Hydrotalcite: Properties, Uses in Plastics and Regulatory Status

Hydrotalcite, a magnesium aluminium layered double hydroxide with the idealised formula Mg6Al2(OH)16CO3·4H2O (CAS 12304-65-3), is used in plastics as an HCl scavenger: a PVC co-stabilizer and a polyolefin acid scavenger that traps chloride between its hydroxide layers. Because the same chemistry is also sold as an antacid tablet, the first question buyers ask is which grade and which identity the plastics industry actually uses.

Hydrotalcite is listed twice in Annex I of Regulation (EU) No 10/2011, as FCM substance 604 and as FCM substance 592, in both cases as an additive with no substance-specific migration limit, so the binding constraint is the Annex II limit of 1 mg/kg for aluminium (consolidated text of 16 March 2025). It is registered under REACH and absent from the Candidate List and the California Proposition 65 list as of 23 September 2026. Hydrotalcite is one of 36 heat-stabilizer pages in our directory of plastic additives, each carrying the same identity, dosage and regulatory fields.

This page carries the data-sheet view and the compliance view together: the two CAS numbers, the neutralisation and anion-exchange mechanism, the mineral and grade properties, the dosage evidence for PVC, polyolefins, PLA and halogenated rubbers, 7 plastics applications, the 190-minute oven figure recorded in one study, a dated regulatory matrix, the comparison with calcium stearate, zinc stearate, zinc oxide, zeolite A, calcium hydroxide and ESBO, and the producers and grades a buyer can source.

Table T1. Hydrotalcite identity card.

Footnote: identity data from PubChem CID 156595104 and ECHA CHEM 100.031.187; food-contact entries from the consolidated text of Regulation (EU) No 10/2011 of 16 March 2025. Status as of 23 September 2026.

What Is Hydrotalcite?#

Hydrotalcite is a layered double hydroxide, an anionic clay in which positively charged magnesium-aluminium hydroxide layers alternate with exchangeable carbonate anions and water. The hydroxide sheet is brucite-like, meaning it has the structure of magnesium hydroxide with part of the magnesium replaced by aluminium, and that substitution is what leaves the layer positively charged. The charge has to be balanced, so carbonate anions and water molecules sit in the gallery between the sheets. Which part of that structure does the acid-scavenging work?

Both parts do, in sequence: the hydroxide layer neutralises acid, and the interlayer exchanges its carbonate for chloride. That two-stage behaviour is why hydrotalcite is the volume leader among the inorganic acid scavengers and catalyst neutralizers, the group that removes acid from a compound instead of masking its effects. Van der Ven and colleagues (Applied Clay Science, 2000) set out the anionic-clay structure and the anion-exchange property that define the class.

Hydrotalcite carries 5 distinct roles in plastics, listed below.

• PVC co-stabilizer, taking up the hydrogen chloride released by the resin
• Polyolefin acid scavenger and catalyst neutralizer, removing chloride from Ziegler-Natta residues
• Halogen scavenger in flame-retardant compounds, capturing the hydrogen halide released by the retardant
• PLA and polyester hydrolysis co-stabilizer, acting as an acid regulator
• Acid acceptor in halogenated rubbers such as chloroprene and chlorosulfonated polyethylene

What is the chemical formula of hydrotalcite?#

The idealised formula of hydrotalcite is Mg6Al2(OH)16CO3·4H2O, which corresponds to a calculated molecular weight of about 604 g/mol. That formula describes the mineral, with a magnesium-to-aluminium ratio of 3 to 1 and one carbonate anion balancing the layer charge. The layered double hydroxide formula that covers the whole class is written [M2+(1-x)M3+x(OH)2]x+(An-)x/n·mH2O, with x, the trivalent fraction, running from 0.20 to 0.33 in the compositions that form a stable single phase, as Jiang and colleagues set out in Materials in 2020.

Commercial grades are non-stoichiometric, so the mineral formula is a description rather than a specification. A synthetic powder made for a polymer melt is precipitated to a chosen magnesium-to-aluminium ratio, a chosen particle size and often a surface treatment, and the supplier's stated ratio governs the calculation, not the 6:2 of the idealised formula. For the same reason, a single fixed molecular weight does not apply to a commercial grade.

Is hydrotalcite the same as a layered double hydroxide (LDH)?#

Hydrotalcite is one member of the layered double hydroxide class, not a synonym for it: LDH covers every divalent-trivalent metal hydroxide with exchangeable interlayer anions, while hydrotalcite is the magnesium-aluminium carbonate member. Zinc-aluminium, magnesium-iron and calcium-aluminium layered double hydroxides exist alongside it, and they share the anion-exchange property without sharing the composition. Supplier data sheets often use the trade term "hydrotalcite-like compound" for exactly this reason, because a synthetic powder with a magnesium-to-aluminium ratio away from 3 to 1 is structurally hydrotalcite and compositionally not the mineral. The structure image above shows the arrangement that all of these compounds share: charged hydroxide sheets, an anion gallery and interlayer water.

Why does hydrotalcite have two CAS numbers?#

Hydrotalcite appears under two CAS numbers: 12304-65-3, the mineral-derived identity that carries EU FCM number 604 and EC list number 602-916-1, and 11097-59-9, aluminium magnesium carbonate hydroxide, which carries EC number 234-319-3 and EU FCM number 592. The second identity is the one most synthetic grades are registered under in REACH, where ECHA CHEM records 10 active full registration dossiers. The distinction matters on a specification sheet: 602-916-1 is an EC list number assigned for regulatory reference, not an EC inventory number, so a compliance file that needs an inventory identity uses 234-319-3.

Is the hydrotalcite used in plastics the same as the antacid?#

The antacid and the plastics additive share the same layered double hydroxide chemistry, but they are different products: plastics grades are synthetic, surface-tailored powders sold under trade names such as ALCAMIZER, DHT-4 and Actilox CAH, and they are specified for dispersion and thermal stability in a polymer melt, not for pharmacopoeial purity. A polymer grade is bought on particle size, surface treatment, magnesium-to-aluminium ratio and acid-uptake capacity, and none of those is a pharmacopoeial parameter. The pharmaceutical and mineral uses sit outside the scope of this page and are summarised at the end.

How Does Hydrotalcite Work? HCl Scavenging and PVC Co-Stabilization#

Hydrotalcite removes acid from a polymer in two steps: the basic hydroxide layers neutralise hydrogen chloride, and the interlayer carbonate exchanges for chloride, which locks the chloride inside the particle. The exchange is irreversible in practice, so the captured chloride is not released back into the melt at processing temperature. Jiang and colleagues (Materials, 2020) record that the stabilizing effect of hydrotalcite in polyvinyl chloride was first reported in the 1980s.

Removal matters because free acid does damage on three fronts. In polyvinyl chloride the hydrogen chloride is autocatalytic, meaning each molecule released accelerates the next elimination, and in every polymer free acid corrodes screws, dies and moulds, antagonises phenolic antioxidants and hindered amine light stabilizers, and hydrolyses phosphite antioxidants. Because hydrotalcite only removes hydrogen chloride and does not substitute labile chlorine on the polymer chain, suppliers class it with the PVC co-stabilizers rather than with the primary stabilizers.

Three acid sources drive the demand for an acid scavenger in a compound.

• Ziegler-Natta catalyst residues in polypropylene and polyethylene, which carry chloride from the catalyst system
• Hydrogen halides released by halogenated flame retardants during compounding and in a fire
• Hydrogen chloride released by polyvinyl chloride itself during processing and service

How does hydrotalcite stabilize PVC against dehydrochlorination?#

Hydrotalcite stabilizes PVC by taking up the hydrogen chloride that the polymer eliminates, which breaks the autocatalytic loop that turns a single lost HCl molecule into a growing polyene sequence. Unstabilized polyvinyl chloride begins to lose hydrogen chloride above about 70 °C (158 °F), its thermal degradation onset is about 250 °C (482 °F) against about 400 °C (752 °F) for polyethylene, and a loss of only 0.1 % of the theoretical hydrogen chloride already produces unacceptable discoloration. Every system in the PVC heat stabilizers family therefore has to remove that acid, and hydrotalcite is the component that does it without leaving a metal chloride behind.

The elimination runs as a zipper: once one chlorine leaves, the neighbouring unit is activated, a conjugated polyene sequence grows along the chain, and colour develops long before any mechanical property changes. The zipper mechanism behind PVC thermal degradation and dehydrochlorination explains why 0.1 % hydrogen chloride loss already discolours the compound. Inside a calcium-zinc package, hydrotalcite occupies the hydrogen chloride uptake slot and contributes long-term stability rather than early colour.

How does hydrotalcite scavenge acid in polyolefins?#

In polypropylene and polyethylene the acid comes from chloride-containing Ziegler-Natta catalyst residues, and hydrotalcite neutralises it before it can corrode tooling or consume the phenolic antioxidant and hindered amine light stabilizer in the stabilizer package. Catalyst residues are present in parts per million, but the acid they generate is continuous over the life of the compound, so the scavenger has to stay where it is needed. Kisuma states that its hydrotalcite grades are non-migratory, unlike the metal soaps used for the same job, which means the scavenger remains distributed through the polymer instead of blooming to the surface. Calcium stearate, the classical alternative, converts to calcium chloride when it reacts with the same acid, and calcium chloride is hygroscopic, so the by-product itself can carry water into the process.

What Are the Physical and Chemical Properties of Hydrotalcite?#

Hydrotalcite for plastics is a white powder; the natural mineral has a specific gravity of 2.03 to 2.09 and a Mohs hardness of 2, the softness that lets it disperse without abrading screws and dies. The mineral is described as white with a greasy luster, and the synthetic powders made for polymer compounding are white free-flowing solids. Two of those values are mineral data rather than grade data, which matters because a specific gravity of 2.03 to 2.09 belongs to a single crystal and not to a packed powder, and because a Mohs hardness of 2 is a statement about the layered structure that every grade shares.

Table T2. Hydrotalcite physical and chemical properties.

Footnote: decomposition temperature, particle size, surface area and moisture are grade properties; take them from the supplier data sheet.

Our source library holds no decomposition temperature, no particle-size distribution, no BET surface area, no oil absorption figure and no moisture content for any commercial hydrotalcite grade, so this page does not print them and a buyer takes them from the grade data sheet. The same caution applies to the molecular weight: about 604 g/mol is a calculated value for the idealised mineral formula, not a measured specification for a manufactured powder, and the mineral specific gravity is not a bulk density.

Which Polymers Use Hydrotalcite, and at What Dosage?#

Hydrotalcite is used in PVC, polypropylene, polyethylene, PLA and halogenated rubbers, always as one component of a package rather than as a stand-alone stabilizer. The only dosage figure supported by a primary source on file is a research formulation in rigid polyvinyl chloride: 2.4 phr of magnesium-aluminium carbonate hydrotalcite with 0.3 phr zinc stearate and 0.3 phr zinc acetylacetonate, reported by Jiang and colleagues in Materials in 2020. At the package level, the European Council of Vinyl Manufacturers puts the total stabilizer content of a polyvinyl chloride formulation at 1 to 5 % of the formulation, with 2 to 4 % typical.

How do phr values convert to weight percent? The conversion is wt%(i) = phr(i) divided by total phr, multiplied by 100. Taking the Jiang formulation as the worked example, 2.4 phr of hydrotalcite in 100 phr of resin plus 3.0 phr of additives gives 2.4 / 103 x 100 = 2.3 wt%. A real compound also carries fillers, lubricants and pigments, so the total phr is higher and the true weight percent is lower; stabilizer recipes are stated in PHR (parts per hundred resin) precisely so that the resin stays the fixed reference while the rest of the formulation changes.

Table T3. Hydrotalcite level by polymer and the evidence behind it.

Footnote: blank levels mean no primary source exists in our source library, not that the additive is unused.

Hydrotalcite in rigid PVC compounds#

Hydrotalcite is the long-term stability component of a calcium-zinc package for rigid PVC: in a formulation studied by Jiang and colleagues (Materials, 2020), 2.4 phr of Mg2Al-CO3 hydrotalcite with 0.3 phr zinc stearate and 0.3 phr zinc acetylacetonate reached 190 minutes to full blackening in static oven ageing at 180 °C (356 °F). In the same study the Congo red maximum was 46 minutes, which is the number to keep beside the 190 minutes: an oven-blackening time and a Congo red time measure different end points and are never interchangeable.

Calcium-zinc and calcium-organic systems account for 83 % of stabilizer use in the European polyvinyl chloride industry according to VinylPlus in June 2023, so the package that hydrotalcite serves is the mainstream European one. Within it the division of labour is explicit: hydrotalcite takes up hydrogen chloride, beta-diketones control early colour, polyols complex the zinc chloride that causes zinc burning, and epoxides and phosphites add secondary protection. Baerlocher reports that calcium-zinc cable systems need hydrotalcite or zeolite together with polyols to reach volume-resistivity and heat-ageing targets. The rest of the compound, from lubricants to impact modifiers, is mapped on additives for PVC.

Hydrotalcite in polyolefins: polypropylene and polyethylene#

Hydrotalcite is used in polypropylene and polyethylene as the catalyst-residue neutralizer, where its advantage over a metal soap is that it stays in the polymer instead of migrating to the surface. Our source library holds no published typical dosage range in parts per million or weight percent for hydrotalcite in either polymer, so this page prints none; the level is set by the residual chloride of the resin and by the process, and it belongs on the supplier data sheet. The comparison anchor that is published belongs to the alternative: calcium stearate is used in polyolefins as an acid scavenger at up to 1000 ppm, and no equivalent published figure exists for hydrotalcite in our sources. The full three-way comparison sits on acid scavengers for polyolefins.

Hydrotalcite in PLA and polyesters#

In PLA hydrotalcite acts as an acid regulator rather than a heat stabilizer: Jannik Hallstein, Elke Metzsch-Zilligen and Rudolf Pfaendner at Fraunhofer LBF (Materials, 2024) combined calcium hydrotalcite with an aziridine hydrolysis inhibitor and reported improved hydrolytic and thermal ageing stability. Polylactic acid degrades by hydrolysis of its ester bonds, and the carboxylic acid end groups released by that hydrolysis catalyse further chain scission, so an additive that buffers acidity can slow the autocatalytic part of the process. The calcium hydrotalcite used in that work is Nabaltec's Actilox CAH. No dosage is published for the system, so none is given here; calcium hydrotalcite sits beside the carbodiimides and aziridines covered under hydrolysis stabilizers, and the wider package question is handled in our guide to additives for PLA.

Hydrotalcite in halogenated rubbers (CR, CSM, FKM, NBR)#

Hydrotalcite also serves as an acid acceptor in halogenated rubbers such as chloroprene (CR), chlorosulfonated polyethylene (CSM), fluoroelastomer (FKM) and nitrile rubber (NBR), where it takes up the hydrogen halide released during cure and service. Our source library records the function but no dosage for any of these elastomers, so the level is taken from the compound supplier.

What Is Hydrotalcite Used For? 7 Applications in Plastics#

Hydrotalcite is used in 7 plastics application areas: lead-free PVC systems, tin-replacement PVC systems, polyolefin acid scavenging, catalyst-residue neutralization, greenhouse film masterbatch, halogen scavenging in flame-retardant compounds and acid acceptance in halogenated rubbers. The list below follows the order in which the volume sits, from pipe and profile compounds down to specialty elastomers.

• Lead-free PVC pipe, profile and cable stabilizer systems
• Tin-replacement PVC stabilizer systems
• Polyolefin acid scavenging in polypropylene and polyethylene
• Ziegler-Natta catalyst-residue neutralization
• Greenhouse film masterbatch, protecting the light stabilizer from agrochemical acid
• Halogen scavenging in flame-retardant compounds
• Acid acceptance in chloroprene, chlorosulfonated polyethylene, fluoroelastomer and nitrile rubber

Lead-free and tin-replacement PVC stabilizer systems#

Hydrotalcite is a building block of the lead-free and tin-free stabilizer systems that replaced lead one-packs in the EU, where REACH Annex XVII entry 63 has prohibited lead at 0.1 % or more by weight of the PVC material since 29 November 2024. The restriction was introduced by Regulation (EU) 2023/923, and articles placed on the market before that date are exempt. The dates and the recycled-PVC derogations behind the switch are set out under lead in PVC.

The replacement chemistry is dominated by one family, the calcium-zinc and calcium-organic systems that VinylPlus put at 83 % of European stabilizer use in June 2023, and those systems need a hydrogen chloride acceptor that does not itself introduce a heavy metal. Kisuma markets its ALCAMIZER grades on exactly that basis, stating that they enable non-heavy-metal heat stabilization and are, in the company's words, perfect for lead-free and tin replacement systems. Cable compounds add a second constraint, because polyvinyl chloride cable insulation is specified in temperature classes of 70, 90, 100 or 105 and 125 °C (158, 194, 212 or 221 and 257 °F) according to Reagens.

Tin replacement is the second driver, because the organotin stabilizers carry their own authorisation and migration constraints. Where a compounder moves from a tin one-pack to a calcium-zinc system, the hydrogen chloride uptake that the tin mercaptide performed has to be rebuilt from separate components, and hydrotalcite is the component that performs it without generating a metal chloride.

BOPP, BOPE and raffia film#

In BOPP, BOPE and raffia the case for hydrotalcite is surface quality: Kisuma states that because its DHT-4 grades do not migrate, they leave metallization, printing and lamination unaffected, while migrating metal soaps can disturb all three. The same supplier reports work with the film producer Taghleef and the line builder Brückner behind those claims, and states that its DHT-4 grades lower haze in biaxially oriented film. In raffia tape the argument is different again: Kisuma's raffia case study reports that calcium stearate converts to hygroscopic calcium chloride, which raises water carry-over in the tape line, while the chloride captured by hydrotalcite stays inside the particle. Kisuma also claims that more than 400,000 square kilometres of film per year contain DHT-4, a volume figure the company publishes without a method. Surface-quality requirements for metallized and printed webs are collected under additives for packaging film.

Greenhouse and agricultural film#

Greenhouse film is the application where the acid does not come from the polymer: sulphur- and chlorine-bearing agrochemicals attack the hindered amine light stabilizers in the film, and Kisuma positions hydrotalcite in the masterbatch to neutralise that acid before it reaches the light stabilizer. Pesticides and fumigants are applied inside the structure, they condense on the film surface, and the acidic species they generate deactivate the amine functionality that the stabilizer depends on. Kisuma presents hydrotalcite as the protective component in the agricultural film masterbatch for that reason; no service-life extension is quantified in our sources, so none is stated here. The whole greenhouse-film package, from light stabilizers to infrared absorbers, is on additives for agricultural film.

Halogen scavenging in flame-retardant compounds#

Halogenated flame retardants release hydrogen halide during compounding, and hydrotalcite captures the free halide ions before they corrode screws, dies and moulds. Brominated and chlorinated retardants are designed to release that halide in a fire, where it interrupts the radical chain in the flame, but a fraction is released at compounding and service temperatures where it has no benefit and does damage. Hydrotalcite is used in those compounds as a halogen scavenger on the same anion-exchange principle it uses for chloride in polyvinyl chloride. Our source library holds no data on the effect of hydrotalcite on UL 94 classification, limiting oxygen index or flame-retardant efficiency, so this page makes no claim about fire performance.

How Does Hydrotalcite Perform, and How Is It Tested?#

The only published performance figure for hydrotalcite in our source library is a formulation result, not a substance result: 2.4 phr with 0.3 phr zinc stearate and 0.3 phr zinc acetylacetonate held a PVC sample 190 minutes before full blackening in static oven ageing at 180 °C (356 °F), while the Congo red maximum in the same study was 46 minutes (Jiang et al., Materials, 2020). Why do the two numbers differ by a factor of four? Because the two tests measure different end points. The Congo red method times the first detectable evolution of hydrogen chloride from the sample, while static oven ageing times the visual progression of colour to complete blackening, so a Congo red time and an oven-blackening time are never compared directly and never quoted as if they were the same stability figure.

Six standard methods define how the numbers are produced. ISO 182-1:1990 is the Congo red method, in which the test temperature is set by the laboratory rather than fixed by the standard; ISO 182-2 measures pH; ISO 182-3 measures the rate of dehydrochlorination conductometrically; ISO 182-4 does the same potentiometrically; ISO 305 measures discoloration by an oven method; and ASTM D2115 is the oven heat-stability method for polyvinyl chloride compositions. The difference between an oven-blackening time and a Congo red time is explained under PVC heat stability testing.

Supplier efficiency claims sit outside all of these methods. Kisuma claims that DHT-4 is 3 times more effective than traditional acid scavengers, a comparison the company publishes without naming the test method, the reference scavenger or the polymer.

Table T4. Hydrotalcite performance indicators and their test methods.

How Does Hydrotalcite Interact with Calcium-Zinc Stabilizers and Other Additives?#

Hydrotalcite never works alone: in a calcium-zinc package it takes the hydrogen chloride that the zinc and calcium carboxylates generate and release, which is why suppliers sell it as a co-stabilizer rather than as a stabilizer. The zinc carboxylate substitutes the labile chlorine atoms responsible for the first elimination and forms zinc chloride in the process, and zinc chloride is itself a strong dehydrochlorination catalyst, so the package has to deal with the by-product of its own primary mechanism. The calcium carboxylate scavenges hydrogen chloride and regenerates the zinc soap.

Four additive groups sit beside hydrotalcite in a calcium-zinc package, each doing a different job.

• Zinc carboxylates, such as zinc stearate, which substitute labile chlorine and deliver early colour
• Calcium carboxylates, such as calcium stearate, which scavenge hydrogen chloride and regenerate the zinc soap
• Beta-diketones, such as dibenzoylmethane and stearoylbenzoylmethane, which improve early colour
• Polyols, such as pentaerythritol, dipentaerythritol and THEIC, which complex zinc chloride and delay zinc burning

Hydrotalcite is a standard long-term component of calcium-zinc stabilizers, which on their own give only moderate long-term stability, and commercial one-packs add epoxides and phosphites on top of the four groups above. Hydrotalcite also appears in pre-blended antioxidant products, where Songwon blends magnesium-aluminium hydrotalcite with a spiro-diphosphite to buffer the phosphite against acid hydrolysis.

Two of these components are routinely confused. Where hydrotalcite removes hydrogen chloride from the system, pentaerythritol complexes the zinc chloride that causes zinc burning, and a formulation that carries one but not the other fails at a different point in the heat-stability curve.

What Is the Regulatory Status of Hydrotalcite?#

Hydrotalcite is REACH-registered under CAS 11097-59-9, is not a Substance of Very High Concern, is listed twice in Annex I of Regulation (EU) No 10/2011 with no substance-specific migration limit, and is not on the California Proposition 65 list (status 23 September 2026). Three cells of the matrix below are open rather than negative: the CLP classification, the United States Food Contact Notification status and the TSCA inventory status are not recorded in our sources, and an absent record is not the same as an absence of classification.

Table T5. Hydrotalcite regulatory matrix, as of 23 September 2026.

How registration, evaluation and the Candidate List apply to additives is set out under REACH, and the three open cells in the table stay open on this page until a primary source closes them.

Is hydrotalcite REACH registered, and is it an SVHC?#

Yes, hydrotalcite is registered under REACH, and no, it is not a Substance of Very High Concern: ECHA CHEM lists 10 active full registration dossiers under CAS 11097-59-9 (EC 234-319-3), and the substance is absent from the Candidate List as of 23 September 2026. The registration sits on the second identity rather than on CAS 12304-65-3, which is the practical reason a compliance file for a synthetic grade quotes 11097-59-9. Our sources do not record the registered tonnage band, so this page does not state one.

Hydrotalcite has never appeared on the SVHC Candidate List, unlike the lead stabilizers it replaces, five of which were added on 19 December 2012 under Article 57(c) of REACH. That contrast is the commercial argument behind the substance, and it is a statement about listing status only, not a comparative toxicological statement.

Is hydrotalcite allowed in food-contact plastics?#

Yes in the EU: hydrotalcite appears twice in Annex I of Regulation (EU) No 10/2011, as FCM substance 604 under CAS 12304-65-3 and as FCM substance 592 under CAS 11097-59-9, in both cases as an additive with no substance-specific migration limit. The reference numbers are 60080 and 34690 respectively, and the status is taken from the consolidated text of 16 March 2025.

The constraint that does apply is a metal limit rather than a substance limit. Annex II of the same regulation caps aluminium at 1 mg/kg in food or food simulant, and because every hydrotalcite particle carries aluminium in its hydroxide layer, that limit is what a compounder models when the loading is high or the contact conditions are severe. How FCM numbers, group restrictions and the Annex II metal limits work is explained under EU 10/2011. A grade-level food-contact statement remains a supplier document: the Annex I entry covers the substance, while purity, surface treatment and any residual impurities are grade properties.

Is hydrotalcite FDA approved?#

Hydrotalcite is not listed in 21 CFR 178.2010, the FDA section that covers antioxidants and stabilizers for polymers, and our verification of its food-contact notification status is still open. Kisuma states that its DHT-4 grades hold global technical and food-contact approvals, which in the United States would normally mean a Food Contact Notification rather than a codified listing, and that is a supplier statement rather than a regulatory record. The difference between a 21 CFR listing and a Food Contact Notification is explained under FDA food contact rules, and until a notification number is verified this page states the absence from 21 CFR 178.2010 and nothing more.

Is hydrotalcite listed under California Proposition 65?#

No, hydrotalcite is not on the California Proposition 65 list published by OEHHA on 31 July 2026, under either CAS 12304-65-3 or CAS 11097-59-9. An absence from that list removes the warning obligation for the substance itself and says nothing about the other components of a compound, so listing dates for every additive we track are collected on California Proposition 65.

Is Hydrotalcite Safe? Health, Safety and Environmental Profile#

Hydrotalcite carries no entry on the REACH Candidate List, the EU POPs Regulation or the California Proposition 65 list, and our source library holds no harmonised or notified GHS classification for it, so this page states what the regulatory lists show and nothing beyond that. No LD50, no NOAEL and no inhalation study is recorded in our sources, and none is invented here. Three statements are supportable, and one common claim is not.

• Not on the REACH Candidate List of Substances of Very High Concern, as of 23 September 2026
• Not on the California Proposition 65 list published by OEHHA on 31 July 2026
• Not a persistent organic pollutant under Regulation (EU) 2019/1021
• No classification data in our sources, so "non-toxic" is not a claim this page makes, whichever supplier page prints it

The supplier safety data sheet governs handling. Hydrotalcite is supplied as a fine mineral powder, so dust is the practical exposure route during weighing, blending and cleaning, and the controls are the ones a compounding plant already applies to fine inorganic powders: enclosed transfer, local extraction and the protective equipment named on the safety data sheet. Our sources hold no occupational exposure limit for hydrotalcite, and the absence of a listed hazard on the three instruments above is a statement about those lists rather than a conclusion about the substance.

What Are the Alternatives to Hydrotalcite?#

The 6 alternatives to hydrotalcite named in our source library are calcium stearate, zinc stearate, zinc oxide, zeolite A, calcium hydroxide and ESBO, and they split into two groups: migrating metal soaps and non-migrating inorganic scavengers. The table compares them on identity, food-contact status, the metal limit each one brings with it and what happens to the chloride after capture.

Table T6. Hydrotalcite compared with 5 alternative acid scavengers.

Footnote: blank cells mark values that are not in our source library, not values that do not exist.

Hydrotalcite vs metal stearates (calcium stearate and zinc stearate)#

The practical difference between hydrotalcite and the metal stearates is what happens to the chloride after capture: hydrotalcite locks it in the interlayer, while calcium stearate converts to calcium chloride, which is hygroscopic. Calcium stearate is used in polyolefins at up to 1000 ppm as an acid scavenger, it has CAS number 1592-23-0 and EC number 216-472-8, and it carries no FCM number of its own because metal stearates are covered as salts of stearic acid under FCM 106. In the United States it is generally recognised as safe under 21 CFR 184.1229 and cleared under 21 CFR 181.29.

The trade-off appears in the process rather than on the certificate. Kisuma's raffia case study reports that the calcium chloride formed when calcium stearate reacts with acid raises water carry-over in a tape line, and the same supplier states that hydrotalcite is non-migratory while metal soaps bloom to the surface and can disturb metallization, printing and lamination. Neither statement is a universal verdict: a lubricating metal soap does a second job that hydrotalcite does not do at all, and many compounds use both.

The zinc member changes the compliance arithmetic. Zinc stearate has CAS number 557-05-1 and brings the zinc Annex II limit of 5 mg/kg with it, which caps the level in food-contact compounds, while hydrotalcite brings the aluminium limit of 1 mg/kg. Neither limit is a hazard statement; each one is a migration ceiling modelled for the specific article, contact time and temperature. Our source library holds no price data for hydrotalcite or for the stearates, so this page makes no cost comparison.

Hydrotalcite vs zinc oxide and other basic oxides#

Zinc oxide, magnesium oxide and calcium oxide neutralise acid as simple bases, without the anion-exchange step that holds chloride inside a hydrotalcite particle. A basic oxide reacts with hydrogen chloride to form the corresponding metal chloride, and that chloride stays in the compound as a discrete salt rather than as an exchanged interlayer anion. All three are recognised in EU food-contact law: zinc oxide is FCM substance 402, calcium oxide is FCM 395, magnesium oxide is FCM 397 and calcium hydroxide is FCM 394.

The regulatory differentiator is sharper than the mechanistic one. Zinc oxide carries a harmonised aquatic hazard classification, H400 and H410, which hydrotalcite does not carry in our sources, and it brings the zinc Annex II limit of 5 mg/kg into any food-contact calculation, while it is separately generally recognised as safe under 21 CFR 182.8991. Hydrotalcite's corresponding constraint is the aluminium limit of 1 mg/kg. A compounder choosing between them is therefore choosing between two different Annex II ceilings and two different environmental classification positions, not between two efficiencies.

Hydrotalcite vs zeolite A, calcium hydroxide and ESBO#

Zeolite A is the closest functional substitute for hydrotalcite inside a calcium-zinc package: Gupta, Agarwal and Banerjee (Journal of Vinyl and Additive Technology, 2009) describe zeolites as absorbing hydrogen chloride and sequestering zinc chloride, which is the same two-job role. Because a calcium-zinc system needs one component in the hydrogen chloride uptake slot, hydrotalcite and zeolite A are direct substitutes for each other in that position, and a formulator normally specifies one or the other rather than both. Calcium hydroxide is the simplest option of the three, a strong base with no sequestration function and no anion-exchange gallery, and it has FCM number 394 under Regulation (EU) No 10/2011.

Epoxidized soybean oil belongs to a different formulation decision altogether. ESBO (epoxidized soybean oil) scavenges hydrogen chloride through its oxirane groups while also plasticizing the compound, so replacing a solid scavenger with it changes hardness, modulus and migration behaviour at the same time. That makes ESBO an alternative in chemistry but not a drop-in swap in a rigid compound. Neither zeolite A nor calcium hydroxide has its own record in our source library, so this comparison stays at the level the cited sources support.

Who Manufactures Hydrotalcite? Grades and Suppliers#

Two producers are documented in our source library: Kisuma Chemicals, which sells ALCAMIZER for PVC and the DHT-4 series for polyolefins, and Nabaltec, which sells Actilox CAH, a calcium hydrotalcite. The hydrotalcite market is wider than two producers, and further hydrotalcite lines are being added to our substance directory, so the table below is a verified subset rather than a census of the supply base.

Table T7. Documented hydrotalcite producers and their trade names.

Footnote: producer positioning is quoted from supplier publications and is not an independent assessment.

Buyers should ask the supplier for the magnesium-to-aluminium ratio, the particle-size distribution, the surface treatment and a food-contact statement, because none of these is a substance property and all four differ between grades that share the same CAS number. More producers, their plants and their brand families are listed in the directory of PVC stabilizer manufacturers.

Kisuma DHT-4 grades and ALCAMIZER#

Kisuma splits the DHT-4 family into 4 grades that differ by surface treatment and thermal stability rather than by core chemistry. Kisuma positions the four DHT-4 grades as follows.

• DHT-4A, described by the supplier as the industry standard grade
• DHT-4V, described as surface-treated with an RSPO-certified vegetable agent
• DHT-4A-2, described as a dehydrated grade with higher thermal stability
• DHT-4C, described as the highest thermal stability grade and the most potent acid scavenger of the four, and as stearate-free

Every descriptor above is the supplier's positioning rather than a measured comparison, and no numeric specification for any of the four grades is recorded in our source library: no loss on drying, no surface area, no decomposition temperature and no magnesium-to-aluminium ratio. ALCAMIZER is the separate line Kisuma sells into polyvinyl chloride, where the requirement is long-term stability inside a calcium-zinc package rather than catalyst-residue neutralization. Which grade holds which regulatory clearance is a question for the supplier's documentation.

How Do Layered Double Hydroxides Fit into the Wider Additive Landscape?#

Hydrotalcite is the commercial centre of the layered double hydroxide class, a family of anionic clays that turns up in five different additive categories on this site: heat stabilizers, acid scavengers, hydrolysis stabilizers, antioxidant blends and laser-marking additives. The common thread is the interlayer: a structure that holds exchangeable anions can capture acid, buffer another additive against acid, or absorb energy in a laser pulse, depending on what is put between the sheets and what it is blended with. Layered double hydroxides cross five of the families in our map of polymer additives, which is unusual for a single structural class.

Hydrotalcite in phosphite antioxidant blends#

Spiro-diphosphite antioxidants hydrolyse in the presence of moisture and acid, so suppliers sell hydrolysis-buffered versions: SONGNOX 6280 is SONGNOX 6260 blended with magnesium-aluminium hydrotalcite at a ratio of 93:7 by weight. The hydrotalcite is not there to stabilize the polymer directly; it protects the phosphite in the bag and in the feed section, because a hydrolysed phosphite causes feeding problems, black specks and acidity in the melt rather than the antioxidant action it was bought for. Hydrolysis is the standing weakness of the phosphites covered under antioxidants for plastics, and buffered blends of Antioxidant 626, sold elsewhere as Ultranox 626, are the standard commercial answer.

Hydrotalcite as a laser-marking booster#

A magnesium-aluminium carbonate LDH can replace most of a commercial laser-marking additive: Chunping Chen, Dermot O'Hare and colleagues at the University of Oxford (ACS Applied Polymer Materials, 2024) substituted 95 % of the Iriotec 8815 in an epoxy with Mg2Al-CO3 LDH and still produced readable QR codes. The Iriotec particles in that comparison are 50 to 200 nm, and the substitution reduced the amount of the commercial additive needed without losing the contrast the code depends on. LDH boosters sit beside the antimony, bismuth and mica chemistries under laser marking additives.

Hydrotalcite outside plastics: antacid, mineral and catalyst uses#

Outside plastics, hydrotalcite is best known as a pharmaceutical antacid, which is why a search for the bare term returns tablets rather than additives. That use is outside the scope of this page, and no indication, dose or efficacy statement is made here. As a mineral, hydrotalcite is white with a greasy luster, has a specific gravity of 2.03 to 2.09 and a Mohs hardness of 2, and it is the compound that gave its name to the whole hydrotalcite-like family of anionic clays. Layered double hydroxides are also a known support and precursor family in heterogeneous catalysis, a field this page names without describing, because our source library holds no catalysis data for the substance.

Is hydrotalcite a filler?#

No: hydrotalcite is a functional additive used at stabilizer levels, not a filler used at loading levels, and it is sold for its acid-scavenging chemistry rather than for volume or stiffness. The sourced polyvinyl chloride formulation uses 2.4 phr, while the loading levels that define fillers for plastics start an order of magnitude above a stabilizer dose, in the tens of phr.

Does hydrotalcite affect nucleation in polypropylene?#

Acid scavenger choice interacts with nucleation: Simanke and colleagues (2016) found a negative interaction between calcium stearate and sodium benzoate at 1000 to 2200 ppm in polypropylene, which is one reason formulators pair phosphate-ester nucleators with a non-soap scavenger. Kisuma sells Setogem RD as a dual nucleator and acid scavenger for polypropylene at 200 to 300 ppm, and a related layered double hydroxide, quintinite surface-treated with cis-1,2-cyclohexanedicarboxylic acid, is covered at up to 2000 ppm in polyolefins by Food Contact Notification 2476, notified by Kisuma on 12 February 2026 for that dual function. Quintinite is not hydrotalcite, and no source in our source library states that hydrotalcite itself nucleates polypropylene; scavenger choice is nevertheless part of the selection logic for nucleating agents.

Is hydrotalcite natural or synthetic?#

Both exist, but plastics use only the synthetic form: hydrotalcite occurs naturally as a mineral with a Mohs hardness of 2, while every grade named on this page is manufactured to a controlled magnesium-to-aluminium ratio and particle size. Synthetic grades are non-stoichiometric, which is why the idealised mineral formula and its calculated molecular weight of about 604 g/mol describe the structure rather than the product in the bag.