Impact Modifiers: 7 Types, Mechanisms, Dosage and Selection

Impact modifiers are rubbery polymers that disperse as small particles in a brittle plastic and absorb impact energy by cavitating and letting the surrounding matrix yield, and this reference sorts them into 7 types. They account for 5 % of all plastic additives by weight and are dosed at about 3-10 phr in rigid PVC, so why does a few percent of rubber turn a brittle pipe or profile into a tough one? The rubber never carries the load itself: it changes the stress field around a growing crack so the plastic between the particles deforms instead of breaking.

The 7 types of impact modifiers are MBS, acrylic impact modifiers, chlorinated polyethylene (CPE), olefin elastomers, styrenic block copolymers, ethylene copolymers and ionomers, and maleic anhydride grafted elastomers. Two of them, MBS and acrylic, arrive as pre-formed core-shell particles whose size is fixed in the emulsion reactor. The other 5 form their rubber phase in the melt, so the extruder and the reactive groups on the rubber decide how fine that phase becomes.

Impact modifiers belong to the property-modifier group of plastic additives, next to plasticizers and compatibilizers. This page covers the 3 toughening mechanisms and the particle-size rules behind them, each of the 7 types with its structure and host polymers, every dosage in our source library in phr and wt%, which type suits rigid PVC, polypropylene, polyamide, polyester, polycarbonate, PLA and recyclate, the 6 selection criteria, how notched Izod and Charpy measure the result, how EU and US food-contact law reaches these polymers through their monomers, who produces them, and the 8 impact-modifier substances in the directory.

The table compares the 7 types of impact modifiers by structure, main host polymers and a sourced example.

Grades are examples from our source library, not recommendations. Types 1-2 are pre-formed particles; types 3-7 form their rubber phase in the melt.

What Is an Impact Modifier?#

An impact modifier is a polymeric additive, usually an elastomer, that forms a dispersed rubber phase in a glassy or semi-crystalline plastic and changes its fracture from brittle to ductile. The additive stays a separate phase: it does not dissolve in the matrix, and its job is done at the moment a crack starts, not during flow or moulding. Industry uses 5 names for the same class, namely impact modifier, toughener, toughening agent, impact improver and rubber toughening agent, with "IM" as the shorthand on a formulation sheet. Impact modifiers are property modifiers, one level below plastic additives as a whole, and their siblings are plasticizers, compatibilizers, coupling agents and chain extenders.

Is every rubber inside a plastic an impact modifier? No. The term covers rubber added during compounding, not rubber built in during polymerisation, which is what high-impact polystyrene, ABS and heterophasic polypropylene contain. The distinction also separates impact modifiers from their closest sibling: an impact modifier changes fracture behaviour, while a compatibilizer changes the interfacial tension between 2 immiscible polymers. SEBS, POE and MAH-grafted rubbers are sold for both jobs, so the same grade appears in 2 families of this reference.

Why do brittle plastics need impact modifiers?#

Brittle plastics need impact modifiers because an unmodified glassy or semi-crystalline matrix, such as rigid PVC or polypropylene below 0 °C, cracks under a sharp blow or a notch before it can yield. The energy a tough part absorbs comes from plastic deformation, and a matrix that cannot deform converts that energy into a running crack instead. Four failure modes drive the demand for impact modifiers.

• Brittleness at room temperature: rigid PVC pipe, fittings and profile fracture cleanly under a hammer blow without an acrylic core-shell, MBS or CPE modifier in the recipe.
• Notch sensitivity: polyamide, polycarbonate and PBT lose most of their unnotched toughness as soon as a moulded corner, a weld line or a machined groove concentrates the stress.
• Low-temperature embrittlement: polypropylene turns brittle as its amorphous phase approaches its glass transition, which is why EPR and POE go into every cold-weather PP compound.
• Recyclate degradation: mixed PE/PP and polyolefin/PET recyclate carries shortened chains and immiscible phases, and 2-5 % POE restores about 3 times the impact strength of an unmodified HDPE/PP 70/30 blend.

All 4 modes end in the same event: a crack that runs through the part faster than the matrix can absorb it.

Is an impact copolymer the same as an impact-modified plastic?#

No: an impact copolymer, such as heterophasic PP, HIPS or ABS, gets its rubber phase during polymerisation, while an impact-modified plastic gets a separate rubber additive during compounding. Heterophasic polypropylene, sold as PP-B or ICP, carries an ethylene-propylene rubber phase made in the reactor that raises low-temperature impact without any compounding step, and high-impact polystyrene is made by polymerising styrene around dissolved polybutadiene, which leaves salami particles of 1-3 µm. ABS needs no added impact modifier for the same reason: its polybutadiene rubber is grafted into the styrene-acrylonitrile matrix in the reactor. A 2019 study of HIPS found that raising rubber content from 5 % to 15 % lifted notched impact strength to 166.2 J/m, about 4 times the starting value.

How Do Impact Modifiers Work?#

Impact modifiers work through 3 energy-absorbing mechanisms described by Clive Bucknall at Cranfield University: the rubber particles start many small crazes, cavitate under triaxial stress, and let the matrix between them yield in shear. All 3 convert kinetic energy into plastic deformation spread over a large volume, instead of into the surface energy of one fast crack. Which mechanism carries most of the energy depends on the host polymer, on rubber particle size and on particle spacing.

Crazing, cavitation and shear yielding#

The 3 toughening mechanisms are crazing, rubber-particle cavitation and matrix shear yielding, and which one dominates depends on whether the host polymer is a brittle glass such as polystyrene or a pseudo-ductile polymer such as PVC. Bucknall's 2007 review in the Journal of Polymer Science Part B (volume 45, page 1399) sets out all 3 in the order below.

1. Crazing: the rubber particle acts as a stress concentrator and starts thousands of load-bearing microvoids bridged by drawn polymer fibrils, the dominant route in low-entanglement glassy matrices such as polystyrene toughened to HIPS and SAN toughened to ABS. In those 2 materials crazing accounts for at most about half of the plastic strain.
2. Cavitation: the rubber particle tears internally under the triaxial stress ahead of the crack, which relieves the hydrostatic component of that stress field.
3. Shear yielding: the matrix ligaments between the cavitated particles deform in shear bands, the mechanism that dominates in ductile and pseudo-ductile polymers such as PVC, polycarbonate, polyamide, PBT and polypropylene.

The order in which the 3 occur matters as much as their identity. In a pseudo-ductile matrix, Bucknall's review records cavitation first and massive shear yielding second, so a particle that resists cavitation blocks the whole sequence and leaves the compound brittle even at a high rubber content. The micro-mechanics of crazing in glassy polymers are defined in the glossary.

Rubber particle size and the critical inter-particle distance#

Particle size decides toughening: crazing polymers such as HIPS work best with rubber particles of 2-5 µm, while nylon becomes tough only when the matrix ligament between particles falls below 0.3 µm, the critical inter-particle distance Souheng Wu measured at DuPont in 1985. Wu published the criterion in Polymer, volume 26 (1985), page 1855, from PA66 and rubber blends, and its power is that the threshold belongs to the matrix alone: a blend is tough whenever the ligament is thinner than 0.3 µm, independently of rubber volume fraction and of particle size taken on their own. Rolf Borggreve and Reinoud Gaymans at the University of Twente refined the criterion for PA6 between 1987 and 1989.

The 2 rules point in opposite directions. A crazing matrix wants particles large enough to initiate crazes, which is why the salami morphology of HIPS sits at 2-5 µm, while a shear-yielding matrix wants particles small and closely spaced enough to bring the ligaments below the critical distance. Cavitation sets the lower bound: cavitation resistance rises with the shear modulus of the rubber, with its surface energy and with decreasing particle size, so a very small or heavily crosslinked particle holds together instead of tearing.

Interfacial adhesion: grafted shells and reactive groups#

An impact modifier toughens only when its rubber particles stick to the matrix, which core-shell grades achieve through a grafted PMMA or SAN shell and olefin elastomers achieve through reactive maleic anhydride or glycidyl groups. A particle with a weak interface debonds from the matrix under load instead of cavitating, and a debonded particle behaves like a void: it lowers stiffness without dissipating energy. Core-shell modifiers solve this in the emulsion reactor, where the shell is grafted onto the rubber core and chosen to adhere to the host, as PMMA does to PVC and polycarbonate.

Reactive adhesion makes the graft copolymer in the extruder instead. A non-polar olefin elastomer dispersed in polar polyamide or PBT carries maleic anhydride or glycidyl methacrylate functionality, and those groups react with the chain ends of the matrix during melt compounding: anhydride with the amine ends of polyamide, glycidyl with the carboxyl, hydroxyl and amine ends of PET, PBT, PPS and polycarbonate blends. The copolymer formed at the interface anchors the rubber and lowers interfacial tension, so the dispersed phase breaks down to a finer particle size in the same mixer.

The stiffness-toughness trade-off#

Every impact modifier trades stiffness for toughness: the rubber phase that absorbs impact energy also lowers modulus and heat deflection temperature, which is why rigid PVC formulators stop at about 10 phr. The patent literature gives about 3-10 phr as the effective window for rigid PVC, with no strength effect below 3 phr and insignificant further gains above 10 phr, so diminishing returns set the upper limit as much as the penalties do. Three penalties follow every addition of rubber.

• Modulus: the dispersed rubber has a shear modulus orders of magnitude below the matrix, so tensile and flexural modulus fall with rubber volume fraction.
• Heat deflection temperature: a soft second phase lowers the temperature at which a loaded bar deflects, which restricts modified compounds in hot-side applications.
• Weatherability: diene rubbers keep carbon-carbon double bonds that UV light and ozone attack, so butadiene-based MBS and ABS-type high-rubber grafts lose toughness and colour outdoors, while saturated acrylate and hydrogenated styrenic rubbers do not.

Strength data show the same trade in a single material. In the 2019 HIPS study, raising rubber content from 5 % to 15 % multiplied notched impact strength by about 4 while tensile strength at break fell from about 17 MPa to about 12 MPa.

7 Types of Impact Modifiers#

The 7 types of impact modifiers are MBS, acrylic impact modifiers, chlorinated polyethylene (CPE), olefin elastomers, styrenic block copolymers, ethylene copolymers and ionomers, and maleic anhydride grafted elastomers. They are ordered here by the size of the host market, so the 3 PVC modifiers come first, the polyolefin elastomers second and the engineering-plastic and recyclate modifiers last.

MBS and acrylic grades are core-shell impact modifiers: emulsion-made particles whose size is fixed before compounding, a class that also includes ABS-type high-rubber grafts and silicone-acrylic grades. The other 5 types form their rubber phase in the melt, so mixing energy and reactive groups set their particle size instead of the reactor.

1. MBS impact modifiers#

MBS impact modifiers are core-shell particles with a crosslinked butadiene rubber core and a methyl methacrylate-styrene shell, and their refractive index can be matched to PVC so that clear bottles and sheet stay transparent. The substance carries CAS 25053-09-2, and the shell is grafted onto the core so the particle disperses without coalescing. Under impact the butadiene core cavitates and triggers shear yielding in the surrounding PVC, the classic pseudo-ductile sequence.

The host polymers are rigid and semi-rigid PVC plus CPVC, where patent literature gives 5-6 phr for an MBS or ABS graft in CPVC. Kane Ace B22 from Kaneka has a refractive index of 1.535, the value that makes transparent blow-moulded PVC bottles possible. The butadiene core is also the type's limit, because its residual unsaturation makes MBS unsuitable for long outdoor exposure. 21 CFR 178.3790 lists modifiers of this chemistry for semirigid and rigid PVC with butadiene-styrene units limited to 15 wt% of the finished article, and clear-grade selection is compared under MBS impact modifiers.

2. Acrylic impact modifiers#

Acrylic impact modifiers are core-shell particles with a crosslinked butyl acrylate rubber core and a PMMA shell, and because the acrylate rubber has no double bonds they are the standard choice for outdoor PVC window profiles and siding. The abbreviation AIM covers the whole family, and its structure mirrors MBS with one decisive change: poly(n-butyl acrylate) replaces polybutadiene in the core. The saturated backbone that results neither absorbs UV light nor reacts with ozone, so the toughening effect survives years of weathering.

Rigid PVC for windows, fencing, decking and siding is the volume application, and the same core-shell chemistry toughens PMMA, polycarbonate and PLA, where the PMMA shell gives the particle its adhesion to an acrylic or carbonate matrix. Under 21 CFR 178.3790, acrylic modifier units in a food-contact PVC article are limited to 5 wt% of the finished article under the first of the listed options. One naming trap belongs here: acrylic processing aids are a different product, high-molecular-weight PMMA copolymers that promote PVC fusion and melt strength rather than toughness. Profile and siding grades are compared under acrylic impact modifiers.

3. Chlorinated polyethylene (CPE)#

Chlorinated polyethylene (CPE) is an amorphous polyethylene with 34-44 % chlorine that toughens rigid PVC pipe, profile and fittings at 1-10 phr, with 2.5-7.0 phr preferred in the patent literature. Its CAS number is 64754-90-1, and chlorination destroys the crystallinity of the polyethylene backbone, leaving a rubbery amorphous polymer whose polarity matches PVC closely enough to disperse as a fine phase. That phase promotes shear yielding in the PVC matrix, and the chlorine it carries gives the compound inherent ignition resistance.

Two reference products define the grade range: Dow's Tyrin CM at 36 % chlorine, and CPE 135A at 35 ± 2 % chlorine, Shore A hardness of 65 or below, tensile strength of at least 22 MPa, elongation at break of at least 530 % and a decomposition temperature of at least 165 °C. CPE is the cost-driven choice for opaque pipe, fittings and profile, and it is less suitable than MBS or acrylic grades for transparent PVC. Chlorine content and grade 135A are explained under CPE impact modifiers for PVC.

4. Olefin elastomers: POE, EPR, EPDM and OBC#

Olefin elastomers are amorphous ethylene copolymers, such as ethylene-octene POE, EPR and EPDM, that disperse in polypropylene and polyethylene and keep them tough at low temperature, the basis of TPO bumper compounds. Polyolefin elastomer, CAS 26221-73-8, is the metallocene ethylene-1-octene copolymer of the group, and the octene comonomer suppresses crystallinity enough to give a low glass transition while leaving enough for pellets that do not block in a silo, an advantage over amorphous EP and EPDM rubber bales. Dow's ENGAGE 8100 is the reference grade, with a density of 0.870 g/cm3, a melt index of 1 g/10 min at 190 °C and 2.16 kg, and a Vicat softening point of 45 °C. The low-Tg phase cavitates and triggers shear yielding in polypropylene at temperatures where unmodified PP is already brittle.

EPDM, CAS 25038-36-2, adds an ethylidene norbornene diene that allows dynamic vulcanisation, and it serves as a compatibilizer for PE/PP blends as well as an impact modifier. Thermoplastic polyolefin compounds combine PP with POE, EPR or EPDM and talc for bumper fascia, exterior trim, door skins and airbag covers. In recyclate the same chemistry repairs degraded blends: adding 2-5 % POE, typically 3 %, to an HDPE/PP 70/30 recyclate raises impact strength and elongation by about 3 times while keeping modulus. Olefin block copolymers extend the family, Dow's INFUSE built on ethylene and INTUNE on propylene. POE, EPR, EPDM and OBC grades are compared under olefin elastomer impact modifiers.

5. Styrenic block copolymers (SEBS)#

Styrenic block copolymers, mainly SEBS, are triblock rubbers whose polystyrene ends anchor in the matrix while a saturated ethylene-butylene midblock absorbs impact, which makes them UV-stable impact modifiers for recycled PP and PP/PET blends. SEBS carries CAS 66070-58-4 and is made by hydrogenating SBS, a step that removes the double bonds of the butadiene midblock and with them the ozone and UV sensitivity of the parent rubber. The block architecture does the anchoring that a core-shell grade achieves with a grafted shell.

Recyclate is where our source library carries hard numbers. Kraton's CirKular+ C1000 at 10 % in a 72/18 PP/PET blend raises notched Izod by 50 % and yield strength by 30 %; C1010 at 5 % in post-consumer HDPE/PET raises notched Izod by 70 % and yield by 40 %; C2000 is used at 3-10 % in post-consumer PP. Kraton G1651 and FG1901 are the reference linear grades, the FG type carrying grafted maleic anhydride for polyamide and polyester. US food contact runs through 21 CFR 177.1810, which covers styrene block polymers subject to specifications.

6. Ethylene copolymers and ionomers#

Ethylene copolymers are ethylene-acrylate rubbers, often carrying reactive glycidyl methacrylate groups, that graft onto polyester chain ends during compounding and toughen PET, PBT and PC blends; ionomers do the same job through ionic clusters. The reactive terpolymer of the group, ethylene-methyl acrylate-glycidyl methacrylate, has CAS 51541-08-3. Its acrylate ester lowers the crystallinity of the ethylene backbone to give a rubbery phase, and its glycidyl groups open against the carboxyl, hydroxyl and amine end groups of PET, PBT, PPS and polycarbonate blends, so the interface is built during melt compounding.

Two grades define the range. LOTADER AX8900 contains 24 wt% methyl acrylate and 8 wt% glycidyl methacrylate with a melt flow index of 6 g/10 min at 190 °C and 2.16 kg, and ELVALOY PTW is composed of 66.75 wt% ethylene, 28 wt% n-butyl acrylate and 5.25 wt% GMA, which also raises the melt strength of CPET trays. Ionomers use a different anchor: the sodium salt of an ethylene-methacrylic acid copolymer, CAS 25608-26-8, with the zinc salt at CAS 28516-43-0, forms ionic clusters that act as physical crosslinks, and 21 CFR 177.1330 covers these resins at up to 20 wt% methacrylic acid. In glass-fibre-filled recycled PET, Monti and colleagues found in a 2021 study in Polymers that E-MA, E-MA-GMA or the ionomer Surlyn 8940 raised notched Izod strength from 5.2 to about 8.1 kJ/m2, a gain of 55 % measured to ISO 180 at 23 °C. E-MA, E-BA, GMA terpolymers and ionomers are compared under ethylene copolymer impact modifiers.

7. Maleic anhydride grafted elastomers#

Maleic anhydride grafted elastomers are olefin or styrenic rubbers carrying anhydride groups that react with polyamide amine ends, which gives the fine, bonded rubber dispersion behind supertough PA6 and PA66. The base rubbers are EPR, EPDM, POE and SEBS, and the grafting level is low: Kraton FG1901 carries about 1-2 wt% maleic anhydride on its rubber midblock according to the patent literature. That small anhydride fraction is enough, because the graft copolymer forms in situ at the interface, drives the dispersed phase down toward Wu's 0.3 µm ligament criterion and holds it there against coalescence.

Supertough polyamide is the flagship application, and Brüggemann states that reactive MAH-grafted POE or EPDM keep polyamide tough down to -40 °C. A study of a PA6/PP/ABS/SEBS blend found that 10 wt% POE-g-(MAH-co-St) together with 10 wt% SEBS-g-(MAH-co-St) raised impact strength by 823 %. Maleic anhydride is the one part of this chemistry with a food-contact number of its own, FCM 234 in group 3, with a total specific migration limit of 30 mg/kg expressed as maleic acid. The same PP-g-MAH, POE-g-MAH and SEBS-g-MAH chemistry is compared as compatibilizers under maleic anhydride grafted polymers.

How Much Impact Modifier Is Needed? Dosage by Type and Polymer#

Impact modifiers are dosed at about 3-10 phr in rigid PVC, where less than 3 phr gives no strength effect, and at about 2-10 % in polyolefin recyclates, while study levels in engineering blends reach 10 wt%. That places the family in the 1-10 phr dosage band of a PVC recipe, alongside heat stabilizers and lubricants, and well below the filler and plasticizer bands. The range is narrow because both ends are hard limits: the lower end is where the rubber ligaments start to interact, the upper end where modulus and heat deflection temperature losses outweigh further toughness.

The table lists every impact-modifier dosage in our source library with its source type.

phr = parts per hundred resin (PVC); % as reported by the source. Legal maxima under 21 CFR 178.3790 and EU FCM 857 belong to the regulation section, not here.

Units follow the host polymer, and mixing the 2 conventions is the most common error in this family. PVC recipes are written in phr, parts per hundred parts of resin, so a 7 phr CPE addition equals a different wt% in every recipe depending on how much filler, plasticizer and stabilizer the formulation carries; see PHR (parts per hundred resin) for the conversion. Polyolefin and engineering compounds are written in wt% of the total compound, which is how the POE, SEBS and ethylene-copolymer values above are reported.

The percentages in 21 CFR 178.3790 and in EU FCM entry 857 are legal maxima a food-contact article must not exceed, not dosages, so they never enter a formulation calculation. Levels for every other family are on additive dosage levels in plastics.

Which Impact Modifier for Which Polymer?#

The right impact modifier depends on the host polymer: rigid PVC takes MBS, acrylic or CPE, polypropylene takes olefin elastomers, and polyamides and polyesters take reactive MAH- or GMA-functional rubbers that bond to their chain ends. Polarity is the first filter, because a non-polar rubber in a polar matrix needs a reactive group to hold the interface together, and end-group chemistry is the second, because polyamide offers amine ends and polyester offers carboxyl and hydroxyl ends to react with.

Impact modifiers for rigid PVC#

Rigid PVC is the largest impact-modifier market, and it uses 3 types: MBS where the part must stay clear, acrylic where it goes outdoors, and CPE where cost and pipe or profile toughness matter most. All 3 work on the same matrix behaviour, because PVC is pseudo-ductile and yields in shear once the rubber particles cavitate, so clarity, weathering and price decide between them rather than mechanism. The effective window is the same for all 3 at about 3-10 phr, with CPE preferred at 2.5-7.0 phr and MBS or ABS grafts at 5-6 phr in CPVC. Below 3 phr the patent literature records no strength effect at all.

The impact modifier is one line of a recipe with 6 functional lines. A rigid PVC compound carries heat stabilizers, lubricants, acrylic processing aids, the impact modifier, calcium carbonate and titanium dioxide, and those lines interact: calcium carbonate at high loading competes with the modifier for toughness, and the stabilizer system decides how much shear the compound tolerates while the modifier disperses. The full stabilizer, lubricant and filler package is on additives for PVC.

Impact modifiers for polypropylene and polyethylene#

Polypropylene is toughened with olefin elastomers, mainly ethylene-octene POE, EPR and EPDM, either compounded into TPO with talc or built into the polymer as an in-reactor impact copolymer. The compounded route gives the formulator control over rubber type, level and particle size, and it is how thermoplastic polyolefin compounds for bumper fascia, exterior trim, door skins and airbag covers are made. The reactor route delivers heterophasic PP with its ethylene-propylene rubber phase already in place, which raises low-temperature impact without a compounding step and competes directly with adding POE.

Polyethylene follows the same chemistry with different drivers. EPDM and EPDM-g-MAH serve HDPE/PP and LDPE/PP blends, where the rubber compatibilizes as well as toughens, and POE is the standard choice in recycled polyolefin streams at 2-5 %. Both polymers accept olefin rubbers so readily because nothing has to react: rubber and matrix are both hydrocarbons, so adhesion comes from co-crystallisation and chain entanglement. Nucleating, antioxidant and talc levels are on additives for polypropylene.

Impact modifiers for engineering plastics: PA, PET, PBT and PC#

Engineering plastics need reactive or core-shell impact modifiers: polyamides take MAH-grafted olefin rubbers, PET and PBT take glycidyl-functional ethylene copolymers, and polycarbonate takes core-shell particles. Polyamide is the most demanding of the 3, because it is notch sensitive and its toughening obeys the ligament criterion, so the modifier has to disperse below 0.3 µm of matrix ligament and stay there. Maleic anhydride grafted EPR, EPDM, POE and SEBS achieve that by reacting with the amine end groups of the polymer during compounding. Copper-halide stabilizers and glass fibre complete the package on additives for nylon.

Polyesters use epoxy rather than anhydride chemistry. Ethylene copolymers carrying glycidyl methacrylate graft onto the carboxyl and hydroxyl chain ends of PET and PBT, the same reaction that rebuilds the properties of recycled polyester, where Monti and colleagues measured a 55 % notched Izod gain in 2021.

Polycarbonate and PC/ABS blends take the third route. Both are notch sensitive and lose toughness in thick sections, and core-shell modifiers, acrylic and silicone-acrylic types, are the grades used, because the PMMA shell adheres to the carbonate matrix without any reaction.

Impact modifiers for recycled plastics#

Recycled plastics need impact modifiers because mixed PE/PP and polyolefin/PET recyclates contain immiscible phases and degraded chains, and 2-5 % POE or 3-10 % SEBS restores much of the lost toughness. Two defects cause the loss. Mechanical recycling shortens chains through repeated melt passes and oxidation, which lowers entanglement density and with it the ability of the matrix to yield, and sorting leaves a second polymer as an immiscible dispersed phase whose interfaces act as ready-made crack initiation sites.

The hard numbers come from 2 sources. In HDPE/PP 70/30 recyclate, ENGAGE POE at 2-5 %, typically 3 %, raises impact strength and elongation by about 3 times while modulus is kept. In polyolefin/PET streams, Kraton's CirKular+ grades deliver 50 % more notched Izod in a 72/18 PP/PET blend and 70 % more in post-consumer HDPE/PET, and recycled polypropylene is also toughened with POE and propylene-based elastomers. Restabilization and odour control are on additives for recycled plastics.

Regulation drives the demand. The EU Packaging and Packaging Waste Regulation, Regulation (EU) 2025/40, applies from 12 August 2026 and sets recycled-content targets for 2030 of 30 % for contact-sensitive PET packaging, 10 % for other contact-sensitive packaging, 30 % for single-use plastic beverage bottles and 35 % for other plastic packaging.

Toughening is half of the recyclate problem, because the interface itself also has to be stabilised against coalescence during processing. Blend-specific choices are compared on compatibilizers for recycled plastics.

How Do You Select an Impact Modifier? 6 Criteria#

Select an impact modifier in 6 steps: identify the host polymer, set the impact target, check transparency, check outdoor exposure, protect stiffness and heat resistance, and screen food-contact limits. The order matters, because the first step alone eliminates most of the 7 types for any given compound.

1. Identify the host polymer and its polarity. Polypropylene and polyethylene take olefin elastomers with no reactive group; polyamide takes maleic anhydride functionality; PET, PBT and PC blends take glycidyl methacrylate; PVC takes the core-shell trio or CPE.
2. Define the impact requirement measurably: notched Izod in J/m or kJ/m2, or Charpy in kJ/m2, with the test temperature stated, because a grade that passes at 23 °C can fail at -20 °C.
3. Check transparency. A clear part needs a modifier whose refractive index matches the matrix, which in PVC means an MBS grade such as Kane Ace B22 at 1.535.
4. Check outdoor exposure. Acrylate cores and hydrogenated styrenic midblocks survive UV and ozone; butadiene-based cores do not, so MBS and ABS-type grafts should stay indoors.
5. Check the stiffness and heat deflection temperature the part still needs. Every phr of rubber costs modulus and HDT, and in rigid PVC the window closes at about 10 phr.
6. Screen food contact, residual monomers and cost together. 21 CFR 178.3790 caps acrylic modifier units at 5 wt% and butadiene-styrene units at 15 wt% of a finished PVC article, and glycidyl methacrylate carries an EU specific migration limit of 0.02 mg/kg.

These 6 criteria are the family-specific form of a screen that every additive class needs, and the general framework for every family is on how to select plastic additives.

How do you keep impact-modified PVC clear?#

Impact-modified PVC stays clear when the modifier's refractive index matches that of PVC, which is why MBS grades such as Kane Ace B22 (RI 1.535) are used in transparent bottles and CPE is not. Light scatters at every interface where the refractive index changes, and a compound holds 5-10 phr of dispersed particles, so any index mismatch turns a water-clear sheet hazy. Matching the apparent refractive index of the modifier to the PVC is the method the patent literature describes for transparent blow-moulded bottles.

Clarity is measured, not judged. A material with a haze value above 30 % is classified as diffusing rather than transparent under ASTM D1003-21, and haze is measured as described in haze and clarity measurement.

Which impact modifiers are weatherable for outdoor and UV exposure?#

Acrylic impact modifiers and saturated rubbers such as SEBS are weatherable, while MBS and other butadiene-based modifiers degrade in UV light because their rubber still carries double bonds. The chemistry is the whole explanation: a carbon-carbon double bond in the polybutadiene core absorbs UV energy and reacts with ozone, so the rubber phase crosslinks or chain-scissions, stops cavitating, and the part returns to brittle behaviour, while poly(n-butyl acrylate) cores and hydrogenated ethylene-butylene midblocks have no such bonds. The rubber phase then still needs UV stabilizers for plastics in exposed parts, because the matrix and the color system degrade on their own timetable.

PVC window profiles show the combination in practice. They carry an acrylic core-shell impact modifier and rutile titanium dioxide as a UV screen and pigment, and their toughness is verified by falling-mass impact testing to EN 12608-1. A full profile recipe is on additives for PVC window profiles.

How Is Impact Strength Tested?#

Impact strength is tested with pendulum methods, notched Izod to ASTM D256 and ISO 180 and Charpy to ISO 179, and with falling-weight or puncture tests on sheet, pipe and profile, and it is reported in J/m or kJ/m2. The notch is the point of the test, because an impact modifier is bought to defeat notch sensitivity, and an unnotched bar of a brittle compound passes where the same compound fails as a molded part with a corner in it. Izod impact strength is the energy absorbed to break the notched bar divided by its thickness, giving J/m under ASTM D256, or divided by its cross-section, giving kJ/m2 under ISO 180.

The table lists the standards that qualify an impact-modified compound, from pendulum tests to the weathering methods that outdoor grades pass through.

Two of these 7 rows measure what the modifier costs rather than what it delivers. Heat deflection temperature to ASTM D648 or ISO 75, at 0.455 or 1.82 MPa, and Vicat softening point to ISO 306 or ASTM D1525-25 both fall as rubber content rises, so a qualification programme runs them alongside the impact test. All methods are indexed under testing plastic additives.

How Are Impact Modifiers Regulated?#

Impact modifiers are polymers, so they are exempt from REACH registration under Article 2(9) of Regulation (EC) No 1907/2006, and their food-contact status in the EU is set by the limits on their monomers under Regulation (EU) No 10/2011. That single structural fact explains the regulatory picture of the whole family. CPE, MBS, SEBS, POE, EPDM, ionomers, PP-g-MAH and the ethylene-acrylate terpolymers are all polymeric, none appears on the REACH Candidate List in its own right, and the substances carrying hazard classifications and migration limits are the monomers left behind as residues.

The table gives the EU monomer limits and US FDA sections for each impact-modifier type in our source library.

EU values from the 16 March 2025 consolidation of Regulation (EU) No 10/2011; FDA percentages are legal maxima, not dosages; "not in our source library" means this page states no value.

Food contact: monomer limits under EU 10/2011 and FDA 21 CFR#

In EU food-contact plastics, an impact modifier is judged by its monomers: butadiene must not be detectable above 1 mg/kg in the final product, 1-octene has an SML of 15 mg/kg and glycidyl methacrylate an SML of 0.02 mg/kg under Regulation (EU) No 10/2011. Each monomer sits on the Union list with its own FCM number: butadiene at 223, 1-octene at 264, glycidyl methacrylate at 220, ethylene at 125 and ethylidene norbornene at 621 with an SML of 0.05 mg/kg. Where a monomer carries no specific limit, as styrene at FCM 193 does not, the generic specific migration limit of 60 mg/kg and the overall migration limit of 10 mg/dm2 apply, and migration testing is explained under EU 10/2011.

One impact modifier appears on the Union list as a polymer instead. FCM 857, the copolymer of methyl methacrylate, butyl acrylate, styrene and glycidyl methacrylate with CAS 37953-21-2, is authorised for rigid PVC only, at up to 2 %, and only for contact at room temperature or below. A grade used outside those 3 conditions falls back on the monomer route.

The US system lists uses rather than products. 21 CFR 178.3790 covers polymeric modifiers in semirigid and rigid PVC food-contact articles, capping acrylic modifier units at 5 wt% of the finished article under the first option and butadiene-styrene units at 15 wt%; olefin and styrenic modifiers run through their own sections, with ethylene/octene-1 copolymers under 177.1520, styrene block polymers under 177.1810 and ethylene-methacrylic acid ionomers under 177.1330 at up to 20 wt% methacrylic acid. The FDA lists substances for uses, it does not approve products, and every 21 CFR section is mapped on FDA food contact rules.

REACH, Prop 65 and residual monomers#

No impact modifier is on the REACH Candidate List, because the polymers themselves are exempt from registration, but 2 residual monomers matter: glycidyl methacrylate is a harmonised Carc. 1B substance and 1,3-butadiene has been on California's Prop 65 list since 1 April 1988. Article 2(9) of Regulation (EC) No 1907/2006 exempts polymers from registration and evaluation, while the monomers used to make them are registered separately, and the polymer exemption is explained under REACH and plastic additives. Exempt from registration is not the same as unregulated, and no substance in this family carries a restriction under Annex XVII.

The hazard sits with the residual monomers. Glycidyl methacrylate has a harmonised classification of Carc. 1B (H350), Muta. 2 (H341) and Repr. 1B (H360F) under index number 607-123-00-4, added by the tenth adaptation to technical progress of the CLP Regulation, and maleic anhydride is classified Resp. Sens. 1 (H334) and Skin Sens. 1A (H317) under the thirteenth adaptation. Neither was on the Candidate List when ECHA's database was checked on 22 September 2026.

California's listings apply to the same monomers rather than to the modifiers. Glycidyl methacrylate was listed as a carcinogen on 27 January 2023; 1,3-butadiene was listed as a carcinogen on 1 April 1988 and as a developmental and female and male reproductive toxicant on 16 April 2004; styrene is listed as a carcinogen. A cured MBS particle in a PVC profile is not a listed substance, so the practical control is a residual-monomer specification on the incoming grade. Warning rules are explained under Proposition 65 and plastic additives.

Who Makes Impact Modifiers? Market Size and Suppliers#

The impact modifier market is worth about USD 3.9-5.0 billion in 2025, depending on the publisher, with The Business Research Company putting it at USD 5.02 billion after USD 4.61 billion in 2024. Published estimates spread widely because analysts draw the family border differently, some counting only the core-shell and CPE grades sold as impact modifiers, others including olefin elastomers that are also sold as compatibilizers and thermoplastic elastomers. By weight, impact modifiers make up 5 % of global plastic additive consumption. Segment data for all families are on plastic additives market.

Arkema also markets acrylic impact modifiers for rigid and flexible PVC. Grades, plants and certifications are compared in impact modifier manufacturers and suppliers.

Complete List of Impact Modifier Substances: 8 Substances#

The table lists all 8 impact-modifier substances in the directory with CAS number, type, main host polymers and food-contact anchor. They follow the type order used throughout this page, from the PVC modifiers to the reactive and thermoset rubbers.

Coupling agents, compatibilizers and chain extenders that are sometimes sold alongside impact modifiers are listed in the plastic additives database under their own families.

How Do Impact Modifiers Differ from Plasticizers, Compatibilizers and Other Property Modifiers?#

Impact modifiers change how a plastic breaks, while plasticizers make the whole matrix soft, compatibilizers bind 2 immiscible polymers, coupling agents bond fillers and chain extenders rebuild molar mass. All 6 belong to the property-modifier group, and 3 of them share substances with impact modifiers, which is where formulation confusion starts. The table separates them by the property each one changes.

Tougheners for epoxy and thermoset plastics#

Thermosets such as epoxy are toughened with reactive liquid rubbers such as CTBN and with core-shell rubber particles, which is what most searches for a "toughening agent" mean. Carboxyl-terminated butadiene-acrylonitrile rubber, CAS 68891-46-3 and EC 641-378-2, dissolves in the uncured resin and phase-separates into rubber domains as the network forms, so the toughening morphology is built during cure rather than during compounding. CTBN is not on the REACH Candidate List and does not appear in Annex I of Regulation (EU) No 10/2011. CTBN and core-shell rubber are compared under tougheners for epoxy and thermosets.

Can fillers toughen plastics?#

Yes, in some cases: fine calcium carbonate particles can toughen polypropylene, as Thio and colleagues (Polymer, volume 43, 2002, page 3661) and Zuiderduin and colleagues (Polymer, volume 44, 2003, page 261) showed, although most fillers raise stiffness rather than toughness. The mechanism resembles rubber toughening with one substitution: the filler particle debonds from the matrix under stress instead of cavitating, and the void it leaves relieves the same triaxial stress. Stiffness and cost reduction remain the normal reasons to add a filler, and loading levels are compared under fillers for plastics.

A short history of impact modification#

Impact modification became a design science with Clive Bucknall's book Toughened Plastics in 1977 and Souheng Wu's 1985 inter-particle-distance criterion at DuPont, the company behind supertough Zytel ST nylon. Bucknall returned to the subject in his 2007 review in the Journal of Polymer Science Part B, which set out the crazing, cavitation and shear yielding sequence in the form used today, and Rolf Borggreve and Reinoud Gaymans at the University of Twente extended Wu's criterion to PA6 between 1987 and 1989. Ownership of the commercial lines has moved since: Arkema sold its functional polyolefins, the LOTADER and OREVAC families, to SK Functional Polymer in 2020. The longer arc from camphor in celluloid is on history of plastic additives.

Frequently asked questions about impact modifiers#

The 4 questions below are the ones formulators and buyers ask most often about impact modifiers: the right type for polypropylene, the right type for PVC, the US food-contact status of MBS and the REACH position of the whole family.

What is an impact modifier for polypropylene?#

An impact modifier for polypropylene is an olefin elastomer, usually ethylene-octene POE, EPR or EPDM, that disperses as rubber particles in PP and keeps it tough at low temperature, for example in TPO bumper compounds. The alternative is to buy the toughness in the resin, as a heterophasic impact copolymer whose ethylene-propylene rubber phase is made in the reactor. Grades and dosages are compared on impact modifiers for polypropylene.

What type of impact modifier is best for PVC?#

No single type is best for PVC: MBS is best for clear parts, acrylic for outdoor profiles and CPE for cost-sensitive pipe and profile, each at about 3-10 phr. MBS wins on clarity because its refractive index can be matched to the matrix, acrylic wins outdoors because its butyl acrylate core carries no double bonds, and CPE wins on cost. Patent literature narrows CPE further to 2.5-7.0 phr and MBS or ABS grafts in CPVC to 5-6 phr.

Is MBS FDA approved for food-contact PVC?#

MBS-type modifiers are listed in 21 CFR 178.3790 for semirigid and rigid PVC, with butadiene-styrene units limited to 15 wt% of the finished article; the FDA lists substances for uses and does not approve products. That 15 wt% is a legal maximum on the finished article, not a dosage, and the technical level sits far below it at about 3-10 phr. In the EU the same grade is assessed through its monomers, where butadiene at FCM 223 must not be detectable above 1 mg/kg in the final product.

Are impact modifiers registered under REACH?#

No: impact modifiers such as MBS, CPE, POE and SEBS are polymers and exempt from REACH registration under Article 2(9), while their monomers, such as butadiene and glycidyl methacrylate, are registered separately. The exemption covers registration and evaluation, not the rest of the regulation, and it does not remove the classification duties that attach to the residual monomers a grade carries. None of the 8 impact-modifier substances in this directory is on the Candidate List.