The principle of wood impregnation entails treating wood with a monomer/impregnating agent that diffuses into the cell walls, often followed by polymerization to change desired properties. Numerous studies related to this matter have been reported and continue to attract more interest, as wood impregnation can significantly improve wood properties. These processes can be grouped into two approaches: active modification involves the chemical alteration of wood structure by cross-linking, and passive modification features filling of cell cavities and/or cell walls with impregnating agents without any chemical reaction taking place. Wood impregnations could have resulted in an increase in its weight gain due to impregnating agents filling its cavities. It will diminish the utilization of wood as an engineering material in selected application fields. Owing to the extensive literature available, this article summarizes the representative achievements of wood impregnation. The mechanisms, benefits, and drawbacks of various impregnating agents on wood properties, along with grouping the impregnating agents that cause greater or lesser weight gain of wood were analyzed, compared, and evaluated. Thus, according to the application state of wood impregnations, the problems existing in those processes and the developmental trends in the future are also discussed in this review.

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.

Chemical, mechanical, and natural durability properties of three lesser-used wood species from North Kalimantan, namely nyatoh (Palaquium lanceolatum), pisang putih (Mezzettia leptopoda), and sepetir (Sindora wallichii) woods,were analyzed to seek the interrelationships amongthem and give an overview related to their utilization. The results showed that pH values of three wood species were categorized into moderate to weak acid levels. The extractive contentsin hot and cold water as well as in NaOH 1% of sepetir wood were higher than those of nyatoh and pisang putih woods. In contrast, the solubility in ethanol-benzene of nyatoh wood was the highest. The ash content in the three wood species were categorized intomedium level. Lignin contents in sepetir and nyatoh woods were classified as moderate, while lignin content in pisang putih wood was high. Holocellulose and hemicellulose contentsin sepetir wood were higher than those in nyatoh and pisang putih woods, whereas alpha cellulose in sepetir wood was the lowest. MOE values of the three wood species were classified as strength class of IV‒V, while MOR and compression parallel to the grain were classified as strength class of IV. The hardness value of nyatoh wood was higher than that of other woods.The durability of the three wood species was classified into poor (low durable). The relationship between chemical characteristics and mechanical properties of wood was primarily influenced by its major components (cellulose, hemicellulose, and lignin), whereas natural durability was influenced by its minor components (extractives and inorganic materials).Keywords: lesser-used wood species, mechanical properties, natural durability, parameters interrelationship, wood chemical characteristics

This research deals with low molecular weight-phenol formaldehyde (LMW–PF) impregnation on sepetir (Sindora spp), nyatoh (Palaquium spp.), and pisang putih (Mezzettia spp.) woods to determine the effect of different anatomical structure on weight percent gain and dimensional stability improvement. The wood samples were impregnated using LMW–PF solutions with 7, 8, 9, 10, and 11% of concentrations (w/w), vacuum-pressured (–98 kPa, 15 min, 350 kPa, 4 h), and re-immersed in 80°C for 3 h. According to the findings, LMW–PF impregnation reduced coefficient of swelling by 9.64–29.95%, and increased anti-swelling efficiency by 12.24–29.91%. Additionally, the water absorption and thickness swelling reduced by 2.43–38.75% and 15.94–34.21%, respectively, indicating the improvement of dimensional stability. Microscopy and NIR analysis revealed the presence and reaction of LMW–PF within porous wood matrix. The effect of diverse anatomical structures caused complexity on LMW–PF impregnation. Sepetir-treated wood with fewer anatomical barriers resulted in better dimensional stability improvement than others.