Organotin Stabilizers: 4 Types, How They Work, Dosage and Regulation

Organotin stabilizers are mono- and di-alkyltin compounds, mainly tin mercaptides, that stop rigid PVC from releasing hydrogen chloride during melt processing, at 0.3-1.0 phr in US pressure pipe. They are the stabilizer of choice where clarity and early colour matter most, so which of the 4 alkyltin types suits which PVC product, and what do EU and US rules allow?

PVC consumes about 20,000 t of tin a year for stabilization, which makes organotins one of the most tin-intensive groups of plastic additives. That figure is an order of magnitude rather than a precise annual total, and it spans mercaptide and carboxylate tin chemistries across pipe, profile, film and CPVC.

Among PVC heat stabilizers, tin systems held about 15% of global demand in 2023, next to calcium-based systems at about 50% and lead at 25.1%. This article defines organotin stabilizers, explains how mono- and di-organotin mercaptides and carboxylates interrupt PVC dehydrochlorination, sets out the 4 commercial alkyltin types and their 2 ligand classes, maps where each type is used, gives sourced dosage ranges in phr, compares tin against calcium-zinc and lead systems, covers heat-stability testing, and lists the EU and US food-contact, drinking-water and REACH status of every type.

• 4 commercial alkyltin types: methyltin, butyltin, octyltin and estertin stabilizers
• 0.3-1.0 phr: organotin stabilizer level in US PVC pressure pipe (PPI TR-2, 2023)
• 0.18 mg/kg as Sn: EU group SML(T) for methyltin stabilizers (Regulation (EU) No 10/2011)
• 1 May 2025: REACH Annex XIV sunset date for DOTE

What Are Organotin Stabilizers?#

Organotin stabilizers are primary PVC heat stabilizers in which a tin atom carries 1 or 2 alkyl groups (methyl, butyl, octyl or ester-alkyl) and 2 or 3 sulfur or carboxylate ligands that react with the degrading polymer. The alkyl group sits on tin through a direct tin-carbon bond, and the remaining coordination sites carry either mercaptide (sulfur) ligands or carboxylate ligands such as maleate. Organotin heat stabilizers work almost exclusively in PVC and other chlorine-containing polymers, where they intercept the hydrogen chloride the resin releases on heating. Commercial products reach the compounder as liquids or powders, sold as mono-organotin and di-organotin blends rather than as single-species chemicals; the blend ratio, not one pure compound, is what a technical data sheet describes.

Mono-, di- and tri-organotins: which ones stabilize PVC?#

PVC is stabilized by mono- and di-organotins, used together as blends, because mono-organotins react fastest with labile chlorine and di-organotins last longer; tri-organotins such as tributyltin are not used as stabilizers. A mono-organotin (RSnX3) carries one alkyl group and reacts as the faster labile-chlorine exchanger, which gives a compound its early colour hold. A di-organotin (R2SnX2) carries two alkyl groups and reacts more slowly, which extends stability later in the heat history. Commercial organotin stabilizers combine both species in one blend so that fast initial protection and durable long-term stability come from the same package. The FDA definition of a methyltin stabilizer under 21 CFR 178.2010 states this directly: 5-90% monomethyltin tris(isooctylmercaptoacetate) blended with 10-95% dimethyltin bis(isooctylmercaptoacetate), with trimethyltin capped at 0.4%. Tri-substituted organotins, such as tributyltin (TBT) and triphenyltin (TPT), are not part of this system; REACH Annex XVII entry 20 limits them to 0.1% tin by weight in articles since 1 July 2010.

How Do Organotin Stabilizers Protect PVC?#

Organotin stabilizers protect PVC by replacing the unstable allylic chlorine atoms in the chain with stable thioether groups, by binding the hydrogen chloride the polymer releases, and by shortening the coloured polyene sequences that form. Unprotected PVC starts losing hydrogen chloride slowly between 100°C and 120°C and degrades rapidly near 250°C, the two-stage pattern that governs every stabilizer's job. The released HCl is autocatalytic: it accelerates further chlorine loss once it forms, and elimination proceeds along the chain in a zipper sequence that leaves conjugated polyene double bonds behind. As little as 0.1% dehydrochlorination already produces unacceptable discoloration, a threshold Tomaszewska et al., Polymers (2021), attribute to the strong chromophore effect of short polyene sequences, which start at the allylic and tertiary chlorine sites Starnes, College of William & Mary, Progress in Polymer Science 27 (2002) 2133, identifies as the zipper mechanism's origin points.

The organotin stabilization cycle works in 4 steps.

1. The tin mercaptide exchanges its sulfur ligand for an allylic chlorine, leaving a stable thioether group on the polymer chain and forming a tin chloride byproduct. This substitution step follows the framework Frye and Horst, Journal of Polymer Science 40 (1959) 419, established for organotin mercaptide chemistry.
2. The tin compound binds the hydrogen chloride the resin has already released, removing it from the system before it can catalyse further degradation.
3. The mercaptan ester released in step 1 adds across the double bonds of any polyene sequence that has already formed, breaking up the conjugation that causes colour.
4. The organotin chloride formed in step 2 catalyses re-addition of HCl across residual unsaturation, which interrupts the zipper elimination before it can propagate further, a re-addition role Van Hoang, Michel and Guyot, CNRS Lyon, Polymer Degradation and Stability (1982), confirmed kinetically.

The zipper mechanism itself, including how allylic and tertiary chlorines initiate it, is covered step by step under PVC thermal degradation and dehydrochlorination.

Why do tin stabilizers give the best transparency and early colour?#

Tin stabilizers give the clearest and least yellow rigid PVC because they substitute labile chlorine before polyenes can grow, and they do so without adding opaque metal salts to the compound. Baerlocher's organotin data describe "very good early color (no yellowing)" and "very good color retention" alongside "high throughput and no plate out," properties that keep the stabilizer package from clouding a clear compound. Arkış and Balköse, Polymer Degradation and Stability 88 (2005) 46, and Fisch and Bacaloglu, Witco/Crompton, Plastics, Rubber and Composites 28 (1999) 119, report the same transparency and early-colour advantage for organotin systems relative to metal-salt stabilizers. Zinc-based systems form zinc chloride as a reaction byproduct, a strong Lewis acid that catalyses further dehydrochlorination and causes the sudden discoloration known as zinc burning. Lead salts substitute labile chlorine less efficiently than tin mercaptides, so lead-stabilized compounds start from a poorer early colour baseline. The general causes of PVC discoloration, beyond the stabilizer choice, are covered under why plastics turn yellow or pink.

What Are the 4 Types of Organotin Stabilizers?#

The 4 types of organotin stabilizers are methyltin, butyltin, octyltin and estertin stabilizers, named after the alkyl group bonded to tin; methyltins dominate US pipe, butyltins US siding and octyltins clear food and pharma film. Arkış, İzmir Institute of Technology thesis chapter 3.3, names methyl, n-butyl and n-octyl as the 3 major organotin types used industrially; estertins form a fourth, smaller commercial class built on a 2-carbobutoxyethyl group rather than a plain alkyl chain. The table below lists an example compound, typical tin content, main PVC use and EU food-contact status for each type.

1. Methyltin stabilizers#

Methyltin stabilizers are blends of dimethyltin and monomethyltin mercaptoacetates with 15-21% tin, and they are the standard heat stabilizer for US rigid PVC pressure, DWV and sewer pipe at 0.3-1.0 phr. The FDA blend covers dimethyltin bis(isooctylmercaptoacetate) and monomethyltin tris(isooctylmercaptoacetate), together with their 2-ethylhexyl mercaptoacetate analogues (CAS 57583-35-4 and 57583-34-3), under 21 CFR 178.2010, with trimethyltin capped at 0.4% of the blend. Beyond pressure pipe, methyltins stabilize clear rigid packaging, pipe fittings and CPVC, and they are not classified as an SVHC and are not covered by REACH Annex XVII entry 20. The EU lists them in food-contact group 9 with a group SML(T) of 0.18 mg/kg as tin. Producers sell methyltin mercaptides under trade names including Advastab TM (PMC Organometallix), Mark (Galata Chemicals), REA TIN (Reagens) and Akcrostab T (Valtris). Identity data and hazard notifications for the leading methyltin mercaptide are on methyltin mercaptide.

2. Butyltin stabilizers#

Butyltin stabilizers such as dibutyltin bis(isooctyl mercaptoacetate) serve weatherable US rigid PVC, above all vinyl siding and window profiles, where Thermolite 137 (14% tin) is a typical grade. Dibutyltin bis(isooctyl mercaptoacetate) carries CAS number 25168-24-5, EC number 246-703-8 and a molar mass of 639.6 g/mol. Thermolite 137 is a clear liquid with a specific gravity of 1.04 at 25°C, and its technical data sheet describes it as "especially designed for weatherable applications such as siding and window profiles." Butyltin dosage in siding and profile formulations is set by supplier starting formulations rather than by a single sourced phr value in the range PPI publishes for pipe. The substance is not an SVHC, and it does not appear in Regulation (EU) No 10/2011's food-contact list; it falls instead under REACH Annex XVII entry 20, which limits dibutyltin (DBT) compounds to 0.1% tin by weight in general-public mixtures and articles since 1 January 2012. Full identity data and the entry 20 derogation history are on butyltin mercaptide.

3. Octyltin stabilizers#

Octyltin stabilizers, mainly DOTE blended with MOTE, stabilize crystal-clear food and pharmaceutical PVC film, sheet and bottles, and since 1 May 2025 DOTE needs a REACH authorisation for non-food uses in the EU. DOTE, dioctyltin bis(2-ethylhexyl mercaptoacetate) (CAS 15571-58-1, EC 239-622-4, 751.8 g/mol), is sold commercially as a reaction mass with MOTE, monooctyltin tris(2-ethylhexyl mercaptoacetate) (CAS 27107-89-7), because the mono- and di-substituted species work together the same way methyltin blends do. Octyltins carry the lowest EU specific migration limit of any organotin group, 0.006 mg/kg as tin for di-n-octyltins under Regulation (EU) No 10/2011. DOTE has been an SVHC since 17 December 2014 for reproductive toxicity and sits on REACH Annex XIV (entries 58 and 59) since Regulation (EU) 2022/586 of 8 April 2022, with a sunset date of 1 May 2025 and no exempted uses; its food-contact use stays outside that authorisation requirement. The outcome of any authorisation application is not established. Identity and the authorisation timeline are tracked on DOTE (dioctyltin bis(2-ethylhexyl mercaptoacetate)).

4. Estertin and other organotins#

Estertins carry a 2-carbobutoxyethyl group on tin instead of a plain alkyl chain, and the EU allows the main estertin mercaptide in food-contact plastics with a specific migration limit of 18 mg/kg. The lead compound is bis(2-carbobutoxyethyl)tin bis(isooctyl mercaptoacetate), CAS 63397-60-4, listed under EU food-contact material number FCM 710 with that 18 mg/kg limit expressed for the substance itself rather than as tin. The US FDA lists the same estertin, together with a second estertin (CAS 63438-80-2) and dodecyltin (CAS 67649-65-4 and 84030-61-5), under 21 CFR 178.2650. In the EU, organotin stabilizers overall serve mainly the high-transparency and demanding-processing segment of the PVC market, a niche where estertins compete alongside octyltins.

Tin Mercaptides vs Tin Carboxylates: What Does the Ligand Change?#

Tin mercaptides give the strongest heat stability and are used in almost all tin-stabilized rigid PVC, while sulfur-free tin carboxylates such as maleates trade some heat stability for better light stability. Tin mercaptides use sulfur-based mercaptoacetate or reverse-ester ligands, and they dominate rigid PVC because sulfur reacts fastest with the labile chlorine that starts degradation. Sulfur-free tin carboxylates, mainly maleates and laurates, give up some of that heat-stability advantage in exchange for better resistance to UV-driven yellowing, because a maleate ligand reacts with polyene sequences by Diels-Alder addition rather than by the mercaptan-addition route mercaptides use. The table below compares the two ligand classes across 5 criteria.

Mercaptoacetates, reverse esters and sulfide-bridged mercaptides#

Most tin mercaptides use isooctyl or 2-ethylhexyl mercaptoacetate ligands, while reverse-ester grades such as methyltin-2-mercaptoethyl oleate sulfide use mercaptoethyl ester ligands instead of the classic thioglycolate structure. Isooctyl and 2-ethylhexyl mercaptoacetates, also called thioglycolates, are the ligands behind the standard methyltin, butyltin and octyltin mercaptides described above. Reverse-ester methyltin stabilizers (CAS 68442-12-6, 151436-98-5 and 201687-57-2) carry their own FDA limits under 21 CFR 178.2010: up to 1.0% in pipe and up to 2.0% in fittings that contact food-plant water. The EU lists the lead reverse-ester compound under food-contact material number FCM 726, inside the same methyltin group 9 that carries the 0.18 mg/kg SML(T). Formulators may add butylated hydroxytoluene (BHT) as an optional antioxidant constituent, up to 5% of the reverse-ester formulation, under the same FDA clearance.

Sulfur-free tin maleates#

Tin maleates such as dioctyltin bis(ethyl maleate) are sulfur-free organotin stabilizers used at about 2 wt% in rigid and flexible PVC where light stability counts more than maximum heat stability. Dioctyltin bis(ethyl maleate) (CAS 68109-88-6, EC 268-500-3, 631.4 g/mol) is not an SVHC and does not appear in Regulation (EU) No 10/2011's food-contact list, though the REACH Annex XVII entry 20 paragraph for dioctyltin (DOT) compounds applies to the listed consumer articles that contain it. ECHA's mapping of plastic additive uses places it in the 100 to 1,000 t/a REACH tonnage band. This compound is distinct from the "di(n-octyl)tin maleate polymer" the FDA lists separately under 21 CFR 178.2650 at 25.2-26.6% tin; the two are different substances despite the shared maleate chemistry. Identity and REACH data for the compound are on dioctyltin maleate stabilizers.

Where Are Organotin Stabilizers Used?#

Organotin stabilizers are used in rigid PVC: pressure and drain pipe, fittings, vinyl siding, window profiles, CPVC and clear film, sheet and bottles, with North America relying on tin for almost all rigid PVC. Europe concentrates organotin use in the high-transparency and demanding-processing segments of the PVC market rather than across the whole rigid PVC volume, because calcium-zinc and calcium-organic one-pack systems together account for 83% of EU stabilizer use (VinylPlus, 2023). The 4 applications below share the same underlying need: a stabilizer that survives a specific processing temperature and end-use environment without sacrificing clarity or colour. Complete recipes for the largest of them are compared under rigid PVC (uPVC) formulations.

Rigid PVC pipe and fittings#

US PVC pressure pipe is stabilized with 0.3-1.0 phr of a PPI-listed tin stabilizer, usually a methyltin mercaptide, under the PPI TR-2 (2023) range composition that qualifies the compound for its hydrostatic design basis. PPI TR-2 lists this range for PVC 1120, cell class 12454 compounds rated to a hydrostatic design basis of 4,000 psi at 73°F, and it names Galata Mark, PMC Advastab and Thermolite, Reagens REA TIN and Valtris Akcrostab as qualifying organotin stabilizers. Individual grades carry narrower ranges inside that envelope: Thermolite 150 runs 0.30-0.40 phr, Thermolite 170 runs 0.30-0.50 phr, and TM-697 spans the full 0.20-1.00 phr. European pipe compounds have used calcium-based stabilizer systems since the region's lead phase-out, while Reagens still lists both octyltin and methyltin grades for pipe applications. Tin, calcium-zinc and lead pipe systems are compared on stabilizers for PVC pipes.

Vinyl siding and window profiles#

US vinyl siding and window profiles use butyltin or methyltin mercaptides, while European window profiles moved to calcium-based one-packs after the lead phase-out. A typical siding capstock runs up to 25% of the product's thickness and carries about 10% titanium dioxide for weathering resistance, over a substrate that carries about 15% ground limestone and a small quantity of tin mercaptide stabilizer. Window profiles follow a similar tin-stabilized recipe in North America. EU one-pack systems covering the same application are described under stabilizers for PVC window profiles.

Clear rigid film, sheet and bottles#

Crystal-clear rigid PVC for blister packs, food trays, sheet and bottles uses octyltin, methyltin or estertin stabilizers, because they combine clarity with EU and FDA food-contact listings. Calcium-based systems exist as an alternative for transparent food packaging, but tin mercaptides remain the reference choice where the compound must stay optically clear through repeated reheating cycles. Octyltin grades dominate the highest-clarity, food-contact end of this segment, while methyltin and estertin grades cover pharma-grade film and sheet that need the same clarity with a different regulatory listing. Blister and food-film grades built on each tin type are compared on heat stabilizers for rigid PVC film and food/pharma packaging.

CPVC#

CPVC (63-69% chlorine, service up to about 93°C) is stabilized mainly with methyltin or butyltin systems, because its higher processing temperature releases more HCl than standard PVC. The added chlorine content that gives CPVC its higher heat-deflection temperature also means more labile chlorine sites for a stabilizer to manage during extrusion or moulding. Reagens markets dedicated "CPVC superpacks" that combine an organotin stabilizer with the lubricant and processing-aid package CPVC compounding needs. Superpacks and resin types are covered on heat stabilizers for CPVC.

How Much Organotin Stabilizer Does PVC Need?#

Rigid PVC pipe needs 0.3-1.0 phr organotin stabilizer, and across all PVC stabilizer types the stabilizer share stays within 1-5% of the formulation (ECVM). This 0.3-1.0 phr range is expressed in PHR (parts per hundred resin), the parts-per-hundred-resin convention that states every PVC formulation ingredient relative to 100 parts of resin. The legal ceilings that regulators publish are maxima, not dosages: the FDA caps methyltin blends at 2 wt% of rigid PVC under 21 CFR 178.2010, reverse-ester methyltins at 1.0% in pipe and 2.0% in fittings, octyltin, estertin and dodecyltin stabilizers together at 3 phr under 21 CFR 178.2650, and ECHA's mapping of dioctyltin bis(ethyl maleate) uses puts a typical concentration at 2 wt% in soft and rigid PVC. The table below sets sourced dosage levels next to these legal caps.

Legal maxima are ceilings, not recommended dosages.

A pipe compound with 0.70 phr tin stabilizer in a 108.03 phr formulation contains 0.65 wt% stabilizer (0.70 / 108.03 x 100), the conversion PPI TR-2's example formulation illustrates. Readers can check any similar conversion with the PHR to weight percent calculator. No sourced phr value exists in our source library for octyltin film, butyltin siding or CPVC tin systems; those levels are set by each supplier's starting formulations rather than by a published range composition.

Organotin vs Calcium-Zinc vs Lead Stabilizers: How Do They Compare?#

Organotin stabilizers give better clarity and early colour than calcium-zinc or lead systems at 0.3-1.0 phr in US pipe, while calcium-zinc dominates the EU (83% of stabilizer use with calcium-organic systems) and lead is restricted to below 0.1% in EU PVC since 29 November 2024. Calcium-zinc systems substitute labile chlorine at the zinc site and rely on the calcium soap to regenerate the zinc chloride byproduct back to an active zinc carboxylate, which is why they need co-stabilizers such as phosphites, polyols and beta-diketones to reach organotin-level performance. Zinc's own reaction byproduct, zinc chloride, is a strong Lewis acid that can trigger the rapid discoloration known as zinc burning if the zinc soap is not continuously regenerated. Lead salts scavenge hydrogen chloride effectively and give PVC very long-term stability and good electrical volume resistivity, which is why cable compounds used lead for decades, but lead substitutes labile chlorine less efficiently than tin mercaptides and starts from a poorer early colour.

Regulation (EU) 2023/923 (Annex XVII entry 63) has limited lead to below 0.1% by weight in PVC placed on the EU market since 29 November 2024, with recovered rigid PVC allowed up to 1.5% until 28 May 2033. Globally in 2023, calcium-based systems held about 50% of PVC stabilizer demand, lead held 25.1% and tin held 15.4%, a split that reflects the EU's calcium-based pipe and profile market alongside continued lead and tin use elsewhere. Co-stabilizer packages for the calcium-based route are explained on calcium-zinc stabilizers, and the entry 63 limits are detailed under lead stabilizers. Formulators who need a heavy-metal-free package outside both routes can compare organic-based stabilizers (OBS).

Global 2023 stabilizer split (Wikipedia, secondary source): calcium about 50%, lead 25.1%, tin 15.4%.

How Is the Heat Stability of Tin-Stabilized PVC Tested?#

The heat stability of tin-stabilized PVC is tested with the Congo red method (ISO 182-1), static oven ageing and dynamic stability in a torque rheometer, each measuring how long the compound resists HCl release or discoloration before failure. The 3 methods below cover the main heat-stability test approaches used on organotin-stabilized compounds.

• Congo red method (ISO 182-1:1990): heats a PVC sample and times the colour change of a Congo red indicator paper as it detects the hydrogen chloride the sample releases, at a temperature the testing laboratory sets, commonly 180°C or 190°C in published studies.
• Static oven ageing: exposes the compound at a fixed oven temperature, typically 180°C, and tracks the colour sequence from yellow through orange and brown to black as polyene sequences lengthen.
• Dynamic (torque rheometer) stability: measures fusion and degradation behaviour under shear and heat together, which reflects processing conditions more closely than a static oven test alone.

No standard fixes a single pass or fail time for tin-stabilized compounds; the temperature and endpoint are set by the testing laboratory and the specification the compound must meet. Test conditions across the 3 methods are compared under PVC heat stability testing.

Which Organotin Stabilizers Are Allowed in Food Contact and Drinking Water?#

Methyltin, octyltin and estertin stabilizers are listed for food-contact PVC in both the EU (Regulation (EU) No 10/2011, with limits expressed as tin) and the US (21 CFR 178.2010 and 178.2650), while butyltin stabilizers are not listed in the EU. Each jurisdiction expresses its limit differently: the EU sets a specific migration limit per organotin group, and the US sets a maximum use level in the finished compound. The 3 sections below give the EU limits, the US limits and the separate drinking-water rules that apply to PVC pipe.

EU 10/2011 limits for methyltin, octyltin and estertin#

Regulation (EU) No 10/2011 limits the migration of methyltins to 0.18 mg/kg of food, di-n-octyltins to 0.006 mg/kg and mono-n-octyltins to 1.2 mg/kg, all expressed as tin, and sets 18 mg/kg for the estertin mercaptide. These limits apply as group restrictions: every methyltin food-contact material number in group 9 shares the single 0.18 mg/kg cap, so a compound using more than one group 9 substance must still stay under that combined limit. Di-n-octyltins and mono-n-octyltins form 2 separate groups with their own, much lower limits, a reflection of the greater regulatory scrutiny octyltin compounds like DOTE have received. Butyltins have no entry in Regulation (EU) No 10/2011's Union list at all, so they carry no EU food-contact clearance. Group restrictions and overall migration limit rules are explained on EU 10/2011.

Source: EUR-Lex consolidated text of 16 March 2025.

FDA 21 CFR 178.2010 and 178.2650 limits#

The FDA clears methyltin mercaptide blends at up to 2 wt% in rigid PVC under 21 CFR 178.2010 and caps octyltin, estertin and dodecyltin stabilizers at 3 phr in total under 21 CFR 178.2650. Section 178.2010 names the methyltin blend components by CAS number (54849-38-6, 57583-34-3, 26636-01-1, 57583-35-4) for food contact up to 88°C, plus a separate allowance for the reverse-ester methyltin in pipes carrying food-plant water. Section 178.2650 covers a wider set of octyltin, estertin and dodecyltin substances, including di(n-octyl)tin S,S'-bis(isooctylmercaptoacetate) at 15.1-16.4% tin, di(n-octyl)tin maleate polymer at 25.2-26.6% tin, a C10-16 alkyl mercaptoacetate octyltin mixture (CAS 83447-69-2) and (n-octyl)tin tris(isooctylmercaptoacetate) (CAS 26401-86-5) at 13.4-14.8% tin, each subject to its own food-type and temperature limit of 75°C, 66°C or 71°C. DOTE itself, the 2-ethylhexyl ester, is not named in section 178.2650. Conditions of use for the methyltin clearance are decoded on 21 CFR 178.2010, and section 178.2650 is covered with the other vinyl rules under FDA food contact rules for plastic additives.

Drinking-water pipe: EU positive lists and NSF/ANSI 61#

From 31 December 2026, EU drinking-water pipe may use methyltin stabilizers listed on the European positive list, which includes dimethyltin bis(isooctyl mercaptoacetate) (entry 0561) and monomethyltin tris(isooctyl mercaptoacetate) (entry 0606). Implementing Decision (EU) 2024/367, adopted under Directive (EU) 2020/2184, sets that 31 December 2026 application date and schedules a review of both entries for 31 December 2028. In the US, drinking-water pipe compounds instead rely on NSF/ANSI/CAN 61 health-effects certification, under which suppliers publish NSF-authorized tin stabilizer grades for PVC pipe alongside the PPI TR-2 range composition. Octyltin, butyltin and dioctyltin maleate drinking-water entries are not established in either system and are not stated here. Entry numbers and review dates for the full EU list are on plastic additives in drinking-water contact, and the complete pipe compound is on additives for PVC pipe.

What Is the REACH Status of Organotin Stabilizers?#

No organotin PVC stabilizer is banned outright in the EU: methyltins are not covered by REACH Annex XVII entry 20, dibutyltin and dioctyltin compounds are limited to 0.1% tin in listed consumer articles, and DOTE needs an authorisation since its sunset date of 1 May 2025. REACH (Regulation (EC) No 1907/2006) treats each alkyltin type differently depending on its substitution level and known hazard profile, so a single "organotin restriction" does not exist; the 3 sections below give the current status type by type. Every paragraph of entry 20 is quoted on organotin restrictions.

Annex XVII entry 20: DBT, DOT and tri-organotin limits#

REACH Annex XVII entry 20 limits dibutyltin (DBT) and dioctyltin (DOT) compounds to 0.1% tin by weight in listed consumer products since 1 January 2012, and tri-substituted organotins to 0.1% tin in articles since 1 July 2010. The DBT restriction carried transitional derogations that ran until 1 January 2015 for specific product categories:

• Soft PVC profiles, whether sold alone or coextruded with hard PVC
• Outdoor PVC-coated fabrics
• Outdoor rainwater pipes, gutters and fittings
• Roofing and facade covering

The DOT restriction applies from 1 January 2012 to skin-contact textiles, gloves, footwear, wall and floor coverings, childcare articles, feminine hygiene products, nappies and RTV-2 moulding kits. Food-contact materials under Regulation (EC) No 1935/2004 are exempt, and the entry traces back through Commission Decision 2009/425/EC to Regulation (EU) No 276/2010, which first introduced the organotin restrictions into Annex XVII. Methyltin compounds are not covered by entry 20 at all. REACH Annex XVII restrictions on plastic additives beyond entry 20 are described under REACH Annex XVII restrictions on plastic additives.

SVHC and Annex XIV: DOTE and dibutyltin dichloride#

DOTE and its reaction mass with MOTE have been SVHCs since 17 December 2014 and sit on REACH Annex XIV (entries 58 and 59), so EU uses outside food contact need an authorisation since the sunset date of 1 May 2025. DOTE (CAS 15571-58-1, EC 239-622-4) and the DOTE/MOTE reaction mass (CAS 64685-81-0, EC 915-270-3) were added to the SVHC Candidate List for reproductive toxicity (Article 57c). Regulation (EU) 2022/586 of 8 April 2022 added both to Annex XIV, with a latest application date of 1 November 2023 and no exempted uses; food-contact uses stay outside the authorisation requirement (Article 56(5)(b)). Dibutyltin dichloride (CAS 683-18-1, EC 211-670-0) has been an SVHC since 19 December 2012, though butyltin mercaptide itself does not carry that listing, and a dioctyltin dilaurate group entry (EC 799-973-9) has been an SVHC since 19 January 2021. Methyltin mercaptides are not SVHCs, and the outcome of any Commission decision on DOTE authorisation applications is not established. Sunset dates for every Annex XIV entry are on the REACH Annex XIV authorisation list.

ECHA's 2023 PVC additives investigation#

ECHA's November 2023 investigation of 63 PVC additives singled out organotin stabilizers, next to ortho-phthalates and lead, as candidates for further REACH restriction rather than restricting PVC itself. The investigation report reviewed the full additive package used in PVC, not organotins alone, and concluded that a restriction dossier targeting specific additive groups would address the risks ECHA identified more directly than a restriction on the polymer. Whether ECHA has since opened a formal restriction process for organotin stabilizers is not established.

Who Makes Organotin Stabilizers?#

Organotin stabilizers are made by PMC Organometallix (Advastab, Thermolite), Galata Chemicals (Mark), Reagens (REA TIN), Valtris (Akcrostab T), Baerlocher and Songwon, with Hubei Benxing among the Chinese methyltin producers. PMC Organometallix, part of the PMC Group in Mount Laurel, New Jersey, covers the methyl, butyl and octyl alkyl types under its Advastab and Thermolite lines. Galata Chemicals (Jersey City, New Jersey) sells its PPI-listed Mark methyltin line alongside mixed-metal and phosphite stabilizers. Reagens (Italy, with plants in Germany, the US and India) sells methyl and octyl tin grades under REA TIN, and Valtris sells a PPI-listed methyltin under the Akcrostab T name. Baerlocher (Unterschleissheim, Germany) offers an organotin line in powder and liquid form, and Songwon runs a dedicated Tin Intermediates/PVC business unit. Buyers outside North America often search for the same product as a tin stabiliser rather than a tin stabilizer, and should compare grades by tin content, alkyl type and food-contact listing, not by trade name. Plants and certifications are compared in the directory of PVC stabilizer manufacturers.

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Which Additives Work Alongside Organotin Stabilizers in PVC?#

Tin-stabilized rigid PVC always carries a lubricant system and usually a processing aid, titanium dioxide and calcium carbonate, so the organotin is one of 6 to 8 additives in the compound. A typical formulation adds heat stabilizer, lubricants (paraffin wax, PE wax, oxidized PE wax or calcium stearate), an acrylic processing aid, impact modifiers where impact resistance matters, calcium carbonate filler, titanium dioxide pigment and co-stabilizers such as ESBO, phosphites, polyols or beta-diketones on top of the organotin itself. The complete additive package for PVC is on additives for PVC.

Lubricants and co-stabilizers in tin-stabilized PVC#

A US tin-stabilized pipe compound pairs 0.3-1.0 phr organotin with 0.4-1.5 phr calcium stearate and 0.6-1.5 phr paraffin wax as its lubricant system. PPI TR-2's range composition adds up to 0.3 phr PE wax, 0.5-3.0 phr titanium dioxide, up to 5.0 phr calcium carbonate filler and up to 2.0 phr processing aid alongside the tin stabilizer and its lubricant package. Formulators using a reverse-ester methyltin stabilizer can add butylated hydroxytoluene (BHT) as an optional antioxidant, up to 5% of that formulation, under the same FDA clearance.

The internal and external balance of a PVC lubricant package is explained on lubricants for PVC compounding, and ESBO, phosphites and polyols are covered under PVC co-stabilizers.

Organotin catalysts are not heat stabilizers#

Dibutyltin dilaurate (DBTDL, CAS 77-58-7) is an organotin used as a crosslinking catalyst in silane-grafted polyethylene, not as a PVC heat stabilizer, and it carries a harmonised Repr. 1B classification. DBTDL catalyses the silanol condensation reaction that crosslinks silane-grafted polyethylene into PEX-b pipe and XLPE cable insulation. Its harmonised CLP classification carries Muta. 2 H341, Repr. 1B H360FD and STOT RE 1 H372, and as a dibutyltin compound it falls under the same REACH Annex XVII entry 20 limit as other DBT species. Its catalyst role is covered on dibutyltin dilaurate (DBTDL).

Are organotin stabilizers banned?#

No: organotin stabilizers are not banned, but in the EU dibutyltin and dioctyltin compounds are limited to 0.1% tin in listed consumer articles and DOTE requires an authorisation outside food contact since 1 May 2025. Methyltin stabilizers, the type used in US pipe, carry neither restriction and are not classified as an SVHC.

Are organotin stabilizers toxic?#

Organotin stabilizers carry reproductive-toxicity hazard notifications, and DOTE is an SVHC for reproductive toxicity, which is why the EU caps their migration from food-contact PVC at 0.006-1.2 mg tin per kg of food. PubChem's aggregated notifications list dimethyltin mercaptide with notified hazard statements H361d, H372 and H317; monomethyltin mercaptide with H341, H361d and H373; butyltin mercaptide with H314, H341, H361f and H372; and DOTE with H360D, H372 and H410. These are notified classifications, not harmonised CLP entries, except where stated otherwise above. PVC safety by additive is discussed under is plastic toxic.

What is the difference between organotin and inorganic tin?#

An organotin has at least one tin-carbon bond, while inorganic tin compounds such as stannous stearate have none; organotins are the tin compounds used as primary PVC heat stabilizers. Stannous stearate instead appears in US regulation as a prior-sanctioned stabilizer under 21 CFR 181.29, with a migration limit of 50 ppm tin, a separate and much older regulatory pathway than the organotin mercaptides and carboxylates covered throughout this article.

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