High-Pressure Treatment of Chinese Fir Wood: Effect on Density, Mechanical Properties, Humidity-Related Moisture Migration, and Dimensional Stability

Abstract

A new densification technique for industrial uses of plantation wood was studied. Chinese fir wood was treated by high pressure (HP) at 50 to 200 MPa for 5 min. The density and mechanical properties, moisture sorption isotherm (MSI), and dimensional changes of the pressure-treated wood under various relative humidity (RH) storage conditions were evaluated. The densities of HP-treated wood ranged from 0.79 ± 0.01 g/cm 3 after treatment at 50 MPa to 0.92 ± 0.02 g/cm 3 at 200 MPa, which was significantly higher (p < 0.05) than that of the control (0.35 ± 0.01 g/cm 3 ). Hardness values in radial and tangential fiber alignment faces also significantly increased by 370% to 470% and 350% to 460%, respectively, as compared with the control. The modulus of elasticity and the modulus of rupture of pressure-treated wood increased by 48% to 88% and 89% to 170%, respectively. The equilibrium moisture content varied with RH, decreasing slightly at 33% and 52% while significantly increasing (p < 0.001) at 86% and 93% RH. Radial, tangential, and volumetric dimensions of densified wood were relatively stable at 33%, 52%, and 67% RH, while remarkable swelling occurred at 86% and 93% RH.

Fabrication of densified wood via synergy of chemical pretreatment, hot-pressing and post mechanical fixation

“…The process of softening is known as a pretreatment and combined with following mechanical pressing, achieving better compressing result. The thermo-mechanical densification [3][4][5], thermal-hydromechanical [6][7][8], hygro-mechanical steam treatment [9,10], mechanical-microwave treatment [11], and highpressure treatment [12,13] were developed to manufacture densified wood, in which the thermal-hydro is the most common and simplest pretreatment method currently. The cell walls of wood would be swelled by water although it cannot penetrate into crystalline region of cellulose.…”

Effects of High-Pressure Treatment on Poplar Wood: Density Profile, Mechanical Properties, Strength Potential Index, and Microstructure

“…Based on their findings, they concluded that the application of pressure in all directions contributed to the prevention of compression defects (e.g., fracture, fragmentation, spreading, checking). Li et al (2016) applied high-pressure (HP) treatments (i.e., purely isostatic compression) to small Chinese fir logs to modify wood properties. Results showed that pressurized woods possessed better mechanical properties and stability at a moderate relative humidity (RH).…”

High-pressure densification and hydrophobic coating for enhancing the mechanical properties and dimensional stability of soft poplar wood boards

“…This advantage makes HP-densified wood attractive for long-term indoor use when the environment relative humidity (RH) is low and the climate is relatively stable. Moreover, results showed that HP densification could make the densities of Chinese fir wood/poplar/paulownia wood to increase 2-3 times within 5 min [20,21,23]. This treatment is shown to be universally effective for various low-density species of wood.…”

“…Another wood densification method developed by Kamke and Sizemore [19] is known as "viscoelastic thermal compression". The process has a wood softening phase above the glass transition temperature (T g ), under saturated steam, followed by a compression phase, heat-treatment, and cooling [20]. High densities are achieved through a dynamic process which combines temperature ranging from 150 to 190 °C, saturated steam and mechanical compression perpendicular to the grain.…”

“…High-pressure (HP) treatment has been proved to be a useful densification method for fast-growing wood species by quickly reducing the void volume of wood through isostatic hydrostatic pressure, in a high-pressure equipment [20,21]. HP densification works as shown in Fig.…”