Preparation of the external surfaces of metal and polymer composites is critical to attaining adhesive bonding and paint or coating performance. Procedures currently in use require extensive manual labor coupled with the use of hazardous detergent solutions and organic solvents to prepare these surfaces, resulting in environmentally undesirable pollutants and waste streams. The surface preparation of the adherend requires careful removal of labile organic compounds from peel plies and mold release or shop floor contamination as well as addition of chemical functionality to the adherend surface to promote strong interactions with the adhesive. The development of an environmentally friendly, cost effective, and robust surface treatment method is needed that can not only clean a surface and create a beneficial chemistry for painting but also produce optimum adhesive bonding of polymers, polymer composites and metal surfaces.
The objective was to develop a low-cost, high-speed, environmentally benign, dry surface treatment method for production and repair of military composite structures using ultraviolet (UV) light surface treatment in ambient air.
Experiments were conducted using pulsed UV lamps, of variable power output (2.5 to 150 watts) and frequency (3 to 120 hertz), with low wavelength cutoffs of approximately 180 nanometers. Samples were treated in an environment of ambient air or of air supplemented with ozone to produce maximum conditions. UV-treated materials typical of current and future inventory were investigated and tested using surface energy measurements and surface compositional analysis coupled with adhesion testing. To define the optimum treatment conditions, an assessment of the level of adhesion, durability, and failure mode was made.
This project has shown that a short application of pulsed UV light under ambient atmospheric conditions can provide beneficial chemical changes on the surface of plastics, composite materials, and metals. This surface treatment can be applied to various materials in the Department of Defense inventory for the application and adhesive bonding of adhesives, paints, and other coatings to non-metallic and metallic surfaces. However, before transition, significant research is needed to optimize the UV lamps for specific materials. This SEED project was completed in FY 2001.
The advantages of pulsed UV technology for surface treatments are low heat generation, minimization and/or elimination of potentially toxic and hazardous byproducts from solvents and detergents such as VOCs, and creation of a robust surface to enhance the wetting and spreading of paints, coatings and adhesives on polymeric and inorganic surfaces. A manufacturing base exists to provide technical and consulting assistance on the pulsed UV process and equipment to assist in commercialization and fielding.