Composite materials
When glass fibers are used to reinforce a resin, what is the main purpose of treating the fiber surface with a silane coupling agent?
- ATo smooth the fiber surface and reduce friction with the resin so that it flows more easily during molding
- BTo bond to both the inorganic glass and the organic resin, strengthening interfacial adhesion and load transfer
- CTo lower the thermal conductivity of the fibers and slow the resin cure during molding so that bubbles escape
Show answer and explanation
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.