Alkaline treatment is widely being promoted to treat natural fibres and improves the fibre bundle surface for better interlocking with the polymer matrix. The aim of this study is to optimize the merceration parameter including natrium hydroxide (NaOH) concentration, soaking and drying time for Bambusa Vulgaris bamboo using response surface methodology (RSM). Here, the treatment conditions were employed by the Box-Behnken design (BBD). The comparative study of the treated and untreated fibre on crack propagation behaviour, Mode I interlaminar fracture toughness (GIC) of the bamboo along the longitudinal direction test was carried out. Through the statistical analysis approach (ANOVA), it is suggested that bamboo treated with 1.5 wt.% concentration of NaOH is capable to reach the fracture toughness value up to 367.25 J/m2. It is also shown that all proposed variables for treatment in this study (i.e., the concentration of the NaOH is highly significant with the 2.85 hours of soaking and drying for 72.5 hours).
TopIntroduction
Normally, fiber reinforced polymer materials are laminate composites consisting of high strength of synthetic fibers (i.e. glass, carbon and kevlar) reinforcement in polymeric matrices. The reinforcement by those fibers provides the polymer substantially enhanced mechanical properties and makes the fiber reinforced polymer composites suitable for a large number of diverse applications. Although this synthetic fiber reinforced polymer possess exclusive mechanical strength, they have also got some serious drawbacks such as high cost, poor recycling and non-biodegradable properties.
For these reasons, natural plant fibers reinforced polymer composites are increasingly gaining attention as viable alternative to replace the synthetic fiber reinforced polymer counterpart. These renewable fiber closely high specific strength to weight ratio and offering less abrasion as compared to glass fibers. Many researcher has studied the mechanical properties of these natural fibers such as bamboo, kenaf and jute (Chen et al., 2017; Bakhori et al., 2017; Bakhori, Zuikafly, Ahmad, & Hassan, 2017). Interestingly, fiber derived from bamboos have attracted more interests due to their offering higher performance and plenty sources for production (Yu, Jiang, Fei, Wang, & Wang, 2011).
In addition, an extensively study have been conducted on chemical treatment for natural fiber. This treatment is being suggested in order to decrease the incompatibility between natural fibre and polymer matrix due to hydrophilic and hydrophobic interaction. The common alkaline treatment (NaOH) on natural fibre has been considered as one of most popular and cost affective methods. The effect of chemical treatments of the bamboo fiber is reported by Yang et al. (2017). They immersed the bamboo fibers in a NaOH solution of 5, 10 and 25% concentration for further removing hemicellulose and heated at 75 °C for 2 h in a water bath. It is found that a higher concentration of NaOH degrades the long chain cellulose molecules at the fiber interface and consequently, weakens fiber load transfer. Reddy and Dhoria (2018) examined the effect of NaOH concentrations of 5% (w/t) on kenaf fibre reinforced composites. Mechanical testings including tensile, flexural and impact are obtained to determine tensile strength, bending and impact strength of the composites. It is found that the chemically treated fiber composites offer good mechanical properties compared to untreated fibers. Similarly, Mishra et al. (2003) reported that sisal fibre treated with 5% concentration of NaOH exhibited good tensile properties than those treated with 10% of alkaline concentration. They suggested that the excessive alkali concentration would cause delignification and weaken the sisal fibre. On the other hand, a comprehensive characterization of wettability and interfacial properties of kenaf fibers polyester composites fabricated by resin transfer molding is reported by Ariawan et al. (2017). Here, kenaf fibers are chemically modified by immersing in 6% NaOH concentration for 1 to 5 h to enhance the interaction between fiber and matrices. In order to investigate the effect of soaking time, surface energy and the interlaminar shear strength value of the composites are evaluated. They reported that 3 h treated of kenaf fiber composite enhanced the interface bonding characteristic of the composite laminate. Furthermore, the effect of alkali treatment under various conditions on physical properties of kenaf fiber is investigated by Khan et al. (Khan, Yousif, & Islam, 2017). In this study, kenaf fiber were treated at alkali concentrations 2, 6 and 10 (w/v%), immersion durations at 30, 240 and 480 minute and temperatures at 27, 60 and 100o C. Kenaf fiber weight loss and density value are decreased after alkali treatment compared to untreated kenaf fiber. Furthermore, Rao et al. (2010) reported that 1% concentration of NaOH is the optimum condition to treat bamboo polymeric composite. On the other hand, few studies claimed that a higher NaOH concentration is the best in treating natural fibre (Yan, Chouw, Huang, & Kasal, 2016) and capable of removing excess moisture thoroughly. In spite of that, the NaOH concentration is the most dominant factor that gives effect on the natural fibre and still remain inconsistency.