ABSTRACT
ME 04469, USA b Department of Chemical and Biological Engineering, University of Maine, Orono, ME 04469, USA
Abstract The adhesion properties of the individual components of wood-plastic composites (WPCs) are highly relevant in determining their compatibility during processing, and in the case of WPC boards, adhesion properties can help to determine their potential application as structural components. Preliminary results indicate that WPCs have a low surface energy between 20 and 25 mJ/m2. The application of forced air plasma treatment (FAPT) appears to be an effective method for increasing WPC surface energy (over 40 mJ/m2), and is also a relatively safe surface treatment process. To characterize WPC surfaces before and after FAPT treatment, and to evaluate bonding effectiveness, chemical (XPS), mechanical (shear strength) and thermodynamic (surface energy) techniques have been used. In this paper, microscopic analysis using Atomic Force Microscopy (AFM) has been proposed as a complimentary tool to evaluate the adhesion properties of individual components comprising WPCs as well as of WPCs before and after FAPT. For the AFM analysis, silicon tips were used to determine pull-off forces (adhesion forces) in contact mode. AFM measurements were performed in air and water (HPLC grade) and the histograms of the adhesion forces were obtained from a series of more than two hundred force curve measurements. Adhesion force in air resulted in significantly higher values than those obtained in HPLC grade water; electrostatic interactions and viscoelastic properties of the surfaces appear to have a great contribution to this phenomenon, especially for the lubricant component of WPCs.
