Effects of pre-heating treatment parameters on dimensional stability and mechanical properties of densified Chinese fir

Abstract

Pre-heating treatment performed by heat plate is an efficient wood softening method that could improve the dimensional stability and mechanical properties of densified wood, having great potential to industrialize. To optimize the properties of densified Chinese fir softened by this method, an improved understanding of the pre-heating treatment parameters is required. An orthogonal experiment with three factors and levels was used in this study to investigate the effects of the pre-heating treatment parameters including heating temperature, duration time and moisture content on set recovery, static bending strength (MOR), modulus of elasticity (MOE) and compression strength parallel to grain (CSP). Chinese fast-growing fir with dimensions of 400 mm(L) 60 mm(T) 40 mm(R) was prepared as raw materials, and the wood densification process including softening, pressing and fixation was performed using a hot-press. The test results suggested that moisture content was the most significant factor influencing set recovery, MOR, MOE and CSP. Although the effect of temperature on MOE and CSP was not significant, it greatly affects set recovery and MOR. Moreover, the effect of duration time changes within the range of 10 min to 30 min was slight in all of the responses in this study. The mechanical properties of densified Chinese fir improved substantially with the increase in moisture content. The values of MOR and MOE raised to 95.17 MPa and 15.43 GPa respectively when moisture content raised from 30 % to 50 %, increased by 32.5 % and 21.8 %. The set recovery induced by moisture adsorption and water absorption decreased from 7.23 % to 3.09 % and from 20.9 % to 12.7 % respectively indicating that the dimensional stability of densified Chinese fir improved significantly with the increase of moisture content from 30 % to 50 %. The conditions of pre-heating treatment at a temperature of 120 ℃, duration time of 20 min and moisture content of 50 % were found to be the optimum parameters for manufactured densified Chinese fir. The proposed pre-heating conditions could be a recommendation for industrial production.