## 3 Results and Discussion
### Drying Defects  
As shown in Figure 9, only the T3 group exhibits a visible collapse defect. When dried to 273 h, the 1# and 2# MC sample boards first collapsed at MCs of 15.50% and 17.10%, reaching the collapse depth at 2.69 and 2.33 mm, respectively; as drying continued, the collapse depth also fluctuated, reaching its maximum at 3.21 and 3.39 mm, respectively. Previous research identified tree species, wood density, water content, drying temperature, drying speed, and so on as external factors for wood collapse [27; 28; 29; 30]. In the current study, T1, T2, and T3 were heart-edged materials with basically similar initial MCs and drying schedules, which could be explained by internal causes, such as uneven water distribution between the tubes, ducts, and films of the wood fibers. In addition, the intrusion in the conduit not only partly or completely blocked the lumen of the catheter but blocked the pores on the side walls of the catheter as well. Therefore, the presence of the invader increased the resistance to moisture movement, rendering the pore size in the water-moving path smaller. This occurrence led to an increase in the tension generated when the moisture moved, enhancing the driving force causing the collapse. Simultaneously, the pressure gradient between capillary tension and drying stress was induced by the excessive movement of moisture during drying. This difference in pressure gradient forced the cell wall to collapse. Owing to the uneven distribution of modifiers, the moisture distribution in the wood became more uneven (T3). The effect potentially increased the content of the intrusion, resulting in a larger difference in pressure gradient, hence the collapse. Although T2 also hindered moisture movement, modifiers were impregnated into the cell cavity and imparted a certain rigidity to the cell wall, such that the difference in pressure gradient failed to sufficiently cause the cell wall to collapse. In addition,  
Figure 8: Stress indices of T1, T2, and T3 at the stages with 30%, 20%, and 12% MC. wood collapse largely depends on shrinkage rate and wood penetration. The three sets of sample boards appeared to shrink at the beginning stage, but shrinkage values changed significantly when the MC reached around 30% (Figure 5). The T1 group appeared no collapse, which attributed to the better penetration and water migration. In the T2 group, the chemicals were fully impregnated inside the tube and caused reduction of wood penetration, but the shrinkage rate was too small to cause collapse (Figure 6a); For the T3 group, the collapse appeared mainly to be a result of uneven immersion, which not only reduced wood penetration but also increased the shrinkage rate (Figure 6a). At the end of the drying process, transverse bending defects appeared in the three experimental groups. The results are listed in Table 3. The maximum WPs of T1, T2, and T3 were 3.76%, 2.59%, and 4.10%, respectively. Overall, T3 and T2 had the largest and smallest defects, respectively. The reason for stress deformation can be explained as follows: (1) The MC of any part of the wood fell below the FSP, causing shrinkage; (2) The normal shrinkage of the wood was inhibited, generating tensile stress in the wood; (3) When tensile stress was applied, compressive stress was generated in other parts, achieving balance in tensile stress. When the wood was subjected to stress, deformation occurred. The uneven impregnation of the modifiers led to the increase in bending defects (T3) because of the superposition of additional tensile stress outside the sheet and the surface tensile stress. However, as a result of the impregnation of DM and MA, the plasticizing property of wood increased. While drying reduced the stress in the wood, it was beneficial to the qualitative deformation of the wood after compression deformation and reduced the bending defects.