Atmospheric Pressure Plasma Activation Of Polymers And Composites For Adhesive Bonding: A Critical Review

A review is presented on the surface preparation of polymers and composites using atmospheric pressure plasmas. This is a promising technique for replacing traditional methods of surface preparation by abrasion. With sufficient exposure to the plasma afterglow, polymer and composite surfaces are fully activated such that when bonded and cured with epoxy adhesives, they undergo 100% cohesive failure in the adhesive. Depending on the material, the lap shear strength and crack delamination resistance (G(IC)) can be increased several fold over that achieved by either solvent wiping or abrasion. In some cases, a plasma-responsive layer must be incorporated into the top resin layer of the composite to achieve maximum bond strength to the adhesive. Adhesion does not correlate well with water contact angle or surface roughness. Instead it correlates with the fraction of the polymer surface sites that are oxidized and converted into active functional groups, as determined by x-ray photoelectron spectroscopy and infrared spectroscopy.