KH-550

Overview

KH-550, also known as 3-Aminopropyltriethoxysilane or γ-aminopropyltriethoxysilane, is the most widely used aminofunctional silane coupling agent in industrial applications. With CAS number 919-30-2 and molecular formula H₂N(CH₂)₃Si(OC₂H₅)₃, KH-550 carries a primary amine group on one end and three hydrolyzable ethoxy groups on the other. This dual reactivity is why it bonds organic polymers — epoxies, urethanes, phenolics — to inorganic substrates such as glass, silica, and metal oxides. It is the direct equivalent of Dow Corning Z-6011, Momentive Silquest A-1100, and Shin-Etsu KBM-903, which means buyers can switch between these trade names without reformulation.

The coupling mechanism proceeds in two stages. First, the three ethoxy groups on the silicon atom hydrolyze in the presence of trace moisture to form silanols (Si–OH). These silanols then condense with surface hydroxyl groups on glass or mineral substrates, forming strong Si–O–Si covalent bonds. Simultaneously, the primary amine at the far end of the three-carbon alkyl chain reacts with epoxy, isocyanate, or carbonyl functionalities in the polymer matrix, creating a durable chemical bridge between the organic and inorganic phases.

This dual-functional design is the defining trait that makes KH-550 a coupling agent rather than a mere adhesion promoter. A plain sizing agent or wetting agent increases surface energy without forming covalent bonds; KH-550 forms them on both sides. The result is dramatically improved dry and wet mechanical strength retention in glass-fiber-reinforced thermoset composites — one of the primary reasons why it is specified in aerospace, wind turbine blade, and high-performance automotive composite lay-up schedules.

Within the amino silane family, KH-550 occupies a specific niche. KH-792 (N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane) has a longer alkyl spacer with a secondary amine — more reactive with epoxies, better for high-crosslink-density systems, but more expensive. KH-540 (γ-aminopropyltrimethoxysilane) uses methoxy rather than ethoxy hydrolysis groups, giving a faster hydrolysis rate but releasing methanol as a byproduct — a regulatory concern in confined manufacturing spaces. KH-550's ethanol byproduct is less hazardous, making it the preferred choice for most industrial volume applications. Buyers searching for an aminosilane coupling agent or an A-1100 equivalent will almost always land on KH-550 unless the end-use specification calls for higher reactivity.

Technical Specifications

Applications

Glass Fiber Sizing

KH-550 is the most widely specified aminosilane in glass fiber sizing formulations for epoxy and unsaturated polyester composites. Applied at 0.3–1.0 wt% on the glass surface during the drawing process, it forms a thin monomolecular layer that bridges the fiber surface to the polymer matrix. The primary benefit is wet-dry strength retention: composites treated with KH-550 sizing retain significantly more of their dry flexural strength after water immersion compared with untreated controls. The amine group reacts directly with epoxy ring opening at cure temperatures, creating a covalent bond that resists hydrolytic degradation — a critical requirement in marine, industrial piping, and structural composite applications.

Rubber and Tire

In rubber compounding, KH-550 serves as a coupling agent for mineral-filled EPDM, HNBR, and SBR formulations where the primary filler is precipitated silica or aluminum hydroxide rather than carbon black. While sulfide-functional silanes such as Si-69 dominate green-tire tread compounding, KH-550 is used in specialty tire cord adhesion systems and in flame-retardant cable compounds based on aluminum hydroxide-filled EPDM. The amine functionality reacts with acid groups on the filler surface and interacts with the polymer matrix via hydrogen bonding and secondary amine reactions, reducing Payne effect and improving processing. Typical loading is 2–5 phr on the silica weight.

Adhesives and Sealants

KH-550 functions as a reactive adhesion promoter and primer in structural epoxy adhesives, single-component polyurethane sealants, and silicone sealants applied to glass, metal, and concrete substrates. In epoxy adhesive systems, the amine end participates directly in the cure reaction, integrating the silane molecule into the crosslinked network rather than leaving it as an unreacted additive. For polyurethane sealants, KH-550 is often applied as a thin primer coat to the substrate surface before sealant application — the silanol groups bond to the glass or metal surface, and the amine group forms a urea linkage with the isocyanate terminus of the approaching sealant. This primer approach eliminates the need for mechanical surface preparation in many bonded-glass construction and glazing applications.

Coatings

In protective coatings, KH-550 acts as an adhesion promoter added at 0.1–1.0 wt% directly to the resin system during formulation. It is effective in epoxy primers for steel and galvanized iron, where it bridges the polar metal oxide surface to the nonpolar organic binder. Anti-corrosion coatings in marine and industrial environments benefit from the moisture-resistant Si–O–Metal bond, which blocks water from undercutting the coating film. Powder coatings for aluminum profiles use KH-550 in the surface pretreatment step — the silane is applied from dilute aqueous solution before the powder deposition, improving adhesion and salt spray resistance markedly. Loading is typically 0.2–0.5 wt% on the total coating formulation weight.

Mineral Filler Treatment

Surface modification of mineral fillers with KH-550 improves their compatibility with thermoset and thermoplastic polymer matrices. Treated kaolin, calcium carbonate, talc, and aluminum hydroxide show reduced agglomeration, better dispersion, and improved mechanical reinforcement at equivalent loading compared with untreated grades. In ATH (aluminum trihydrate) and MDH (magnesium dihydroxide) flame-retardant cable compounds, KH-550 treatment at 1–2 wt% on filler weight enables higher filler loading — often 60 wt% or above — without unacceptable viscosity increase during extrusion. This is commercially significant because higher filler loading directly improves the limiting oxygen index (LOI) of the compound, a key regulatory metric for low-smoke zero-halogen (LSZH) cable specifications.

Equivalent Grades

KH-550 is sold under different brand names but the chemistry and CAS number are identical. Common equivalents:

• Dow Corning Z-6011 — primary North American equivalent
• Momentive Silquest A-1100 — formerly GE/OSi Specialties
• Shin-Etsu KBM-903 — Japanese equivalent
• Wacker GENIOSIL GF 93 — European equivalent
• Evonik Dynasylan AMEO — German equivalent

Buyers sourcing KH-550 from Chinese suppliers should expect the same specifications (>99% purity by GC) at lower price points than the Western brands. The CAS number 919-30-2 is the definitive identifier — any product with this CAS and a purity certificate from a certified laboratory is functionally equivalent regardless of brand name.

Selection Notes

Choosing the right amino silane depends on the specific polymer system and processing conditions. KH-550 (CAS 919-30-2, primary amine, ethoxy hydrolysis) is the general-purpose choice for epoxy, polyurethane, and phenolic matrices where moderate reactivity and low byproduct toxicity are priorities. KH-792, the di-amine variant with a secondary amine in the alkyl chain, offers higher reactivity with epoxy resins and is preferred in demanding structural adhesive systems — but costs more and may cause pot-life issues in fast-cure formulations. KH-540 (methoxy version) hydrolyzes faster than KH-550, which can be advantageous in waterborne systems, but releases methanol, requiring ventilation controls in enclosed production environments. KH-560 (3-glycidoxypropyltrimethoxysilane) is the epoxy-functional silane chosen for anhydride-cured or acid-cured systems rather than amine-curable matrices, and is the standard coupling agent for high-performance optics and electronic encapsulation. For a side-by-side comparison, see the KH-550 vs KH-792 page via the navigation block below.