Study on the bonding performance of the moso bamboo dowel welded to a poplar substrate joint by high-speed rotation

Abstract

The wood friction welding technique with its high bonding strength, low cost, high efficiency, and without any adhesive has been increasing concern in China. Moso bamboo (Phyllostachys pubescens) and poplar (Populus sp.) are widely planted and used in the furniture industry, interior decoration, and wood structure construction in China. The aim of this work was to investigate the bonding performance of moso bamboo dowel rotation welded joints with different dowel/receiving hole diameter ratios. The results indicated that the ratio of dowel/receiving hole diameter was an important parameter that influenced the welding performance. The bonding strength of the bamboo-to-poplar welded joints at the optimal ratio of 10/7 was as high as 7.50 MPa, which was higher than that of the beech (Fagus sylvatica, L.), schima (Schima superba) dowels and PVAc glued joints. The temperature measurement results showed a peak temperature of bamboo dowel welding as high as 350–360°C. Some differences in the temperature curves between each dowel/hole diameter ratio group were observed at the three different hole depths, such as the friction time, peak temperatures, and stabilization time at the maximum temperature, which could explain the differences in welding strengths between different ratios. The SEM results showed the tempera-ture-induced softening, melting and flowing of cell-interconnected polymer material in the wood and bamboo struc-ture. In addition, the bamboo fibers (mainly vascular bundles) were wrapped to form a dense continuous bonding layer, similar to the reinforced concrete, thus producing a good bonding effect. The Fourier transform-infrared spectroscopy (FT-IR) analyses showed that the high temperature resulted in the increase of the lignin relative content due to the degradation reaction of cellulose in the welding zone, which improved the bonding properties.