Chapter 2: Literature Review
2.1: Bamboo
Bamboo has gained lots of attention from the scientists and researchers because bamboo has a lot of potential for structural applications. Bamboo can be used as an alternative raw material for the composite boards, oriented strand board, and particle board. The reason that bamboo can be used as a building material is due to their properties. Bamboo has a high compressive strength, high tensile strength, low weight, short rotation cycle, medium to high density and has high resistance to interlaminar shear stress. Another important reason that bamboo has high potential to replace the current structural material is because bamboo grows in abundance in many parts of the world, especially in tropical and subtropical regions. The best merit of using bamboo is because even the usage of bamboo increases dramatically, this increasing trend will not pose a risk for bamboo forest as bamboo grows very fast. Bamboo is one of the fastest-growing plants on Earth because of distinctive rhizome-dependent system and this has been proven by referring to a report. The growth rates of bamboo are so fast that the reported growth rates are 100cm in 24 hours. Although the growth rates are still depending on the local soil or environments, the species of bamboo and the growing period. Bamboo has a higher advantage when it is compared to the trees as bamboo has a faster growth rate. Therefore, they are considered as easily renewable natural resources. As mention above, the increasing of usage of bamboo will not pose a risk but increasing the usage of trees does possess risks as the decreasing quantity and deteriorating quality of forest resources. Thus, the global interest in bamboo utilization has considerably increased.
Figure : Bamboo waste
Bamboo is a tribe of flowering perennial evergreen plants in grass family. Giant bamboos are the largest members of the grass family. It is mainly composed of cellulose and lignin, about 70% and 20% respectively. The anatomical structure of the bamboo in the bamboo culm is a transverse section is characterized by numerous vascular bundles. The inner and middle layer of the bamboo is much denser than the outer layer. Bamboos has a common fibre length that is around 1.6-3.1mm but the older bamboo will have more shorter fibre compare to the younger bamboo.
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There are several reasons that bamboo has high potential to replace certain material as the structural building material. Firstly, bamboo has a considerably heterogeneous structure. The tissue is primarily composed of vascular bundles and parenchyma. The structure looks alike with fibre-reinforced composite, with the vascular bundles (composed of fibres and conducting cells) and parenchyma acting analogous to fibre and matrix respectively. The volume fractions of vascular bundles and their associated fibres increase sharply radially, going from the inside to the outside of the culm wall. This heterogeneity and the resulting density gradient are important to consider in manufacturing and modelling of structural bamboo products. For instance, the heterogeneous tissue of bamboo can lead to significant strand roughness, if they are not sliced cleanly, this could impact the bonding and performance of a bamboo product.
2.1.1 Properties of Bamboo
Renewability
Unlike the woods, bamboos grow at a faster rate because they are considered as grass. Their stems are ready for harvest within 5 years.
Sustainability
The new shoots will continue develop from the root system after the mother plant harvested.
Evenly distributed stresses
In bamboo, the stresses can be distributed evenly throughout its length because there are no rays or knots.
Coherent appearance
Since the bamboo does not has any rays or knots, naturally the appearance of the bamboo is smooth and coherent.
Edibility
The young bamboo shoots have been food supply for a few decades and there is no need to worry about the material safety when used as kitchenware.
Mechanical properties
Bamboo has high tensile strength, high compressive strength, light weight, and resist to interlaminar shear stress.
2.1.2 Applications of Bamboo in construction or building purpose
Bamboo has a wide application in construction or building field. Examples, bamboos are used for housing especially in the wake of residential shortages around the globe. Bamboo are also used to hold up suspension bridges in many nations. In United State of America, the bamboos are used as floor foundation because of their excellent properties. The bamboos are built in several shapes such as flattened, mambo mats which is as thin as 5-6mm or as a composite. Bamboo is also used for walls construction and roofing purpose by positioning the bamboo fibre or tube directions to withstand forces.
2.1.3 Pros and Cons of bamboo
Advantages Disadvantages
High tensile strength (if fibres run axially, bamboo has a higher tensile strength compare to steel) Bamboo require preservation because bamboo can easily get attacked by fungi
Fire resistance (able to withstand temperature up to 4000? due to presence of high value of silicate acid and water) Shrinkage (shrinkage will occur if the bamboo loses big amount of water)
Elasticity (bamboo is preferred in earthquake prone regions) Durability (Bamboo need to be treated to resist the threat from insects or fungus attack)
Posses no danger to health (non-toxic) Jointing (Despite prevalence of various techniques of jointing, structural reliability of bamboo is questionable)
Less cost and easy to use
2.2 Wood composition boards
Flakeboard is a term that also includes waferboard (WB) and oriented strand board (OSB). The main concern in this project is oriented strand board (OSB). OSB is a performance rated structural wood-based panel engineered for uniformly, strength, versatility and workability. OSB is utilized internationally in a wide array of applications including residential and commercial construction and renovation, packaging/crafting, furniture and shelving. Since OSB is engineered, it can be custom manufactured to meet specific requirements in thickness, density, panel size, surface texture, strength and rigidity. This engineering process makes OSB the most widely accepted and preferred structural panel among architects, specifiers and contractors.
2.2.1 Oriented Strand Board (OSB)
OSB is the culminating product in the development of structural particleboards. It is a three-layered flakeboard panel crossbanded by a core of oriented flakes at a right angle to the orientations of the face and back layers of flakes (Federation, 2016). Due to these oriented flakes, OSB is consider to be strong and stiff structural panel. OSB became a leading commercial competitor for structural sheathing markets in the 1980s, and correspondingly a major contributor to improved forest management practices (John I. Zerbe, Zhiyong Cai, George B. Harpole , 2015). OSB is an engineered wood panel that shares many of the strength and performance characteristics of plywood. Generally, OSB is a combination of wood and adhesive to create a strong, dimensionally stable panel that resists deflection, delamination and warping; likewise, panels resist racking and shape distortion when subjected to demanding wind and seismic conditions. Relative to the OSB’s strength, OSB panels are light in weight and easy to handle and install. (APA, 2018). OSB uses the wood resources very efficiently in parts because sheathing panels can be made using smaller, younger fast-growing tree species such as aspen and southern yellow pine. Additionally, there are about 85-90% of a log can be used to make high quality structural panels.
Scientist and researches have spent nearly three decades of laboratory test and the use in field of the OSB and OSB has been proven is an excellent performer. The panels remain flat and square during storage and transportation, so they arrive at the jobsite flat and easy to install; tongue-and-groove panels effortlessly fit together. Relative to their strength, OSB panels are light in weight and easy to handle and install. Frequently, the panels are textured or splatter-coated on one side to increase traction on the panel surface.
There are three basic criteria for qualifying OSB products under the performance standards such as structural adequacy, dimensional stability and bond durability. Performance criteria in each of these categories were established by building code requirements and through tests of panel products with known acceptance in the marketplace. These tests assure that panels possess the structural requirements necessary for uniform load, concentrated load, shear wall, diaphragm, and other demanding end-use applications.
2.2.1.1 Appearance of OSB
OSB is a readily to be identified because of its unique large and long wood strands. The orientation of the surface strands is not always visually apparent, especially those in smaller cut pieces. The best merit of the OSB is mechanical performance and this is directly related to the geometry of the strands and their orientation throughout the whole panel. Although OSB is made up of relatively large amount of wood flakes, its surface is still smooth because of additional work and this can be further improved by sanding without losing the aesthetic character which is unique to OSB.
Figure :wood fibre in an oriented direction
2.2.1.2 Types of adhesive used in OSB
There are four types of OSB such as OSB/1, OSB/2, OSB/3 and OSB/4. OSB makes efficient use of wood chips and this will rise the concern about adhesive so also known as glue. Commercial OSB normally use urea-formaldehyde or phenol-formaldehyde (UF or PF) as the adhesive. These types of adhesive have been reported to emanate formaldehyde gas, and formaldehyde has carcinogenic effect which will cause serious health hazards to human health. The following is a general description about OSB/1 to OSB/4.
OSB/1 – OSB/1 is a general-purpose building panel designed for dry areas, such as building interiors. This type of OSB cannot withstand a load or weight because they are considered as non-structural panel. The applications for this type of OSB are furniture or shipping crates. The adhesive for this category of OSB is Urea Formaldehyde (UF glue). As mention above, UF will release the formaldehyde gasses especially when the material become wet. The droplets or the water will start to dissolve UF and this will trigger the emission process.
OSB/2 – Unlike the OSB/1, OSB/2 is consider as structural panel that means OSB/2 are able to withstand load or weight. The applications for this type of OSB are flooring, building panels and crafting. This kind of OSB is also design to be used in dry condition only just like the OSB/1. The adhesives for OSB/2 are Isocyanate, Melamine-Urea-Formaldehyde (MUF) and Phenol Formaldehyde (PF). MUF adhesive is very dangerous once the OSB get interact with water as they will emit poisonous gasses and cause health hazards to human.
OSB/3 – OSB/3 is quite similar to OSB/2 but there is a main difference between them. OSB/3 is able to be used in damp or humid conditions. The main adhesive for OSB/3 is PF. Since PF is fully waterproof, so the formaldehyde will not dissolve in water and emit poisonous gas. However, it is not recommended for the OSB to expose to the water all the time as the wood itself is not waterproof. The wood will eventually swell if the wood always expose to water for a very long period. The applications for OSB/3 are roofing, or wall.
OSB/4 – OSB/4 is just an upgrade version of OSB/4 and OSB/4 is said to be a heavy-duty version of OSB/3. This means that OSB/4 is able to bear a higher load or weight compare to OSB/3.
2.3 Coconut Fibre
Coconut fibre is extracted from the outer shell of a coconut. The common name, scientific name and plant family of the coconut fibre is coir (MajidAli, 2009). Coconut fibres has one of the highest concentrations of lignin. This makes the coconut fibres stronger but less flexible and unsuitable for dyeing. Coconut fibre has good resistance to microbial action and salt water damage. A coarse and short fibre can be extracted from the outer shell of coconuts (discovernaturalfibres, 2009).
Figure : Coconut fibre, also known as coir
Generally, there are two major types of coconut fibres such as brown fibre and white fibres. The brown fibres can be extracted from matured coconuts while the white fibres can be extracted from the immature coconuts. The brown fibres have better mechanical properties because it has higher strength, thick and high abrasion resistance. On the other hand, the white fibres are smoother, finer and weaker in strength. There are three types of commercial coconut fibres such as bristle (long fibres), mattress (relatively short) and decorticated (mixed fibres). These different types of fibres have different uses depending upon the requirement. For engineering purpose applications, the favour fibre is brown fibre.
According to official website of International Year for Natural Fibres 2009, approximately, 500 000 tonnes of coconut fibres are produced annually worldwide, mainly in India and Sri Lanka. Its total value is estimated at $100 million. India and Sri Lanka are also the main exporters, followed by Thailand, Vietnam, the Philippines and Indonesia. Around half of the coconut fibres produced is exported in the form of raw fibre.
2.3.1 Pros and cons of using coconut fibre
Advantages Disadvantages
Moth-proof Provide woven texture (rock wool)
Resistant to fungi and rot Low mechanical strength performance because it is a natural fibre
Excellent insulation against temperature and sound Inflammable
Tough and durable
Unaffected by moisture and dampness
2.3.2 Properties of coconut fibre
Mechanical properties
Coconut fibre has low mechanical strength, high toughness because they are natural fibres and natural fibre always has weak mechanical strength performance compare to other type of fibres.
Renewability
Coconut fibre is very easy to obtain as the coconut fibre is extracted from the coconut husk.
As reinforcement
Coir is a good reinforcement for other type of material such as cement (Joshi, 2003). The coir fibre can increase the toughness of the material so that the material can withstand handling and a structural load (Noor Md. Sadiqul Hasan, Habibur Rahman Sobuz, Md. Shiblee Sayed and Md. Saiful Islam, 2012).
2.4 Wood
Wood is an organic material, produced by a large number of woody plants and quite variable in properties. Using wood as the building structural material is nothing new as the wood has been used to build structural buildings for more than thousands of years and it is still the most widely used building materials. Throughout the ages, the engineers have successfully built from houses to boat and other shelters as well as furniture. Since wood has lots of application purpose, wood has been one of the most favourite products by the humans for few centuries.
Generally, there are tons of wood species throughout the world such as maple, beech, hickory and others. Different types of wood species have their own applications as the applications have to base on the properties of the wood. Some of the wood are use to make furniture and normally this kind of wood is known as softwood while the wood that used to build structural buildings are known as hardwood.
Softwood is collected from the conifer trees which are evergreen having needle-shape leaves while hardwood is obtained from deciduous trees (losses leaves in autumn). Softwood are usually light weight than hardwood but hardwood has higher tensile and shear strength than the softwood (James E. Houck and Brian N. Eagle, 2007).
Figure : Cordwood pile in New Hampshire
2.4.1 Pros and Cons of wood (Larry Loffer, 2007)
Advantages Disadvantages
Size does not change with temperature Shrinkage and swell
Good sound absorption Deterioration
Light weight Attack by biological agents
High mechanical strength
2.4.2 Properties of Wood
Working properties
Wood is very easy to maintain and repair. However, if the wood is too old, the repairing cost will be high and they are usually disposed of.
Variation
There are more than 5000 kinds of woods in the wold. Their microscopic structures are different. Accordingly, their physical, thermal, acoustic and other problems will be different too.
Renewability
Woods are renewable but they take longer time to grow.
Mechanical properties
Wood has good mechanical strength performance and they are light weight.
2.5 Adhesive
The definition of adhesive is a substance that is capable of holding at least two surfaces together in a strong and permanent manner. Cured adhesives, like other materials can also be characterised by their internal strength, or the force required to cause permanent deformation. To differentiate from adhesion, cohesive strength of adhesives and substrates is used for the internal strength as shown in figure . One thing can be observed from the adhesive is that, after the adhesive is applied, there is a flow phase. The adhesive will slowly flow to every parts of the surfaces and building up the adhesion (Gareth McGrath, 2001).
Figure : The types of forces in an adhesive joint
When a bond is formed at a joint that perform load bearing function, it is known as structural bonding. This means that the forces in a structure have been transmitted from one member to another member through the joint. The highlighted part is the force that is transmitting will be taken up by the adhesive and spread to another member.
2.5.1 Application for various type of adhesive
There are different types of adhesive for various applications such as structural adhesive and pressure sensitive adhesive. Structural adhesive is referring to the adhesive that works well under the glass transition temperature. The example of structural adhesives are epoxies, cyanoacrylates and acrylic adhesives. These kinds of adhesive are able to carry a large amount of stress. Thus, they are suitable for structural applications. Next, the pressure sensitive adhesives is referring to very low modulus elastomers which they deform easily under small pressure, permitting them to wet surfaces. When the substrate and adhesive are brought into intimate contact, van der Waals forces are sufficient to maintain the contact and can provide relatively durable bonds for lightly loaded applications. Example of pressure sensitive adhesives are tapes or labels.
2.5.2 Pros and cons of using adhesives
Pros Cons
The materials can be joined even if they are dissimilar Bond strength decrease with increase in temperature
A stronger and stiffer structures can be designed Surface roughness must be enough
Porous materials can be bonded Some adhesive has carcinogenic effect
Improved fatigue resistance of the material
Local stress concentration can be avoided
2.5.3 Types of adhesive
2.5.3.1 Methyl Diphenyl Diisocyanate (MDI)
Diisocyanate is also known as isocyanates. They are highly reactive and versatile chemicals with widespread commercial and consumer use. There are two types of diisocyanate actually dominated the diisocyanate market and they are MDI and toluene diisocyanate (TDI) (Allport, D., Gilbert, D., and Outterside, S, 2003). When the isocyanates combined with other compounds that contain free hydroxyl functional groups, they will react and begin to form polyurethane polymers. This chemical reaction is completed with all of the initial free N=C=O groups are bound within the polymer network. This process is commonly referred to as “curing”. Example, the adhesive which is initially uncured, but after it cures, it will be able to bond two pieces of wood together. MDI is also used in high-strength adhesive products such as super glue. However, the MDI bonds the wood by penetrate into the cracks or spread over the surface of the wood. The penetration can up to 1mm deep and this has beyond the three cell depth.
2.5.3.1.1 Pros and Cons of using MDI
Pros Cons
High water resistance MDI will bond with metal surfaces (unable to remove from mould)
Form covalent bonds (stronger bonding strength) Highly flammable
Faster press cycle may be possible May cause respiratory sensitization when inhale
2.5.3.2 Polyvinyl Acetate (PVA)
PVA is a colourless, non-toxic thermoplastic resin prepared by the polymerization of vinyl acetate. Polyvinyl Acetate is one of the most widely use water dispersed resins. PVA is also consider as the latex adhesive because latex adhesive can be separate into two major groups such as organic-based adhesive and water-based adhesive. PVA belongs to the water-based adhesive. PVA water-based emulsions have been used as latex house paints since 1945 and they are used for common household white glues. PVA is an aliphatic rubbery synthetic polymer with the formula (C4H6O2)n, and it is belong to the polyvinyl ester family with the general formula -RCOOCHCH2-.
2.5.3.2.1 Pros and Cons of using PVA (Matthew Teague, 2009)
Pros Cons
PVA glues do not emit strong fumes Bonding time is long (around 30minutes)
Does not need chemicals to clear the excess PVA Poor water resistance
Cheaper cost compares to other adhesive such as epoxies
Curing time is very fast
2.5.3.3 Soy-Bean Adhesive
In this new era. The amount of petroleum-based adhesives consumed in the forestry industry is extensive. This has generated a strong desire to develop bio-based adhesives that can satisfy the needed properties, in addition to being eco-friendly under working conditions (Meier, M.A.; Metzger, J.O.; Schubert, U.S, 2007) (He, Z, 2007). The bio-based adhesives include soybean (Chen, N.; Lin, Q.; Zeng, Q.; Rao, J, 2013), cottonseed, and canola products. They are the abundant renewable resources and have high activities. Soy Bean Adhesive is also known as soy-bean glue. The idea of the soy-bean glue was found out by Kaichang Li who think that the soy protein is able to be modified to perform like the proteins that allow mussels to cling unfailingly to rocks in the ocean. New soy bean adhesive is an ingenious chemical construct, something of a Holy Grail in the search to make vegetable proteins that are strong enough and water-resistant enough to hold up in industrial applications (Liu Y, Li K, 2002). Soy proteins are abundant, renewable, affordable but are relatively weak and easily degraded.
However, the applications of soy-based adhesives are very limited due to their poor water resistance (Chen, N.; Zeng, Q.; Lin, Q.; Rao, J, 2015). The scientists and researchers have put all their efforts to search a method to overcome the poor water resistance of the soy-based adhesives (Amaral-Labat, G.; Pizzi, A.; Goncalves, A.; Celzard, A.; Rigolet, S.; Rocha, G, 2008). The methods include chemical and enzyme treatment. Although some of the efforts work well where the modifiers are added in the preparation stage of soy-based adhesive, it still resulting the adhesives to have a short shelf-life (Vnu?cec, D.; Kutnar, A.; Goršek, A, 2017). Currently, there is a method that is able to increase the water resistance of the soy-bean adhesives and that is resin as it appears to be an efficient and feasible curing agent for soy-bean adhesives. It has been reported that the soy-based adhesive with an epoxide compound and soy mean was used in plywood and it is able to met the type II wet shear strength and water resistance requirements for interior plywood (Luo, J.L.; Luo, J.; Li, X.N.; Li, K.; Gao, Q.; Li, J.Z, 2016).
2.5.3.3.1 Pros and Cons of using soy-bean adhesives (United (USB) Soybean, 2010)
Pros Cons
Does not release formaldehyde emissions Poor water resistance
Cheaper cost compares to other types of adhesives Weaker bonding strength compare to UF and PF
Green adhesives Slow curing time
Environmentally friendly
