## 1 Introduction  
Poplar wood is a green and environmentally friendly material that is recyclable and degrades naturally. It has the advantages of a fast growth rate, high yield, and a short harvesting period, which meets market demand, but has characteristics of low mechanical properties and dimensional stability, as well as low resistance to biocidal factors, which markedly affects its service life [1; 2]. To date, many studies have been conducted on the chemical impregnation of wood: the functional improvement of the wood cell cavity or cell wall is achieved by treatments at a cell level or molecular level [3; 4; 5; 6]. Water-soluble low-molecular-weight resin impregnation is a commonly used wood modification technique. Studies have shown that although in situ polymerization of monomers occurs inside the wood, it is difficult to improve the physical and mechanical properties of the wood because the polymer mainly fills the cell cavities and does not easily enter the cell walls: therefore, the wood bulk density cannot be increased significantly [5]. Improvements in the density and mechanical properties of wood are closely related to weight percent gain (WPG), and the improvement of the dimensional stability of wood is closely related to the distribution ratio of the wood cell cavity/wall after resin impregnation [7]. The substance 1,3-dimethylol-4,5-dihydroxypheneurea (DM) is active with two nitrogen methylol groups and is commonly used in the textile industry [8]. The use of DM for wood modification has resulted in good performance and has improved the dimensional stability [9], durability [10], coating properties [11], and weathering resistance of wood [12; 13]. Maltodextrin (MA) has been widely used in food [14], pharmaceutical [15], papermaking [16], and other industries because of its low sweetness, low viscosity, low odor, and low browning reaction [17]. [PERSON] et al. used a combination of DM and MA for the impregnation of poplar wood and found that its antiswelling efficiency increased by more than 60% and that mechanical properties were also improved. However, a leaching test indicated that the weight leaching ratio was 50% and increased with the MA concentration [18]. Subsequently, [PERSON] et al. investigated drying characteristics during the curing process of DM/MA-impregnated wood materials, where it was found that the lower the deposition amount of the chemical, the more likely it was that the impregnated samples exhibited drying defects, including shrinkage and cross bending: When the amount of impregnation chemicals was higher, there was significantly less shrinkage, and fewer drying defects were observed [19]. Moreover, the higher the WPG of the modified material, the greater the functional improvement was [9]. [PERSON] et al. studied the curing process of DM and found that the addition of 2% ZnCl\({}_{2}\) ensured the stability of DM under normal temperature (23 \(\pm\) 2 \({}^{\circ}\)C) immersion conditions and ensured that the moisture discharge during the drying process of the impregnated material was compatible with the curing of the resin: the addition of ZnCl\({}_{2}\) ensured that the DM remained clear compared to other hardener, which facilitated observation during a subsequent immersion test, and also the addition of ZnCl\({}_{2}\) allowed for more chemicals to remain in the wood cell wall and cell cavity, making the modified wood more effective [20]. In addition, the curing temperature affects the degree of reaction between the modifier and the cell wall. [PERSON] et al. [21] and [PERSON] et al. [22] investigated the effect of different curing temperatures on the WPG of impregnated material: it was concluded that a curing temperature of 120 \({}^{\circ}\)C was the most suitable temperature for DM. [PERSON] et al. investigated the effect of different curing temperatures on the static flexural strength of DM-modified wood.