THEIC (Tris(2-Hydroxyethyl) Isocyanurate): Properties, Uses in Plastics and Regulatory Status

THEIC (tris(2-hydroxyethyl) isocyanurate, CAS 839-90-7) is a polyol co-stabilizer used in calcium-zinc heat stabilizer packages for PVC, where it complexes the zinc chloride that the zinc soap leaves behind. Because a co-stabilizer only works as part of a package, the first question is what THEIC contributes that the calcium and zinc soaps cannot.

Its regulatory record consists largely of absences. THEIC is not on the Union list of Regulation (EU) No 10/2011 in the consolidated text of 16 March 2025, not on the REACH Candidate List of substances of very high concern, and not on the California Proposition 65 list of 31 July 2026. THEIC is one of 437 substance profiles in our directory of plastic additives, each carrying the same identity, dosage and regulatory fields.

This page holds the identity of an isocyanurate triol, the zinc chloride complexation that makes it a co-stabilizer rather than a primary heat stabilizer, 3 documented uses, a matrix across 10 regulatory instruments dated 23 September 2026, the notified statements H315, H319 and H335, the comparison with pentaerythritol and dipentaerythritol, and the specification points a buyer sends out where no verified producer list exists.

Table T1. THEIC identity card.

Not to be confused with TAIC (triallyl isocyanurate, CAS 1025-15-6), a crosslinking coagent, or with the English noun "theic".

Footnote: identity, physical data and GHS notifications from PubChem CID 13286; regulatory entries from the EU, US and Californian legal texts cited in each section. Status as of 23 September 2026.

What Is THEIC (Tris(2-Hydroxyethyl) Isocyanurate)?#

THEIC is a triol: a six-membered isocyanurate ring (1,3,5-triazinane-2,4,6-trione) that carries a 2-hydroxyethyl group on each of its three ring nitrogens, which gives the molecule three reactive hydroxyl groups. Positions 1, 3 and 5 of that ring are the nitrogen atoms and positions 2, 4 and 6 the carbonyl carbons, which the systematic name 1,3,5-tris(2-hydroxyethyl)-1,3,5-triazinane-2,4,6-trione states in full. The molecule has the formula C9H15N3O6 and a molecular weight of 261.23 g/mol. Which part of that structure does the work in a PVC compound?

The three hydroxyl groups do. A polyol is a compound carrying two or more hydroxyl groups, and the polyol co-stabilizers used in PVC (pentaerythritol, dipentaerythritol, THEIC, sorbitol and trimethylolpropane) have those groups in common and little else in their skeletons. Those hydroxyls give THEIC both its chemical class, polyol (isocyanurate triol), and its function, co-stabilizer in calcium-zinc systems for PVC. The isocyanurate ring contributes thermal robustness rather than stabilizing chemistry, which is why the same ring reappears in the hindered-phenol antioxidants described further down this page.

What does THEIC stand for?#

THEIC stands for tris(2-hydroxyethyl) isocyanurate, and the same substance appears in catalogues as tris(2-hydroxyethyl)cyanurate and as 1,3,5-tris(2-hydroxyethyl)cyanuric acid. A fourth synonym, isocyanuric acid tris(2-hydroxyethyl) ester, is a legacy Chemical Abstracts name that describes an ester connectivity the molecule does not have, so CAS 839-90-7 rather than any name is the identifier to quote on an order.

Is THEIC a heat stabilizer or a co-stabilizer?#

THEIC is a co-stabilizer, not a primary heat stabilizer: it does not scavenge hydrogen chloride and it does not substitute labile chlorine, so it cannot stabilize PVC on its own. A formulator buys it as one component of a package, never as the stabilizer itself.

Five functions make up a complete PVC stabilizer system in the Frye and Horst framework: scavenging hydrogen chloride, substituting labile chlorine, interrupting polyene sequences, deactivating Lewis-acidic metal chlorides and acting as an antioxidant. Metal soaps, hydrotalcite and epoxides scavenge hydrogen chloride; zinc soaps, organotin mercaptides and beta-diketones substitute labile chlorine; polyols such as THEIC and organic phosphites deactivate metal chlorides, which is function 4 and the only one THEIC performs. The hub on PVC heat stabilizers compares the calcium-zinc, organotin, lead and organic-based systems a co-stabilizer can join, and all components together are 1 to 5 % of a PVC formulation according to ECVM, 2 to 4 % typically in Ullmann's.

Is THEIC the same as isocyanuric acid?#

No: isocyanuric acid is the unsubstituted ring, while THEIC carries a 2-hydroxyethyl group on each of the three ring nitrogens, which is why its formula is C9H15N3O6 and its molecular weight 261.23 g/mol. That substitution is what makes THEIC a polyol at all, because the unsubstituted ring has no hydroxyethyl arms to offer a metal ion. Our source library holds no record for isocyanuric acid, which is not a plastics additive, so this page gives no CAS number or property value for it.

How Does THEIC Stabilize PVC?#

THEIC stabilizes PVC indirectly: its three hydroxyl groups complex the zinc chloride that forms when the zinc soap of a calcium-zinc package substitutes labile chlorine, and removing that Lewis acid stops it from catalysing further dehydrochlorination. Polyol-type zinc chloride complexation is the only mechanism our source library records for THEIC, and it places the substance downstream of the primary stabilizers rather than in competition with them. Why does one Lewis acid matter so much in this polymer?

PVC degrades earlier than any other commodity thermoplastic. Unstabilized PVC loses hydrogen chloride above about 70 °C (158 °F), its thermal degradation sets in near 250 °C (482 °F), and polyethylene by comparison holds to about 400 °C (752 °F). Each eliminated hydrogen chloride molecule leaves a conjugated double bond behind, the sequence grows into a polyene, and 0.1 % dehydrochlorination is already enough to cause unacceptable discoloration. Zinc chloride catalyses that elimination, so an agent that removes it protects colour long after the first minutes of processing. The zipper elimination that the zinc chloride catalyses is set out on PVC thermal degradation.

Our source library records no rate constant, no complexation stoichiometry and no comparative efficiency for THEIC, so this page quantifies none of it.

What is zinc burning, and how do polyols delay it?#

Zinc burning is the sudden blackening of a PVC compound once the zinc chloride formed from the zinc soap builds up faster than the calcium soap can convert it back, and polyols such as THEIC delay it by complexing that zinc chloride. The calcium soap regenerates the zinc soap by ligand exchange, ZnCl2 + Ca(OOCR)2 → Zn(OOCR)2 + CaCl2, which returns the zinc to its active carboxylate form and moves the chloride onto calcium. The labile-chlorine substitution step that creates the zinc chloride in the first place was described by Frye and Horst in the Journal of Polymer Science in 1959. The zinc soap in question is usually zinc stearate, which supplies the zinc that later becomes zinc chloride, while calcium stearate supplies the regenerating calcium.

What Are the Physical and Chemical Properties of THEIC?#

THEIC is a white powder with a melting point of 135 °C (275 °F) and a molecular weight of 261.23 g/mol. Those two values, together with the formula C9H15N3O6, are the complete set of physical constants that PubChem record CID 13286 carries for the substance.

Table T2. THEIC physical and chemical properties.

PubChem record CID 13286 does not carry a boiling point, a density or a water-solubility figure for THEIC, so this page states none; ask the supplier for the grade's technical data sheet. Trader listings print solubility and bulk-density values without naming a source, and none is reproduced here. The melting point of 135 °C (275 °F) is the one number a compounder uses directly, because it marks the temperature at which the white powder starts to change state inside a dry blend.

Which Polymers Use THEIC, and at What Dosage?#

THEIC is used in PVC, and only in PVC: it appears as a polyol component inside calcium-zinc stabilizer packages rather than as a stand-alone additive. Rigid and flexible PVC take the same class of package, and our source library records no second polymer for the substance.

No sourced phr range for THEIC exists in our source library, so this page gives none. What is documented is the total: all stabilizer components together make up 1 to 5 % of a PVC formulation, and 2 to 4 % is typical. PVC recipes are written in PHR (parts per hundred resin), which is why a stabilizer level and a weight percent are not the same number, and a polyol quoted in phr has to be converted before comparison with any weight-percent limit.

Table T3. THEIC by polymer, role and documented level.

Trader pages quote THEIC levels in a 0.1 to 0.5 phr style. None of those figures carries a source, and that gap is stated here rather than filled. Where the stabilizer package sits among the other additives for PVC is shown in the full formulation guide.

What Is THEIC Used For? Applications in Plastics#

THEIC has 3 documented uses: as a polyol co-stabilizer in calcium-zinc PVC packages, as a raw material for the hindered-phenol antioxidant registered under CAS 34137-09-2, and as a building block for polyester wire enamels outside plastics. The 3 documented uses are listed below.

• Calcium-zinc stabilizer packages for rigid and flexible PVC, in which THEIC is the polyol that complexes zinc chloride.
• Antioxidant synthesis, in which all three hydroxyl groups are esterified to give the hindered phenol CAS 34137-09-2.
• Wire enamel polyesters, a non-additive use in which THEIC is a monomer, covered below the contextual border.

Calcium-zinc stabilizer one-packs#

THEIC reaches the compounder inside a one-pack: a pre-blended calcium-zinc stabilizer package that combines metal soaps, a polyol, an acid scavenger, a beta-diketone and lubricants in a single product. VinylPlus put calcium-zinc and calcium-organic systems at 83 % of EU PVC stabilizer use in its June 2023 summary to ECHA, which makes the package type THEIC belongs to the default European system. Calcium-zinc stabilizers combine the fast zinc soap with the regenerating calcium soap, and a polyol such as THEIC keeps the resulting zinc chloride out of the way.

Pre-blended one-pack additive systems are how most compounders buy a polyol at all, because the polyol is dosed in fractions of a phr. Our source library records no commercial one-pack that contains THEIC by name, so this page names no product, and what the buyer verifies is the heat stability of the finished compound rather than its polyol content.

THEIC as a building block for a hindered-phenol antioxidant#

Esterifying all three THEIC hydroxyl groups with 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid gives a hindered-phenol antioxidant, CAS 34137-09-2, which the US Food and Drug Administration lists in 21 CFR 178.2010 while THEIC itself is not listed there. The triester belongs with the phenolic antioxidants, not with the heat stabilizers, and no substance page on this site covers it yet, so it appears here by CAS number only.

Two isocyanurate hindered phenols are easy to confuse. Irganox 3114, tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, CAS 27676-62-6, carries its hindered phenols on benzyl groups bonded directly to the ring nitrogens, which is a different molecule from the THEIC triester. The THEIC triester is linked through ester groups instead, the structural consequence of building an antioxidant from a triol.

How Is THEIC Performance Measured in PVC?#

A co-stabilizer such as THEIC is judged by how long a compound resists dehydrochlorination and discoloration, measured with the Congo red test (ISO 182-1:1990) and with static oven aging. The Congo red method detects the first hydrogen chloride evolved from a heated sample by an indicator colour change, and static oven aging tracks plaque colour over time. ISO 182-1 does not fix the temperature; the laboratory sets it, and published studies use 180 °C (356 °F) or 190 °C (374 °F).

What order of magnitude do those methods return? Jiang and colleagues reported in Materials in 2020 that a compound stabilized with 2.4 phr hydrotalcite, 0.3 phr zinc stearate and 0.3 phr zinc acetylacetonate reached 190 minutes to blackening in a 180 °C (356 °F) oven, while the Congo red time in the same study peaked at 46 minutes. That benchmark belongs to a hydrotalcite and zinc system, not to a THEIC system. The Congo red and oven methods are described in full on PVC heat stability testing.

No thermal stability time, no yellowness index and no percentage improvement is recorded for THEIC, so Table T4 leaves those cells open.

Table T4. What is measured on a THEIC-containing compound, and what our source library holds.

How Does THEIC Interact with Other PVC Stabilizers?#

THEIC shares a package with 4 other co-stabilizer classes, each of which closes a different gap left by the calcium and zinc soaps. Sodium perchlorate is used as a booster in calcium-zinc and organic-based systems, with no primary source for its mechanism in our source library. Every calcium-zinc package draws on more than one of the PVC co-stabilizers at once, and the 4 classes that sit beside a polyol are listed below.

• Beta-diketones, such as dibenzoylmethane and stearoylbenzoylmethane, which protect early colour by alkylating allylic chlorine.
• Acid scavengers, such as hydrotalcite, zeolite A and calcium hydroxide, which take up hydrogen chloride.
• Epoxides, such as epoxidized soybean oil and epoxidized linseed oil, which scavenge hydrogen chloride and plasticize at once.
• Organic phosphites, such as triphenyl phosphite and diphenyl isodecyl phosphite, which chelate metal chlorides and act as secondary antioxidants.

Epoxides and phosphites overlap the polyol function. ESBO (epoxidized soybean oil) scavenges hydrogen chloride and plasticizes at once, and it is listed for EU food contact as FCM 532 with a specific migration limit of 60 mg/kg.

Organic phosphites complex metal chlorides too, so choosing between a polyol and a phosphite is choosing between a solid carrier and a liquid one, not between two functions. Triphenyl phosphite does it from a liquid carrier and is REACH registered at 1,000 to 10,000 tonnes a year, a completeness of record THEIC does not have.

What Is the Regulatory Status of THEIC?#

THEIC is absent from the three lists that matter most to a PVC compounder: it is not on the Union list of Regulation (EU) No 10/2011, not on the REACH Candidate List of substances of very high concern, and not on the California Proposition 65 list of 31 July 2026. Our source library does not yet hold THEIC's REACH registration status, its position under Annex XIV or Annex XVII, its CLP harmonised classification or its US TSCA status, so those five cells read as being verified rather than carrying an assumption.

Table T5. THEIC regulatory matrix, status 23 September 2026.

What a registration, an authorisation and a restriction each mean is explained on REACH and plastic additives. An absence from a list is not a permission, and the five open cells above are the reason this page stops short of calling THEIC unregulated.

Is THEIC allowed in food-contact plastics?#

No, not in the EU as a listed additive: Annex I of Regulation (EU) No 10/2011 does not include THEIC, and an additive used in a food-contact plastic has to appear on that Union list unless a specific exemption in Article 6 applies. Two of the polyols that compete with THEIC are listed: pentaerythritol as FCM 279 and dipentaerythritol as FCM 311, both without a specific migration limit. The Union list, the Article 6 exemptions and the generic limits are set out on EU 10/2011, where a generic specific migration limit of 60 mg/kg and an overall migration limit of 10 mg/dm2 apply to listed substances.

In the United States, 21 CFR 178.2010 lists the THEIC triester (CAS 34137-09-2) but not THEIC itself. The same section caps pentaerythritol at 0.4 wt% of a rigid PVC compound as free pentaerythritol and stearoylbenzoylmethane at 0.5 wt% of vinyl chloride homopolymers. How 21 CFR 178.2010 lists a stabilizer is explained on FDA food contact rules (21 CFR).

Is THEIC an SVHC or restricted under REACH?#

No, THEIC is not a substance of very high concern: it does not appear on the REACH Candidate List as of 23 September 2026. Our source library does not record THEIC's REACH registration tonnage band, nor a check of Annex XIV or Annex XVII, so this page states neither. A neighbouring co-stabilizer shows what a complete record looks like: triphenyl phosphite is REACH registered at 1,000 to 10,000 tonnes a year, and its own absence from the Candidate List was confirmed against ECHA CHEM. Every plastic additive that has reached the SVHC Candidate List is tracked there; THEIC has never been added.

Is THEIC listed under California Proposition 65?#

No, THEIC does not appear on the California Proposition 65 list published by OEHHA on 31 July 2026. Pentaerythritol and dipentaerythritol are absent from the same list, so a switch between the three polyols changes nothing in a Proposition 65 assessment. Listing dates for the plastic additives that are on the list are on California Proposition 65.

Is THEIC Hazardous? Health and Safety Profile#

Suppliers notify THEIC to the ECHA classification and labelling inventory with three hazard statements: H315 for skin irritation, H319 for serious eye irritation and H335 for respiratory irritation. A notification is a self-classification by the companies placing the substance on the market, not a harmonised entry under the CLP Regulation, and only a harmonised classification binds every supplier alike. The 3 parts of the safety picture are listed below.

• Notified classification: skin irritation (H315), serious eye irritation (H319) and respiratory irritation (H335), reported through PubChem from the ECHA inventory.
• Absent from our source library: a harmonised CLP entry, LD50 and NOAEL values, and any ecotoxicity data. This page states none of them and does not repeat trader-page toxicity summaries.
• Consequence for handling: control dust when the powder is weighed into a blend and protect the eyes, both following from the three notified statements.

THEIC is not on the California Proposition 65 list and not listed under the POPs Regulation (EU) 2019/1021. Whether it carries a harmonised classification is open, so a supplier's safety data sheet reflects the notified statements rather than an agreed EU entry.

What Are the Alternatives to THEIC?#

The 2 direct alternatives to THEIC are the other polyols used in calcium-zinc packages, pentaerythritol and dipentaerythritol, while beta-diketones and hydrotalcite replace it only in part because they attack different steps of the degradation chain. Table T6 compares the 5 co-stabilizers by identity, melting point, mechanism and food-contact status, and the regulatory columns are where the polyols separate most sharply.

Table T6. THEIC compared with 4 co-stabilizers used in the same packages.

Footnote: °F values are converted from the °C values in our source library. Empty cells mean the value is not in our source library, not that the value is zero.

THEIC vs pentaerythritol#

Pentaerythritol is the regulated alternative: it does the same job as THEIC, complexing zinc chloride in a calcium-zinc package, but it is listed for EU food contact as FCM 279 and capped by the US Food and Drug Administration at 0.4 wt% of a rigid PVC compound, while THEIC is on neither list. The physical difference comes from the melting points: pentaerythritol melts at 258 to 260.5 °C (496 to 501 °F), roughly 125 °C (225 °F) above THEIC's 135 °C (275 °F), so the two powders behave differently in a dry blend. Pentaerythritol carries that FDA cap because it is listed, and its technical grade is about 88 % mono and 12 % di rather than a single compound.

THEIC vs dipentaerythritol#

Dipentaerythritol is the closest match to THEIC by molecular weight, 254.28 g/mol against 261.23 g/mol, and our source library records it as the polyol chosen where long-term stability matters in a calcium-zinc system. It melts at 212 to 220 °C (414 to 428 °F) and has a density of 1.33 g/cm3 at 25 °C, two values THEIC's record does not carry. The regulatory split repeats itself here: dipentaerythritol is listed for EU food contact as FCM 311 without a specific migration limit, and THEIC is absent from Annex I. Dipentaerythritol therefore answers the same formulation question with a complete food-contact record.

THEIC vs beta-diketones and hydrotalcite#

Beta-diketones and hydrotalcite are not substitutes for THEIC but partners: dibenzoylmethane alkylates allylic chlorine to protect early colour, hydrotalcite absorbs hydrogen chloride, and neither one complexes zinc chloride the way a polyol does. Dibenzoylmethane protects early colour by alkylating allylic chlorine, a step no polyol performs, and Michel and colleagues described that zinc-catalysed C-alkylation in 1981.

The acid scavenger works on a third species again. Hydrotalcite absorbs hydrogen chloride by exchanging interlayer carbonate for chloride, and it is listed for EU food contact as FCM 604 with no substance-specific migration limit. A calcium-zinc package therefore carries all three mechanisms at once rather than choosing between them.

Who Manufactures THEIC? Grades and Suppliers#

Our source library does not yet carry a verified manufacturer list for THEIC, so this page names no producer: naming one we have not verified would break the rule that every company entry on this site is checked. Catalogue and trading sites rank for the term, but an offer is not a verified production record.

What a buyer does instead is specify. A THEIC enquiry carries the identity (CAS 839-90-7 and EC 212-660-9), the assay, the melting point of 135 °C (275 °F) as the reference value, the colour, the moisture, the particle size and the form, meaning the substance itself or a calcium-zinc one-pack. Buyers should request the supplier's technical data sheet, safety data sheet and a statement of the notified GHS classification before qualifying a grade. Verified PVC stabilizer manufacturers and the families they cover are listed in our directory.

Table T7. What to ask a THEIC supplier for.

How Do Polyol Co-Stabilizers Fit into the PVC Stabilizer System?#

THEIC is one of 5 polyols that the literature groups as calcium-zinc co-stabilizers, beside pentaerythritol, dipentaerythritol, sorbitol and trimethylolpropane. The global PVC heat stabilizer split in 2023 was about 50 % calcium-based, 25.1 % lead and 15.4 % tin according to a secondary compilation, which is why the polyol class matters more every year: every calcium-based system produces zinc chloride that something has to hold. How the calcium, lead and tin systems divide the market is set out under PVC heat stabilizer types, and the polyols are the quiet component inside the largest of the three.

Non-plastics uses of THEIC: wire enamels and polyester resins#

Outside plastics, THEIC is a monomer rather than an additive: its three hydroxyl groups are esterified into the polyester backbone of wire enamels, where the isocyanurate ring raises the thermal class of the coating. Our source library records that use as a non-additive one, which is why THEIC also appears in catalogues aimed at coating formulators. PlasticAdditives.net does not cover paints and coatings, so this page gives no dosage, no thermal class number and no producer for the enamel application. Polyester resins built on THEIC belong in the same category, because the substance is consumed into the polymer rather than added to it.

THEIC and TAIC: two isocyanurate additives that are not interchangeable#

THEIC and TAIC share the isocyanurate ring and nothing else: THEIC carries three hydroxyethyl groups and complexes zinc chloride in PVC, while TAIC (CAS 1025-15-6) carries three allyl groups and acts as a crosslinking coagent in EVA and cable compounds. TAIC (triallyl isocyanurate) carries those three allyl groups on the same ring and crosslinks rather than stabilizes, and it belongs with the crosslinking coagents, a different additive family entirely.

What does "theic" mean outside chemistry?#

Outside chemistry, "theic" is an English noun that the Oxford English Dictionary and Collins record for a heavy tea drinker, which is why a search for the bare word returns dictionary entries rather than chemical data. In plastics, THEIC is always the abbreviation of tris(2-hydroxyethyl) isocyanurate, CAS 839-90-7.

Does THEIC need an SDS?#

Yes: suppliers issue a safety data sheet for THEIC, and its section 2 reflects the notified statements H315, H319 and H335 rather than a harmonised CLP entry. That sheet records identity, handling, storage and the supplier's own hazard assessment, and it is the one document in which a buyer sees the classification the producer actually applies.