## 3 Results and Discussion
### Main Phase of the Study  
In the second phase of the study, 5% and 10% wollastonite gel (W) was added to panels made with a mixture of UF resin and soy flour (only two optimal SF contents of 10% and 15% were tested in the main phase). Results illustrated that, apart from slight fluctuations which were attributed to the standard deviation among different specimens, the addition of wollastonite had no significant effect on formaldehyde emissions (Figure 7). However, both contents of wollastonite had a decreasing impact on shear strength (Figure 8), although the shear strength in W-added panels was still higher than that of control panels. The decrease in shear strength was attributed to the absorption of part of the resin by wollastonite particles. Results of the delamination tests revealed that all panels passed this test, \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Binder** & **First Round 1** & **Third Round 2** & **Result 3** \\ \hline UF 4 100\% & 1/20 & 1/20 & P \\ UF 95\% + SF 5 5\% & 0/20 & 0/20 & P \\ UF 90\% + SF 10\% & 1/20 & 1/20 & P \\ UF 85\% + SF 15\% & 0/20 & 0/20 & P \\ UF 80\% + SF 20\% & 0/20 & 0/20 & P \\ \hline \end{tabular} 1
[FOOTNOTE:1]Footnote 1: No. of delaminated cases after the first round of the soaking/drying cycle. 2 No. of delaminated cases after the third round of the soaking/drying cycle. 3  
\end{table} 
Table 2: Delamination test on plywood produced with different binders. Figure 5: Shear strength (MPa) in three-layer plywood panels produced with urea-formaldehyde resin and 5%, 10%, 15%, and 20% soy flour substitution of UF resin. acting as reinforcing filler to improve thickness swelling; therefore, a W content of 5% is recommended as an optimum. \begin{table} \begin{tabular}{l l l l} \hline \hline
**Binder** & **First Round 1** & **Third Round 2** & **Result 3** \\ \hline UF 4 100\% & 1/20 & 1/20 & P \\ UF 90\% + SF 5 10\% & 1/20 & 1/20 & P \\ UF 90\% + SF 10\% + W 6 5\% & 1/20 & 2/20 & P \\ UF 90\% + SF 10\% + W 10\% & 0/20 & 0/20 & P \\ UF 85\% + SF 15\% & 0/20 & 0/20 & P \\ UF 85\% + SF 15\% + W 5\% & 0/20 & 0/20 & P \\ UF 85\% + SF 15\% + W 10\% & 0/20 & 0/20 & P \\ \hline \end{tabular}  1
[FOOTNOTE:1]Footnote 1: No. of delaminated cases after the first round of the soaking/drying cycle. 2
[FOOTNOTE:2]Footnote 2: No. of delaminated cases after the third round of the soaking/drying cycle. 3  
The addition of both SF and W to UF resin resulted in a decrease in pH of the resin mixture (Table 4). Gel time was significantly increased as a result of the addition of both SF and W (Table 4); however, the gel times of all mixtures were below the hot-press time of 5 min. Therefore, it is unlikely that alterations in different properties measured in this study can be attributed to the difference in gel time. The addition of SF significantly increased viscosity, while W had a decreasing effect. The decreasing effect of W on viscosity was attributed to the water content of the W gel that was added to the resin mixture. Figure 10: Thickness swelling (%) in three-layer plywood panels (Soy% = soy flour content; W% = wollastonite content; TS = thickness swelling). Cluster analysis as a function of the properties measured demonstrated that control panels were remotely clustered away from panels containing soy flour and wollastonite (Figure 11). This showed the significant effect of both soy flour and wollastonite on the overall properties of plywood panels. Panels containing either 5% or 10% wollastonite were also clustered differently from those containing only soy flour, indicating the significant impact of wollastonite. On the basis of the results of each property considered individually and altogether, it was concluded that panels containing 10% soy flour and 5% wollastonite are recommended to achieve the optimum decrease in carcinogenic formaldehyde emission, as well as the optimum physical and mechanical properties.