Hydrolysis Stabilizers: 5 Types, Mechanisms, Dosage and Selection

Hydrolysis stabilizers are additives that keep water from cutting the ester and amide bonds of polymers such as PET, PBT, PLA, TPU and TPE-E, by scavenging the carboxylic acid end groups that make the reaction self-accelerating. Most of the market is one chemistry, the carbodiimide, dosed at 0.5 to 2.5 parts per 100 parts of polymer, so what do the other four types do and when is each one the right choice?

The 5 types are monomeric carbodiimides, led by Stabaxol I; polymeric carbodiimides, sold as Stabaxol P and CARBODILITE; epoxy chain extenders of the Joncryl type; oxazolines, in practice 1,3-PBO; and aziridines, which exist so far only as the research inhibitor tested at Fraunhofer LBF. Only the two carbodiimide classes are sold specifically as hydrolysis stabilizers, while epoxides and oxazolines reach the same carboxyl end groups under the name chain extender. LANXESS states that polymers containing Stabaxol usually show a threefold increase in service life.

This reference covers what a hydrolysis stabilizer is and how it differs from the other 5 stabilizer families, how water destroys a polyester and why the reaction accelerates itself, the 4-step carbodiimide mechanism, the 5 chemical types with their identity data, which polymers take a stabilizer and which do not, dosage in parts per hundred and wt% with masterbatch let-down, a 7-step selection route, the interactions with drying and chain extenders, how hydrolysis resistance is measured, the EU and US regulatory position of the monomeric carbodiimide, the companies behind the trade names, and the 2 substances in the directory that carry this family label.

The table below compares the 5 types of hydrolysis stabilizers by chemistry, the group each one reacts with, example grades, typical level and host polymers, in the type order used throughout this page.

Acid scavengers such as hydrotalcite are used with these types as co-stabilizers; they are documented under acid scavengers and are not counted as a hydrolysis stabilizer type.

What Is a Hydrolysis Stabilizer?#

A hydrolysis stabilizer is a polymer stabilizer that protects ester- and amide-containing polycondensates against hydrolytic chain scission, either by scavenging water and the carboxylic acid end groups that catalyse the reaction or by buffering that acid. Three further names describe the same function: anti-hydrolysis agent, anti-hydrolysis additive and hydrolysis inhibitor. All four names cover one job, which is holding the molar mass of PET, PBT, PLA, PBS, PHA, polyester polyurethane, TPU, TPE-E, polyamide and EVA steady while the part stays wet and warm. Where does this family sit among the other stabilizers?

Hydrolysis stabilizers are one of the 43 families of plastic additives documented on this site, and one of 6 stabilizer families, alongside antioxidants, PVC heat stabilizers, UV stabilizers, acid scavengers and metal deactivators. Each of those 6 families answers a different attacker: heat, oxygen, ultraviolet light, acidic catalyst residues, and catalytic metal ions. The hydrolysis stabilizer is the only one aimed at water, and it is the only stabilizer family consumed stoichiometrically by the species it removes, which is why an anti-hydrolysis agent is dosed in parts per hundred rather than in the few hundred ppm a phenolic antioxidant needs.

Which plastics need a hydrolysis stabilizer, and which do not?#

Only condensation polymers need a hydrolysis stabilizer: PET, PBT, PLA, PBS, PHA, polyester-based polyurethanes and TPU, polyester elastomers, polyamides and EVA carry ester or amide bonds that water can cut, while polyethylene, polypropylene and other addition polymers have no such bond. Condensation polymers are more susceptible to hydrolysis and to ultraviolet attack than addition polymers, because the reaction that built the chain is the reaction water reverses. Melt temperature sets the pace, since engineering polymers are processed at roughly 240 to 320 °C, and moisture carried into the feed appears within one pass as lost molar mass.

The two groups are listed below.

• Polymers that need one: polyesters such as PET, recycled PET, PBT, PLA, PBS and PHA; polyester-polyol polyurethanes and thermoplastic polyurethane; polyester elastomers (TPE-E); polyamides, where hydrolysis is an equilibrium and absorbed moisture also plasticises the polymer; and EVA.
• Polymers that do not need one: polyethylene, polypropylene, polystyrene, ABS and PVC, whose carbon-carbon backbones give water no ester or amide bond to attack.

Polycarbonate is the exception that proves the rule. Polycarbonate is a polycondensate and it hydrolyses above 70 °C at high humidity, releasing bisphenol A, but the established route there is drying plus hydrolysis-resistant phosphite grades rather than a carbodiimide. PBT sits at the other end of the same scale, with a melting point of 223 °C and a documented sensitivity to hot water above 60 °C. Each polymer's full package is listed under additives by polymer.

How Hydrolysis Destroys a Polyester, Polyamide or Polyurethane#

Hydrolysis cuts the ester bond of a polyester with a molecule of water, and each cut leaves behind a carboxylic acid end group that catalyses the next cut, so molar mass and intrinsic viscosity fall faster the longer the part stays wet and warm. Water cleaves ester, amide and carbonate bonds alike, which is why the same reaction limits polyesters, polyamides and polycarbonate. Excess moisture in a PET feed lowers the molecular weight of the resin by chain scission before a part is even formed.

Autocatalysis turns a slow reaction into a failure mode, and it is the reason this family exists. Each scission event produces one hydroxyl end group and one carboxylic acid end group, the acid number rises with every cut, and the rising acid concentration accelerates the attack on the remaining ester bonds, so molar mass and intrinsic viscosity fall on a self-feeding curve rather than a straight line. Hydrolysis is one of four degradation routes in plastics, and two conditions set how fast this one runs: residence in the melt at 240 to 320 °C, which makes the loss measurable in a single extrusion pass, and service exposure, where a PBT part in hot water above 60 °C or a polycarbonate part above 70 °C at high humidity loses properties over months. The other three routes, thermal, thermo-oxidative and photo-oxidative attack, are covered under polymer degradation.

How does a carbodiimide stop hydrolysis?#

A carbodiimide works in 4 steps: it disperses in the melt, its N=C=N group reacts with a carboxylic acid end group to form an N-acylurea, it reacts with free water to form a urea, and with the acid gone the autocatalytic loop stops. The 4 steps below run in that order, from the extruder barrel to the finished part.

1. Disperse the carbodiimide through the melt as neat powder, pellets, liquid or masterbatch.
2. React the N=C=N group with a carboxylic acid end group, R-N=C=N-R plus R'COOH, which forms an N-acylurea and removes that acid from the system.
3. React the same group with free water, which forms a urea and takes the water out of circulation.
4. Break the autocatalytic loop, because the acid that would have catalysed the next scission no longer exists.

LANXESS documents both reactions in its Stabaxol brochure (10245 EN 0922), and the second one carries the family's main limitation. Jannik Hallstein, Elke Metzsch-Zilligen and Rudolf Pfaendner at Fraunhofer LBF in Darmstadt note that carbodiimides are consumed by their direct reaction with the penetrating moisture, so they must be added in high concentrations and are comparatively expensive (Polymers, 2024, 16, 506). The acylurea reaction has a second consequence as well: because an N-acylurea can join two chain ends, a carbodiimide can act as a mild chain extender, rebuilding part of the molar mass that each act of chain scission has already removed.

What a hydrolysis stabilizer does not do: drying, oxidation and UV#

A hydrolysis stabilizer does not replace drying: it protects the polymer from the water that is still there and from the acid the first cuts create, which is why compounders dry the resin and dose the stabilizer. Drying and solid-state post-condensation stay part of the additive story for every step-growth polymer, and the stabilizer buys service life rather than immunity, because it is used up as it works. Three jobs belong to another process step or another additive family.

• Drying and melt residence: the resin is dried to its supplier's specification before extrusion and residence in the melt is kept short, because no stabilizer level compensates for a wet feed.
• Thermo-oxidative degradation: chain scission driven by heat and oxygen is the job of antioxidants for plastics, and that mechanism runs independently of water.
• Photo-oxidative degradation: weathering under ultraviolet light is handled by UV absorbers and hindered amine light stabilizers, which do nothing about hydrolysis.

One further distinction prevents a common confusion between the hydrolysis of a polymer and the hydrolysis of an additive. Phosphite antioxidants have a hydrolytic stability problem of their own, since the phosphite itself hydrolyses in storage and in a humid melt, and the answer there is a hydrolysis-resistant phosphite grade, not an anti-hydrolysis agent added to the polymer.

5 Types of Hydrolysis Stabilizers#

The 5 types of hydrolysis stabilizers used in plastics are monomeric carbodiimides, polymeric carbodiimides, epoxy chain extenders, oxazolines and aziridines, and the two carbodiimide types carry almost all commercial use.

The order of the 5 types follows commercial weight and evidence depth, and it is the order used in every table, image and list on this page. The two carbodiimide classes come first, because they are the only chemistry every supplier names and the only one with an entry in the EU Union list. Epoxides and oxazolines follow, since both reach the same carboxyl end groups while being sold as chain extenders, and aziridines close the list as a laboratory chemistry with one published data set.

1. Monomeric carbodiimides (Stabaxol I, Stabilisator 7000)#

Monomeric carbodiimides are single-molecule, sterically hindered aromatic carbodiimides, in practice one substance: bis(2,6-diisopropylphenyl)carbodiimide (CAS 2162-74-5), sold as Stabaxol I by LANXESS and as Stabilisator 7000 by Raschig. Steric hindrance from the four isopropyl groups is what makes the substance usable in a melt, because it slows the carbodiimide's own reaction with water enough for the additive to survive compounding and reach the acid end groups. The identity data of the single commercial substance are listed below.

• Chemical name: N,N'-bis[2,6-di(propan-2-yl)phenyl]methanediimine, also written bis(2,6-diisopropylphenyl)carbodiimide.
• CAS number 2162-74-5; EC number 218-487-5.
• Molecular formula C25H34N2, molar mass 362.5 g/mol.
• Chemical class: sterically hindered aromatic carbodiimide.
• Trade names: Stabaxol I and Stabaxol I LF (LANXESS); Stabilisator 7000 (Raschig).
• Appearance: pale yellowish crystalline melt or powder.

Dosage for the monomeric grade runs from about 1 part per 100 parts of polyester polyol in polyurethane systems to 1.0 to 2.0 parts per 100 parts of polymer in TPU extrusion, and in PLA the Fraunhofer LBF group found significant stabilization only from 1.5 % of the Raschig grade upwards. Two properties of the same small molecule set the limits of this type. Its volatility produces fuming at melt temperature, which is why low-fuming and polymeric grades were developed, and its hazard profile is documented only as notified self-classification: suppliers and notifiers classify the substance as H302, H360(F), H372 and H373, and no harmonised CLP entry exists for it. The substance is nonetheless the only member of the family with a named entry in the EU Union list, as FCM substance 438.

2. Polymeric carbodiimides (Stabaxol P, Carbodilite)#

Polymeric carbodiimides are oligomeric chains carrying more than one N=C=N group, supplied as Stabaxol P grades by LANXESS and as CARBODILITE by Nisshinbo, and they are the default choice because higher molar mass means less volatility and less fuming than the monomeric grade. Polycarbodiimide has no single CAS number, since each producer's grade is a distinct oligomer, and the class is identified commercially by grade name rather than by registry number. The grades in general use are listed below.

• Stabaxol P and P LF: pale yellowish powder and pellets for direct dosing into finished polyester products.
• Stabaxol P 100 and P 110: the grades documented in PLA and PLA blend work.
• Stabaxol P 200: a liquid grade metered into the polyol component of a polyurethane system.
• Stabaxol KE 7646 and MB PET 3040: masterbatches at 15 % active in a PET carrier.
• Stabaxol MB TPE 6030: masterbatch at 20 % active in a TPE-E carrier.
• CARBODILITE HMV-15CA and HMV-5CA-LC (Nisshinbo): granules with softening points of 70 °C and 65 °C, 5 % weight loss at 330 °C and 300 °C, and an NCO content of 0 %, for PLA, PBS, PHA, starch blends, recycled PET, PBT and polyester elastomers.

Levels for the polymeric type are 0.5 to 2.5 parts per 100 parts of finished polyester product for Stabaxol P and P LF, 1.0 to 4.0 parts per 100 parts of polyol for the liquid P 200, and 0.5 to 1.0 wt% of the compound for P 110 in PLA. LANXESS reports that P 110 lowers the melt volume rate of PLA by 20 to 30 % against once-extruded unstabilized PLA, and plots that effect on PLA 3052D aged at 65 °C in water at 0.5, 0.75 and 1.0 wt%. Performance against the monomeric grade has also been measured outside the supplier literature: in the Fraunhofer LBF comparison in PLA, the polymeric carbodiimide outperformed the monomeric one, which is the independent evidence behind the market's default choice.

Monomeric or polymeric carbodiimide: how to decide#

The polymeric grade is the default: it is less volatile, fumes less and performed better than the monomeric grade in the Fraunhofer LBF PLA study, while the monomeric grade keeps two advantages, faster diffusion into a liquid polyol system and a named entry in the EU Union list. That Union-list entry needs reading carefully, because FCM 438 authorises bis(2,6-diisopropylphenyl)carbodiimide as a monomer or starting substance, not as an additive, so it is not a food-contact clearance for dosing the substance into a compound. For the polymeric grade, Nisshinbo states that CARBODILITE HMV-5CA-LC can be used as a prepolymer of resin material under Regulation (EU) No 10/2011, which is a supplier statement rather than a Union-list entry. The 8 criteria that separate the two classes are compared below.

3. Epoxy chain extenders (Joncryl-type multifunctional epoxides)#

Epoxy chain extenders are multifunctional styrene-acrylic oligomers, such as Joncryl ADR-4368 with about 9 epoxy groups per molecule, and they raise hydrolytic stability indirectly: the epoxide consumes the carboxyl end groups that autocatalyse hydrolysis and rebuilds molar mass at the same time. Joncryl ADR-4368 has a weight-average molar mass of 6,800 g/mol and an epoxy equivalent weight of 285 g/mol, and its epoxide groups react fast with carboxyl end groups and more slowly with hydroxyl end groups, which is what makes the chemistry selective for the acid that drives autocatalysis. Reaction speed is a processing advantage: Karl and co-workers report 99 % conversion at 200 °C in 120 seconds or at 280 °C in 30 seconds (Industrial and Engineering Chemistry Research, 2024), so the reaction finishes inside a normal extrusion window.

Dosage decides whether the result is a stabilized polymer or a gelled one. In recycled PET, 0.5 to 1.5 wt% keeps gel content at or below 2 %, while 3 wt% produces about 32 % gel, because a nine-functional epoxide crosslinks once it has more end groups than it needs. The same reactive chemistry is sold as chain extenders for polymers when the goal is molar-mass rebuild rather than protection, and the two goals are usually met together in recyclate. One regulatory point belongs to the type rather than to the oligomer: the residual monomer glycidyl methacrylate is FCM 220 with a specific migration limit of 0.02 mg/kg, carries the harmonised CLP classifications Carc. 1B, Muta. 2 and Repr. 1B, and was listed under California Proposition 65 for cancer on 27 January 2023. The food-contact status of the Joncryl grades themselves is not established in our source library, so a monomer-residue check belongs in every food-contact file that uses them.

4. Oxazolines (1,3-PBO)#

Oxazolines are bifunctional ring compounds, chiefly 2,2'-(1,3-phenylene)bis(2-oxazoline), whose rings open against carboxyl end groups to form ester-amide links without releasing a by-product, which lowers the acid number and with it the driving force for further hydrolysis. Bifunctionality is the defining property: with two reactive rings per molecule, 1,3-PBO couples chains linearly rather than branching them, so it raises molar mass without the gel risk that a nine-functional epoxide brings. The substance is used in PET, recycled PET and PLA, often together with anhydrides or diisocyanates in the same reactive extrusion step.

Two points about this type are open rather than settled. No dosage for PET or recycled PET is sourced in our source library, so no level is published here, and the applicability of the generic "oxazoline" entry in 21 CFR 175.105, which covers adhesives, to 1,3-PBO in a food-contact compound is unverified. Neither gap prevents the chemistry from being specified, but both belong in a formulator's own verification list.

5. Aziridines (research stage)#

Aziridines are the newest hydrolysis inhibitors and are still a research chemistry: in work at Fraunhofer LBF an aziridine system held the molar-mass loss of PLA to about 10 % after 850 hours of ageing in water, a level a commercial polycarbodiimide reached after only 300 hours. Jannik Hallstein, Elke Metzsch-Zilligen and Rudolf Pfaendner reported that comparison in Polymers in 2024, using an aziridine inhibitor they refer to as PolyU, and the same system held number-average molar-mass loss to about 20 % after 1,200 hours. Both the polycarbodiimide and the aziridine suppressed PLA crystallinity to below 5 % in this study, which is a property change a formulator has to plan for rather than a side note.

No aziridine is sold as a commercial hydrolysis stabilizer, and the results above come from one research group, so the chemistry can be read as a direction of travel rather than as a purchasable option. Its interest lies in the economics: an inhibitor that is not consumed as fast as a carbodiimide addresses the cost argument that limits the whole family.

Acid scavengers as co-stabilizers, not as a sixth type#

Acid scavengers are the family's usual partner rather than a sixth type: a layered double hydroxide such as hydrotalcite buffers the acid instead of consuming it, and in the Fraunhofer LBF PLA work a calcium hydrotalcite acid regulator plus an aziridine inhibitor improved both hydrolytic and thermal ageing stability. Buffering and scavenging are different mechanisms with different stoichiometry, which is why the two are combined rather than substituted: the carbodiimide removes the acid permanently as an N-acylurea, while the hydrotalcite holds the acid in a layered structure and keeps the local pH from falling. Hallstein, Metzsch-Zilligen and Pfaendner published that combination in Materials in 2024. Because the same layered double hydroxide also neutralises catalyst residues in polyolefins and buffers phosphite antioxidants against hydrolysis, it is documented on this site under acid scavengers rather than counted as a hydrolysis stabilizer type.

Which Polymers Take Hydrolysis Stabilizers?#

Hydrolysis stabilizers are used first in polyester-based polyurethanes and TPU, then in PET and PBT engineering parts, in polyester elastomers and in PLA and other bio-based polyesters, and they are not the answer for polycarbonate, where drying and hydrolysis-resistant phosphites do the work. LANXESS names PU, PET, PBT, TPU, TPE-E, EVA, PLA, PHA and PA as the target polymers for Stabaxol, and states that polymers containing Stabaxol usually show a threefold increase in service life, which is a supplier claim rather than a measured average across compounds. Nisshinbo lists a partly different set for CARBODILITE: PLA, PBS, PHA, starch blends, recycled PET, PBT and polyester elastomers.

The named applications show where the money is. LANXESS lists PET monofilament for paper-machine dryer screens running at about 100 °C in aqueous media, polyurethane auxiliary suspension springs, rollers, drive belts and hot-melt shoe-sole adhesives, TPU ski boots and safety shoes with Stabaxol P 200 added to the polyol, TPE-E cable sheathing, PBT optical-fibre sheathing and electrical mouldings, and durable PLA goods. Every one of those parts sees liquid water or high humidity at temperature for years, which is the condition that justifies a stabilizer at parts-per-hundred level. The 11 polymers below are compared by the reason each one hydrolyses, the stabilizer type and level in use, and the named application behind that level.

Service-life and application claims in this table come from supplier documents and are attributed in the text.

TPE-E cable sheathing is one of the named uses, alongside the rest of the wire and cable compounds package, and it shows why the delivery form matters as much as the chemistry: the stabilizer arrives in a TPE-E carrier so that the masterbatch does not dilute the jacket with a foreign polymer.

How Much Hydrolysis Stabilizer Does a Polymer Need? Dosage in Parts per Hundred and wt%#

Hydrolysis stabilizers are dosed at 0.5 to 2.5 parts per 100 parts of polymer in finished polyester products, at 1.0 to 4.0 parts per 100 parts of polyol in polyurethane systems, and at 0.5 to 1.0 wt% of a polymeric carbodiimide in PLA, which is 10 to 50 times more than a typical antioxidant because the stabilizer is consumed as it works. Consumption is the reason for the high level: a carbodiimide reacts stoichiometrically with the acid and the water it removes, so the dose sets the service life rather than a steady-state concentration. In PLA the Fraunhofer LBF group found no significant stabilization below 1.5 % for the monomeric grade, which fixes a floor rather than an optimum.

Every level on this page carries its basis, because three different bases are in circulation and they are not interchangeable: parts per 100 parts of polymer, parts per 100 parts of polyol, and wt% of the finished compound. Supplier data for polyurethane systems are given in parts per hundred resin against the polyol component alone, which is a smaller denominator than the finished elastomer, so a level copied across without conversion overdoses or underdoses the part. Masterbatch adds a fourth basis, parts of masterbatch per 100 parts of polymer, which converts to active content through the let-down ratio. The table below gives the evidenced level for each grade and polymer with the basis it is expressed on and the source it comes from.

Levels are supplier recommendations or published study values, not regulatory limits. The only regulatory number in this family is the EU specific migration limit of 0.05 mg/kg for the monomeric carbodiimide.

Cost follows directly from these levels, since 2 parts per hundred of a specialty additive is a line item rather than a rounding error, and parts per hundred convert into cost per tonne with the additive dosage and cost-in-use calculator.

Masterbatch or neat additive: let-down ratios and dosing practice#

Hydrolysis stabilizers reach the melt in three forms: powder or pellets for direct dosing, a liquid grade metered into a polyurethane polyol, and a masterbatch carrying 15 to 20 % active in a matching carrier resin. Each form answers a different dosing problem, and the 3 forms are described below.

• Powder and pellets: Stabaxol P and P LF are pale yellowish powder or pellets, and CARBODILITE grades are granules with softening points of 70 °C and 65 °C, so they melt far below polyester processing temperature and disperse before the polymer reaches peak melt; the monomeric grade is a crystalline melt or powder.
• Liquid: Stabaxol P 200 is metered into the polyol component of a polyurethane system at 1.0 to 4.0 parts per 100 parts of polyol, which puts the stabilizer in place before the isocyanate reaction starts.
• Masterbatch: most converters dose the stabilizer as additive masterbatch in a matching carrier, with Stabaxol KE 7646 and MB PET 3040 at 15 % active in PET and MB TPE 6030 at 20 % active in TPE-E.

Both masterbatches are let down at 10 to 20 parts per 100 parts of polymer, which delivers 1.5 to 3.0 wt% active from the 15 % PET grade and 2.0 to 4.0 wt% active from the 20 % TPE-E grade, and those 10 to 20 parts convert into active content with the let-down ratio calculator. Carrier choice is not cosmetic. A PET carrier in PET and a TPE-E carrier in TPE-E keep the compound in one polymer family, which avoids the dispersion and clarity penalties an incompatible carrier brings, and powder, granule and liquid handling is compared under additive product forms.

How Do You Select a Hydrolysis Stabilizer? 7 Steps#

Select a hydrolysis stabilizer in 7 steps: confirm the polymer hydrolyses, define the service condition, fix drying first, choose the chemistry, set the level and the delivery form, screen the food-contact and hazard route, then verify the effect by measuring molar mass after a wet ageing test. The 7 steps below run in order, because each one narrows the choice the next one makes.

1. Confirm that the polymer is a polycondensate and name the bond at risk, ester, amide or carbonate, since an addition polymer such as polypropylene needs no stabilizer at all.
2. Define the service condition that drives the specification: temperature, humidity or liquid water, and the required service life in hours or years.
3. Fix drying and melt residence time first, because the stabilizer does not replace them and a wet feed consumes the additive before the part is formed.
4. Choose the type: a polymeric carbodiimide as the default, a monomeric grade for liquid polyol systems, and an epoxide or oxazoline when molar-mass rebuild in recyclate matters as much as protection.
5. Set the level from the polymer and the delivery form: 0.5 to 2.5 parts per 100 parts of polymer, 1.0 to 4.0 parts per 100 parts of polyol, or 10 to 20 parts of masterbatch, and allow for the fact that the stabilizer is consumed.
6. Screen the regulatory route for the target market: the monomeric carbodiimide is a monomer or starting substance under FCM 438 with an SML of 0.05 mg/kg, and its hazard data are supplier self-classifications rather than a harmonised entry.
7. Verify on the compound: measure intrinsic viscosity or melt volume rate before and after a hot-water or humid-heat exposure, and add retained tensile properties on the aged part.

Two of these steps decide most projects. Step 3 should come before any additive trial, since a formulator who doses a stabilizer into an undried resin is paying for a consumable that the process water uses up, and step 7 should be run on the actual compound rather than on the neat polymer, because pigments, fillers and other additives change the acid balance. The general framework behind this sequence is on how to select plastic additives.

How Do Hydrolysis Stabilizers Interact with Drying, Chain Extenders and the Rest of the Package?#

A hydrolysis stabilizer never acts alone: drying sets the starting water content, chain extenders compete for the same carboxyl end groups, acid scavengers buffer what is left, and the carbodiimide itself changes crystallinity. One distinction has to be made explicitly, because it is constantly confused. The hydrolysis of the polymer is what this family prevents, while the hydrolysis of an additive, most often a phosphite antioxidant, is a separate problem solved by grade choice within the antioxidant family. The 7 interactions that matter in a real package are set out below.

Epoxides and carbodiimides are paired in these packages more often than they are substituted, because the two additives reach the same end group on different timescales and at different functionalities. The full synergy and antagonism matrix across all additive families is on additive interactions.

How Is Hydrolysis Resistance Measured?#

Hydrolysis resistance is measured as molar mass before and after a wet exposure: intrinsic viscosity for PET and other polyesters, melt volume rate for PLA and compounded grades, and retained tensile properties on the aged part. No standard test method for hydrolytic ageing is established in our source library, which is an honest gap rather than an omission: the two exposure conditions cited below come from published work, not from a numbered standard, and a specification that needs a standard method has to name its own. The 7 measurements that carry the evidence are compared below.

Intrinsic viscosity is the number a PET buyer already knows, which makes it the cheapest entry point into a hydrolysis study: a bottle grade at 0.78 to 0.85 dL/g and a monofilament grade at 1.00 to 2.00 dL/g start from different places, so the comparison has to be made against the unaged sample of the same grade rather than against a table value. Every method named here is indexed under testing plastic additives.

How Are Hydrolysis Stabilizers Regulated?#

Hydrolysis stabilizers are regulated in 3 layers: chemical registration under REACH and the national inventories, food-contact clearance under Regulation (EU) No 10/2011 in the EU and 21 CFR in the US, and hazard classification under the CLP Regulation. Only one substance in the family carries entries in all three layers, the monomeric carbodiimide, and all instruments that apply to additives are summarised in plastic additive regulations.

Registration is the layer with the clearest position. Bis(2,6-diisopropylphenyl)carbodiimide is registered under REACH with 3 active Article 10 full dossiers, the first dated 14 February 2013, and registration status for additives is explained on REACH and plastic additives. For the polymeric carbodiimide, no REACH, EU 10/2011, FDA, Proposition 65, POPs or TSCA entry was found in our source library, and the absence of an entry is not the same as an absence of compliance obligations: it means the position has to be established from the supplier's own documentation for the specific grade.

EU food contact: FCM 438 and the SML of the monomeric carbodiimide#

In the EU the monomeric carbodiimide appears in the Union list of Regulation (EU) No 10/2011 as FCM substance 438, and its specific migration limit of 0.05 mg/kg counts the substance together with its hydrolysis product 2,6-diisopropylaniline. That sum is the compliance detail a formulator must not miss, because a migration test that measures only the carbodiimide underestimates the result: the substance hydrolyses to the aniline in exactly the conditions a migration test creates. The entry is listed under Ref 13303 in Annex I of the consolidated text of 16 March 2025, and it authorises the substance as a monomer or starting substance, not as an additive, so it is not a clearance for dosing the carbodiimide into a finished compound. The Union list and its limits are explained on EU 10/2011. The regulatory position of each substance in and around this family is compared below across the EU, REACH, CLP and the non-EU inventories.

Hazard classification, REACH registration and the rest of the world#

The monomeric carbodiimide has no harmonised CLP classification: the hazard statements quoted by suppliers, including H302, H360(F), H372 and H373, come from notified self-classifications, and they are the practical reason the market moved to low-fuming and polymeric grades. Self-classification means that notifiers have assigned those statements themselves under the CLP Regulation, so the classification can differ between suppliers and it carries less legal weight than a harmonised entry in Annex VI. No hydrolysis stabilizer was found on the SVHC Candidate List, in Annex XIV or in Annex XVII when ECHA CHEM was checked on 22 September 2026, and no Proposition 65 entry was found for the monomeric carbodiimide.

Outside the EU the picture is thinner rather than negative. For the monomeric substance no FDA, POPs or TSCA entry was found in our source library, and for the polymeric grades the only inventory information available is what the supplier publishes: Nisshinbo lists its CARBODILITE polymer grades on TSCA, REACH as polymers, KECI, IECSC, TCSI and ENCS as of June 2020. Those listings are supplier statements about specific grades, and a compliance file needs the grade-specific declaration rather than a family-level assumption.

Who Makes Hydrolysis Stabilizers? Suppliers and Trade Names#

Three companies supply most of the world's hydrolysis stabilizers: LANXESS with the Stabaxol line, Nisshinbo Chemical with CARBODILITE and Raschig with Stabilisator 7000, while BASF supplies the Joncryl epoxides that formulators use for the same carboxyl end groups. LANXESS is headquartered in Cologne, lists STABAXOL among its additive brands, and completed its acquisition of Chemtura on 21 April 2017, which is how part of its current additive portfolio arrived. No independent market size for hydrolysis stabilizers is published; the family sits inside the wider polymer-stabilizer market, and the total additive market is sized on plastic additives market. The 4 producers behind the trade names are listed below with their headquarters, brand lines, product forms and coverage.

Company data come from our source library. No independent market size is published for this family.

Company profiles are in the directory of plastic additive manufacturers and suppliers.

Complete List of Hydrolysis Stabilizer Substances (2 Pages)#

Two substances on this site carry the hydrolysis-stabilizer function as their primary family: the monomeric carbodiimide bis(2,6-diisopropylphenyl)carbodiimide (CAS 2162-74-5) and polycarbodiimide, the polymeric grade sold as Stabaxol P and CARBODILITE. The other chemistries on this page are documented under the family they belong to commercially, so Joncryl ADR and bisoxazoline sit under chain extenders and hydrotalcite sits under acid scavengers. The 2 substances of the family are listed below with their identity, chemical class, trade names, typical level and EU food-contact status.

All substance pages sit in the plastic additives database, where each grade is cross-linked to its polymer, test and regulation pages.

Are Hydrolysis Stabilizers Safe, and What Do They Mean for Recycling and Compostable Plastics?#

No hydrolysis stabilizer in this family appears on the REACH Candidate List, in Annex XIV or in Annex XVII, and none is listed under Proposition 65, but the monomeric carbodiimide carries notified hazard classifications, and any additive that slows hydrolysis raises a fair question about compostable plastics. The hazard side of that sentence is documented above and is the weaker of the two open areas, since the self-classified statements attach to the monomeric substance and the market has largely moved to polymeric grades. The end-of-life side is genuinely open. A stabilizer that suppresses PLA crystallinity to below 5 % and holds molar mass for hundreds of extra hours in water changes both of the properties a composting standard measures, and no study in our source library has measured the outcome.

Do hydrolysis stabilizers block composting or recycling?#

The honest answer is that our source library has no measured data on the compostability of stabilized PLA: hydrolysis stabilizers are sold for durable PLA goods, where a long service life is the point, while EN 13432 demands at least 90 % biodegradation within 6 months. EN 13432 also requires disintegration with less than 10 % residue after 3 months, and both criteria are tested on the finished article rather than on the polymer, so the question cannot be answered from the additive's mechanism alone. What can be said is that the two uses point in opposite directions by design, and that no certification claim for a stabilized compostable grade should be made without its own test data. How additives are judged for recyclability is covered under design for recycling.

Mechanical recycling is the clearer case. In recycled PET, carbodiimides and chain extenders are used precisely to rebuild the molar mass that moisture and contamination have taken away, which makes the stabilizer an enabler of recyclate quality rather than an obstacle to it. For food-contact recyclate the migration question returns in full, and simulants and conditions are on migration testing.

Is this the same carbodiimide as in peptide chemistry?#

The functional group is the same and the use is not: peptide chemistry uses small carbodiimides such as DCC and EDC as coupling reagents in solution, while plastics use a sterically hindered aromatic carbodiimide or its polymer, dosed at parts per hundred into a melt. Searches for the bare word "carbodiimide" are dominated by that peptide-coupling and bioconjugation intent, and the general reference literature on carbodiimides omits the hydrolysis-stabilizer use entirely. The plastics substance is a 362.5 g/mol molecule with four isopropyl groups shielding the N=C=N centre, or an oligomer of the same functionality, and the steric shielding is exactly what a coupling reagent must not have.

Where the research is going: aziridines and acid-regulator systems#

The research front is the cost and consumption problem: because a carbodiimide is used up by the water it scavenges, Rudolf Pfaendner's group at Fraunhofer LBF has tested aziridine inhibitors and calcium hydrotalcite acid regulators that hold PLA molar mass longer at lower loadings. Jannik Hallstein, Elke Metzsch-Zilligen and Pfaendner published the aziridine comparison in Polymers in 2024 (16, 506), where the inhibitor held number-average molar-mass loss to about 10 % after 850 hours against 300 hours for a commercial polycarbodiimide, and the hydrotalcite combination in Materials in 2024 (17, 2761), where an acid regulator plus an aziridine inhibitor improved both hydrolytic and thermal ageing stability. Petr Stloukal and colleagues had earlier studied carbodiimide control of PLA hydrolytic stability in Polymer Testing in 2016. All of this is laboratory work on one polymer, and none of these systems is a commercial class.

What is the purpose of hydrolysis?#

In plastics, hydrolysis has no purpose for a durable part: it is the degradation route that cuts ester and amide bonds and lowers molar mass. The same reaction becomes the intended end-of-life route for a compostable polyester, where EN 13432 requires at least 90 % biodegradation within 6 months, so the identical chemistry is a failure in a TPU boot and a specification in a compost bag.

How do you inhibit hydrolysis in a plastic part?#

Hydrolysis in a plastic part is inhibited in three moves: dry the resin before processing, keep melt residence short, and dose 0.5 to 2.5 parts of a carbodiimide per 100 parts of polymer so the carboxyl end groups never build up. The three moves work in that order, because drying and residence time set how much water and acid the stabilizer has to absorb, and the level chosen from the dosage table then decides how long the protection lasts in service.