Zinc Stearate: Properties, Uses in Plastics and Regulatory Status

Zinc stearate (zinc distearate, CAS 557-05-1) is a metal soap used in plastics as an external lubricant, an internal mold release agent, a dispersion aid for pigments and fillers, an acid scavenger and the zinc half of calcium-zinc PVC stabilizers. One white powder does five different jobs, and the reason is a single number: it melts at about 120 °C (248 °F) according to Baerlocher, roughly 40 °C below calcium stearate. Its molecular formula is C36H70O4Zn, its molecular weight 632.3 g/mol and its EC number 209-151-9.

In the European Union the substance carries no food-contact number of its own: Article 6(3)(a) of Regulation (EU) No 10/2011 covers it as a salt of authorised stearic acid, FCM substance 106, and the Annex II limit for zinc of 5 mg/kg applies to the finished article since Regulation (EU) 2020/1245 lowered it from 25 mg/kg. In the United States it is listed as generally recognised as safe under 21 CFR 182.8994, and it is absent from the REACH Candidate List of Substances of Very High Concern as of 22 September 2026. Zinc stearate is one of 437 substance profiles in our directory of plastic additives, each with the same identity, dosage and regulatory fields.

Everything below follows from that melting point: the production routes, the five functions, the dosage per polymer, the failure modes of over-lubrication and zinc burning, the regulatory matrix, the comparison with calcium and magnesium stearate, and the three producers whose data sheets this page draws on.

What Is Zinc Stearate?#

Zinc stearate is the zinc salt of stearic acid, a metal soap in which one zinc atom carries two stearate chains, which is why its systematic name is zinc distearate. What separates a metal soap from the fatty acid it is made from? The soap replaces the acidic hydrogen with a metal, so the molecule gains an ionic head that adsorbs on steel, on pigment surfaces and on the polar sites of a PVC chain, while its two hydrocarbon tails stay compatible with the melt.

Zinc stearate is one of three metal stearates that matter in plastics, beside calcium stearate and magnesium stearate, separated in practice by their metal and their melting range. Baerlocher classes it as an external lubricant in PVC, the classification that organises this page.

What is zinc stearate made of?#

Zinc stearate is made from stearic acid and a zinc source, and commercial grades carry 10.4 to 11.3 % zinc according to Peter Greven's grade data. The acid half of the soap, stearic acid, is itself an authorised food-contact substance, which is what makes the EU route work, and it is a commercial C16 to C18 cut rather than a pure compound. Our data set records the process types, not the zinc reactant, so no reaction equation is printed.

Is zinc stearate the same as zinc distearate?#

Yes: zinc stearate, zinc distearate and zinc octadecanoate are three names for the same substance, CAS 557-05-1, and "distearate" is simply the precise form, because the zinc atom carries two stearate groups. Chemical inventories also list it as octadecanoic acid, zinc salt, and all four names resolve to EC number 209-151-9 and 632.3 g/mol.

How is zinc stearate made? Precipitated, direct, melt and COAD grades#

Peter Greven describes 4 production routes for metal soaps, and the route, not the chemistry, decides whether a zinc stearate is fine and dusty or coarse and free-flowing: precipitation, direct conversion, the melt process and the continuous COAD process. The four are set out below.

• Precipitation, the indirect two-step route, gives a very fine powder with a high surface area, a low bulk density and a higher salt content.
• Direct conversion adds the metal base as a powder below the melting point of the soap and runs at a pH above 7.
• The melt process runs above the melting point of the soap and yields a dust-free product from a clear melt.
• The COAD continuous process is dust-free and neutral in pH, and it builds layered particles that dissolve faster and give a low filter index for polypropylene fibre.

Why should a buyer care which route made the powder? Because the route sets how the grade runs on a line: Peter Greven reports that precipitated grades release best in sheet and bulk moulding compound because of their fineness, while melt and COAD products are the dust-free ones. The filter index, in bar per kilogram, measures how much a powder raises screen pressure and separates a fibre grade from a general-purpose one.

What Does Zinc Stearate Do in a Plastic? 5 Functions#

Zinc stearate does 5 jobs in plastics: it lubricates the melt against metal, releases parts from the mold, disperses pigments and fillers, neutralises acid from catalyst residues and supplies the zinc in calcium-zinc PVC stabilizers. The five are listed in the order the rest of this page treats them.

• External lubricant, which is the Baerlocher classification for zinc stearate in PVC.
• Internal mold release agent, used in sheet moulding compound, bulk moulding compound and polystyrene.
• Dispersion aid for pigments in colour concentrates.
• Acid scavenger in polyolefins, where metal soaps generally run at 0.05 to 0.20 %.
• Co-stabilizer supplying the zinc of a calcium-zinc PVC system, and a densifying or partitioning agent in the same powder form.

All four lubricant classes are compared on processing lubricants for plastics, where the metal soaps sit beside the hydrocarbon waxes, the fatty-acid esters and the fatty amides.

Why is zinc stearate classed as an external lubricant?#

Baerlocher classes zinc stearate as an external lubricant, which means its main job is to reduce adhesion between the melt and hot metal rather than to lower the friction between polymer chains. An internal lubricant in PVC reduces friction between the PVC chains themselves, lowers melt viscosity, stays compatible with PVC, keeps transparency and does not exude. An external lubricant is mostly non-polar, prolongs fusion, and causes haze and exudation when overdosed. A combined lubricant produces both effects.

The classification is counter-intuitive, because the higher-melting soap is the internal one: Baerlocher places calcium stearate at about 160 °C (320 °F) on the internal side and zinc stearate at about 120 °C (248 °F) on the external side, rating both in a matrix covering release, inner friction, fusion time, torque, transparency, exudation, printability and weldability. Balancing internal against external lubricant is the craft of lubricants for PVC compounding, and the label is a shorthand rather than a theory: Rabinovitch, Lacatus and Summers called it "deficient in explaining performance" in 1984.

Why does the melting point of zinc stearate decide its behaviour?#

Zinc stearate melts between about 115 and 130 °C (239 and 266 °F) depending on the grade and the source, roughly 40 °C below calcium stearate, and Baerlocher attributes its even spreading in the melt to exactly that low melting point. PubChem and the NIOSH pocket guide give 130 °C (266 °F), Struktol's technical data sheet 115 to 125 °C (239 to 257 °F), Peter Greven 118 to 122 °C (244 to 252 °F) and Baerlocher about 120 °C (248 °F). Baerlocher states that the low melting point "means it spreads very evenly when heated", the mechanism behind both the release and the dispersion functions.

Blending the two soaps lowers the melting point further: Peter Greven reports that the LIGASTAB CZ 30 calcium-zinc preblend melts at about 100 °C (212 °F) against 120 to 130 °C (248 to 266 °F) for the single soaps.

How does zinc stearate work as an internal mold release agent?#

Zinc stearate works as an internal mold release agent by migrating to the surface of the part during molding and forming a thin release layer between the polymer and the steel, which is why it is compounded into the resin rather than sprayed onto the tool. Peter Greven describes that migration as the mechanism. Release agents divide into three application types: sacrificial coatings applied before every cycle, semi-permanent coatings bonded to a clean mold, and internal agents blended into the compound. The competing chemical classes are the waxes, the fatty esters, the silicones and the metallic soaps.

Compounded release agents are compared on internal mold release agents.

How does zinc stearate act in PVC?#

In PVC, zinc stearate substitutes the labile chlorine atoms that start dehydrochlorination, which gives good early colour but produces zinc chloride, a Lewis acid that then accelerates degradation unless a calcium soap regenerates the zinc soap. Peter Greven describes that substitution and the regeneration step. Unstabilized PVC begins losing hydrogen chloride above about 70 °C (158 °F), and 0.1 % dehydrochlorination already causes unacceptable discoloration, so the initial-colour benefit is immediate.

The cost of that benefit is the zinc chloride. Because the calcium soap converts it back into zinc stearate and takes up the chloride itself, neither soap is used alone in a modern recipe, which is the basis of calcium-zinc stabilizers.

What Are the Physical and Chemical Properties of Zinc Stearate?#

Zinc stearate is a white, hydrophobic powder with a slight characteristic odour, a density of 1.095 g/cm3 at 25 °C (77 °F) and no boiling point: it decomposes instead of boiling. The table gives every property held in our verified data set.

Four sources disagree about the melting point by 15 °C, so always take the figure from the grade's own data sheet. Four further specifications buyers compare, namely decomposition temperature, particle size, bulk density and ash content, are not held in our verified data set for zinc stearate.

Which Polymers Use Zinc Stearate, and at What Dosage?#

Zinc stearate is used at about 0.5 % across most plastics according to Struktol's technical data sheet, and the two documented exceptions run in opposite directions: 1.0 wt% in a highly filled masterbatch and 0.05 to 0.20 % when metal soaps act only as acid scavengers. Why do PVC recipes give phr while masterbatch recipes give wt%? Because a PVC formulation is counted against 100 parts of resin, so its parts sum to more than 100. PVC recipes give zinc stearate in PHR (parts per hundred resin), which converts to weight percent as phr divided by the total phr, multiplied by 100: 0.3 phr in a formulation totalling 103.0 phr is 0.29 wt%.

Only four sourced dosage figures exist for this substance, and the table prints all four; where a cell reads "no published level", none has been interpolated.

Zinc stearate in PVC (calcium-zinc systems)#

In PVC, zinc stearate is almost never dosed on its own: it arrives inside a calcium-zinc one-pack, and calcium-zinc together with calcium-organic systems account for 83 % of EU PVC stabiliser use according to VinylPlus in June 2023. The whole stabiliser package runs at 1 to 5 % of the formulation according to ECVM, with 2 to 4 % typical, and the zinc soap is a minority component inside it.

The polyols, phosphites and beta-diketones that hold the zinc in check are covered under PVC co-stabilizers.

Zinc stearate in polystyrene, EPS and ABS#

Polystyrene, EPS and HIPS use zinc stearate together with ethylene bis stearamide and zinc/amide blends, and Baerlocher sells ZINCUM PS and ZINCUM TX specifically for them. Acrylonitrile butadiene styrene and SAN take a different set, namely ethylene bis stearamide, magnesium stearate and calcium stearate. The rest of the package is on additives for polystyrene. No dosage figure for polystyrene or EPS is held in our verified data set.

Zinc stearate in polyethylene and filler masterbatch#

Filler masterbatch is where the effect of zinc stearate has actually been measured: Radebe, Focke and colleagues at the University of Pretoria found in 2022 that a 60 wt% calcium carbonate masterbatch in LLDPE had three times the melt viscosity of the neat polymer, and that 3 wt% wax plus 1.0 wt% zinc stearate brought it back to just above the neat value. In that study magnesium stearate alone was less effective than zinc stearate, while a blend of the two performed well.

Typical recipes and let-down ratios are on filler masterbatch, where filler loading raises melt viscosity and the lubricant package buys the loading back.

Zinc stearate in SMC and BMC (unsaturated polyester)#

In sheet and bulk molding compound, zinc stearate is the preferred internal release agent precisely because it melts lower than calcium stearate, and Peter Greven reports that precipitated grades release best thanks to their fineness. Particle size sets a trade-off inside that preference: at the same dosage a coarser stearate raises the paste viscosity less, while a finer one releases at a lower dosage. Peter Greven's Brookfield comparison ran at 1.23 wt%, a test condition and not a recommended level; no recommended dosage for unsaturated polyester is held in our verified data set.

Internal and external release for these processes is compared on mold release agents for composites. The grades named here are Baerlocher ZINCUM SW 1626 and, on the calcium side, CEASIT SW 1725.

What Is Zinc Stearate Used For? Applications in Plastics#

Zinc stearate is used in 6 plastics application areas: SMC and BMC molding, polystyrene and EPS, color concentrates and masterbatch, polyethylene compounds, calcium-zinc PVC systems and general mold release. The 6 areas are listed.

• SMC and BMC molding, where the soap is the internal release agent.
• Polystyrene and EPS, where it is part of the standard lubricant set.
• Color concentrates and masterbatch, where it wets pigment surfaces.
• Polyethylene compounds, including highly filled masterbatch.
• Calcium-zinc PVC systems, where it supplies the zinc.
• General mold release and lubrication across moulding processes.

Mold release for composite parts#

Composite molders use zinc stearate where the release agent has to sit inside the compound rather than on the tool, which is the normal case for sheet and bulk molding compound running at high cycle rates. The reason zinc stearate is preferred over calcium stearate here is its lower melting point, not a general superiority among metal soaps.

Pigment dispersion in color concentrates and masterbatch#

In color concentrates zinc stearate wets the pigment surface and lowers the viscosity of the highly loaded melt, which is why masterbatch producers list it beside the waxes rather than beside the stabilizers. Waxes, soaps and polymeric dispersants are compared on dispersing agents for plastics and masterbatch.

Acid scavenging in polyolefins#

Metal soaps neutralise the chloride left by Ziegler-Natta catalysts at 0.05 to 0.20 % according to Peter Greven, and although calcium stearate carries most of this role, the zinc soap works the same way. Calcium dominates because its chloride is not a strong Lewis acid while zinc chloride is. The full set of neutralisers is on acid scavengers and catalyst neutralizers.

How Does Zinc Stearate Perform, and When Does It Go Wrong?#

The one measured performance figure for zinc stearate in the public literature is a viscosity result: 1.0 wt% zinc stearate with 3 wt% wax returned a 60 wt% calcium carbonate LLDPE masterbatch from three times the neat melt viscosity to just above it, in the 2022 study by Radebe, Focke and colleagues at the University of Pretoria. Everything else is directional rather than numerical.

Fusion time and torque are measured as described on PVC fusion testing, and melt flow rate under ISO 1133 and ASTM D1238. No coefficient-of-friction, fusion-time, oxidation-induction-time or Congo red value is held in our verified data set, so the methods are named without values.

Over-lubrication: haze, exudation, plate-out and fusion delay#

Too much zinc stearate shows up as four separate defects, all of them consequences of the same external-lubricant behaviour: delayed fusion, surface haze, exudation and plate-out on calender rolls, dies and screws. The four are listed below.

• Delayed fusion, because an external lubricant keeps the melt off the metal and lowers the shear that fuses a PVC dry blend.
• Surface haze, the optical symptom of an overdosed external lubricant.
• Exudation, which Baerlocher's performance matrix links to reduced printability and weldability.
• Plate-out, the PVC-specific deposit of formulation components on calender rolls, dies and screws, to which over-lubrication and incompatible external lubricants both contribute.

No threshold dosage at which these defects begin is held in our verified data set.

Zinc burning in PVC#

Zinc burning is the failure mode specific to zinc soaps: the zinc chloride they release is a strong Lewis acid that catalyses further dehydrochlorination, so a PVC compound can pass from stable to black in a short window. Lead chloride by contrast is only weakly Lewis-acidic and produces no autocatalytic burning.

Four co-stabilizer classes prevent the failure: polyols, phosphites, beta-diketones and hydrotalcite, alongside the calcium soap. Hydrotalcite works by exchanging the carbonate between its layers for chloride rather than by reacting as a soap.

How Does Zinc Stearate Interact with Other Additives?#

Zinc stearate is a partner additive rather than a solo one: it is paired with calcium stearate in PVC, with waxes in filler masterbatch, with phenolic antioxidants in white polyolefins and with a calcium salt inside the nucleating agent Hyperform HPN-20E. The four interactions are set out below.

• With calcium stearate in PVC: the calcium soap scavenges the zinc chloride and regenerates the zinc soap, and the LIGASTAB CZ 30 preblend melts at about 100 °C (212 °F) against 120 to 130 °C (248 to 266 °F) for the single soaps.
• With waxes in filler masterbatch: 3 wt% wax plus 1.0 wt% zinc stearate restored the melt viscosity of the LLDPE compound in the Radebe study, and a magnesium/zinc stearate blend also performed well.
• With phenolic antioxidants in white polyethylene and polypropylene: over-oxidation of the antioxidant to quinones can turn the part pink, and the soap can suppress that by forming colourless zinc-quinone complexes (Ampacet).
• With calcium cis-1,2-cyclohexanedicarboxylate in Hyperform HPN-20E: the commercial nucleator is two thirds the calcium salt and one third zinc stearate, the zinc soap acting as the acid scavenger inside the product.

Zinc stearate is therefore a formulated component of a commercial nucleator, which is explained under nucleating agents.

What Is the Regulatory Status of Zinc Stearate?#

Zinc stearate is registered under REACH, is not a Substance of Very High Concern, carries no FCM number of its own in the EU because it is covered as a salt of authorised stearic acid, and is listed as GRAS in the United States under 21 CFR 182.8994, all as of 22 September 2026. The matrix gives each instrument separately.

Four cells read "status being verified" rather than "not restricted", because an absence that has not been checked against the primary list is not a negative finding. Article 6(3)(a) and the Annex II metal limits are explained on EU 10/2011.

Is zinc stearate REACH registered, and is it an SVHC?#

Yes, zinc stearate is registered under REACH, and no, it is not a Substance of Very High Concern: ECHA's database showed 13 active full registrations under CAS 557-05-1 on 22 September 2026, and the substance is absent from the Candidate List. A buyer may see either of two identifiers on a supplier's dossier reference, because a further 76 dossiers sit under EC entry 293-049-4, "Fatty acids, C16-18, zinc salts", which is a separate substance identifier and not a figure to be added. Registration and the dossier identifiers are explained on REACH and plastic additives.

The lead stearates were added to the SVHC Candidate List on 19 December 2012 as toxic for reproduction under Article 57(c); the zinc soap has never been added.

Is zinc stearate allowed in food-contact plastics?#

Yes in the EU, but by an indirect route: zinc stearate has no entry of its own in Annex I of Regulation (EU) No 10/2011, and it is instead covered as a salt of authorised stearic acid (FCM No 106) under Article 6(3)(a), with the Annex II limit of 5 mg/kg for zinc applying to the finished article. That limit has been 5 mg/kg since Regulation (EU) 2020/1245 lowered it from 25 mg/kg, so a specification quoting 25 mg/kg is out of date. The overall migration limit of 10 mg/dm2 applies in addition. In the United States the route is direct: zinc stearate is listed by name as generally recognised as safe under 21 CFR 182.8994.

Why does zinc stearate have no FCM number of its own?#

Because Article 6(3)(a) of Regulation (EU) No 10/2011 covers the salts of authorised acids automatically: stearic acid is authorised as FCM No 106, so its calcium, zinc and magnesium salts are covered without separate entries, and the metal itself is then controlled by the Annex II limits. A declaration of compliance therefore cites FCM 106 and the Annex II zinc limit, not a number belonging to the soap. No FCM number exists for zinc stearate, calcium stearate or magnesium stearate.

Is zinc stearate FDA approved?#

The FDA does not "approve" additives in that sense: zinc stearate is listed as generally recognised as safe under 21 CFR 182.8994. A GRAS listing, a prior sanction and a food contact notification are three different legal routes, and what each one means is set out on FDA food contact rules for plastic additives. The distinction matters here, because 21 CFR 181.29 lists zinc orthophosphate and zinc resinate among the prior-sanctioned stabilizers, each with a 50 ppm migrant limit expressed as zinc, while zinc stearate is not on that list.

Is Zinc Stearate Safe? Hazard Classification and Handling#

Zinc stearate has no harmonised hazard classification recorded in our verified data set, and 61.3 % of the 2,108 companies that notified it to ECHA report that it meets no GHS hazard criteria, but the minority notifications matter: 30.9 % give H400 and 22.7 % give H413, the aquatic hazard statements. Three points follow from that distribution.

• No harmonised classification under Regulation (EC) No 1272/2008 is recorded, so no legally binding entry exists that every EU supplier must apply.
• The notified self-classifications split: no classification in 61.3 % of 2,108 notifications, H400 (very toxic to aquatic life) in 30.9 %, H335 (may cause respiratory irritation) in 28.3 % and H413 (may cause long-lasting harmful effects to aquatic life) in 22.7 %.
• The split reaches the buyer through the safety data sheet and the aquatic labelling of any masterbatch carrying the soap.

The difference between a harmonised classification and a self-notification is explained on CLP classification of plastic additives. No occupational exposure limit, LD50 or NOAEL is held in our verified data set, and this page gives no skin, cosmetic, dietary or inhalation health advice.

Dust: powder, pastille, flake and granule forms#

The practical problem on a compounding line is dust rather than toxicity, and that is why zinc stearate is sold in four physical forms: fine powder, flakes, pastilles and granules. Baerlocher describes its SMS flakes and TX pastilles, melt products covering zinc stearate and multi-component stabilizers, as absolutely dust-free, suitable for silo storage and high in abrasion resistance, and its AV granules as very low in dust and high in bulk density. Buyers should match the physical form to the feeding system before comparing prices.

What Are the Alternatives to Zinc Stearate?#

The 4 substitutes for zinc stearate are chosen on different grounds: calcium stearate for thermal headroom and food-contact simplicity, magnesium stearate for ABS and polyamide, ethylene bis stearamide for higher processing temperatures, and hydrotalcite or zinc oxide when only acid scavenging is needed. The table compares the five substances on the properties that decide the substitution.

Melting points differ by source and by grade; take the value from the grade's own data sheet. The full three-way metal stearate comparison, including bulk density and ash, sits on the page rather than on this substance page.

Zinc stearate vs calcium stearate#

Zinc stearate wins where a low melting point and clean mold release decide the job, and calcium stearate wins where thermal headroom, acid scavenging or food-contact simplicity decide it: the gap between about 120 °C (248 °F) and about 160 °C (320 °F) is the whole argument. Moulding compounds prefer the zinc soap because it melts lower and releases better. Calcium stearate melts about 40 °C higher and takes the acid-scavenger role in polyolefins, where its chloride does no catalytic harm. In PVC the question is not a substitution at all, because the two soaps are used together inside one pack.

Zinc stearate vs magnesium stearate#

Magnesium stearate is the ABS and polyamide soap, used at 0.3 to 3 parts according to Struktol, while zinc stearate is the polystyrene, masterbatch and composite soap. Magnesium distearate carries CAS 557-04-0, EC 209-150-3 and 591.2 g/mol, with 4.0 to 4.8 % magnesium; PubChem gives 88.5 °C (191 °F) pure and 132 °C (270 °F) technical, Struktol 125 to 145 °C (257 to 293 °F). Magnesium stearate also acts as a dusting agent against surface adhesion in ABS. No REACH registration statement is made for it here, because no active dossier was found under CAS 557-04-0 on 22 September 2026.

Zinc stearate vs EBS and ester lubricants#

Ethylene bis stearamide melts between 135 and 146 °C (275 and 295 °F) according to PubChem, about 20 °C above zinc stearate, which is why the two are blended rather than substituted in polystyrene and ABS. Ethylene bis stearamide (EBS) carries an FCM number of its own, FCM No 250 with no specific migration limit, which makes its food-contact paperwork simpler than the indirect route the stearates take. It is also broader in function, working as lubricant, dispersant, release and antiblock agent, and it is cleared under 21 CFR 178.3860.

The ester route to the same effect is covered on ester lubricants, where glycerol monostearate, pentaerythritol tetrastearate and the montan esters replace the soap without introducing a metal, which is decisive wherever the Annex II zinc limit of 5 mg/kg binds.

Zinc stearate vs hydrotalcite and zinc oxide#

When the only job is acid scavenging, hydrotalcite and zinc oxide compete with the stearates directly, and hydrotalcite works by a different mechanism: it exchanges the carbonate between its layers for chloride instead of reacting as a soap. Hydrotalcite is a magnesium-aluminium layered double hydroxide, CAS 12304-65-3 and also 11097-59-9, used as a PVC co-stabilizer and a polyolefin acid scavenger, covered by FCM 604 and 592 with no specific migration limit and an Annex II aluminium limit of 1 mg/kg. It contributes no lubrication.

Zinc oxide delivers the same metal without the fatty acid, so it scavenges acid and feeds the same zinc chemistry in PVC while doing nothing for lubrication or release. The three-way choice is worked through on acid scavengers for polyolefins, where the Annex II metal limits usually decide it.

Who Manufactures Zinc Stearate? Grades and Suppliers#

Three producers appear across the technical literature this page draws on: Baerlocher, which sells zinc stearate under the Zincum name, Peter Greven with LIGASTAR ZN, and Struktol with STRUKTOL Zinc Stearate. The table lists the grades and physical forms each of them names.

Buyers should ask for the grade's technical data sheet, its safety data sheet and its zinc content, because the melting range and the particle size differ between production routes even at an identical CAS number. More producers and their locations are in the directory of calcium and zinc stearate manufacturers.

No price figure for zinc stearate is held in our verified data set, so none is quoted here. Price drivers for the metal soaps, which follow the stearic acid feedstock rather than the zinc, are tracked on calcium and zinc stearate prices.

How Do Metal Stearates Fit into the Lubricant Family?#

Zinc stearate is one of three metal stearates that matter in plastics, beside calcium stearate and magnesium stearate, and the metal soaps in turn sit beside the polymer waxes, the ester lubricants and the fatty amides in the processing-lubricant family. Melting point orders that family more usefully than the internal and external labels do: zinc stearate melts at about 120 °C (248 °F) and calcium stearate at about 160 °C (320 °F).

Beside the metal soaps sit the polymer waxes, the other large external-lubricant class, covering the polyethylene, oxidized polyethylene, Fischer-Tropsch, montan and paraffin grades.

What is a metal soap?#

A metal soap is the salt of a long-chain fatty acid and a metal, and in plastics the fatty acid is almost always stearic acid, which is why "metal stearate" and "metal soap" are used interchangeably. Beyond the three plastics soaps, the family includes lead stearate and dibasic lead stearate, both added to the Candidate List on 19 December 2012, as well as cobalt stearate, aluminium stearate and lithium stearate. Lead, cobalt, aluminium and lithium soaps are listed with their plastics relevance under metal soaps in plastics, and their main uses in grease, paint and gelling fall outside the scope of this site.

Non-plastics uses of zinc stearate (outside the scope of this site)#

PlasticAdditives.net covers additives used in plastics, so the cosmetic, pharmaceutical, paper, paint and sporting uses of zinc stearate fall outside its scope and are named here only so that readers arriving from those searches know where they have landed. This page gives no dosage, no INCI guidance and no skin-safety statement for any of those sectors, and it makes no health claim about the substance. The plastics reader takes one point from those markets: a grade sold against a cosmetic or pharmacopoeia specification is bought on different numbers from a lubricant grade.

Buying and documentation questions#

The three questions below arrive most often from the sourcing side of the search results.

What is the melting point of zinc stearate?#

Between about 115 and 130 °C (239 and 266 °F), depending on the grade and the source: PubChem and NIOSH give 130 °C (266 °F), Struktol 115 to 125 °C (239 to 257 °F), Peter Greven 118 to 122 °C (244 to 252 °F) and Baerlocher about 120 °C (248 °F). No single value is correct for every grade, so cite the producer and the data sheet with the number.

Is zinc stearate soluble in water?#

No: zinc stearate is insoluble in water, alcohol and ether, and it dissolves only in benzene and in hot aromatic or chlorinated solvents according to PubChem, which is the hydrophobic behaviour that makes it a release agent. That hydrophobicity keeps the powder in place.

Does zinc stearate have an HS code?#

Customs classification of zinc stearate depends on the physical form and on the destination tariff, and no HS code for the substance is held in our verified data set, so none is printed here. A shipper takes the code from the destination country's current tariff schedule or from the producer's export documentation.