Adhesion Theories in Naturally‐Based Bonding

This chapter covers the adhesion theories in naturally-based adhesive bonding and adhesion and surface issues with naturally-based adhesives. Chemicals and polymers derived from nature have been used as adhesives for thousands of years. The primary adhesion theories include mechanical interlocking, electronic, adsorption or wetting, diffusion, chemical bonding, acid-base, weak boundary layers, and stickiness/tackiness. Nature-based chemicals and polymers used for adhesives include proteins, carbohydrates, plant/wood extractives, and oils. The variety of nature-based chemicals and polymers provide for a myriad of adhesive and coating materials that can be used in applications ranging from wood composite manufacture, packaging, adhesive tapes, and coating applications. Proteins and carbohydrates benefit from inherent chemical functionalities that contribute to adhesion through hydrogen bonding. Extractive chemicals like rubber and rosin rely on stickiness to produce adhesive behavior. Many of the plant-based oils have characteristics that provide for excellent coating behavior that makes them useful in packaging, paints and sealants. Although naturally-based adhesives have been around for a long time, there is renewed interest in these materials as they contribute greatly to low energy production, carbon sequestration and sustainability.