3. 1. Chemical compositions and morphological characterization of fibers
Chemical compositions of natural fibers are different due to the methods of cultivation and environmental conditions such as soil water, air and chemicals used.
Table 2 shows the chemical compositions of coconut coir fiber and oil palm fiber before and after pretreatment. Pretreatment of the fibers by washing with tap water until having a pH of 7.
boiled in boiling water for 2 h and oven dried, resulting in improving the chemical properties of both types of fibers I4]. It was found that the ash content, alco hol-benzene solubili 1x NaoH solubility decreased by the reduction of the amount of impurities such as ash, resulting in a more stable, stronger and lighter fiber 128l. Lignin starts to softe and dissolve at temperature over 70 °C, and acts as a binding agent for cellulose fibers132]. The pretreated(washed and boiled) fibers have higher lignin, holocellulose and alpha-cellulose contents than the unpretreated fibers. Thus, pretreated fibers are stiffer and tougher. However, the percentage increase of lignin content in pre- treated fibers are lower than that of holocellulose and alpha-cellulose due to the fact that cellulose is insoluble and more durable than other components 19]. In addition, cellulose is an important factor for heat insulation and sound absorption proper- ties of fiber cement materials Morphological and structural changes of the fibers were investigated using scanning electron microscopy(SEM), SEM is an important tool for observing the surface morphology of 2 shows SEM micro- unpretreated and pretreated fiber graphs of coconut coir fiber and oil palm fiber before and after pretreatment. The surface morphology of unpretreated fibers were different to those of pretreated fibers in terms of rough ness, smoothness and cavity. The surfaces of the unpretreated fibers were not smooth, spread with nodes and irregular stripes, which is covered with substances and other impurities. A com parison between coconut coir fiber and oil palm fiber showed that coconut coir fiber has a smoother and more uniform surface due to the lower amount of impurities such as as content Pretrea ment removal of low molecular pounds. resulting in a formation of slightly rough surface and I. Consequently, the washed increasing amount of voids l and boiled fiber has an increment of surface area, lower density and greater moisture absorption