A compound with, in a single molecule, a group that bonds to inorganic materials and a group that reacts with resin. It is used to treat the surface of glass fibers, improving interfacial adhesion and water resistance.
Japanese name: シランカップリング剤
Silane coupling agent appears in 1 practice question across 1 topic, including Composite materials.
Field: Composite materials
A silane coupling agent is generally a molecule that can be written Y−R−Si(OR′)₃. The Si(OR′)₃ part carries alkoxy groups such as methoxy or ethoxy groups; these hydrolyze in water to silanols (Si−OH), which condense with hydroxyl groups on the surface of glass or metal oxides to form strong bonds such as Si−O−Si. At the other end, Y is an organic functional group such as amino, epoxy, methacryl or vinyl, which reacts or entangles with the resin. In this way the molecule links inorganic and organic materials by covalent bonds, chemically bridging the interface.
The effect of a coupling agent depends greatly on whether its organic functional group can react with the resin. For epoxy resins, amino silanes, which react like a curing agent, or epoxy silanes, which carry the same epoxy group, are often used; for unsaturated polyester and vinyl ester, methacryl silanes, which can copolymerize by radical reactions, are common. Typical molecules include 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane. In dental composite resins as well, filler surfaces are treated with methacryl silanes so that they bond chemically to the resin. In combinations that cannot react, the agent has almost no effect.
Silane coupling agents bond strongly to materials with many surface hydroxyl groups, such as glass, silica, alumina and many metal oxides. They work poorly on carbon fibers, which have few surface hydroxyl groups, or on hard-to-oxidize gold; for carbon fibers, the surface is electrochemically oxidized to create functional groups and then coated with a sizing, and for gold, compounds with thiol groups are used. Applying too thick a layer can backfire, as the condensed silane layer itself becomes a weak layer and weakens adhesion. It is important to cover the surface thinly and evenly with a small amount.
Without silane treatment, water readily penetrates the interface between glass fibers and resin, and strength drops sharply in humid environments or boiling water. The bonds formed by the silane and the hydrophobic layer created at the interface suppress water ingress and hydrolysis of the interface, greatly improving strength retention in wet conditions. This effect is exploited not only in glass-fiber-reinforced plastics but also in plastics filled with inorganic powders, primers for adhesives and paints, and silica-filled automobile tires. In tires, sulfur-containing silanes link the silica filler to the rubber during vulcanization.
Answer: B. To bond to both the inorganic glass and the organic resin, strengthening interfacial adhesion and load transfer
A silane coupling agent is a molecule with an alkoxysilyl group at one end that bonds to the hydroxyl groups on the glass surface, and at the other end a group such as amino, epoxy or vinyl that reacts with the resin. Because it links the inorganic glass and the organic resin by chemical bonds, interfacial adhesion is strengthened and load is transferred more readily to the fibers through interfacial shear. It is also very effective at preventing water from penetrating the interface and weakening adhesion, limiting the loss of strength in humid environments. Smoothing the surface to reduce friction would weaken load transfer, the opposite of the purpose. Changing the thermal conductivity or the cure rate of the resin is not the purpose of a coupling agent.
There are 2 approaches: making a dilute aqueous or alcohol solution, applying it to or dipping the surface, and then drying and heating to form bonds; or mixing the agent directly into the resin. For glass fibers, it is included in the sizing applied right after spinning.
Sizing refers to the whole treatment applied to fiber surfaces, including components that bind the fibers into strands, lubricants and coupling agents. The silane coupling agent is the component within it that is responsible for bonding at the interface.
Because a single molecule couples, or joins, inorganic and organic materials with completely different properties. It is not an adhesive itself but a molecule that chemically mediates the interface between 2 materials.
A silane coupling agent is a molecule with an alkoxysilyl group at one end that bonds to the hydroxyl groups on the glass surface, and at the other end a group such as amino, epoxy or vinyl that reacts with the resin.
When glass fibers are used to reinforce a resin, what is th…Ceramic matrix composite CFRP (carbon-fiber-reinforced plastic) Critical fiber length Delamination GFRP (glass-fiber-reinforced plastic) Metal matrix composite Quasi-isotropic laminate