15 - Adhesion Promoters

Abstract

Adhesion promoters, also known as coupling agents, are chemicals that act at the interface between an organic polymer and an inorganic substrate to enhance adhesion between the two materials. The use of adhesion promoters will not only alter physical and chemical forces at the interface, but also provide a “glue,” or compatibility bridge, to give a much greater level of adhesion. Furthermore, adhesion promoters can impart resistance to environmental and other destructive forces, such as heat and moisture, which often act on the bonded site to destroy adhesive strength. Organosilane coupling agents are the predominant chemical type of adhesion promoter. A silicon-based chemical that functions as an adhesion promoter has a general structure of four substituents attached to a single silicon atom. The most common structure has three inorganic—reactive alkoxy groups, methoxy or ethoxy, and one organic group. Silane-coupling agents will act in the interphase region, the area between an inorganic and an organic substrate, and act as a bonding or bridging agent to improve the adhesion between the two dissimilar materials. These agents are best suited for fiberglass cloth, mat, chopped glass, mineral-filled composites, and moisture-cured cross-linking systems for polyethylene.