90.9 ± 12.7
1.4.1.8 Jute/OPEFB FRP Hybrid Composites
Oil palm (Elaeis guineensis) is a perennial crop known for its high‐value fruits from which oil is produced. It mostly grows in tropical regions, such as Southeast Asia and West/Southwest Africa. Oil is extracted by stripping the fruits (nuts) from the bunches, a process that leaves the empty‐fruit bunches (EFBs) as waste material [37]. Fibers of oil palm are usually derived from the oil palm empty‐fruit bunches (OPEFB) as well as mesocarp. In composite materials, the OPEFB fibers are mostly used, as they contain the highest hemicellulose content in comparison with pineapple, coir, banana, as well as soft and hardwood fibers [11].
A three‐ply hybrid sample of jute/OPEFB fibers composites with epoxy resin reinforcement was prepared by Jawaid et al. [38], fixing the jute/OPEFB ratio (by weight) at 1 : 4. They investigated the void content, chemical resistance, as well as tensile behaviors of the hybrid composites. From the results obtained, the OPEFB/jute/OPEFB and jute/OPEFB/jute composites showed great resistance to chemicals: toluene (C7H8), benzene (C6H6), water (H2O), 40% of nitric acid (HNO3), carbon tetrachloride (CCl4), hydrochloric acid (HCl), 5% of acetic acid (CH3COOH), 20% sodium carbonate (Na2CO3), 10% of sodium hydroxide (NaOH), and 10% of ammonium hydroxide (NH4OH). A lower void content was displayed in the jute/OPEFB/jute than pure OPEFB as well as OPEFB/jute/OPEFB composites, because the mats of the jute fiber adhered better to the epoxy resin with higher compatibility. At the outer ply, the jute fibers withstood the tensional stress due to their high strengths, and the core (OPEFB fiber) absorbed and distributed the stresses evenly within the composite sample systems. Also, it was evident from Table 1.7 that the jute/OPEFB hybrid exhibited higher tensile responses (both strength and modulus) as well as improved adhesion bond between the fiber and the matrix, when compared with pure OPEFB composite.
1.4.1.9 Kenaf/PALF FRP Hybrid Composites
A tropical plant, pineapple (Ananas comosus) belongs to the family of bromeliad (Bromeliaceae). In South America, it is next in line to banana and mango in total production across the globe [39]. Pineapple leaf fibers (PALFs) are waste products when cultivating pineapples and are extracted from pineapple leaves. It has a significant mechanical behavior, because it is high in cellulose (70–82%) as well as in crystallinity (44–60%) [40]. Combining these properties with that of Kenaf fiber, excellent tensile and flexural strengths from FRP composite are obtained, which promises a good material for different applications [4].
Aji et al. [41] studied hybridized Kenaf/PALF specimens with HDPE reinforcement, using 1 : 1 fiber ratio. They investigated into how the size of fiber and its loadings affected the mechanical responses of the hybrid biocomposites (Table 1.8). The four reinforcement lengths considered at a fiber loading range of 10–70% were 0.25, 0.50, 0.75, and 2.00 mm. The smallest of these fiber lengths (0.25 mm) yielded the best result in terms of its flexural and tensile properties, while both 0.75 and 2 mm exhibited enhancement in impact strength. As observed further, an increase in the fiber length reduced some of the mechanical behaviors, which is credited to the entanglement in fibers as against fiber attrition. An inverse proportionality was established between the tensile and impact properties, as the rule of mixture was satisfied by flexural strength. The adhesion between the fiber and the matrix interface was good, as evaluated by scanning electron microscopy (SEM).
Table 1.8 Mechanical behaviors of kenaf/PALF, roselle/sisal, and silk/sisal FRP hybrid composites.
Source: Nguyen et al. [4]. © 2017, Elsevier.
| Hybrid biocomposites | Fibre ratio (by weight or volume) | Flexural modulus (GPa) | Flexural strength (MPa) | Tensile modulus (GPa) | Tensile strength (MPa) | Impact strength (kJ/m2) |
|---|---|---|---|---|---|---|
| Kenaf/PALF | 1 : 1 (At 0.25 mm fiber length and 60% fiber loading) | 4.114 | 34.01 | 0.874 | 32.24 | 6.167 |
| 1 : 1 | ||||||
| Sisal/roselle | Dry condition, fiber length = 15 cm | — | 76.5 | — | 58.7 | 1.30 |
| Wet condition, fiber length = 15 cm | — | 62.9 | — | 44.9 | 1.28 | |
| Sisal/silk | 1 : 1, fiber length = 20 mm | |||||
| Untreated | — | 46.18 | — | 18.95 | — | |
| Alkali treatment | — | 54.74 | — | 23.61 | — | |