PRIMERS FOR ADHESIVE BONDING TO POLYOLEFINS

When polypropylene (PP) and low density polyethylene (LDPE) are coated with about 100 nm of triphenylphosphine (TPP) or cobalt acetylacetonate (CaAcac2) primers, adhesive bonds can be made using ethyl cyanoacrylate (CA) adhesive. These bonds are sufficiently strong so that the bond strength exceeds the bulk shear strength of the polyolefin, and are sufficiently durable as to withstand immersion in boiling water for long periods of time. The dependence of adhesive bond performance on primer thickness, application solvent, aging of primed surface, and the durability of bond, are explained on the basis of a model where the primer dissolves in the polymer surface and facilitates interpenetration of the polyolefin and the monomeric CA. The primer catalyzes cure of the CA, resulting in entanglement of adhesive and adherend chains. This model is tested using infrared (IR) spectroscopic, x-ray spectroscopic (XPS), and microscopic (SEM) analysis.