?#

Internal release is judged by coefficient of friction, dropping or melting point, torque rheometry and, for fibre grades, filter index, because no single standard measures mold release directly. The property is controlled indirectly, through 4 measures.

• Coefficient of friction, to ASTM D1894-24 and ISO 8295, tracks how the surface behaves once the additive has bloomed; because amides and stearates bloom over time, results depend on how long after production the part is tested.
• Dropping or melting point of the incoming additive, to ASTM D566, is the specification cited directly in 21 CFR 178.3770 for montan esters.
• Torque rheometry tracks lubricant and processing-aid behaviour; Ampacet's polyolefin method runs at 45 g, 90 rpm and 190 °C, looking for a stable plateau by 13 minutes and degradation onset by 27.5 minutes.
• Filter index, in bar/kg, is the incoming-goods specification for stearates in PP fibre and film grades.

No ejection-force or release-force test standard is established in our source library, and none should be invented. Ejection force is measured on the molder's own tool, and the acceptance criterion is a production specification, not a published standard.

ASTM D1894 and the bloom-time caveat are explained under coefficient of friction, and compound consistency during processing is tracked with melt flow rate.

Which Internal Mold Release Agents Are Allowed in Food-Contact Plastics?#

In the EU, a release agent must be on the Union list under Regulation (EU) No 10/2011; in the US, it must be cleared in the relevant section of 21 CFR; and the two systems limit the same chemistry in different ways: the EU caps what migrates into food, the US caps how much goes into the polymer. A food-contact part may only carry release agents that clear one of these two systems, and the limits are never interchangeable between them.

EU 10/2011: FCM numbers and migration limits#

Zinc stearate shows how the EU system works for a metal soap: the soap itself carries no FCM number, so it is authorised as a salt of stearic acid (FCM 106), and what is actually limited is the zinc, at 5 mg/kg of food under Annex II since Regulation (EU) 2020/1245. The same logic covers calcium and magnesium stearate, all salts of the authorised stearic acid (FCM 106, ref 24550 monomer / 89040 additive) under Article 6(3)(a), with Annex II metal limits of 5 mg/kg zinc, 1 mg/kg aluminium and 0.6 mg/kg lithium, and none for calcium, magnesium, sodium or potassium. The regulation's generic specific migration limit is 60 mg/kg; its overall migration limit is 10 mg/dm².

FDA figures are maximum use levels, not recommended dosages. Check the food type and condition of use in the cited section. 21 CFR 184.1229 prints the calcium stearate CAS number as 1529-23-0; the correct number is 1592-23-0, and the CFR text contains a digit transposition.

How FCM numbers, specific migration limits and the overall migration limit work is explained in full on EU 10/2011.

US 21 CFR: the release-agent and lubricant sections#

The US route runs through 4 parts of 21 CFR, and which one applies depends on what the additive is, not what it does: 178.3860 for release agents generally, 177.1580 for polycarbonate, 178.3770 for montan esters in PVC, and the GRAS sections of Parts 182 and 184 for the metal stearates.

• 178.3860: release agents for polymeric resins, erucamide, oleyl palmitamide, stearyl erucamide, the saturated fatty acid amides, plus rice bran wax (up to 1.0 %, dry foods) and N,N'-dioleoylethylenediamine (up to 0.055 mg per square inch, PVC film).
• 177.1580: PETS for use only as a mold release agent in polycarbonate, up to 0.5 percent of the finished resin.
• 178.3770: montan wax esters as PVC lubricants, dropping point 76 to 105 °C.
• Part 184 GRAS listings: 184.1229 calcium stearate, 182.8994 zinc stearate, 184.1440 magnesium stearate, 184.1090 stearic acid, 184.1324 glycerol monostearate.
• 181.29: prior-sanctioned calcium, magnesium, aluminium and sodium stearates.

A GRAS listing is never "FDA approved": it is a listing under a named section, subject to that section's conditions. Food types and conditions of use are decoded on FDA food contact rules for plastic additives.

Who Supplies Internal Mold Release Agents?#

Internal mold release agents come from a short list of specialist producers, usually as part of a wider lubricant or metal-soap portfolio. Baerlocher, in Unterschleissheim near Munich, employs about 1,150 people and is family-owned for more than 200 years; Peter Greven, also in Germany, holds FDA FCN 001963. Croda's performance technologies business moved to Cargill in July 2022 for about GBP 667 million, and Fine Organics, in Mumbai, an oleochemical producer since 1971 with more than 450 products, acquired US plant land in July 2025. Named release grades include LIGASTAR CA, ZN and MG 700 (Greven), Kemamide W-39/W-40 (PMC), Advawax 280 (Croda) and Baerolub L-AK (Baerlocher).

Buyers should compare grades by CAS number, metal content and melting range, not by trade name, since several producers sell chemically equivalent grades under different brand names. Plants, grades and certifications are in the directory of calcium and zinc stearate manufacturers, and one request through the plastic additive supplier finder reaches several release-additive suppliers at once.

Request quotes for internal mold release additives: substance or CAS number, polymer, volume and country.

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What Else Sits Next to Internal Mold Release in a Formulation?#

Almost every internal mold release agent has a second job in the formulation, which is why the same CAS number turns up on our lubricant, slip agent and acid scavenger pages. Calcium and zinc stearate are lubricant, acid scavenger, PVC co-stabilizer and release agent at once; EBS is lubricant, dispersant, antiblock and release agent; and GMS is both a PVC internal lubricant and a polyolefin antistat. The same substances appear under processing lubricants for plastics in their friction-reducing role.

External release agents applied to the mold#

External release agents are sprayed, wiped or bonded onto the tool rather than compounded into the resin, which makes them process chemicals: this site covers them only where they are used to mold plastics. They split into sacrificial types, reapplied every cycle, and semi-permanent types, which give several releases per application from a bonded film, carried in water, solvent or co-solvent bases. Concrete, plaster, bakery, die-casting and asphalt release fall outside this site's scope entirely.

Sprays, semi-permanent coatings and cycle practice are covered on mold release agents for injection molding.

Lubricants, slip agents and anti-scratch additives compared#

A lubricant is defined by where it reduces friction, a slip agent by the surface friction of finished film, and a release agent by whether the part leaves the tool, which is why one substance can be all three at different loadings. Baerlocher defines internal lubricants as additives that reduce the frictional forces between polymer chains and lower melt viscosity, external lubricants as additives that reduce the adhesion between the polymer and metal surfaces, and combined lubricants as additives that do both. Oleamide again shows the pattern: it is a slip agent at about 0.05 % and a release agent above 0.5 %.

Surface additives with a different target are compared under anti-scratch additives for plastics.

Is zinc stearate a mold release agent?#

Yes: zinc stearate is used both as a dry-powder spray on the tool and as an internal release agent compounded into the part, and it is the preferred internal release agent for SMC and BMC because its melting point of about 120 °C lets it spread and migrate evenly. Both routes rely on the same wetting mechanism at the metal surface.

What are mold release agents made of?#

Mold release agents are made from waxes, fatty esters, silicones and metallic soaps, and the internal types used as plastics additives add the amide waxes to that list. That 5-class list, metal stearates, fatty acid esters, amide waxes, polyolefin and montan waxes and silicones, is the internal branch of a wider taxonomy that also includes purely external systems.

Does WD-40 work as a mold release?#

WD-40, petroleum jelly and cooking spray belong to the external, applied-to-the-tool side of the question and are not plastics additives, so this page does not cover them. Whether any of these household products performs as a release agent is not established in our source library, so no verdict is given here; readers looking for the applied-to-the-tool route should start at the mold release agents hub.

Is an internal mold release agent the same as an internal lubricant?#

No: an internal lubricant reduces friction between the polymer chains and lowers melt viscosity, while an internal mold release agent has to reach the part surface, so the two roles ask for opposite compatibility with the polymer. A good internal lubricant stays miscible with the melt throughout processing; a good internal mold release agent is deliberately formulated to become immiscible enough to bloom out.

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Every figure on this page is checked against primary sources; see our methodology and fact-checking(/methodology/) process.