Analysis of Adhesive-Free Bonding Performance of Poplar Wood Surface Swelled with NaOH Solution

Abstract

Poplar wood specimens were fabricated via surface swelling pretreatment with NaOH solution combined with a hot-pressing process. The three factors NaOH concentration, hot-pressing temperature, and hot-pressing time were considered relative to shear strength. The optimal process parameters for poplar adhesive-free bonding were surface swelling with 5% NaOH solution, a hot-pressing temperature of 140 ºC, and a hot-pressing time of 60 min. Under these parameters, the shear strength of the prepared specimens’ bonding interface reached 4.87 MPa. Analysis of variance showed that hot-pressing temperature exerted a highly significant effect on shear strength and that temperature was the dominant factor influencing adhesive-free bonding performance. Scanning electron microscopy observations indicated that NaOH solution surface swelling had a notable impact on the adhesive boundary, facilitating the formation of a dense adhesive layer in this area. Furthermore, a distinct phenomenon of molten lignin encapsulating fibers was observed at the bonding interface. As a natural bonding medium, molten lignin effectively enhances the bonding between fibers, thereby improving the adhesive-free bonding strength of poplar wood. Hemicellulose underwent substantial degradation, while no significant degradation was observed in the skeletal structure of lignin. This study provides a theoretical foundation and technical reference for optimizing the poplar wood adhesive-free bonding process.