Abstract
The effect of NaOH, succinic acid and their combination used as pretreatments on selected properties of densified wood samples of pisang putih (Mezzettia spp.), nyatoh (Palaquium spp.) and sepetir (Sindora spp.) has been studied. The properties of these samples were then compared with those of untreated wood (control) and densified wood samples without any pretreatment (HD wood). For alkali-pretreatment, after immersion in 10% NaOH (w/w) for 1, 2 and 3 h, the samples were immediately compressed; for acid-pretreatment, the sample was impregnated with 10% succinic acid (w/w) using a vacuum of −50 kPa for 30 min and a pressure of 7 bar for 2 h before pressing; while for the combination-pretreatment, the sample was initially immersed in 10% NaOH then impregnated with 10% succinic acid (w/w) and finally densified/compressed. Compression was applied in a radial direction and carried out in an open system using a hot press machine at 180 °C and 7 MPa specific pressure for 30 min with a 40% compression ratio. The results showed that densified wood with or without pretreatment had a higher specific gravity (SG) than the control, whereas sepetir wood showed the greatest increase in SG. The alkali- and combination-pretreatments resulted in a higher C-set value than in the control, HD and acid-pretreated samples. Acid-pretreatment resulted in the best improvement in dimensional stability compared to the other pretreatments. Increasing the immersion time in NaOH solution was proven to be able to increase dimensional stability both in alkali- and combination-pretreatments, although water absorption values varied.
Highlights
Densification is a process that has been extensively used to improve the properties of wood through heating and compressing
Results showed that the specific gravity of densified wood with or without pretreatment was higher compared to untreated wood
Spectra shifted in the wavelength ranging from 1000–1700 cm−1, especially in those densified with alkali-pretreatment (Figure 8)
Summary
Densification is a process that has been extensively used to improve the properties of wood through heating and compressing During this process, the wood is deformed as its volume decreases, followed by an increase in its density and specific gravity [1,2,3,4]. When soaked in water or exposed to high relative humidity, they tend to exhibit non-reversible swelling or spring-back due to the release of internal stresses that occur during densification [9] This finding is consistent with those of Rautkari et al [10] for beech- and spruce-densified wood, as well as those of Augustina [11] and Augustina et al [12] for nyatoh, sepetir and pisang putih densified wood, where the initial specific gravity range was around 0.35–0.52
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