Surface analysis of sheet molded composite (SMC) material as related to adhesion

The surface chemical properties of Sheet Molded Composite (SMC) materials, formulated to contain polyester binder, calcium carbonate filler, and glass fibers, have been investigated with emphasis on how the surface properties are related to adhesion. These surface properties, relative elemental concentratibns and their chemical states, were studied using x-ray photoelectron spectroscopy (XPS) before and after a series of surface treatments as well as after mechanical lap shear fracture tests for SMCs bonded with urethane adhesive. Surface chemical functionalities, including -C-0·R(X)/-NCOZR and -C=0 (ester carbonyl) groups, were found to promote good adhesion using urethane adhesives. These chemical functionalities_were particularly enhanced after treating the SMC surface with an isocyanate primer as well as after a solvent/abrasive surface pretreatment done with a Scotch Brite abrasive pad soaked in methylene chloride and after washing the SMC surfaces with hot aqueous chemicals at high pressures.