Abstract
Acidic aluminum sulfate hydrolysis solutions can be used to catalyze the thermal degradation of wood in a mild temperature environment, and thus reduce the temperature required for heat treatment process. To improve the dimensional and thermal stability of Chinese fir during heat treatment at 120 °C, 140 °C and 160 °C, this study investigated the effects of soaking pretreatment with 5%, 10% and 15% aluminum sulfate on the chemical and structural changes of the heat-treated Chinese fir. The results indicated that the samples treated at 15% aluminum sulfate concentration and 160 °C heat treatment achieved the best dimensional and thermal stability. Chemical analyses by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) indicated that the catalysis of aluminum sulfate resulted in degradation of hemicelluloses during the heat treatment, and an increase in the soaking concentration and heat treatment temperature also affected the thermal degradation of celluloses. The scanning electron microscope (SEM) and mass changes test results proved that the hydrolyzed aluminum flocs mainly adhered to the inner wall of the wood tracheid as spherical precipitates, and when the soaking concentration reached 10% and 15%, a uniform soaking effect could be achieved. The thermogravimetric (TG) analysis revealed the soaking pretreatment effectively improved the thermal stability of the heat-treated wood by physically wrapping and promoting the formation of a carbon layer on the wood surface during heat treatment. Thus, aluminum sulfate soaking pretreatment exerted a great effect on the dimensional and thermal stability of wood, allowing heat treatment to be performed at a lower temperature.
Highlights
70% of wood products are used as building materials, such as decorative frames for structures, doors, and windows, and floor and wainscot systems (Grosse et al 2019; Jiang et al 2018)
The weight percentage gain (WPG) of the samples treated with different aluminum sulfate concentrations is shown in Fig. 1, which indicates that the WPG rate gradually increased with the soaking concentration
The aluminum sulfate soaking treatment exerted a catalytic effect on the heat treatment of wood, and the desired heat treatment effect was achieved at a reduced temperature
Summary
70% of wood products are used as building materials, such as decorative frames for structures, doors, and windows, and floor and wainscot systems (Grosse et al 2019; Jiang et al 2018). Heat treatment is used to improve the dimensional stability, durability, and corrosion resistance of wood, as well as modify its color, which allows heat-treated wood to be used as an element in facades, terraces, urban furniture, and windows (Nguyen et al 2018; Wang et al 2015; Windeisen et al 2007). Heat treatment accounts for 40–70% of the energy consumption of the entire wood production process and is typically conducted at 180–240 °C for 2–8 h (Aydemir et al 2015; Huang et al 2012a; Kol and Sefil 2011; Nuopponen 2005; Obataya et al 2006). Materials can only be heated using electricity, which is expensive and increases the cost of wood processing. Temperature and duration are the two main factors that affect the heat treatment of wood.
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