Surface Densification of Poplar Solid Wood: Effects of the Process Parameters on the Density Profile and Hardness

Qiaofang Zhou, Chuanfu Chen, Dengyun Tu, Zhipeng Zhu, Kaifu Li

Abstract


Poplar (Populus tomentosa Carr.) solid wood was surface densified in the tangential direction, and the vertical density profile (VDP) and hardness of the treated and untreated samples were measured. The effects of the process parameters on the VDP and hardness were investigated. To explicitly describe the VDP of the surface densified wood, five indices (AD, ADx, PD, PDi, and DTh) were used. The compressing temperature and closing speed influenced the formation and shape of the VDP. A higher temperature yielded a greater PD and Pdi, and a faster closing speed yielded a higher PD, but smaller PDi and DTh. Increasing the compression ratio increased the AD, ADx, and maximum load, and the poplar wood was compressed in the overall thickness as the compression ratio exceeded a certain degree. The Janka hardness of the poplar wood was significantly improved after surface densification; a higher temperature resulting in a higher surface hardness was explained by the higher PD. The closing speed and compression ratio affected the hardness by impacting the VDP, specifically the PD and DTh indices. When the PD and DTh were greater the surface hardness was greater. By this study, a compressing temperature of 140 to 160 °C and the closing speed of 10 mm/min is recommended, and to prevent the deformation of unheated side of the wood samples and obtain a higher surface hardness, the compression ratio is restricted to 20%.

Keywords


Surface densification; Process parameters; Vertical density profile; Hardness; Characterizing index; Thermo-hydro-mechanical

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