# Effect of Heat Treatment on Water Absorption of Chinese fir Using TD-NMR
## 4 Conclusions  
In this work, various NMR methods were applied to investigate the water absorption process of untreated and heat-treated Chinese fir wood. The integral peak area and the gravimetrically determined MC had a significant linear correlation relationship, which indicate that it was a feasible method to use the T\({}_{2}\) relaxation curve to characterize the dynamic changes of moisture in wood samples during the water absorption process. Two water components, corresponding to bound water and free water, were reflected by the T\({}_{2}\) relaxation curve for the samples heat-treated at 160 \({}^{\circ}\)C and  
Figure 7: Axial NMR images of free water absorbed in the samples heat-treated at 220 \({}^{\circ}\)C as well as the untreated samples, measured after immersed for 1, 5, 10, 20, 30, and 60 days, the images were took from the two ends and the middle of samples (the color bar which reflects the signal intensity is shown under the figures). Three-dimensional reconstructions of the samples are shown below the images.  
180 \({}^{\circ}\)C, as well as the untreated sample. However, a small amount of new water components with T\({}_{2}\) values of about 20 ms appeared in the 200 \({}^{\circ}\)C and 220 \({}^{\circ}\)C heat-treated samples. They are most likely to be water existing in very small pores or cracks that were generated on the cell walls due to degradation of wood components after heat treatment at high temperatures. In addition, the T\({}_{2}\) values of water in heat-treated wood samples were greater than that of the untreated one, which to some extent indicates that heat treatment might decrease the wood wettability and result in the reduction of the water absorption rate. The results calculated by the area integration method showed that the contents of bound water and free water in heat-treated samples were less compared to the untreated sample, and the water absorption decreased correspondingly due to the increasing heat-treated temperature. The reason was that heat treatment might partially block the access of water to wood cell walls, and in consequence improve the dimensional stability of heat-treated wood. 1D NMR imaging showed that the moisture transport was more internally limited and difficult to penetrate into the center of heat-treated wood samples. The main reason might be that the pits, which play a crucial role in connecting the wood cell walls, were closed after heat treatment. Moreover, 2D NMR images of the untreated and 220 \({}^{\circ}\)C heat-treated samples revealed that the free water absorption in latewood was faster than in earlywood. This was likely to be the result of the internal diameter of the cell lumen is smaller in latewood and could a stronger capillary force than in earlywood.  
[PERSON] and [PERSON] planned and designed the research. [PERSON] performed the experiments and wrote the paper. All authors read and approved the manuscript. This research was sponsored by the National Key Research and Development Program of China (2017 YFD0600202). The authors would like to thank the engineer [PERSON] at Niumag Cor. Ltd. in Suzhou for the technical support. The authors declare no conflict of interest.