## 1 Introduction  
Wood from planted forests is a natural material with a complex hierarchical structure consisting mainly of a cellulose, hemicellulose, and lignin matrix [1]. Poplar wood (_Populus adenopoda_ Maxim) has become an important industrial raw material for the timber industry worldwide. However, this material has different properties, such as low density, softness, and poor dimensional stability, resulting in low-value materials [2; 3; 4; 5; 6]. Improving the quality and use of poplar wood can not only promote the timber industry but can also effectively reduce the shortage in wood resources. Woodmodification has developed rapidly in recent years. Industrial production of some modified wood products has begun [7; 8; 9]. One of the major modification methods used is wood impregnation, which mainly refers to a technique in which a low-molecular-weight resin chemically reacts with a wood cell-wall polymer or physically fills and is fixed in a wood cell cavity [10]. A type of resin commonly used in the textile industry is 1,3-dimethylol-4,5-dihydroxytheurea (DM) which has achieved desirable results in wood modification, effectively improving the dimensional stability of wood and obtaining an anti-swelling efficiency (ASE) of up to 70%. These properties are attributed to its low molecular weight and strong polarity; in addition, the material can penetrate into the cell wall of wood, cross-link with wood cell-wall components, or self-condense and inflate cell walls [11]. [PERSON] et al. systematically studied the modification of an aqueous mixture of sucrose and DM on the radiata pine wood. The effects on coating and weathering properties suggested that the adhesion of the modified wood film was significantly higher than that of the untreated wood, indicating that the modification treatment helped increase the durability of the paint film on the wood surface [12]. Maltodextrin (MA) has a wide range of applications in food, pharmaceutical, papermaking, and other industries because of its low sweetness, low viscosity, low odor, and low browning reaction [13]. [PERSON] et al. impregnated poplar wood with an MA-modified urea-formaldehyde resin, which not only retained the original natural properties of the wood but also conferred excellent properties on the treated material [14]. [PERSON] et al. used MA and DM as a joint modifier to systematically determine whether MA and DM could markedly improve the dimensional stability and mechanical strength of fast-growing poplar, providing an important theoretical basis for the current study [15]. Wood impregnation is divided into two stages: modifier infusion and curing treatment. Drying removes moisture and causes modifiers to solidify and inflate within the cells [16]. Wood drying is an important aspect of ensuring the quality of wood, reducing its degradation, and improving its utilization [17; 18; 19]. It is also the most energy-intensive process in the production of wood products, comprising 40%-70% of the total energy consumption of wood processing enterprises in China [20]. In wood drying, the surface moisture evaporates and then internal moisture moves toward the surface. Power is mainly derived from the water-vapor partial-pressure gradient and moisture content (MC) gradient. [PERSON] et al. evaluated the effect of initial MC on the impregnation of Chinese fir with BLW. The results indicated that with a decrease in initial MC, both the curing weight percent gain (WPG) and wet WPG of the Chinese fir increased, meanwhile, the compressive elastic modulus of modified Chinese fir at a higher initial MC was improved and met the standard of use, which meant modification under a relatively high initial MC could reduce energy consumption during drying [21]. Most relevant studies on drying impregnated wood have focused on the drying aspect rather than the drying characteristics of impregnated wood. [PERSON] et al.