Compatibilizers: 5 Types, Mechanisms, Dosage and Selection

Compatibilizers are block, graft or reactive copolymers that sit at the interface between two immiscible polymers, lower the interfacial tension, stop the dispersed droplets from merging and carry stress across the boundary, and this reference sorts them into 5 types. They are dosed at roughly 2 to 10 wt% of the blend, and 3 wt% of a polyolefin elastomer is enough to roughly triple the impact strength and elongation of a 70/30 HDPE/PP recyclate, so which chemistry belongs in which blend?

The 5 types of compatibilizers are maleic anhydride grafted polymers, epoxy-functional GMA copolymers and oligomers, acid-functional copolymers and ionomers, non-reactive block and graft copolymers, and low-molar-mass reactive and catalytic systems. Types 1, 2, 3 and 5 are reactive compatibilizers, which build the interfacial copolymer inside the extruder from a functional group on the additive and an end group on one of the polymers. Type 4, the block and graft copolymers such as SEBS, polyolefin elastomers and olefin block copolymers, is the non-reactive route, added ready-made when neither polymer offers anything to react with.

Compatibilizers belong to the property-modifier group of plastic additives, next to impact modifiers and coupling agents. This page covers the three interfacial effects, the 5 types with their reactions and grades, dosage in wt% of the blend, which type suits PP/PE, PA/PP, PET/polyolefin, PE/EVOH film and wood-plastic composites, a 6-step selection route, the test methods, the REACH and food-contact route through the monomers, the producers, and all 9 compatibilizer substances in the directory.

The table compares the 5 types of compatibilizers by reactive group, the blends they suit and a sourced example.

Grades are examples from our source library, not recommendations. Types 1 to 3 form a graft copolymer in the extruder (reactive compatibilization); type 4 is added ready-made (non-reactive compatibilization).

What Is a Compatibilizer?#

A compatibilizer is a polymeric additive that locates at the interface of two immiscible polymers, where it lowers the interfacial tension so the minor phase disperses more finely, suppresses coalescence of the droplets and raises adhesion so stress can pass from one phase to the other. The molecules that do this are block or graft copolymers whose segments are each miscible with one of the two phases, so one part of the chain dissolves in the matrix while the other dissolves in the dispersed phase and the chain stays anchored across the boundary. Addition levels run from about 2 to 10 wt% of the blend, enough to cover the interface without changing the bulk composition.

Which additives are then not compatibilizers? A coupling agent works between a polymer and an inorganic or natural surface, glass fibre, talc, calcium carbonate or wood flour, rather than between two polymers, and most coupling agents are low-molar-mass reactive molecules such as silanes rather than copolymers. Producer pages sometimes present the two words as interchangeable, and this reference keeps them apart, with the genuine overlap treated below the contextual border.

Why are most polymer pairs immiscible?#

Two polymers stay separate because mixing long chains gains almost no entropy, so the free energy of mixing stays positive and the blend splits into a matrix and a dispersed phase. Entropy scales with the number of independent particles in the melt, and a chain of 10,000 repeat units counts as one particle rather than as 10,000, so the entropic reward for combining two high-molar-mass polymers is very small while the enthalpy of mixing is usually positive because unlike segments have to sit next to each other. The Gibbs free energy of mixing therefore stays positive for almost every commercial pair.

Morphology is what that separation looks like in a real compound. An uncompatibilized blend shows coarse droplets of the minor phase inside the major phase, the droplet diameter drifts upward through the rest of the process, and the boundary carries almost no load, so the part delaminates or breaks at low stress. Two polymers that behave this way are immiscible in the thermodynamic sense, and the definition of miscibility, with the phase-behaviour criteria behind it, is in the glossary.

Compatibilizer, compatibiliser and compatibilization: the terms in use#

Compatibilizer and compatibiliser are the same word in US and UK spelling, compatibilization is the process, and the older literature also uses compatibilizing agent, interfacial agent and blend modifier for the same additive. Compatibilisation, mould and fibre are the British forms that appear in European datasheets, where US sources write compatibilization, mold and fiber. A blend treated this way is described as compatibilized, and supplier catalogues sell the same products as polymer compatibilizers and as plastic compatibilizers without any difference in chemistry. In coextruded film the identical chemistry carries a third name, tie layer, because there it bonds two layers rather than two phases. The word therefore describes a job at an interface and not a chemical class, which is why one grade can appear in two different type groups on this page.

How Do Compatibilizers Work?#

Compatibilizers work in 3 ways at the interface between the two polymers: they lower the interfacial tension, they suppress coalescence of the dispersed droplets, and they raise adhesion so the two phases share load. The three effects follow each other in the order listed below, and a compatibilizer that produces only the first two improves the look of a micrograph without improving the mechanical properties.

1. Lower interfacial tension, so mixing shear breaks the minor phase into smaller droplets.
2. Suppress coalescence, so those droplets survive the rest of the process instead of merging again.
3. Raise interfacial adhesion, so stress passes from the matrix into the dispersed phase.

All three come from the same structural feature, a copolymer chain with one segment miscible in each phase, and the interface has a finite capacity, so an excess ends as micelles in the matrix rather than at the boundary.

Lower interfacial tension and finer dispersion#

Lower interfacial tension lets the mixing shear break the minor phase into smaller droplets, and the domain size of the minor phase is the first thing a compatibilizer changes. Droplet break-up in an extruder is a contest between the shear stress that deforms a droplet and the interfacial tension that pulls it back into a sphere. A copolymer at the boundary replaces one high-energy contact between unlike segments with two lower-energy contacts between like segments, which lowers the interfacial tension and lets the same screw produce finer domains at the same throughput.

The effect is measurable on a micrograph rather than on a tensile bar. A 2025 study by de Ballesteros and colleagues found that 5 wt% of a propylene-based olefin block copolymer, the INTUNE chemistry, reduced the size of the minor-phase domains in isotactic polypropylene-rich blends with LDPE and HDPE. Domain size matters because the interfacial area per unit volume rises as the domains shrink, and that larger interface is what the next two effects have to stabilize.

Suppressed coalescence and a stable morphology#

Fine droplets merge again as soon as shear stops, and the copolymer layer around each droplet is what keeps them apart through the die and the mould. Coalescence is the reverse of break-up: two droplets that touch in a low-shear zone lower their total surface energy by fusing. A compatibilizer prevents that fusion by steric stabilisation, because the copolymer chains anchored in each droplet surface block the two interfaces from draining the melt film between them.

Stability is the practical output. The morphology that survives to the finished part, not the morphology inside the mixing zone, sets the mechanical properties, and an uncompatibilized blend loses its fine structure in the calm sections of the line: the melt pump, the die, the runner and the slowly cooling wall of the moulding. Suppressed coalescence also makes the compound reproducible, because the final domain size stops depending on how long the melt sat still.

Interfacial adhesion and stress transfer#

Adhesion decides what the blend does under load: without it the interface fails first and the blend breaks at low stress, and with it the dispersed phase can absorb energy. A copolymer chain that has one block entangled in the matrix and the other block entangled in the dispersed phase transmits force across the boundary, so the rubber particle deforms and cavitates instead of debonding. This is why impact strength, not stiffness, is the property that reveals whether a compatibilizer is working: modulus follows the rule of mixtures whatever the interface does, while notched impact strength collapses without adhesion.

The published gains are large and they belong to specific systems. A 2024 study found that 10 wt% POE-g-(MAH-co-St) together with 10 wt% SEBS-g-(MAH-co-St) raised the impact strength of a PA6/PP/ABS/SEBS blend by 823 % against the uncompatibilized blend, which is a single-study result for a four-component system and not a typical gain. Supplier data for post-consumer streams sit an order of magnitude lower: Kraton reports that CirKular+ C1010 at 5 % in a PCR HDPE/PET blend raises notched Izod by 70 % and yield strength by 40 %.

Non-reactive and reactive compatibilization#

A compatibilizer reaches the interface in one of two ways: it is added as a ready-made copolymer, or it is made there during extrusion by a reaction between a functional group on the additive and an end group on one of the polymers. The non-reactive route uses a pre-made block or graft copolymer miscible with both phases, and it is the only route open when neither polymer carries a reactive end group. SEBS serves that role in PP/PS and PE/PS, a propylene-based olefin block copolymer serves it in isotactic PP/PE blends, and the di-block Polarfin chemistry serves it in PE/PP film.

Reactive compatibilization builds the copolymer in situ. Maleic anhydride reacts with the amine end groups of polyamides to form imide links, and the glycidyl epoxide of GMA reacts with the carboxyl or hydroxyl ends of polyesters to form ester links, so the graft copolymer appears at the boundary during the residence time of the extruder. Reactive compatibilization is the industrial standard for PA/PP, PA/ABS, PC/PBT and PET/polyolefin blends, because those pairs all bring a condensation polymer with reactive chain ends.

5 Types of Compatibilizers#

The 5 types of compatibilizers are maleic anhydride grafted polymers, epoxy-functional GMA copolymers and oligomers, acid-functional copolymers and ionomers, non-reactive block and graft copolymers, and low-molar-mass reactive and catalytic systems. The order is industrial weight: type 1 carries the most sourced dosage data and the largest number of commercial grades, and type 5 is the smallest group.

One question splits the five into two groups: does either polymer carry a reactive end group? Types 1, 2, 3 and 5 are reactive and need one, because the anhydride, the epoxide, the acid group or the titanate has to find an amine, a carboxyl or a hydroxyl to attach to. Type 4 needs nothing, which is why two polyolefins, with no reactive chain ends at all, are compatibilized by physical placement of a block copolymer rather than by chemistry.

1. Maleic anhydride grafted polymers (PP-g-MAH, PE-g-MAH, POE-g-MAH, SEBS-g-MAH)#

Maleic anhydride grafted polymers are polyolefins and elastomers carrying succinic anhydride groups on the chain, which open and react with the amine end groups of polyamides or hydrogen-bond to hydroxyl groups on wood, glass and minerals. Maleated polypropylene (PP-g-MAH, CAS 25722-45-6) is the volume representative, and commercial grades carry about 0.5 to 1.5 % grafted maleic anhydride: POLYBOND 3200 is specified at 0.8 to 1.2 %. The backbone does the second half of the work, because a PP backbone co-crystallises with a PP matrix, so the grafted chain is held in one phase while the anhydride is bonded into the other.

Grafting is a peroxide-initiated reaction run in the extruder at 180 to 190 °C: peroxide radicals abstract hydrogen from the chain, maleic anhydride adds to the macroradical, and beta-scission of the polypropylene competes for the same radicals and intensifies as the peroxide level rises. Maleic anhydride does not homopolymerize at that temperature, and molar mass falls as the anhydride content rises to about 1 wt% and then plateaus, which is why melt flow rate climbs with grafting level. Grafting levels and grade differences are compared under maleic anhydride grafted polymers.

Dosage data for this class come mostly from recyclate work. Plastics Technology reports that recycled PP/PA compounded with 5 % POLYBOND 3150 or 3002 reaches roughly 3 times the notched and reverse Izod of the uncompatibilized blend. FUSABOND is Dow's anhydride-modified polyolefin range, with E-series polyethylenes, N-series polyethylene copolymers and P-series polypropylenes, of which E205 is used in wood-plastic composites and E226 improves adhesion to non-halogenated fillers in LLDPE. The monomer carries the food-contact limit: maleic anhydride is FCM 234 in EU 10/2011 with group restriction 3 and an SML(T) of 30 mg/kg expressed as maleic acid.

2. Epoxy-functional (GMA) copolymers and oligomers#

Epoxy-functional compatibilizers are ethylene copolymers and styrene-acrylic oligomers carrying glycidyl methacrylate, whose epoxide ring opens against the carboxyl and hydroxyl chain ends of polyesters and the amine ends of polyamides. The reaction forms an ester link and needs no peroxide, only melt temperature and residence time. Two commercial architectures dominate: random ethylene terpolymers and low-molar-mass multi-epoxide oligomers.

The terpolymers carry the epoxide on a soft, rubbery backbone. LOTADER AX8900 (E-MA-GMA, CAS 51541-08-3) contains 24 wt% methyl acrylate and 8 wt% glycidyl methacrylate, with a melt flow index of 6 g/10 min at 190 °C/2.16 kg, a melting point of 65 °C and a density of 0.94 g/cm3, while ELVALOY PTW is an ethylene, n-butyl acrylate and GMA terpolymer at 66.75, 28 and 5.25 wt%. A study found that 10 wt% E-nBA-GMA raised the strain at break of a PET/HDPE blend. The epoxide route is set out under GMA functional compatibilizers.

Epoxy-functional styrene-acrylic oligomers work by functionality rather than by rubber content. Joncryl ADR-4368 has a weight-average molar mass of 6,800 g/mol and an epoxy equivalent weight of 285 g/mol, which is about 9 epoxy groups per molecule, and it compatibilizes PLA/PBAT and PLA/PA11, where the interfacial reaction saturates at about 1.0 wt%. One limit applies to the whole class and belongs to the residual monomer: glycidyl methacrylate is classified Carc. 1B, Muta. 2 and Repr. 1B under CLP and was listed under California Proposition 65 as a carcinogen on 27 January 2023. That classification attaches to free GMA, never to the copolymer.

3. Acid-functional copolymers and ionomers#

Acid-functional compatibilizers are ethylene copolymers carrying acrylic or methacrylic acid, partly neutralised to sodium or zinc salts in the case of ionomers, whose polar and ionic groups associate with polyester and polyamide chain ends. The bond is ionic and polar rather than covalent, so the class sits between the reactive and the non-reactive routes: ionic clusters give the copolymer melt strength and polarity, and they associate with carboxyl and amide groups across the interface without forming a new chemical link.

Ethylene-methacrylic acid ionomers are the best-documented members, with CAS 25608-26-8 for the sodium salt and 28516-43-0 for the zinc salt, and Surlyn 8940 as the reference grade. Their food-contact route is unusually clear, because US rules list the copolymer family directly: 21 CFR 177.1330 covers ethylene-methacrylic acid copolymers with up to 20 wt% methacrylic acid, reduced to 15 % when vinyl acetate is present, together with their sodium, zinc and other partial salts, and 21 CFR 177.1310 covers ethylene-acrylic acid copolymers at up to 10 % or up to 25 % acrylic acid depending on the use. Those percentages are composition limits, not dosages.

Recycled polyester is where the class earns its place. Monti and colleagues reported in Polymers in 2021 that glass-fibre-filled recycled PET modified with ethylene-acrylate copolymers and Surlyn 8940 rose from 5.2 to about 8.1 kJ/m2 in notched Izod, a gain of 55 %, to ISO 180 at 23 °C.

4. Non-reactive block and graft copolymers (SEBS, POE, OBC, propylene-based elastomers)#

Non-reactive compatibilizers are ready-made block and graft copolymers with one segment miscible in each phase, which is the only route open when neither polymer carries a reactive end group, as in a PP/PE blend. SEBS (CAS 66070-58-4) is the structural model: the polystyrene end blocks anchor in styrenic phases while the saturated ethylene-butylene midblock gives a rubbery phase stable to UV and ozone, so SEBS compatibilizes PP/PS, PE/PS and polyolefin/PET recyclate. The maleic anhydride grafted version belongs to type 1, because grafting turns it into a reactive compatibilizer for polyamides and polyesters.

Supplier data for post-consumer streams are the densest dosage source in this class. Kraton gives CirKular+ C1000 at 3 to 5 % in a 72/18 PCR PP/PET blend for notched Izod plus 50 % and yield strength plus 30 %, CirKular+ C1010 at 3 to 5 % in PCR HDPE/PET for notched Izod plus 70 % and yield plus 40 %, and CirKular+ C2000 at 3 to 10 % in PCR polypropylene.

Polyolefin elastomers and olefin block copolymers cover the polyolefin pairs. Polyolefin elastomer (POE, CAS 26221-73-8), sold as ENGAGE 8100, is compatible with polyethylene and is used at 2 to 5 % of a 70/30 HDPE/PP recyclate, typically 3 %, where trade press reports about 3 times the impact strength and elongation with the modulus kept. Vistamaxx, a propylene-based elastomer, starts at 5 % in PE/PP recyclate, a PP-based olefin block copolymer at 5 wt% reduces the minor-phase domain size in iPP-rich blends, and EPDM (CAS 25038-36-2) is described as an effective PP/PE compatibilizer.

5. Low-molar-mass reactive and catalytic systems#

Low-molar-mass reactive and catalytic systems are titanates and peroxides that act on the interface without being copolymers themselves, and they are used mainly in mixed recyclate where no single blend pair can be named. Kenrich markets neoalkoxy titanates as compatibilizing catalysts for exactly that case, and the supplier claims that Ken-React CAPS KPR 12/LV at 1.5 to 1.75 % in mixed post-industrial resin lets the line run 20 % faster at a 9 % lower melt temperature. Peroxides belong to the same small group, because they generate the radicals that graft one polymer onto another during extrusion rather than acting as an interfacial layer. Both are added in tenths of a percent to low single figures, far below the copolymer classes, and both are process tools rather than structural additives.

How Much Compatibilizer Is Needed? Dosage, Units and Addition in Compounding#

Compatibilizers are dosed at about 2 to 10 wt% of the blend, and the number is set by the amount of interface to be covered, which means by how much minor phase there is and how fine the dispersion has to be. Two systems sit below that band: multi-epoxide oligomers work at about 0.5 to 1.0 wt% because each molecule carries roughly 9 reactive groups, and titanate catalysts at 1.5 to 1.75 %. The table lists 17 sourced dosages with the result each one produced and the type of source it came from.

Dosages are the values published with the cited result, not recommendations. Percentages are by weight of the blend unless the source states otherwise.

Units for this family are almost always wt% of the finished blend, because both phases are polymers and there is no single resin to count against. That distinguishes compatibilizers from PVC additives, which are dosed in parts per hundred resin, and blend percentages and phr are converted on PHR (parts per hundred resin). Legal maxima in 21 CFR and EU 10/2011 are percentages of a polymer composition, so 2 % grafted maleic anhydride describes what the listed polymer may contain, not how much compatibilizer to add.

Addition happens in the melt. A compatibilizer has to be dispersed while both phases are molten and under shear, which is why reactive grades are fed into a co-rotating twin-screw extruder with vented two-stage screws, typically at an L/D of 36:1, a configuration described on plastic compounding. Levels for every other additive family are on additive dosage levels in plastics.

Which Compatibilizer for Which Blend?#

The choice follows the chain ends: a polyamide brings amine groups and asks for a maleic anhydride grafted polymer, a polyester brings carboxyl and hydroxyl groups and asks for a GMA copolymer, and two polyolefins bring nothing reactive at all, so they need a block copolymer that is simply miscible with both. The matrix below applies that rule to the 10 blend pairs our source library documents, and every dosage in it is the value from the table above.

Recyclate and virgin engineering blends behave differently even when the chemistry is identical, because a post-consumer stream carries unknown proportions, legacy additives and moisture. Virgin engineering blends are treated separately under compatibilizers for polymer blends, while the sections that follow take the five stream types that dominate demand.

Compatibilizers for PP/PE blends and mixed polyolefin recyclate#

Polypropylene and polyethylene are immiscible, and post-consumer bales cannot separate them economically, so the mixed polyolefin stream is the largest single use of compatibilizers. The two polymers have nearly identical densities and no reactive chain ends, which rules out both float-sink separation and the reactive route in one step, so what remains is a non-reactive block or graft copolymer with a segment miscible in each polyolefin.

Four chemistries hold that position, each with its own sourced starting point. Polyolefin elastomer at 2 to 5 % of a 70/30 HDPE/PP recyclate, typically 3 %, raises impact strength and elongation by about a factor of 3 while keeping the modulus, according to trade press reporting. Vistamaxx starts at 5 % in PE/PP recyclate, CirKular+ C2000 runs at 3 to 10 % in post-consumer polypropylene, and EPDM is described as an effective PP/PE compatibilizer as well. Restabilization and odour control complete the package on additives for recycled plastics.

Morphology data separate these options where mechanical data do not. A 2025 study by de Ballesteros and colleagues found that a PP-based olefin block copolymer at 5 wt% reduced the minor-phase domain size in iPP-rich blends with LDPE and HDPE.

One caution applies to every figure above. The ratio of PP to PE in a real bale moves from load to load, so the minor phase changes identity and a dosage validated on a 70/30 stream does not transfer to a 50/50 one. Stream-by-stream choices are compared on compatibilizers for recycled plastics.

Compatibilizers for polyolefin/polyamide blends (PA/PP, PA/PE)#

A polyamide carries amine end groups, so the standard compatibilizer for a PA/PP or PA/PE blend is a maleic anhydride grafted polyolefin or elastomer, which forms imide links across the interface during extrusion. The anhydride ring opens against the terminal amine, and the polyolefin backbone of the grafted chain entangles with the polyolefin phase, which gives a covalent bridge on one side and an entanglement on the other. Reactive compatibilization is the industrial standard for this pair and for PA/ABS.

Two sourced results bracket what the route delivers. Recycled PP/PA compounded with 5 % POLYBOND 3150 or 3002 reaches about 3 times the notched and reverse Izod of the untreated blend according to Plastics Technology, and a 2024 study found an 823 % impact gain in a PA6/PP/ABS/SEBS blend using 10 wt% POE-g-(MAH-co-St) plus 10 wt% SEBS-g-(MAH-co-St), a four-component system whose result is not a typical figure. The rest of the polyamide package is on additives for nylon.

Moisture decides whether either number is reachable. A polyamide that enters the extruder wet hydrolyses, which changes the end-group population the anhydride is supposed to react with, so drying the polyamide is part of the compatibilizer specification.

Compatibilizers for polyolefin/polyester blends and PC/PBT#

Polyesters carry carboxyl and hydroxyl chain ends, so a glycidyl methacrylate copolymer is the usual compatibilizer for PET or PBT with a polyolefin, and the same chemistry serves PC/PBT and PC/PET blends. The epoxide opens against the acid end group to form an ester link, and the ethylene backbone of the terpolymer carries the polyolefin side of the bridge. LOTADER AX8900, with 24 wt% methyl acrylate and 8 wt% GMA, and ELVALOY PTW, with 5.25 wt% GMA, are the reference grades, and their supplier application lists run across PBT, PET, PPS, PC/PBT, PC/PET and PC/ABS.

Published results exist for both virgin and recycled polyester. A study of PET/HDPE found higher strain at break with 10 wt% E-nBA-GMA, and Monti and colleagues measured notched Izod rising from 5.2 to about 8.1 kJ/m2 in glass-fibre-filled recycled PET with ethylene-acrylate copolymers and the Surlyn 8940 ionomer. PET grades and their additive package are on additives for PET.

Recyclate changes the preferred chemistry rather than the physics. Where PET is a contaminant in a polyolefin stream rather than a designed phase, supplier data favour the non-reactive SEBS route: CirKular+ C1000 at 3 to 5 % in 72/18 PCR PP/PET and C1010 at the same level in PCR HDPE/PET.

Compatibilizers for multilayer film recycling: PE/EVOH and PE/PA#

A barrier film is built from layers that do not stick to each other, and the maleic anhydride grafted polyethylene that bonds them as a tie layer is the same chemistry that compatibilizes the film when it is recycled. EVOH brings hydroxyl groups and polyamide brings amine ends, and the anhydride reacts with both, so one resin family covers adhesion in the new film and dispersion in the reclaim.

Design limits are published. The Association of Plastic Recyclers design guide for PE flexible packaging rates a co-extruded structure as Preferred when EVOH stays at or below 10 wt% of the structure and the tie layer carries more than 0.1 wt% maleic anhydride, while adhesive lamination is limited to 5 wt% EVOH. Layer structures and tie-resin levels are compared on compatibilizers for multilayer film recycling.

FUSABOND and the other anhydride-modified polyolefins are the tie-resin chemistry behind those numbers. The EVOH percentage is a structure limit, not a dosage, and the tie layer is specified by its anhydride content rather than by an addition level.

Film formulators reach the same resin from two directions. The tie layer is chosen for adhesion during coextrusion and the compatibilizer for dispersion during reclaim, and the full film additive package is on additives for packaging film.

Compatibilizers for wood-plastic and natural fibre composites#

Wood flour and natural fibres are hydrophilic and a polyolefin is not, so a maleic anhydride grafted polyolefin is used to bond the two, which lowers water uptake and raises tensile and flexural strength. MAPP for polypropylene and MAPE for polyethylene both work by hydrogen bonding and esterification between the anhydride and the hydroxyl groups of cellulose, with POLYBOND 3200 and the FUSABOND E-series HDPE grades as the documented products.

This is the one section where the same product is sold under two family names: in a wood-plastic composite the maleated polyolefin is a coupling agent, because its counterpart is a filler and not a second polymer. The composite sense is treated in full as coupling agents for wood-plastic composites.

Optimum loadings differ by property, so a single recommended level does not exist. Peer-reviewed work on glass-fibre and wood-filled polypropylene gives 1 wt% MAPP as the optimum for flexural strength, where it raised the value by 24.7 %, and 3 wt% for tensile strength, modulus and impact. A hybrid cellulose-basalt/PP composite with 5 wt% MA-g-PP reached 45 % higher tensile strength, 97 % higher flexural strength and 13 % higher notched Charpy impact than neat polypropylene. A wood-plastic compound cannot be processed above about 200 °C because cellulose degrades, which caps the melt temperature available for grafting.

How Do You Select a Compatibilizer? 6 Steps#

Select a compatibilizer in 6 steps: identify the end groups of both polymers, choose the reactive or the non-reactive route, match the backbone to the major phase, set the dosage from the interfacial area, check the processing window, and confirm the choice by testing. The steps below should be worked in order, because each one narrows the options for the next.

1. Identify both polymers and their reactive end groups. A polyamide offers amine ends, a polyester offers carboxyl and hydroxyl ends, and a polyolefin offers nothing.
2. Decide between the reactive and the non-reactive route: reactive when at least one polymer has a reactive end group, non-reactive when neither does.
3. Match the backbone to the major phase. A PP-g-MAH belongs in a PP-rich blend and a PE-g-MAH in a PE-rich one, whatever the minor phase is.
4. Set the dosage from the amount of interface, starting from the sourced values in the dosage table. More minor phase and finer domains mean a higher level within the 2 to 10 wt% band.
5. Check the processing window. Grafting needs residence time and melt temperature, a grafted polypropylene raises the melt flow rate, and a wood-filled compound cannot go above about 200 °C.
6. Check the regulatory route through the monomers, then confirm by impact, tensile and morphology testing.

Step 3 is the one most often skipped, and skipping it produces compounds that test worse than the uncompatibilized blend, because a compatibilizer miscible with neither phase acts as a third immiscible component. The general framework for every additive family is on how to select plastic additives.

How Is Compatibilization Measured?#

Compatibilization shows up first in notched impact strength and in the size of the dispersed domains, and both are measured on the compounded blend rather than on the additive. Impact is the sensitive property because it depends on stress transfer across the interface, while modulus and density follow the rule of mixtures whether the phases are bonded or not. Elongation at break behaves like impact strength and for the same reason. The 7 methods below are the ones the sourced results on this page were measured with.

Two cautions apply when these numbers are compared between sources. Izod results in kJ/m2 to ISO 180 and in J/m to ASTM D256 are not interchangeable, because the ISO value is normalised to the cross-sectional area behind the notch and the ASTM value to the notch length. Domain-size microscopy is not standardised in this reference, so a domain size quoted without its preparation method cannot be compared across laboratories. A compatibilized compound is therefore judged against an uncompatibilized control made on the same line rather than against a published figure. All methods are indexed under testing plastic additives.

How Are Compatibilizers Regulated?#

Compatibilizers are regulated through their monomers and their residual monomer content, because the copolymers themselves are polymers and therefore exempt from REACH registration under Article 2(9) of Regulation (EC) No 1907/2006. The practical consequence is that a compatibilizer has no registration number of its own, while maleic anhydride, glycidyl methacrylate, methacrylic acid, styrene, 1-octene and ethylene each carry their own classification and their own food-contact limits. Three regulatory questions therefore have to be asked about a monomer rather than about a product: is it registered, is it on the Candidate List or Proposition 65, and is it on the Union list of Regulation (EU) No 10/2011 with a specific migration limit. Exempt from registration is not the same as unregulated, and a grade that satisfies REACH may still fail a food-contact specification. The table maps the 5 types onto the monomer entries that govern them.

EU values were checked against the consolidated text of 16 March 2025.

REACH, the SVHC Candidate List and Proposition 65#

The compatibilizer itself is a polymer and carries no REACH registration, while the monomers behind it do: maleic anhydride and glycidyl methacrylate are both registered substances with harmonised CLP classifications. Article 2(9) of REACH exempts polymers from registration, which covers PP-g-MAH, E-MA-GMA, SEBS, POE, EPDM and the ionomers alike. Exempt from registration is not the same as unregulated, and the polymer exemption is explained under REACH and plastic additives.

Registration volume shows where the regulatory attention sits: maleic anhydride carries at least 100 active REACH dossiers and glycidyl methacrylate carries 32.

Neither monomer is an SVHC today. A check of ECHA CHEM on 22 September 2026 found neither maleic anhydride nor glycidyl methacrylate on the Candidate List, while two substances from the neighbouring coupling-agent and crosslinker space are listed: TGIC, included on 18 June 2012, and tris(2-methoxyethoxy)vinylsilane, included on 17 January 2022. Every listed additive is tracked on the SVHC Candidate List page.

Harmonised classification applies to the monomers as substances. Glycidyl methacrylate has index number 607-123-00-4 with Carc. 1B (H350), Muta. 2 (H341) and Repr. 1B (H360F), and maleic anhydride has index number 607-096-00-9 with Acute Tox. 4, Skin Corr. 1B, Resp. Sens. 1 (H334), Skin Sens. 1A and STOT RE 1. Neither classification transfers to the copolymer.

California treats the same monomer the same way. Glycidyl methacrylate was listed under Proposition 65 as a carcinogen on 27 January 2023, which makes residual free GMA the item to control rather than the copolymer, and warning rules for residual monomers are explained under Proposition 65 and plastic additives.

Food contact and recycled plastics: EU 10/2011, FDA 21 CFR and Regulation (EU) 2022/1616#

A compatibilizer may be used in food-contact plastics when its monomers are on the Union list of Regulation (EU) No 10/2011 and their specific migration limits are met, for example 30 mg/kg as maleic acid for maleic anhydride and 0.02 mg/kg for glycidyl methacrylate. FCM 857, the MMA/butyl acrylate/styrene/GMA copolymer, is narrower still: it is authorised only in rigid PVC at up to 2 % and only at room temperature or below. Migration testing is explained under EU 10/2011.

Compliance for a blend runs monomer by monomer. A PCR PP/PET compound with an SEBS compatibilizer brings styrene into the calculation, and a POE-modified polyethylene brings 1-octene at 15 mg/kg.

The US route is a listing route rather than an approval route. Ethylene-methacrylic acid ionomers are covered by 21 CFR 177.1330, ethylene-acrylic acid copolymers by 177.1310, styrene block polymers by 177.1810, and olefin polymers by 177.1520, which also covers ethylene-maleic anhydride copolymers with up to 2 % maleic anhydride as an adhesive or sealant layer used up to 49 °C. PP-g-MAH has no generic section, so its food-contact status is grade-specific. The FDA lists substances for uses and does not approve products, and every 21 CFR section is mapped on FDA food contact rules.

Recycled food-contact plastic adds a second layer of law. Recycled PET falls under Regulation (EU) 2022/1616, and an additive used during recycling must itself be authorised under Regulation (EU) No 10/2011. Regulation (EU) 2025/40, the PPWR, applies from 12 August 2026, and its Article 7 recycled-content targets apply from 1 January 2030 at 30 % for contact-sensitive PET packaging, 30 % for single-use plastic beverage bottles, 10 % for other contact-sensitive plastic packaging and 35 % for other plastic packaging. Those targets are set out in recycled plastics regulations.

Who Makes Compatibilizers? Brands and Suppliers#

Compatibilizers are not reported as a separate segment of the plastic additives market, which analysts size between USD 43.5 billion (2023, MarketsandMarkets) and USD 63.71 billion (2025, Precedence Research), so the picture has to be built from the producers and their brand lines. Ceresana puts the same total at 36.7 Mt in 2023 by volume, and the published family splits cover plasticizers, fillers, flame retardants, antioxidants, impact modifiers and light stabilizers without a compatibilizer line. No compatibilizer market size is established in this reference, and figures circulating on seller pages are not sourced. Segment data for the families that are reported separately are on plastic additives market.

Nine producers with named brand lines cover the chemistry described above. The demand driver behind most of them is regulatory, because the PPWR recycled-content targets that apply from 1 January 2030 force mixed streams into applications previously served by virgin resin.

Brand lines are listed only where our source library carries them.

Four of these producers have profile pages on this reference: SI Group, Dow, ExxonMobil and BYK. Grades, plants and certifications are compared in the directory of compatibilizer and coupling agent suppliers, which covers both families because the same maleated polyolefins are sold into each.

Complete List of Compatibilizer Substances: 9 Substances#

The 9 substances below are the compatibilizers in the directory, with their CAS number, chemical class and the blends they serve. They are listed in the type order used throughout this page, from the maleic anhydride grafted polyolefins to the epoxy-functional oligomers. Seven of them carry a second function in another additive family.

Seven of these records are filed under impact modifiers or chain extenders in the current site inventory although our source library assigns their compatibilizer function here.

Each record is part of the plastic additives database, where the same substance carries its full regulatory and dosage profile across every family it serves.

How Do Compatibilizers Differ from Coupling Agents, Impact Modifiers and Chain Extenders?#

All four families work at an interface or a chain end, but they differ in which one: a compatibilizer joins two polymers, a coupling agent joins a polymer to a filler or a fibre, an impact modifier disperses a rubber phase inside one polymer, and a chain extender rebuilds the molar mass of a single condensation polymer. The confusion is real rather than careless, because one molecule can do two of these jobs depending on what else is in the compound, and supplier catalogues file the same grade under whichever heading sells it. Two questions separate them in practice: what is the counterpart, another polymer, a mineral or fibre surface, a matrix to be toughened or a chain end, and is the additive a polymer or a small molecule. The table applies both to the four property-modifier families.

Coupling agents: the polymer-filler interface#

A coupling agent bonds a polymer to an inorganic or natural surface, so its counterpart is a filler or a fibre rather than a second polymer, and most coupling agents are small reactive molecules such as silanes rather than copolymers. Silanes are dosed at 0.2 to 1.0 wt% of the total mix in an integral blend.

Substrate decides whether a silane works at all. Silanes bond well to silica, quartz and glass, and poorly to calcium carbonate as chalk or marble, to gypsum, barytes, graphite and carbon black, where titanates or a stearic-acid coating take their place. Maleated polyolefins sit in both families, which is why SI Group describes POLYBOND 3200 as a coupling agent while this page files it as a type 1 compatibilizer.

Reactive elastomers: the impact-modifier overlap#

The same reactive elastomer often appears in both families, because a rubber particle that is well anchored to the matrix toughens it, and a copolymer that anchors two phases compatibilizes them. LOTADER AX8900 is sold both as an impact modifier for engineering thermoplastics such as PPS, PBT and PET and as a compatibilizer for polyester and polyolefin blends, and SEBS-g-MAH is both an impact modifier for polyamides and polyesters and a compatibilizer for PA/PP, PP/PET and PE/PA.

The difference is the job, not the molecule. A grade is an impact modifier when the compound has one polymer phase and the rubber absorbs energy, and a compatibilizer when the compound has two polymer phases and the rubber holds them together.

Do compatibilizers become legacy additives in recycled plastics?#

Yes: a compatibilizer is not consumed, it stays in the material, and when that material is recycled again it enters the next stream as a legacy additive. Scholz and colleagues describe this in 2026 for the additive load of recyclate generally, and compatibilizers are a clear case because they are added at percent levels rather than at the tenths of a percent typical of stabilizers.

Each loop adds to the additive inventory of the polymer. A PCR polyolefin compatibilized with 3 % polyolefin elastomer carries that elastomer into its next life, where it changes the phase behaviour of a blend nobody designed, and what that means for a recyclable design is on design for recycling.

Frequently asked questions about compatibilizers#

The 4 questions below are the ones formulators and recyclers ask most often about compatibilizers: the purpose, reactive compatibilization, the PP/PE case and REACH status.

What is the purpose of a compatibilizer in polymers?#

The purpose of a compatibilizer is to make a blend of two immiscible polymers behave as one material: it lowers interfacial tension so the minor phase disperses finely, keeps those domains from merging again, and bonds the phases so the blend carries load instead of splitting at the interface. The effect shows up in notched impact strength and elongation at break rather than in modulus.

What is reactive compatibilization?#

Reactive compatibilization means the compatibilizer is formed in the extruder rather than added ready-made: a functional group on the additive, usually maleic anhydride or glycidyl methacrylate, reacts with an end group on one of the polymers and the resulting graft copolymer sits at the interface. Maleic anhydride forms imide links with polyamide amine ends, and the GMA epoxide forms ester links with polyester chain ends. It is the industrial standard for PA/PP, PA/ABS, PC/PBT and PET/polyolefin blends.

Which compatibilizer works for PP and PE?#

Neither polyolefin carries a reactive end group, so PP/PE blends use non-reactive compatibilizers: polyolefin elastomers at 2 to 5 % (typically 3 %), propylene-based elastomers from 5 %, SEBS types and PP-based olefin block copolymers at about 5 wt%. In a 70/30 HDPE/PP recyclate, 3 % polyolefin elastomer raises impact strength and elongation by about a factor of 3 while keeping the modulus. EPDM is documented for the same pair.

Are compatibilizers registered under REACH?#

No: compatibilizers such as PP-g-MAH, E-MA-GMA, SEBS and POE are polymers and exempt from REACH registration under Article 2(9), while their monomers, among them maleic anhydride and glycidyl methacrylate, are registered separately. Exemption from registration removes no other obligation: food-contact use still runs through the monomer entries of Regulation (EU) No 10/2011, and residual monomers still carry their CLP classifications.