# The Influence of Wood Moisture Content on the Processes of Freezing and Heating
## 3 Results and Discussion  
A total of 30 samples were used for this experimental work. Their average oven-dry density was 395.5 kg\(\cdot\)m\({}^{-3}\) with a variance from mean value of \(\pm\)3.4 kg\(\cdot\)m\({}^{-3}\). The average initial \(MC\) of the first group of samples (\(MC>FSP\)) was 81.38% with a variance of \(\pm\)0.43%. The average initial \(MC\) of the second group of samples (\(MC\cong FSP\)) was 35.47% with variance of \(\pm\)0.21%. Table 1 shows the average values of the initial \(MC\) after the freezing and heating process, and the moisture losses in the individual stages of the process. It can be seen from the measured data that with this freezing process, the decrease in the _MC_ of the samples was approximately the same in both groups. On average, moisture content was reduced by 4.2% in both groups. The initial moisture of the samples had no effect on this decrease. Before the freezing process, the average value of the humidity gradient was higher for samples with higher humidity. In both groups, the increase in moisture gradient was similar. Higher values were measured for samples with higher _MC_. In this group, the value of the humidity gradient increased twice after the freezing process and the standard deviation also increased. Higher moisture loss was in the surface layers (5-6%) due to the sublimation of free water. The change in _MC_ of the middle layers was only about 1%. Humidity affected the amount of moisture gradient after freezing. After heating of the frozen samples, the loss was significantly greater in the samples whose _MC_ was above the _FSP_ compared to the second group of samples. The values of moisture gradients decreased. The values of humidity gradients decreased, but for a given thickness of the samples, the values were high; this was due to a slow increase in the relative humidity of the environment in the first hour of heating (Figure 3). The Figure 2 shows the course of temperatures on the cross section of wood in the freezing process. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Before freezing**} & \multicolumn{2}{c}{**After Freezing and before Heating**} & \multicolumn{2}{c}{**After Heating**} \\ \cline{2-7}  & _MC_ **(\%)** \(\geq\) FSP & _MC_ **(\%)** \(\cong\) FSP & _MC_ **(\%)** \(>\) FSP & _MC_ **(\%)** \(\cong\) FSP & _MC_ **(\%)** \(>\) FSP & _MC_ **(\%)** \(\cong\) FSP \\ \hline Moisture content of sample (\%) & 81.38 & 35.47 & 77.27 & 31.29 & 59.76 & 22.90 \\  & \(\pm\)0.43 & \(\pm\)0.21 & \(\pm\)0.32 & \(\pm\)0.43 & \(\pm\)0.21 & \(\pm\)0.30 \\ \hline Moisture loss (\%) & & & **4.11** & **4.19** & **17.51** & **8.39** \\  & & & \(\pm\)0.38 & \(\pm\)0.32 & \(\pm\)0.27 & \(\pm\)0.37 \\ \hline  & & & **Moisture Gradient** \(\Delta\)**MC** & & & \\ \hline Moisture content of the surface (\%) & 79.19 & 35.04 & 73.15 & 30.04 & 56.61 & 21.82 \\  & \(\pm\)0.56 & \(\pm\)0.29 & \(\pm\)1.1 & \(\pm\)0.6 & \(\pm\)0.72 & \(\pm\)0.41 \\ \hline Moisture content of the middle layers (\%) & 83.56 & 36.96 & 82.23 & 35.22 & 61.72 & 25.06 \\  & \(\pm\)0.13 & \(\pm\)0.15 & \(\pm\)0.69 & \(\pm\)0.11 & \(\pm\)0.31 & \(\pm\)0.28 \\ \hline Moisture gradient (\%) & **4.37** & **1.92** & **9.08** & **5.18** & **5.11** & **3.23** \\  & \(\pm\)0.35 & \(\pm\)0.22 & \(\pm\)0.89 & \(\pm\)0.36 & \(\pm\)0.52 & \(\pm\)0.35 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Moisture content of the samples, moisture loss, and values of the moisture gradient. Figure 2: Temperatures of sample in the cross-section and the temperature of the environment depending on time (freezing process). Additionally, as in similar research studies [5; 8; 9; 10; 11; 12], we discovered that freezing and the time of exposure to negative temperatures significantly reduced all mechanical wood properties and increased the dimensional instability inside the wood. Conversely, other researchers [13; 14; 15] discovered that as temperature decreased, the efficiency of cutting processes for frozen wood decreased.