CHAPTER 2
LITERATURE REVIEW
2.1 Natural Fiber
Natural fiber are fibers that are produced by plants, animals and geological processes. Table 2.1 shows the type of reinforcing natural fiber which are classified into two categories. According to the researcher, the natural fibers are the renewable sources that can be disposed at the end of its useful life (Dos Santos, 2009). This characteristic is called as biodegradable and it is an important characteristic that should have in a competent. High-strength fibers are used as reinforcements in composites materials and these include steel fibers, glass fibers, synthetic fibers and natural fibers (Ede, 2014). Another researcher said that when compared with mineral wool, the insulation based on natural fibers has comparable and sometimes even better thermal technical characteristics for example heat capacity or the afore-mentioned thermal conductivity (Hroudova, 2011).
Figure 2.1: Categories of natural fibre
(Source: Ni, 1995)
2.1.1 Rice Straw
Rice straws scientific name is Oryza sativa L is the vegetative part of the rice plant. According to the researcher, the rice straw may be burned and left on the field before the next ploughing, ploughed down as a soil improver or used as a feed for livestock (Kadam et al., 2000). Rice straw can be treated in order to improve its nutritive value. Those treatment are designed to improve the feed intake and digestibility. This improvement may be achieved by mechanical, chemical, heat and pressure treatments. In mechanical treatments, chopping and grinding the rice straw may reduce the time passage in the rumen and to improve feed intake (Doyle et al., 1986). Buzarovska et al. (2008) stated that among the various agricultural straws, rice straw could be very interesting materials as filler in polymer composites due to its thermal stability compared to the other agricultural waste. Besides, rice straw particles has a very high porosity value inside rice straw and between particles, which has a dominant influence on thermal and moisture behaviour of the thermal insulating material (Kangcheng, 2015). Rice straw could be used as a biodegradable eco-friendly reinforcement at end-of-use in polypropylene composites, to minimize environmental pollution rather than to perform a strong reinforcing effect. (Grozdanov, 2006).
2.1.2 Coconut Husk
Coconut husks are usually being wasted after the coconut fruit being extracted. It has a high amount of lignin and cellulose. The chemical composition of coconut husk consists of cellulose, lignin, pyroligeous acid, gas, charcoal, tar, tannin and potassium. These natural fiber can be transformed into a value-added fuel source which can be replaced wood and other traditional fuel sources. Furthermore, the coconut husk could be a good thermal conductivity and need no chemical binder to manufacture. However, if it is tending to be applied in building sector, it should be protected from moisture due to its high moisture content and water absorption (Panyakaew et al., 2008). Another researcher also proves that the coconut fiber can be sustainably adopted for enhancing the properties of concrete especially in the tropics where this fiber abound and are not economically being put to use in the spirit of waste to wealth (Anthony et al., 2015).
2.1.3 Jute
Jute is widely grown in India and Bangladesh. It took only two to three months to growth and then already to be harvested. The length of jute at that maturity growth is already at three to five meters. The jute is one of the most affordable natural fibre and it is renewable resources. The fibers of jute are comes from the stem and ribbon (outer skin) and the fibers are extracted by retting process. The retting process consists of bundling jute stems together and immersing them in slow running water. After the retting process, stripping process are done which is non-fibrous matter in the jute is scraped off. The fibers of jute are get from the dig and grab process within the jute stem.
Korjenic et al. (2011) developed a new organic thermo insulating material from renewable resources which are jute, flax and hemp and used bicomponent fibers as a binders with comparable building physics and mechanical properties to convectional insulation materials. Deepak (2015) also concluded that although the mechanical properties of jute or polyester composites do not process strengths and moduli as high as those of conventional composites but it do have better strengths than wood composites and some plastics.
2.1.4 Bagasse
Bagasse is the fibrous matter that remains after sugarcane stalks are crushed to extract their juice. Besides, bagasse also well-known as a residue product from sugar making. It is dry pulpy residue left after the extraction of juice from sugar cane. According to the data of the Food and Agriculture Organization of United Nations, the amount of sugarcane produced in the world in 2010 was approximately 1711 trillion tons. In Malaysia, the extraction of juice in sugarcane are quite popular among the Malaysians. Instead of being wasted and waiting to be disposed, these bagasse can be processed by extracting the fiber which can be used to produce a valuable product such as particle board and fibreboard. Transforming bagasse into high-quality panel products provides a prospective solution. Saha (2003) stated that sugarcane fibre is a plant that is harvested for its surcose content. After the extraction of sugar from the sugarcane, the residue of plant material is called as bagasse. Bagasse is composed about of 40% cellulose, 24% hemicellulose and 25% lignin.
2.1.5 Sunflower
Sunflower or its scientific name helianthus annus L is one of the most important industrial plant in Turkey and main cultivated for oil production. Apart from that, the waste product of sunflower are consumed for animal feed fertilizer or heat production. 700 hectares field has being utilized for sunflower farming in Turkey generating roughly 3-3.5 million tons of waste sunflower stalks every year (Bektas, 2005)
Bark Pitch
Density (kg/m?) 350 29
Cellulose percentage (%) 48 31.5
Lignin percentage (%) 14 2.5
Porosity (%) 53 56
Diffusion coefficient (?10?^(-5)mm?/s) 1.4 110
Youngs Modulus (GPa) 6.4 1??10?^(-3)
Strength (MPa) 31 2.3??10?^(-3)
Heat Capacity (J/kg.K) 1400 1300
Thermal Conductivity (W/mK) 0.12 0.039
Bark Pitch
Density (kg/m?) 350 29
Cellulose percentage (%) 48 31.5
Lignin percentage (%) 14 2.5
Porosity (%) 59 63
Diffusion coefficient (?10?^(-5)mm?/s) 3.8 200
Youngs Modulus (GPa) 4.6 0.15??10?^(-3)
Strength (MPa) 25 3.3??10?^(-3)
Heat Capacity (J/kg.K) 1400 1300
Thermal Conductivity (W/mK) 0.12 0.039
Figure 2.2: Main physical and chemical properties of sunflower stems
(Source: Jean-Denis, 2015)
2.1.6 Kenaf
Kenaf (hibiscus cannabinus L) is an herbaceous annual plant of the family Malvacae that can be grown under a wide range of weather conditions. Kenaf is able to reach a height of three to five meters within three to five months and supplies between 12 and 25 t/ha of biomass annually when is planted under warm and wet conditions (Paridah et al., 2011). The fibers in kenaf are found in the bast (bark) and core (wood). According to the researcher, lignocellulosic fibers including kenaf can be potential raw material for the manufacture of medium density fibreboard (MDF) (Juliana et al., 2012). MDF is a fiber composite material comprised of refined wood fibers, adhesive (resin), process additives and a minor amount of wax.
2.2 Binder
Binder is a material or substance that used as reinforced material which holds materials together and sometimes could be a filler in between them. Binder also known as a resin or matrix. The binder acts as a glue which provide adhesion or coating in the making of natural fibre board. ). Kamke et al. (1996) believes that a uniform distribution of small resin spots will produce particleboard with the best properties for a given resin content. There are two types of synthetic binder which are thermoset and thermoplastic. Thermoset is defined as a synthetic materials that strengthen during being heated but cannot be successfully remolded or reheated after their initial heat-forming. The example of thermoset resin is amino resin, epoxy resin, polyurethanes resin. Meanwhile thermoplastic is defined as a material that softens when heated and hardens again when cooled. The example of thermoplastic resin is polyethylene resin, polypropylene resin and polycarbonates resin. Some researcher believed that the resin solution may penetrate and diffuse into fibres too easily, since the fiber in the blending process is wet and hot, which explain the greater resin consumption (Frashour, 1990). Roger et al. (1993) conclude that composite materials are classified as natural synthetic and inorganic matrix composite as shown in Figure 2.3 below.
Figure 2.3: Types of binding materials
(Source; Roger et al., 1993)
2.2.1 Methylene Diphenyl Diiscyanate (MDI)
Figure 2.4: Structure of Polymeric MDI
(Source: Tury et al., 2003)
Methylene diphenyl diisocyanate (MDI) is used in the preparation of polyurethane resin and spendex fibers, and to bond rubber to rayon and nylon. Figure 2.4 shows the structure of MDI found by Tury et al. (2003). Grigorious (1998) stated that the straw was suitable for the production of good quality surface layers for particleboard if bonded with polymeric diphenylmethane diisocyanate (pMDI) resin or combination of urea-form-aldehyde (UF) and polymeric diphenylmenthane diisocyanate (pMDI). Rowell et al. (1981) also seek out that MDI binders are unique and react with both the moisture in the material, and the hydroxyl groups, which make up the lignocellulosic furnish. Thitiwan et al. (2012) carries out an experiment which the result indicated that the thermal insulation from narrow-leaved cattail fibers which bonded by MDI during hot-pressing have a good physical, mechanical and thermal properties.
2.2.2 Epoxy
Epoxy is the thermosetting matrix or resin materials, having at least one or more epoxide groups in the molecule. The epoxide also formed as oxirane or ethoxyline group and is regarded as representative unit of epoxy polymer (Yu, 2009). The advantage and limitations of epoxy resins can be present by the chemical structure of the resin and hardener as well as by the network achieved after curing (Alamri et. al, 2012).
2.2.3 Urea-Formaldehyde
Urea-formaldehyde (UF) resins are formed by the reaction of urea and formaldehyde. UF is the one of most important type of adhesive resins which is a polymeric condensation product of formaldehyde with urea, and being widely used to manufacture wood-based composite panels such as plywood, particleboard and fiberboard. In other words, the wood panel industry is a major consumer of UF resin adhesive. The use of UF as a major adhesive by the forest products industry due to a number of advantages. The advantage of UF is low cost, lost cure temperatures, water solubility, resistance to microorganisms and to abrasion, hardness, excellent thermal properties and lack of colour especially of the cured resin. The disadvantages of UF is the lack of resistance to moist conditions especially in combination with heat. So, UF resins are usually used for the manufacture of products intended for interior use only. Boquillon et al. (2004) found that the properties of wheat straw particleboards using UF resins were poor, especially for internal bonding (IB) strength and the thickness swelling (TS).
