Adhesion Promoters: Silane Coupling Agents
Organic and inorganic materials differ in many ways, for example, compatibility, chemical reactivity, surface properties, and coefficient of thermal expansion, making it very difficult to form a strong adhesive bond between them. Adhesion promoters, or coupling agents, act at the interface between an organic polymer and an inorganic surface to chemically and physically wed these dissimilar materials into a strong cohesive bond. Other approaches to improve adhesion involve chemical modification of the polymer surface by oxidation and abrasion of the inorganic substrate to increase the bonding surface area. The use of adhesion promoters not only alters physical and chemical forces at the interface but also provides a “glue” to greatly increase adhesion. Adhesion promoters also impart resistance to forces, such as heat and moisture that act on the bonded site to destroy adhesive strength. Organosilane coupling agents are the main chemical type used as adhesion promoters.