**7.1 Static bending strength of composite board from compressed oil palm fronds**

According to Erwinsyah [35], the static bending strength refers to the tests performed. Bending stress is applied to the specimen to determine the stiffness or MOE of the samples and the amount of force required to cause the sample to fail expressed as the MOR. Erwinsyah also postulated that the bending strength of wood is commonly expressed in MOR and is the most vital parameters that is occasionally used for engineering purposes [61].

The summary result in the static bending, which included the MOE and MOR strength, can be referred to **Tables 4** and **5**. Composite boards made from the bottom portion of the fronds possess the highest value for MOE and MOR strengths. The intermediate and young maturity groups follow this. The strength values of the boards both from phenol and urea-formaldehyde resin decreases from the bottom to top portions for every maturity group and from the old to young maturity groups for each portion, respectively. The MOE values of the maturity group from the bottom, middle, and top portions for the phenol-formaldehyde composite board were at 999.61, 952.29, and 844.18 N/mm2, respectively. The MOE for the ureaformaldehyde composite board at 980.31, 949.40, and 840.40 N/mm<sup>2</sup> . The MOE


#### **Table 4.**

*MOE static bending strength of the composite board.*


#### **Table 5.**

*Mean value for MOR static bending strength of the composite board.*

#### *Processing and Properties of Oil Palm Fronds Composite Boards from* Elaeis guineensis *DOI: http://dx.doi.org/10.5772/intechopen.98222*

strength decreases from bottom to top portion for the maturity group either for phenol or urea-formaldehyde composite board, and the same situation was done for the other two maturity groups, the intermediate and young maturity groups.

Based on the results obtained from the study of the effect of resin types in static bending, it was found that the composite board from phenol-formaldehyde resin possessed a high value of both MOE and MOR test than urea-formaldehyde resin. The latter contained a high amount of solid content compared to phenolformaldehyde resin.

The MOE strength of boards made from the bottom portion from the matured, intermediate, and young maturity groups of the phenol-formaldehyde composite board was 999.61, 979.15, and 935.36 N/mm2, respectively. The MOE strength of the urea-formaldehyde composite board was at 980.31, 953.93, and 936.24 N/mm<sup>2</sup> from the matured, intermediate, and young maturity groups. The MOE strength decreases from the matured to young maturity groups for the bottom portion for both resin types of the composite boards. The MOE strength when the specimen reached the breaking point and then could not recover its shape, where the load achieves its maximum value, is called MOR. This strength property is one of the significant parameters which usually used for engineering purposes. Relating to the resulting test of MOR of the composite board from compressed oil palm fronds at the different maturity groups, portions, and resin types, the summarised data of mean values is presented in **Table 5**.

The MOR of the compressed oil palm fronds composite boards increases in strength from the top to the bottom portions for the maturity group and from young to matured fronds for every portion. The MOR strength for the maturity group was at 16.66, 12.55, and 11.72 N/mm2, respectively for the top, middle, and bottom portions for phenol-formaldehyde resin, while the MOR for the ureaformaldehyde were at 11.63, 12.38, and 15.40 N/mm<sup>2</sup> . Similar trends were observed in the intermediate and young maturity groups from the bottom towards the top portions. The results in **Table 5** showed that the bottom portion for each maturity group (matures, intermediate, and young) and the portions grouping from the phenol-formaldehyde composite boards were at 16.66, 14.38, and 12.16 N/mm<sup>2</sup> and, the MOR for urea-formaldehyde composite boards at 15.40, 12.62 and 12.25 N/mm<sup>2</sup> respectively. The strengths decrease from the matured towards the bottom portion for both resin types used in the maturity groups. Similar trends were noted in the MOE values. The MOR decreases from bottom to top portions for each maturity group and from old towards young maturity groups for every portion.

The values of both the MOE and MOR for the oil palm frond compressed composite boards increases from the top to the bottom portions. Similar observations were noted in the frond maturity groups from young, intermediate, and matured groups. These occurred to both of the composite boards made from phenol and urea-formaldehyde resin. The decreases can explain the trend of variations in the MOE and MOR values and the tree height in the maturity of wood and fibre length from top to the bottom of the tree [62]. This is logically accepted due to vascular bundles that decrease from the bottom to top portions along with the oil palm fronds and the old to young maturity groups. A large amount of the vascular bundle in the oil palm fronds containing a higher quantity of fibre cells gives higher density and basic density values in both the composites. According to Haygreen and Bowyer [57], the woody materials with higher values density and basic density will directly possess higher strength. The bottom portion has a higher value for both MOE and MOR strengths compared to the middle and top portions for the maturity group in every portion [57]. Based on the results obtained from the study of the effect of resin types in static bending, it was found that the composite panel from phenol-formaldehyde resin possessed a high value of both MOE and MOR test than urea-formaldehyde resin. By the latter contained a high amount of solid content compared to phenol-formaldehyde resin [63].

The static bending was significantly affected by the density and basic density value [63]. This thus gives effect to the MOE and MOR strengths of the composite boards from top to bottom portions. The ANOVA in **Table 7** supports this statement. The result also showed that the composite boards from phenol-formaldehyde resin possessed a higher value of both MOE and MOR test than urea ureaformaldehyde resin, which contained a higher amount of solid content compared to phenol-formaldehyde resin.

Furthermore, the distribution of phenol-formaldehyde resin is located irregularly in the composite boards'structures [40]. When the stress was applied, the stress could not be transferred consistently between the fibre and matrix. Besides, the penetration of high viscosity of urea-formaldehyde resin probably breaks the cell wall of the composite board from compressed oil palm fronds [40].
