Renewable Resources for Surface Coatings, Inks, and Adhesives
Natural resins refer to noncrystalline solid or semi-solid amorphous materials or viscous liquid sticky substances produced by plants. They are typically transparent or translucent and are mostly yellowish to brown in colour. Natural resins are formed in plant secretions and are soluble in various organic liquids but not in water. They soften or melt at moderate temperatures and burn with smoky flames. Nature supplies resins as complex mixtures of terpenes with volatile oils (oleoresins), as resinous substances that contain benzoic acid or cinnamic acid or its esters (balsams) or as mixtures of polysaccharides that are water-soluble or that absorb water and swell to form a gel or jelly when placed in water (gum resins). Natural resins can be fossil (amber, bitumen) or recent (rosin) or of animal origin (shellac). They are typically harvested by tapping, or by collecting hardened exudates, or they are obtained, such as rosin in particular, as a side-stream of cellulose manufacturing in pulp mills and pine biorefineries. In coatings, inks and adhesives, resins are used as film formers, binders, and tackifiers. In one way or the other, they influence the properties of hardness, gloss, adhesion, cohesion, and flexibility of surface coatings, prints, and glues.