Surface modification of poplar veneer by means of radio frequency oxygen plasma (RF-OP) to improve interfacial adhesion with urea-formaldehyde resin

Abstract

The radio frequency oxygen plasma (RF-OP) treatment of wood was in focus, namely the surface properties of poplar veneer has been analyzed as a function of RF-OP treatment power concerning the chemical composition, free radicals, morphology and roughness. In addition, the interfacial adhesion of plywood composites was measured by determining the shear strength. The results show that RF-OP treatment introduced free radicals and polar groups onto the veneer surface, changed the surface morphology, and increased the surface roughness. Shear strength of the composite was improved. It can be concluded that RF-OP treatment is most effective at the optimal treatment power of 200 W.

Effect of Plasma Processing Rate on Poplar Veneer Surface and its Application in Plywood

“…Increased surface roughness of wood induced by plasma etching on a scale of several micrometers have already been reported by using laser scanning confocal microscope tests (Jamali and Evans 2011;Tang et al 2015;Xie et al 2015). However, surface etching is difficult to observe for wood veneer, as rotary cutting makes the veneer surface terribly rough with high roughness variation (Dundar et al 2008).…”

“…Also, by calculating the arithmetic mean roughness (Ra) and quadratic mean roughness (Rq) from at least eight images (presented in Table 1), maximum roughness for Ra (10.18 nm) and Rq (14.61 nm) were present at 14 m/min. The high energy eximers were generated by plasma (Shen et al 1998;Bhat and Upadhyay 2002;Tang et al 2015), and struck the wood surface. As a result, the wood surface was etched and became rougher.…”

“…2 as a function of the DBD plasma processing rate. During plasma treatment, air was excited in terms of atoms, molecules, ions, free radicals, and electrons (Shen et al 1998;Bhat and Upadhyay 2002;Tang et al 2015). The excited particles attacked the wood surface, generating free radicals through absorption and proton exchange (Fischer 1965).…”

“…The excited particles accumulated on the wood surface and generated more free radicals with a longer exposure time. As oxygen in air is easily excited, the accumulated free radicals were primarily oxygen-based (Kossyi et al 1992;Tang et al 2015). The excited oxygen-based free radicals would introduce more oxygen-containing groups on the wood surface.…”

“…Xie et al (2015) roughened the wood surface to control interaction with another phase by using radio-frequency oxygen plasma. Tang et al (2012Tang et al ( , 2015 treated poplar veneer surface with radio-frequency oxygen plasma. They found that the plasma treatment would introduce polar chemical groups onto the surface, change the surface morphology, and increase the roughness, all of which improved the interfacial adhesion of the plywood product.…”