Silane Coupling Agents: 6 Types, How They Work, Dosage and Selection

Silane coupling agents are organofunctional trialkoxysilanes, general structure Y-(CH2)n-Si(OR)3, that are added at 0.2 to 1.0 wt% of a filled compound to build a chemical bridge between an inorganic surface and the surrounding polymer. One end of the molecule bonds to glass, silica or a mineral, the other end reacts with or entangles in the matrix; so which of the six organofunctional types belongs on which filler and in which polymer?

Coupling agents are the interface layer of the plastic additives that go into filled and reinforced compounds, and silanes are the largest single chemistry inside that layer.

This article works through the hydrolysis-condensation mechanism in four steps, the six organofunctional types and their Chinese KH codes, which silane matches which matrix polymer, which fillers and fibres respond and which do not, the four dosing routes with their separate percentage bases, how a finished treatment is verified, and which silanes carry an EU 10/2011 or FDA food-contact status. It closes with the cross-supplier grade map and the boundary against titanates, maleated polyolefins and the unrelated uses of the phrase "coupling agent" in dentistry and chemistry.

Key figures

• 0.2 to 1.0 wt% is the standard integral-blend dosage, calculated on the total compound
• 6 organofunctional types cover the whole class, from amino silanes to non-reactive alkyl and dipodal silanes
• 1.0 % on the filler is the minimum-monolayer loading for a 1 to 10 µm siliceous filler
• 0.05 mg/kg is the specific migration limit set for APTES under EU 10/2011, FCM 377

What Is a Silane Coupling Agent?#

A silane coupling agent is a small organosilicon molecule that carries a hydrolysable alkoxysilyl end for the inorganic surface and an organofunctional end for the polymer, which lets it bond a filler or a glass fibre chemically to the plastic around it. The molecule acts at the polymer-filler or polymer-fibre interface, which is a narrower job than a compatibilizer performs: a compatibilizer bonds two immiscible polymers to each other, while a coupling agent bonds a polymer to an inorganic or natural surface.

The hub on coupling agents for filled and reinforced plastics compares silanes with titanates, zirconates and maleated polyolefins, the other three chemistries that do the same interface job by different mechanisms.

The Y-(CH2)n-Si(OR)3 structure and its two ends#

Every silane coupling agent follows the same pattern, Y-(CH2)n-Si(OR)3: three hydrolysable alkoxy groups (OR, usually methoxy or ethoxy) on the silicon, a short propyl spacer, and an organofunctional group Y such as amino, epoxy, methacryl, vinyl or mercapto. The alkoxy end is the inorganic anchor, and it is the same across most of the class regardless of which polymer the silane is built for; the organofunctional end is what changes from type to type and what decides the matrix match.

Four molecules cover most industrial use. 3-Aminopropyltriethoxysilane (APTES, CAS 919-30-2, 221.37 g/mol) carries a primary amine. 3-Glycidoxypropyltrimethoxysilane (GLYMO, CAS 2530-83-8, 236.34 g/mol) carries an epoxide ring. 3-Methacryloxypropyltrimethoxysilane (MEMO, CAS 2530-85-0, 248.35 g/mol) carries a methacrylate group. Vinyltrimethoxysilane (VTMS, CAS 2768-02-7, 148.23 g/mol) carries a vinyl group.

What a silane coupling agent changes in a filled or reinforced plastic#

A silane coupling agent does not fill or stiffen anything by itself: it transfers stress across the boundary between the mineral and the polymer, so the composite behaves like one material instead of two. The effect is strongest on siliceous surfaces, where the alkoxy end has hydroxyl groups to react with, and it shows up in four ways in the finished compound.

• Stress transfer across the filler-polymer or fibre-polymer interface
• Wetting and dispersion of the filler during compounding
• Resistance to water attacking the interface in service
• Retention of mechanical properties after moisture exposure

The percentage property gains that circulate for coupling chemistry belong to a different class of coupling agent, not to a silane. A hybrid cellulose-basalt/PP compound treated with 5 wt% maleated polypropylene reached tensile strength 45 % higher, flexural strength 97 % higher and notched Charpy impact strength 13 % higher than neat PP; that result belongs to the maleated-polyolefin comparison later on this page, not to a silane treatment, because our source library holds no equivalent property-gain percentage for a silane. Glass-fibre sizing, by contrast, carries a silane at 0.5 to 2.0 wt% of the total size on the fibre, alongside a film former.

Is a silane coupling agent the same as silane gas?#

No: the silane coupling agents used in plastics are liquids, for example 3-aminopropyltriethoxysilane at a boiling point of 217 °C or vinyltrimethoxysilane at 123 °C, and they are not the gaseous compound that shares the word "silane" in its name. APTES is a clear colourless to light yellow liquid with a density of 0.946 g/mL, and VTMS is a colourless liquid with a flash point of 25.5 °C. This article covers the organofunctional trialkoxysilanes used as coupling agents in plastics; it does not cover monosilane (SiH4) or its hazard profile, which is a separate compound outside this article's data scope.

How Do Silane Coupling Agents Work?#

Silane coupling agents work in four steps: the alkoxy groups hydrolyse to silanols, the silanols condense with the hydroxyl groups on the mineral surface to form Si-O-M oxane bonds, the excess silanols self-condense into a polysiloxane interphase, and the organofunctional group reacts with or entangles in the polymer.

The four steps: hydrolysis, condensation, oxane bonding, polymer bonding#

Hydrolysis comes first: water, whether added deliberately or carried on the filler surface, converts the three alkoxy groups into silanols and releases the corresponding alcohol, methanol from a trimethoxysilane and ethanol from a triethoxysilane.

1. Water hydrolyses the three Si-OR groups to Si-OH silanols, releasing methanol or ethanol as a by-product
2. Silanols condense with the M-OH hydroxyl groups on the mineral or glass surface, forming a Si-O-M oxane bond
3. Excess silanols self-condense with each other into a crosslinked polysiloxane interphase around the particle or fibre
4. The organofunctional group Y reacts with or entangles in the surrounding polymer: an amine reacts with epoxide, acid and polyamide end groups, an epoxide reacts with amines, acids and hydroxyls, and a methacrylate copolymerizes in a radical cure

When the silane is added directly in the extruder rather than pre-hydrolysed, the alcohol by-product has to be removed by vacuum devolatilization, the same vacuum-venting practice used elsewhere in plastic compounding; left in the melt, the alcohol stays as a volatile.

Why methoxy silanes hydrolyse faster than ethoxy silanes#

The alkoxy group sets the speed: methoxy hydrolyses faster than ethoxy, and ethoxy faster than isopropoxy or t-butoxy, which is why trimethoxysilanes such as GLYMO and MEMO react quickly on the filler while triethoxysilanes such as APTES give a longer working window. This relative-rate order comes from the size of the leaving alcohol: a smaller methoxy group leaves faster than a bulkier isopropoxy or t-butoxy group.

Aqueous silane solutions have a limited pot life because the silanols keep condensing with each other once hydrolysis starts: 2 to 12 hours of working stability for simple alkyl silanes before the solution gels or the treatment loses effectiveness. A premix has to be used within that window, not stored for a later shift.

Hydrolytic stability of the interphase and dipodal silanes#

The oxane bond is reversible in water, so the durability of a silane treatment in a wet or humid application depends on how many bonds hold the interphase together. Dipodal silanes, which carry two silicon atoms and six hydrolysable groups per molecule instead of one silicon and three, are reported by Gelest to give up to 100,000 times greater hydrolysis resistance than conventional monosilanes; Barry Arkles of Gelest is the primary source for this comparison and for silane hydrolytic-stability data in general. A monosilane interphase relies on a smaller number of Si-O-M bonds per molecule, so each bond that hydrolyses back to a silanol and a surface hydroxyl removes a larger share of the total anchoring; a dipodal silane spreads that risk across twice as many bonding points.

What Are the 6 Types of Silane Coupling Agents?#

Silane coupling agents are grouped by their organofunctional end into 6 types: amino silanes, epoxy silanes, methacryl silanes, vinyl silanes, mercapto and sulfido silanes, and non-reactive alkyl and dipodal silanes. They differ only in the organofunctional group Y and, as a result, in which polymer end groups they can react with.

1. Amino silanes (APTES / KH-550, APTMS, AEAPTMS / KH-792)#

Amino silanes such as 3-aminopropyltriethoxysilane (APTES, CAS 919-30-2, sold as KH-550, Silquest A-1100 and Dynasylan AMEO) are the most widely used class in thermoplastics, because their primary amine reacts with, or hydrogen-bonds to, the end groups of polyamides, PBT, polycarbonate, phenolics and epoxies.

• APTES: CAS 919-30-2, EC 213-048-4, C9H23NO3Si, 221.37 g/mol, boiling point 217 °C, density 0.946 g/mL, clear colourless to light yellow liquid with a fishy odour
• APTMS: CAS 13822-56-5, EC 237-511-5, 179.29 g/mol, the trimethoxy analogue of APTES
• AEAPTMS (KH-792): CAS 1760-24-3, an amine-functional diamine variant

Aminosilane is also the sizing silane for glass fibre in polyamide and polypropylene, applied at the bushing before the fibre ever reaches a compounder. Identity, dosage and the full regulatory record sit on [3-aminopropyltriethoxysilane (APTES, KH-550)].

2. Epoxy silanes (GLYMO / KH-560)#

Epoxy silanes, above all 3-glycidoxypropyltrimethoxysilane (GLYMO, CAS 2530-83-8, sold as KH-560, Dynasylan GLYMO and Z-6040), carry an oxirane ring that opens against amines, acids and hydroxyls, which makes them the sizing silane for glass fibre in polyesters, polycarbonate and epoxy. GLYMO is a clear colourless liquid, boiling point 290 °C at 760 mmHg, density 1.065 to 1.075 g/mL at 25 °C, also sold as KBM-403 and Silquest A-187.

[3-Glycidoxypropyltrimethoxysilane (GLYMO, KH-560)] carries the tightest EU food-contact restriction of any silane on this page, a sizing-use-only restriction covered in full under the food-contact section below.

3. Methacryl silanes (MEMO / KH-570)#

Methacryl silanes such as 3-methacryloxypropyltrimethoxysilane (MEMO, CAS 2530-85-0, sold as KH-570 and Silquest A-174) copolymerize into the resin during a free-radical cure, which is why they belong in unsaturated polyesters, acrylics and peroxide-cured compounds rather than in a neutral thermoplastic melt. MEMO is a colourless transparent liquid, boiling point 190 °C at 760 mmHg, density 1.045 g/mL at 25 °C, also sold as Dynasylan MEMO.

MEMO has been identified by FTIR, presumed alongside a peroxide and a triallyl isocyanurate co-agent, in one commercial UV-transparent EVA/POE photovoltaic encapsulant study; that is an identification, not a dosage recommendation, and the exact loading of MEMO in unsaturated polyester or acrylic composites is not established in our source library. [3-Methacryloxypropyltrimethoxysilane (MEMO, KH-570)] is limited to inorganic filler treatment in EU food contact.

4. Vinyl silanes (VTMS, VTES)#

Vinyl silanes such as vinyltrimethoxysilane (VTMS, CAS 2768-02-7) and vinyltriethoxysilane (VTES, CAS 78-08-0) couple mineral fillers in peroxide-cured polyethylene and EPDM compounds, where the vinyl group takes part in the same radical reaction that cures the matrix. VTMS is a colourless liquid with a fruity odour, melting point -97 °C, boiling point 123 °C at 1013 hPa, flash point 25.5 °C, sold as KBM-1003 and SZ 6300 / Z-6300.

In a vinyl silane the organofunctional group does not merely bond to the polymer: it is grafted onto it with a peroxide, which turns the silane into a crosslinker rather than a coupling agent. [Vinyltrimethoxysilane (VTMS)] is used more often as a crosslinker than as a coupling agent, and that crosslinking role is described in the supplementary section below the contextual border.

5. Mercapto and sulfido silanes#

Mercapto and sulfido silanes carry a sulfur-functional end that reacts into a sulfur-cured network, which places them in silica-filled rubber compounds rather than in thermoplastics. Bis(triethoxysilylpropyl) tetrasulfide (TESPT) is the class representative in tyre-grade silica compounds; our source library holds no CAS number, no dosage and no property data for this class inside a plastics context, so this page names the class and its rubber application without further detail. Mercaptopropyltrimethoxysilane is not on the REACH Candidate List, checked 22 September 2026.

6. Alkyl and dipodal silanes#

Alkyl silanes carry no reactive organofunctional group at all: they make a mineral surface hydrophobic so that it disperses and stops picking up water, which is the role octyltriethoxysilane plays on surface-treated titanium dioxide, authorised under EU 10/2011 FCM 873 at up to 2 % w/w on the pigment. Simple alkyl silanes share the 2 to 12 hour aqueous stability of the reactive types, while dipodal silanes, carrying two silicon atoms per molecule, give up to 100,000 times greater hydrolysis resistance, as described above.

Which Silane Coupling Agent Suits Which Polymer?#

The silane is chosen by what its organofunctional end can react with in the matrix: amino silanes for polyamide, PBT, polycarbonate, phenolics and epoxies, epoxy silanes for epoxies, PBT and polyurethane, methacryl silanes for unsaturated polyesters, acrylics and peroxide-cured systems, and vinyl silanes for peroxide-crosslinked polyethylene and EPDM.

Polyamide takes an amino silane because the primary amine reacts with the carboxylic acid and amine end groups on the polyamide chain, which is why aminosilane sizing is standard on glass-filled nylon.

PBT takes both amino and epoxy silanes; see [additives for PBT]. Epoxy resin composites take amino or epoxy silanes because both react into the curing network; filler and toughener choices are on [additives for epoxy resins and composites].

The complete additive package for polyamide, beyond the coupling silane alone, is on additives for nylon (polyamide).

Polypropylene is the exception that has to be stated plainly: a polyolefin offers no reactive end group, so a silane alone couples poorly to PP and a maleated polyolefin does the coupling instead. Why PP uses a maleated polyolefin instead is set out under [coupling agents for glass- and talc-filled polypropylene]. A silane is not the standard coupling agent for glass-filled PP.

Matching list from the Gelest silane guidance held in our source library. Trials decide the final grade.

Which Fillers and Fibres Respond to Silane Treatment?#

Silanes need surface hydroxyl groups, which is why their effect follows the chemistry of the substrate: excellent on silica, quartz and glass, good on alumina and aluminosilicates, only slight on talc, titanium dioxide and iron oxides, and poor on calcium carbonate, gypsum, barytes, graphite and carbon black. Fillers and fibres are ranked by how many hydroxyl groups their surface carries, from a hydroxyl-rich siliceous surface at the top to a nearly hydroxyl-free carbonate or carbon surface at the bottom.

Loading levels for every mineral are on fillers for plastics.

Wollastonite is the acicular filler that responds best to an aminosilane among the calcium silicate minerals, because its surface, like glass, carries reactive hydroxyl groups; grades and surface areas for the acicular class are on wollastonite in plastics and for the amorphous class on [silica in plastics].

E-glass, the standard reinforcing fibre, carries a density of 2.58 g/cm3, a tensile strength of 3445 MPa and a modulus of 76.0 GPa; fibre grades and loadings are on glass fiber reinforced plastics.

Effectiveness ranking from the Gelest guidance in our source library; it ranks surface chemistry, not commercial grades.

Why silanes do not work on calcium carbonate#

Silanes fail on calcium carbonate because the carbonate surface carries almost no hydroxyl groups for the silanols to condense with, so no Si-O-M oxane bond forms. The same limitation extends to gypsum, barytes, graphite and carbon black, all of which our sources record as substrates where a silane is ineffective and a titanate or stearic acid should be used instead. Calcium carbonate in plastics uses stearic-acid coating as its standard surface-treatment route.

Titanates react with surface protons rather than hydroxyl groups, so they need no surface hydroxyls at all, which is why a titanate such as KR-TTS works on calcium carbonate and on carbon black where a silane cannot. All three coating routes are compared under [filler surface treatment].

How Much Silane Coupling Agent Does a Compound Need?#

There is no single silane dosage, because the number depends on what it is a percentage of: 0.2 to 1.0 wt% of the total mix for an integral blend, or 0.75 % to 1.5 % on the filler itself for a pretreatment, set by the particle size. The two numbers are never interchangeable: one is a share of the whole compound, the other is a share of the filler alone.

Minimum-monolayer values are estimates for siliceous fillers, not supplier recommendations for a named grade.

Request quotes for silane coupling agents: grade or CAS (KH-550, KH-560, KH-570), filler type, volume, country. Use the plastic additive supplier finder.

Integral blend: 0.2-1.0 wt% of the total mix#

The simplest route is the integral blend: 0.2 to 1.0 wt% of the silane, calculated on the total mix, is sprayed onto the dry pre-blend of resin and filler and the compound is then extruded. The methanol or ethanol released during compounding has to be pulled off through a vacuum vent, or it stays in the melt as a volatile.

As a calculation example only: a compound with 30 wt% filler dosed at 0.6 wt% silane on the total mix carries 0.6 divided by 30, or 2.0 %, silane relative to the filler. The arithmetic shows how the two percentage bases relate; it is not a recommended loading for any specific filler or grade.

Filler pretreatment: minimum monolayer by particle size#

Pretreating the filler before compounding puts the silane exactly where it is needed, and the amount follows the surface area: the finer the particle, the more silane a monolayer costs. A filler under 1 µm needs at least 1.5 % silane on its own mass to reach a minimum monolayer, a 1 to 10 µm filler needs about 1.0 %, a 10 to 20 µm filler needs about 0.75 %, and a filler above 100 µm needs no more than 0.1 %, because its surface area per gram is far smaller.

The 1.0 % value for a 1 to 10 µm siliceous filler is the anchor number most formulators start from, since that particle-size band covers the majority of ground mineral grades used in filled thermoplastics.

Aqueous-alcohol deposition and glass-fibre sizing#

Glass fibre never reaches the compounder untreated: the sizing is applied at the bushing, straight after the filaments are drawn, from an aqueous bath holding 0.5 to 2.0 % silane at pH 5.5, and it is cured at 110 to 120 °C for 20 to 30 minutes. Sizing combines the silane, aminosilane for PA and PP or the epoxy silane GLYMO for polyesters, polycarbonate and epoxy, with a film former such as polyurethane, epoxy or a polypropylene dispersion, plus lubricants and antistats; the finished size makes up 0.5 to 2.0 wt% of the fibre's total weight.

A laboratory batch treatment instead uses an aqueous-alcohol bath: 95 % ethanol and 5 % water at pH 4.5 to 5.5, adjusted with acetic acid, carrying 2 % silane and allowed 5 minutes of hydrolysis before the filler is dipped. Fibre types and loadings are on reinforcing fibers for plastics, and the full size formulation is covered under [coupling agents for glass fiber].

How do you calculate silane loading from filler surface area?#

The stoichiometric method divides the filler's surface area in square metres per gram by the silane's specific wetting surface, which is about 208 to 528 square metres per gram for common silanes, and the quotient is the mass of silane per gram of filler. As a worked example: a filler with a BET surface area of 10 m2/g and a silane whose specific wetting surface is 350 m2/g needs 10 divided by 350, or 0.029 g of silane per gram of filler, that is about 2.9 % on the filler. This is a calculation method, not a fixed recommendation for a named grade, since the specific wetting surface varies within the 208 to 528 m2/g range by silane type.

Silane vs Titanate vs Maleated Polyolefin: Which Coupling Agent?#

A silane needs hydroxyl groups on the surface and a reactive end group in the polymer; a titanate needs neither, and a maleated polyolefin works the other way round, by grafting an anhydride onto the matrix instead of onto the filler. The three chemistries solve the same interface problem with three different bonding routes, and the filler and the polymer, more than personal preference, decide which one fits.

A coupling agent bonds a polymer to an inorganic or natural surface; a compatibilizer bonds two immiscible polymers to each other, typically at 2 to 10 wt%. Maleated polyolefins are sold as both, which is why the two words are often used for one product.

[Titanate coupling agents] need no surface hydroxyls, which is why they work on chalk and carbon black. Kenrich Petrochemicals of Bayonne, New Jersey, is the source of the neoalkoxy titanate chemistry (LICA and NZ grades) referenced here; the company's president, Salvatore J. Monte, entered the Plastics Hall of Fame in 2021 for that body of work.

The whole grafted family is on maleic anhydride grafted polymers. A maleated polypropylene such as POLYBOND 3200 carries 0.8 to 1.2 % maleic anhydride content, and it is studied in PP composites with short glass fibre at 0.5 to 2 wt%; grade data such as the 0.8-1.2 % anhydride content of POLYBOND 3200 sits on [maleic anhydride grafted polypropylene (PP-g-MAH)].

The polymer-to-polymer case, where two resins rather than a resin and a filler are joined, belongs to compatibilizers rather than to a coupling agent.

How Do You Check That a Silane Treatment Worked?#

A silane treatment is judged on the compound, not on the filler: dry and wet tensile strength to ISO 527-1/-2 or ASTM D638-22, measured at a filler loading that has been confirmed by ash content to ASTM D5630-22 or ISO 3451. Our source library holds no pass/fail percentage for a silane treatment and no contact-angle, XPS or FTIR method entry, so the end point for any given compound is set by that compound's own product specification, not by a generic target.

• Tensile strength, measured dry and again after water immersion
• Filler content, confirmed by ash content
• Mass loss of the organic layer on the treated filler, measured by TGA to ISO 11358
• Melt viscosity and dispersion quality, compared at constant filler loading

Specimen and speed conventions are on [tensile testing of plastics]. Filler loading is confirmed by [ash content and filler content testing], and the mass loss of the silane layer itself is measured by thermogravimetric analysis to ISO 11358, which separates the small organic fraction from the mineral filler by heating the sample and tracking the weight loss.

Which Silane Coupling Agents Are Allowed in Food-Contact Plastics?#

In the EU, five silanes are listed in Annex I of Regulation (EU) No 10/2011 with a specific migration limit; in the US, silanes are cleared through adhesive and coating sections of 21 CFR rather than as polymer additives; and GLYMO carries the tightest restriction of the group, sizing use only. Silanes reach food-contact plastics as residues of a surface treatment, not as free additives, which is why Regulation (EU) No 10/2011 lists them as monomers or starting substances with a specific migration limit of 0.05 mg/kg and, for most of them, a restriction on what they may be used for.

EU Regulation (EU) No 10/2011: FCM numbers and SMLs#

Five silanes appear in Annex I of Regulation (EU) No 10/2011 in the consolidated text of 16 March 2025, each as a monomer or starting substance: APTES (FCM 377), vinyltrimethoxysilane (FCM 453), vinyltriethoxysilane (FCM 142), MEMO (FCM 788) and GLYMO (FCM 1068). EU 10/2011 sets out how the specific migration limit, overall migration limit and group restrictions apply across the full additive list.

EU values from the consolidated text of Regulation (EU) No 10/2011 of 16 March 2025; REACH and CLP status checked against ECHA CHEM on 22 September 2026.

GLYMO is the tightest case: it is not authorised as a general coupling agent at all, only inside a glass-fibre sizing for the named low-diffusivity plastics.

US FDA status under 21 CFR#

The US route for silanes runs through the adhesive and coating sections rather than through a polymer additive listing: 21 CFR 175.105 names gamma-aminopropyltrimethoxysilane and N-beta-aminoethyl-gamma-aminopropyltrimethoxysilane among the permitted adhesive components, and 21 CFR 175.300 allows the latter at up to 1.3 % by weight of the resin in repeated-use coatings. We found no 21 CFR entry for APTES, GLYMO, MEMO, VTMS or VTES as coupling agents in food-contact polymers as such; a specific grade's status in a finished article is set by a food contact notification or a supplier's own regulatory letter, not by a blanket rule.

Glass fibre itself is cleared at 21 CFR 177.2410 for phenolic moulded articles. How FCNs and the 21 CFR sections fit together is on FDA food contact rules for plastic additives (21 CFR).

REACH registration, SVHC status and CLP classification#

All the common coupling silanes are registered under REACH as substances in their own right, with 21 to 28 active dossiers each and first registrations in 2010, and none of them is on the SVHC Candidate List as of 22 September 2026. Every additive on the SVHC Candidate List is tracked with its inclusion date, and the one silane on that list is tris(2-methoxyethoxy)vinylsilane, listed on 17 January 2022 as toxic for reproduction under Article 57(c). It is a vinyl silane used in rubbers, plastics and sealants, which makes it a substitution topic rather than a coupling agent recommendation.

Only APTES and VTMS carry a harmonised CLP entry: APTES under index 612-108-00-0 (Acute Tox. 4*, H302; Skin Corr. 1B, H314) and VTMS under index 014-049-00-0, added in ATP15 (Skin Sens. 1B, H317). GLYMO and MEMO have no harmonised classification; the classifications in circulation for them are notified entries, not harmonised ones. Registration duties for additives are set out on REACH and plastic additives.

Who Supplies Silane Coupling Agents?#

Silane coupling agents come from Evonik (Dynasylan AMEO, GLYMO, MEMO, VTMO), Momentive (Silquest A-1100, A-187, A-174, A-171), Dow (XIAMETER OFS and Z-series), Shin-Etsu (KBE-903, KBM-403, KBM-503, KBM-1003), Wacker (GENIOSIL) and Gelest, alongside Chinese producers in Hubei and Jiangsu who sell the same molecules under the KH codes.

Trade names from the substance records in our source library. Grades with the same CAS number are not automatically interchangeable; check the supplier TDS for purity, water content and stabilisation.

Buyers should compare silanes by CAS number and food-contact restriction, not by trade name or KH code, since two grades that share a CAS number can still differ in purity, water content and stabilisation. Plants and grades by company are in the directory of [compatibilizer and coupling agent suppliers].

Send one request to several silane suppliers with the plastic additive supplier finder.

Get EU 10/2011 and SVHC Candidate List updates for coupling agents.

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What Else Does a Filled Compound Bond With?#

Silanes are one of four coupling chemistries in a filled compound, next to titanates, zirconates and maleated polyolefins, and the choice between them is usually decided by the filler rather than by the polymer. Titanates and zirconates share the same proton-coordination mechanism and come from the same commercial source, Kenrich Petrochemicals of Bayonne, New Jersey.

[Zirconate coupling agents] follow the same proton-coordination mechanism as titanates, and are treated as a related but distinct grade family. Cellulose surfaces such as wood flour and natural fibre are handled under [coupling agents for wood-plastic and natural fibre composites], where a maleated polyolefin usually replaces the silane because the matrix is a polyolefin. The complete WPC package is on [additives for wood-plastic composites (WPC)].

Silane crosslinking is a different job#

The same vinyl silane can do two entirely different jobs: as a coupling agent it bonds a filler to the polymer, and as a crosslinker it is grafted onto polyethylene with a peroxide and then cured with moisture into a Si-O-Si network. VTMS is used mainly for this second role, silane crosslinking of polyethylene under the Sioplas and Monosil processes, where peroxide radicals graft the vinyl group onto the PE backbone and the methoxysilyl groups then hydrolyse and condense into Si-O-Si crosslinks, catalysed by a tin catalyst. The same molecule also couples fillers in those crosslinked compounds, which is why the two functions are easy to conflate. The grafting and moisture-cure route is covered under [silane crosslinking (Sioplas and Monosil)].

"Coupling agent" in dentistry, ultrasound and peptide chemistry#

The phrase "coupling agent" is used in several unrelated fields: dentistry calls a silane primer for ceramic repairs a coupling agent, ultrasound calls the transmission gel one, and organic chemistry calls a class of amide-forming reagents one. None of these three uses is a plastics additive, and this page covers plastics only, so no product name, dosage or claim from those fields is repeated here.

When should you use a silane coupling agent?#

Use a silane coupling agent when the filler or fibre is siliceous, glass, silica, quartz, wollastonite or kaolin, and the matrix polymer offers a group the organofunctional end can react with. Outside that combination, a titanate or a maleated polyolefin is usually the better fit, as the comparison table above sets out.

What is KH-550 silane coupling agent used for?#

KH-550 is the Chinese grade code for 3-aminopropyltriethoxysilane (CAS 919-30-2), the aminosilane used to couple glass fibre and mineral fillers to polyamide, PBT, polycarbonate, phenolics and epoxies, and as the silane in glass-fibre sizing.

What is a good silane coupling agent for epoxy?#

Both classes work in an epoxy: an amino silane such as APTES reacts with the epoxide groups of the resin, and an epoxy silane such as GLYMO reacts with the amine hardener.

What are the disadvantages of silane coupling agents?#

Silanes have four practical limits: they need surface hydroxyls, so they fail on calcium carbonate and carbon black; they need a reactive matrix, so they do little in plain polypropylene; their hydrolysed solutions have a pot life of hours; and they release methanol or ethanol that has to be vented during compounding.

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