# Optimization of Processing Parameters to Increase Thermal Conductivity of Rice Straw Fiber Film
## 3 Results and Discussion
### Response Surface Analysis  
#### 3.2.1 Interactive Effects on Dry Tensile Strength  
The combined effect of basis weight and wet strength agent on dry tensile strength of the BMF with others staying constant (0.7% neutral sizing agent, 10% charcoal addition ratio, and 45 \({}^{\circ}\)SR beating degree) is shown in Figure 2a. The dry tensile strength increased as basis weight increased, however, the increase was not significant at low wet strength agent content. This is mainly because the dry tensile strength of the BMF was proportional to the fibers per unit area of the sample. Dry tensile \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Source** & & **Sum of Squares** & **Mean Square** & \(f\)**Value** & \(p\)**Value** & \(R^{2}\) \\ \hline \multirow{4}{*}{Dry tensile strength (N)} & Model & 607.69 & 55.24 & 19.78 & \textless{}0.0001 & 0.901 \\  & Residual & 67.02 & 2.79 & & & \\  & Lack of fit & 36.60 & 2.44 & 0.72 & & \\  & Total & 674.71 & & & & \\ \hline \multirow{4}{*}{Wet tensile strength (N)} & Model & 93.03 & 8.46 & 14.97 & \textless{}0.0001 & 0.873 \\  & Residual & 13.56 & 0.56 & & & \\  & Lack of fit & 10.89 & 0.73 & 2.45 & & \\  & Total & 106.59 & & & & \\ \hline \multirow{4}{*}{Thermal conductivity (W/m\(\cdot\)K)} & Model & \(7.352\times 10^{-4}\) & \(1.470\times 10^{-4}\) & 5.57 & \textless{}0.0010 & 0.781 \\  & Residual & \(7.926\times 10^{-4}\) & \(2.642\times 10^{-5}\) & & & \\ \cline{1-1}  & Lack of fit & \(6.229\times 10^{-4}\) & \(2.966\times 10^{-5}\) & 1.57 & & \\ \cline{1-1}  & Total & \(1.528\times 10^{-3}\) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Significance of the regression model parameters. strength also increased as wet strength agent content improved. Wet strength agent in the BMF not just forms a covalent bond with carboxyl of fiber, but enhances the network structure of the BMF through the self-bridging reactions within the wet strength agent and between the wet strength agent and fibers, thus wet strength agent has the function to increase the dry tensile strength [43]. Figure 2a also shows that the interaction of basis weight and wet strength agent content had a significant effect on dry tensile strength. Dry tensile strength reached the highest at 70 g/m\({}^{2}\) basis weight and \(1.6\%\) wet strength agent content. The combined effect of basis weight and beating degree on dry tensile strength of the BMF with others staying constant (0.7% neutral sizing agent content, 10% charcoal addition ratio, and 1.2% wet strength agent) is shown in Figure 2b. Dry tensile strength improved initially when basis weight increased from 50 to 60 g/m\({}^{2}\) and then decreased slightly when the basis weight increased from 60 to 70 g/m\({}^{2}\) at a low beating degree. At a low beating degree, even the addition ration keeps constant, the charcoal content increased as basis weight increased. The increase in charcoal reduces the binding force between fiber and fiber. Therefore, dry tensile strength decreased at a high basis weight. However, at a high beating degree, dry tensile strength increased as basis weight increased. This is mainly due to when at a high beating degree, the hydrogen bonds on the fiber surface and the bond strength between the fibers increased. The result also indicates that the effects of basis weight on dry tensile strength were greater than that of beating degree based on ANOVA analysis. The interaction of basis weight and beating degree also had significant effect on dry tensile strength. Dry tensile strength reached the highest at 70 g/m\({}^{2}\) basis weight and 55 \({}^{\circ}\)SR beating degree. The combined effect of neutral sizing agent content and charcoal addition ratio on dry tensile strength of the BMF with other parameters remaining constant (60 g/m\({}^{2}\) basis weight, 1.2% wet strength agent content, and 45 \({}^{\circ}\)SR beating degree) is shown in Figure 2c. It was observed that at low charcoal addition ratio, dry tensile strength decreased as neutral sizing agent content improved.