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Adhesion Through Silane Coupling Agents

From a study of silane coupling agents in reinforced plastics, a general mechanism of adhesion to hydrophilic mineral surfaces has been devised. According to this theory, adhesion of polymers to dissimilar surfaces is described as a dynamic equilibrium of making and breaking of adhesion bonds between polymer segments and the surface through the agency of a low molecular weight material—usually water. A dynamic equilibrium at the interface allows relaxation of thermal stresses. Water resistance results from a favorable equilibrium toward bonding through polar groups in the polymer. Silanol groups generally give optimum bonding to hydrophilic mineral surfaces.

Such a dynamic mechanism of adhesion not only explains many complex adhesion problems of plastics to mineral surfaces, but also is compatible with the adhesion of ice, barnacles and tooth plaque to surfaces in an aqueous environment and with the requirements for rubber reinforcement by finely divided particulate fillers.