Improving bonding strength of oven-dried poplar veneers using atmospheric cold plasma treatment

Abstract

Poplar veneers are typically oven-dried at high temperatures to shorten the dying period, and thus reduce energy consumption, which also leads to poor bonding strength. In this study, an atmospheric cold plasma system was self-designed to quickly modify the surface of oven-dried poplar veneers (dried at 120 °C, 200 °C, and 240 °C) to yield high bonding strength samples. The physical and chemical properties of treated samples were investigated with an optical contact angle measuring apparatus, fluorescence microscope (FM), and X-ray photoelectron spectroscopy (XPS). The results showed that surface wettability and adhesive permeability of poplar wood veneer were improved after the atmospheric cold plasma treatment. Moreover, the plasma treatment resulted in the incorporation of oxygen-containing groups onto the surface of the oven-dried poplar veneer. For example, the O-C=O group saw its relative content dramatically increase from 1.37% to 13.57%. These effects synergistically resulted in a high increase (76.2%) in bonding strength when using urea-formaldehyde (UF) resin as the adhesive. The plasma modification system used in this study can be utilized at atmospheric pressure, which is easier to realize industrially as compared to using a radio frequency plasma treatment, which is the currently preferred technique.