2.1 Natural Fibre

Natural fibre are fibres that are produced by plants, animals and geological processes. According to the researcher, the natural fibres 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 fibres are used as reinforcements in composites materials and these include steel fibres, glass fibres, synthetic fibres and natural fibres (Ede, 2014). Another researcher said that when compared with mineral wool, the insulation based on natural fibres has comparable and sometimes even better thermal technical characteristics for example heat capacity or the afore-mentioned thermal conductivity (Hroudova, 2011).
2.1.1 Rice Straw

Rice straw’s 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).
In this study, it is all began with the preparation of raw materials which are the process of extracting the rice straw fibre. The following step is preparation of rice straw board using hot-press machine. From the past study, a researched had given …………….
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 fibre can be transformed into a value-added fuel source which can be replace 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). Other than that, another researcher also proves that the coconut fibre can be sustainably adopted for enhancing the properties of concrete especially in the tropics where this fibre 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 fibres of jute are comes from the stem and ribbon (outer skin) and the fibres 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 fibres 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 fibres 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/polyester composites do not process strengths and moduli as high as those of conventional conposites, they, 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 fibre 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 sucrose content. After the extraction of sugar from the sugarcane, the residue of plant material is called as bagasse. Bagasse is compose 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)

Figure 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 fibres in kenaf are found in the bast (bark) and core (wood). According to the researcher, lignocellulosic fibres including kenaf can be potential raw material for the manufacture of medium density fibreboard (MDF) (Juliana et al., 2012). MDF is a fibre composite material comprised of refined wood fibres, 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. 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 remoulded or reheated after their initial heat-forming. Some researcher believed that the resin solution may penetrate and diffuse into fibres too easily, since the fibre in the blending process is wet and hot, which explain the greater resin consumption (Frashour, 1990).
2.2.1 Methylene Diphenyl Diiscyanate (MDI)

Figure 2.1: Structure of Polymeric MDI
(Source: Tury et al., 2003)
Methylene diphenyl diisocyanate (MDI) is used in the preparation of polyurethane resin and spendex fibres, and to bond rubber to rayon and nylon. 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). Other than that, 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 fibres 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 fibreboard. 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).
2.2.4 Phenol-Formaldehyde
Phenol-formaldehyde (PF) resin is also an alternative adhesive. It is very durable resin and has an irreversible cure reaction. Despite the higher cost and higher press temperatures, PF can be integrated into a fibreboard manufacturing plant by changing the temperatures to achieve the speed required (Conner, 2001).The petrochemical-based phenol-formaldehyde adhesive, have commonly used in the production of wood-based panels (Yang et al., 2009).
2.2.5 Polypropylene
Polypropylene (PP) is one of the thermoplastic binders which have been used a lot in making useful product. Anand (2008) said that due to the usage of thermoplastic PP, any excess material in the production cycle can be chipped and reused during the blending stage. These materials also have the advantage of being recyclable due to the use of PP.
2.3 Hot-Press Machine
Hot-press machine is a high pressure machine that used to consolidate and to cure the adhesive in the natural fibre board. Carvalho et al. (2003) said that hot-pressing process refers to a process where the raw board is under the combined function of temperature and pressure. The function of hot-pressing process is subjected to moisture evaporation, to increase the density of board, glue solidification and water proof agent distribution and the compositions in the raw materials which are subjected to a series of physical and chemical changes to form bonding force between the fibres and form the products confirming to quality requirements. In hot-pressing, the energy is directly delivered into the whole board and absorbed by the asymmetric molecules, and then the energy is transformed into heat. The basic principle of hot-pressing is the application of heat, which activates the chemical components of the raw material used. The raw material basically put inside the mould and then it placed inside the hot-pressing machine. The mould will be pressed depends on the parameters set up. According to the researcher, it is necessary to apply enough heat and pressure to melt lignin through the entire board, allowing good distribution of lignin between the fibres during the manufacturing process (Mancera et al., 2008; Zhou et al., 2010).
2.4 Effect towards Rice Straw Board using Hot-Press Machine
2.4.1 Thermal Insulation
The term of thermal insulation refers to the material that used to reduce the rate of heat transfer and the methods and processes used to reduce the amount of heat transfer. Besides, thermal insulation also means material capable of blocking the transmission of heat from on side to other side easily. In heat transfer, conduction is the transfer of thermal energy neighbouring molecules in a substance due to a temperature gradient. Besides, thermal insulation prevents the heat from escaping or entering the container. Panyakaew (2011) stated that the production of low density thermal insulation boards made from coconut husk and bagasse without the use of chemical binding activities. The results is both thermal insulation boards have thermal conductivity values ranging from 0.046 W/mK to 0.068 W/mK which were close to those of conventional insulation materials such as cellulose fibres and mineral wool. The successful use of straw bales as thermal insulation within the envelope of buildings has been demonstrated by the increasing number of successful contemporary projects around the world. (Thomson, 2014; Shea, 2013). These environment-friendly thermal insulation materials are excellent insulating components for building materials as wall or ceiling for energy conservation except for relative lower bonding strength and sensitive to moisture and humidity. Then comparison of thermal conductivity of the selected material and other materials that are stated in the literature is given in Table 2.1
Table 2.1
(kg/m³) Thermal Conductivity (W/mK) Source
Oil Palm Fibre 100 0.0567 Manohar. 2012a
Sugarcane 686 0.0461 Manohar, 2012a
Coconut husk with phenol formadehyde 510-540 0.1036 Khedari et al., 2003
Bagasse 90-100 0.0483 Manohar et al., 2006
Corn Cub 211 0.1390 Pinto et al., 2012
Oil palm frond 108-141 0.0340-0.0830 Sihabut, 2010
Rice hull 149 0.0449 Yarbough et al., 2005

2.4.2 Moisture Content
According to the researcher, most natural fibres absorb more moisture compared to synthetic fibre (Swamy, 2004). Moisture content affects the processibility, shelf-life, usability and quality of a product. Moisture content depends on the circumstances at the time of baling and during subsequent storage and transport. The impact of moisture content on thermal insulation conductivity varies with the type of insulation depending on the composition, properties and internal structure of the material used, which determine the modes of heat transfer and the moisture storage capacity of the material (Abdou, 2013). The composition of wood and straw of natural fibre are quite similar which is both of them consist largely of cellulose and inorganic content.
2.4.3 Board Density
Based on the previous research of (Wei et al, 2015), they found out that the higher the density of the rice straw thermal insulation board, the higher the thermal conductivity of the rice straw thermal insulation board. As the board density increases, the solid substances are increased and the voids in the board are decreased. The boards with the higher had the best mechanical and physical properties. Suleiman (1999) said that as the board density increases, the solid substances are increased and the voids are decreased. The thermal conductivity of a solid substance is much higher than the air within the voids which leads to a higher conductivity of the whole material.

(Source: Wei et al., 2015)
2.4.4 Particle Size
Particle size is an important factor affecting the thermal conductivity of a thermal insulation boards. The higher the amounts of fine particles with larger surface need more adhesive, which could decrease the resin distribution of unit area of the straw particles, thus reducing the mechanical properties of the boards (Li, 2010).
Yang et al. (2003) prepared the composite boards with rice straw without considering the size and wood particles with the specific gravities of 0.4 and 0.6 and found them suitable as a sound absorbing insulation in wooden constructions.
2.5 Mechanical and Physical Test
2.5.1 Tensile Test
Tensile test is a test to develop how something will react when it is pulled apart when a force is applied to it in tension. An experiment was carried out by Zhang et al. (2016) where there are three specimens for tensile test were cut from five bio-boards which named A, B, C, D and E. The specimens from every board made under different heating temperature. The result from the experiment were shown Figure. Based on the curve at Figure, the relationship of stress-elongation for every specimen from five different bio-boards was similar. The rupture stresses of tensile test were in the range of 3 MPa to 17.22 MPa.

Figure: The stress-deflection curve of 5 bio-boards
(Source: Zhang et al, 2016)
2.5.2 Hardness Test
Hardness test is a test to determine the resistance a material exhibits to permanent deformation by penetration of another harder material. This test is to evaluate a materials properties such as ductility and strength.
2.5.3 Thermal Conductivity Test
Thermal conductivity is defined as the rate of heat is transferred by conduction through a unit cross-section area of a material, when the temperature gradient exits perpendicular to the area. It is well known that board density is one of the important factors that affect mechanical properties of the board.
2.5.4 Young’s Modulus Test
Young’s modulus is defined as the measurement of the rate of change strain as a function of stress. Young’s modulus is also well-known as modulus of elasticity.