Abstract: An adhesive composition for use in coupling together two substrates to form a structure, such as for use in coupling together two wooden substrates to form a wooden structure, includes a mixture of a modified guayule resin and soy protein. The modified guayule resin can be a base-solvent modified guayule resin or can be an HiCh-modified guayule resin each respectively formed from an unmodified guayule base resin. The unmodified guayule base resin is obtained in a rubber extraction process of guayule at solvent removal temperatures ranging from 104 to 166 degrees Celsius. The method for forming the adhesive composition includes forming a modified guayule resin and mixing the formed modified guayule resin with soy protein. The adhesive composition, when used in forming structures, provides enhanced wet shear strength as compared with adhesive compositions including soy protein alone.

Abstract: A particleboard includes a fiber component and an adhesive composition including a mixture of a modified guayule resin and soy protein. The modified guayule resin can be a base-solvent modified guayule resin or an H2O2-modified guayule resin. The fiber component can be a natural fiber such as a natural fiber selected from guayule bagasse, wood chips, wood particles, wood waste straw, wood fiber, and any combination thereof. The particleboard is formed by mixing the adhesive composition with the fiber component, introducing the mixture to a press, and pressing the mixture in the press.