## 5 Mechanical Properties of the Natural Fibers Reinforced Epoxy Composites
### Flexural Behaviour  
The flexural strength of a material is its ability to withstand maximum tensile stress during bending without failure, or it can withstand bending forces perpendicular to its longitudinal axis. For the components subjected to bending, the flexural test is more appropriate, such as the beam in housing. The flexural modulus and strength of the composites can be increased with fiber loading and epoxy due to the fibers' higher flexural strength and modulus. Natural fibers such as past and leaf fibers have the best effectiveness among the lignocellulosic reinforcements. Kenaf and bast fiber-reinforced epoxy composites have greater strength than kenaf core fiber composites [104]. The effect of fiber length on flexural strength was investigated by [PERSON] et al. [92]. They reported that with an increase in fiber length, flexural strength increases. [PERSON] et al. [70] studied the effect of fiber loading and orientation. They found that as the fiber content increased, flexural strength increased. Whereas, when the fiber orientation increased from 0\({}^{\circ}\) to 30\({}^{\circ}\), the flexural strength decreased, but with a further increase (45\({}^{\circ}\)) in fiber orientation, the flexural strength increased. The 45\({}^{\circ}\) orientation was found to be optimum for all fiber loading. [PERSON] et al. [44] studied the effect of pine fiber loading and found that as the fiber loading increased beyond 10 wt.%, the flexural strength decreased due to the high cellulose content and the poor epoxy and pine fiber adherence. [PERSON] et al. [35] investigated the ramie fiber-reinforced epoxy composite fabricated using vacuum-assisted resin infusion moulding. They established that hot compaction significantly improves the mechanical strength of the composites with the same fiber content. [PERSON] et al. [115] indicated that the hybridization on the bilayer of oil palm empty fruit bunches and jute fiber-reinforced epoxy resin increased the tensile and flexural characteristics of the hybrid composites. [PERSON] et al. [116] investigated okra/kenaf and okra/banana-reinforced epoxy hybrid composites. Compared to okra fiber composites, the inter-lamina hybrid composites improved the composite's strength. [PERSON] et al. [117] investigated the effect of fiber loading in wood dust-reinforced epoxy composites on the tensile and flexural strength of composites. The composites with 10 wt.% fiber loading exhibited better mechanical characteristics (161% increase in tensile strength and a 200% increase in flexural strength). In another study using the  
Figure 2: Effect of the fiber loading (10–60 wt.%) and chemical treatment on impact strengths of abaca-reinforced epoxy composite [110]. Reprinted with permission. Copyright 2014 MNFR. Taguchi technique, [PERSON] et al. [118] found that the speed of the test affects load and tensile strength, while flexural characteristics are mostly influenced by fiber loading. This was because, during tensile testing, the load is applied along the length; hence, the fibers have less time to be oriented at a higher speed. While in the case of flexural testing, the load is applied along the thickness role [118]. [PERSON] et al. [41] studied the mechanical behaviour of bamboo fiber-reinforced epoxy composites concerning fiber content and length. They established that the composites' fracture toughness and flexural/bending modulus increased monotonically with fiber length and content. The hemp fiber has hemicelluloses, lignin, and cellululosic constituents, which need to be reduced for better flexural strength. Higher flexural properties can be achieved with bleached fiber than untreated fibers due to greater interfacial adhesion in bleached fiber composites [34]. [PERSON] et al. [87] examined the influence of surface modification with different alkali (NaOH) treatment concentrations (0.5-20%) on the banana-reinforced epoxy composite. The NaOH treatment converted cellulose-I to cellulose-II with lattice transformation.