Surface treatments of wood–plastic composites (WPCs) to improve adhesion

Abstract

In an effort to improve the adhesive bonding between wood-plastic composites (WPCs) formulated with polypropylene and a commercial epoxy adhesive, surface treatments were performed to chemically and/or physically modify the surface of WPCs. The treatments were performed on extruded WPC that had been planed and consisted of chromic acid treatment, flame treatment, water treatment, flame then water treatment and water then flame treatment. The strength of the adhesive bonds of the treated samples was tested following ASTM D 905 and the maximum shear stress was calculated for each treatment. The chromic acid and flame treatments increased their respective average shear strengths by 97% and 67% compared to an untreated control group. The increase in bond strength due to these two treatments is believed to be a result of their oxidative mechanisms. The water treatment, which consisted of covering the planed surface of a WPC with water for 10 min, resulted in an increase in shear strength of 31% relative to the control. Characterization of the watertreated WPC surface with profilometry and scanning electron microscopy indicated that the likely mechanism for the increase in bond strength was the absorption of water and subsequent swelling of the wood present in the WPC, creating greater surface area for bonding. The combination of flame and water treatments showed increased shear strength relative to the individual treatments alone, indicating that the two processes might act synergistically to facilitate the formation of stronger adhesive bonds.

Allyloxy-modified starch with low degree of substitution for fiber reinforced thermoset starch composites

“…Although difficult to quantify, a fine dispersion was observed by microscopy for all cross-sections with no apparent fiber bundles or agglomerates. For matrix systems composed of non-polar polymers with limited affinity to the fiber surface 20 , the fibers tend to agglomerate and form cluster of fibres, which act as stress concentrations and reduce the strength of the composite. It is therefore desirable to avoid fiber agglomeration.…”

Combined Surface Treatment of Wood Plastic Composites to Improve Adhesion

“…In this study, the combined treatment for polyethylene WPCs of sanding then coating with a silane coupling agent, followed by plasma discharge, was utilized to achieve a fast treatment method and a satisfactory bonding performance. Gramlich et al (2006) combined flame and water surface treatments to treat the surface of WPCs. The experimental results showed that the combined treatment of the composites obtained a better bonding performance, and the combination of the two methods may appear as an unexpected combined action.…”

Combined Surface Treatment of Polyethylene Wood-plastic Composites to Achieve Rapid Bonding with Desired Adhesion Properties

“…Unfortunately, the polyethylene ingredient present within the polyethylene WPCs results in poor polarity, lower surface energy, and difficult adhesion of the composites (Tahara et al 2003;Gramlich 2006;Liu et al 2010). Hence, a surface treatment is necessary for the polyethylene WPCs to obtain optimal bonding properties.…”

“…Besides the individual surface treatments mentioned, a combined treatment was also employed to treat the WPCs materials. For example, Gramlich et al (2006) combined flame and water surface treatments to treat the surface of the WPCs. Moghadamzadeh et al (2011) employed a combination treatment of sanding followed by a corona discharge treatment to improve the bonding strengths of the WPCs.…”