## 1 Introduction  
Wood is a natural and reproducible material. It has been widely used in constructions, buildings, and woodworks, due to its natural advantages, such as high strength-to-weight ratio, insulating properties, sound insulation performance, lack of electrical conductivity, and temperature stability. In contrast, wood also has natural defects, such as drying shrinkage, poor dimensional stability,and durability [1; 2; 3], limiting accordingly its extensive utilization. The amount of water, especially the bound water in wood, influences the dimensional stability, and physical and mechanical properties of wood-based products [4]. Wood mainly contains three components: cellulose, hemicellulose, and lignin. Wood hygroscopicity is mainly attributed to the strong hydrophilic capacity of hemicellulose [5; 6]. Reducing the hygroscopicity of wood is an effective way to improve wood dimensional stability, durability, and hydrophobicity [7]. In order to increase the dimensional stability, durability, and hydrophobicity, against frequent use under natural environmental conditions, many modifications have been applied to wood to reduce the hygroscopicity, such as steam-heat modification [8], methyltrimethoxysilane modification [9], boron and compatibilizer modification [10], surface modification [11], impregnation modification [12], and thermal modification (TM) [8; 13; 14]. These modifications can be classified into chemical modification and physical modification. Chemical modification of wood can achieve good results for improving wood dimensional stability and hydrophobicity, however, the modifications might be environmentally detrimental. TM can successfully improve wood dimensional stability and durability by thermal degradation of hemicellulose [15; 16]. TMs have been commercially applied to wood and are considered as an environmentally friendly method. However, after severe thermal modification, wood components undergo chemical degradation, which increases its brittleness, reduces its mechanical properties, and results in serious color deterioration [17; 18], thereby, limiting the further application of TM wood. In addition, TM at higher temperature is a high energy-consuming process. Wax is a good water repellent and suitable for wood protection [19], which can decrease water uptake rate and improve the dimensional stability of wood [20]. Wax is also an environmentally friendly material, and is cost-effective, abundant, and non-toxic [21]. Wax can be applied to wood in a melted state, diluted in organic solvents, or in the state of emulsions or suspensions via impregnation or combined with other treatments [22; 23]. Wax impregnation consists of three major processes: first, microcrystalline wax is heated to liquid state, then the wood is impregnated with hot wax fluid, either with or without pressure, and the final process is the solidification of the microcrystalline wax in cell cavities and the intercellular space of the wood. The hygroscopicity and water absorption of wood are reduced after wax fills the cell cavity [24; 25], thereby improving the dimensional stability of wood for long-term service life. In contrast to TM, wax impregnation may increase wood mechanical properties [26], and maintain the natural color and texture of wood [27]. Both TM and WI are environmentally friendly treatments of wood. The combined treatments may further improve wood properties, against the effect of water, and the mechanical strength [28], and also might reduce processing energy consumption. However, the normal procedure for the combination is that wax is impregnated first, and subsequently subjected to higher temperature TM, which results in the same shortcomings as TM for wood. A few studies have been conducted with the opposite procedure [29; 30], but the temperature of TM was higher. This might lead to severe color change, strength loss, and higher energy consumption. In the current study, the combined treatment of TM and WI was carried out for _Pterocarpus macrocarpus_ Kurz wood.