# Lignocellulosic Composites from Acetylated Sunflower Stalks
## 3 Results and Discussion  
The thickness swell values (TS) after 24 h immersion in water are summarised in Table 1. The results revealed that acetylation improved the dimensional stability. The TS values for Acetylated boards 1 and 2 were about 62.5 and 240% lower, respectively, than those of the controls. In a previous study concerning oriented strand board (Oriented Strand Board) from acetylated strands with 11.2% weight gain, a 147% improvement in TS value was reported [39]. Table 1 also reveals that the equilibrium moisture content (EMC) was reduced due to acetylation. Figure 3 depicts the change in thickness at 30% and 90% relative humidity of the boards produced in this study. It is revealed that, at the end of the third cycle, control boards swelled over 27%, while the Acetylated 1 and 2 boards swelled approximately 14% and 6%, respectively. This is in good agreement with the reported results on acetylated OSB [39]. The IBS values are shown in Table 1. It is revealed that acetylation caused a significant decrease in IBS. The IBS values for the Acetylated 1 and 2 boards were about 13% and 39% lower than those for the controls. This reduction appears to be higher than values reported in the literature, since acetylation of strands to 20.4% weight gain previously resulted in a 30% decrease in IBS [39]. A similar observation was also made for chemically modified flakeboards and particleboards [40; 41]. This seems to be attributed to the raw material used, since acetylation resulted in poor wetting of the raw material. Failure in control boards was observed in the raw material. On the other hand, in modified boards, failure was mainly due to the resin. When the data were examined in the light of industry standards, we noted that control boards met the requirements of P1 general purpose boards for use in dry conditions and P2 boards for interior fitment for use in dry conditions. Acetylated 1 boards, on the other hand, did not meet the requirements of P2 criteria. Acetylated 2 boards conformed to the more stringent P3 Non-Load-Bearing--Humid and P4 Load Bearing--Dry criteria as far as the thickness swell value is concerned, since values lower than 17% and 16%, respectively, were achieved. However, the IBS value for Acetylated \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Board Type**} & **TS (\%)** & **EMC (\%) at RH** & **IBS (N-mm\({}^{-2}\))** & **Density** \\ \cline{2-6}  & **24 h** & **30\%** & **90\%** & & **(g-cm\({}^{-3}\))** \\ \hline Control & 41.6 (3.1) & 5.2 (1.2) & 23.4 (1.7) & 0.43 (0.03) & 0.658 (0.03) \\ Acetylated 1 & 25.6 (2.2) & 3.8 (0.8) & 16.8 (1.2) & 0.38 (0.02) & 0.662 (0.04) \\ Acetylated 2 & 12.2 (0.8) & 2.7 (0.9) & 11.8 (0.9) & 0.31 (0.03) & 0.648 (0.05) \\ EN 312 (P1 General Purpose) & N/A & & & 0.28 & \\ EN 312 (P2 Interior Fitments—Dry) & N/A & & & 0.40 & \\ EN 312 (P3 Non-Load-Bearing—Humid) & 17 & & & 0.45 & \\ EN 312 (P4 Load Bearing—Dry) & 16 & & & 0.40 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical and mechanical properties for control and acetylated particleboards. Standard deviations in parentheses. boards 2 was far below the standards and did not meet the more stringent requirements of P3 Non-Load-Bearing--Humid and P4 Load Bearing--Dry. An option to improve the IBS value is to increase the amount of resin; however, this will increase the production cost. It is concluded, therefore, that sunflower stalks could be an alternative raw material for use in the particleboard industry since the requirements of P1 general purpose boards for use in dry conditions and P2 boards for interior fitment for use in dry conditions are easily satisfied. Acetylation of sunflower stalks greatly improves the TS value but adversely affects the IBS. It is suggested that combinations of industrial wood chips with sunflower raw material may be an avenue for the overall improvement of the performance of the particleboards. Methodology, A.N.P. and G.Z.K. ; Validation, A.N.P. and G.Z.K. ; Investigation, A.N.P. ; Writing-Original Draft Preparation, A.N.P., G.Z.K.