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Abstract
Four surface activation methods were evaluated on a series of wood-fiber reinforced thermoplastic composites (WPCs) as a means to improve the adhesion of a water-based acrylic coating. Treatments with chromic acid and oxygen plasma performed best, increasing the acrylic coating peel load to WPCs by 170 and 122%, respectively, and yielding adhesion levels equivalent to or higher than those obtained on wood. The benzophenone/ultraviolet and flame treatments also improved the coating adhesion by 100 and 64%, respectively, but did not reach the adhesion levels achieved on wood. For both the chromic acid and oxygen plasma treatments, the WPC formulation impacted the treatment efficacy. Profilometry and scanning electron microscopy (SEM) showed that the chromic acid treatment acted mainly by roughening WPC surfaces. While surface oxidation was not evident from attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), the improved wettability of WPCs with water suggested that the oxygen plasma treatment oxidized WPCs.
ACKNOWLEDGMENTS
This work was sponsored by the Office of Naval Research, under the direction of Mr. Ignacio Perez, under Grant N00014-03-1-0949. Special thanks go to Kieffer Tarbell from Drew Paints, Portland, OR, for formulating and supplying the acrylic coating. The authors are also thankful to Dr. Patrick Pedrow, Washington State University, for sharing his expertise and equipment for the plasma treatment.
Notes
∗Average across all WPC formulations. Letter indicates grouping from the Tukey-test from high (A) to low (E) values.
∗Letter indicates grouping from the Tukey-test from high (A) to low (E) values.