Carbon Fiber Reinfoced Polymer - Book Report/Review Example

MANUFACTURING CASE STUDY CARBON FIBER REINFOCED POLYMER (CFRP) by Physical address INTRODUCTION Polymers have wide applications in industrial and structural processes. The word polymer is derived from two Greek words ‘poly’ meaning many and ‘meros’ meaning constituent. A polymer is therefore, a big molecule (macromolecule) made from smaller molecules or structural units. The molecules are joined together by covalent bonds. This involves overlapping of partly filled atomic orbital. The process of joining up small molecules known as monomers into a chain of chemically linked macromolecules is called polymerization. Hence, a monomer is the repeating sub unit that makes up a polymer. For example ethylene (monomer) can be joined up to make a polymer called polyethylene. There are two types of polymers namely: synthetic and natural polymers which are found in substances such as rubber and wood. Cellulose is the largest component of natural polymer found in wood. Other natural polymers include proteins which are important in life processes like growth. The most dominant elements present in natural polymers include carbon, hydrogen, oxygen, nitrogen and sulphur. On the other hand, synthetic can be produced by man in laboratories or industries. They include polystyrene, nylon, polythene, polypropylene and polyvinyl chloride. These types of polymers are sometimes referred to as the plastics. The laboratory process of making polymers can take up a step growth or chain growth mode. In step growth method, different functional groups react leading to formation of a new bond. Sometimes a by-product like water may be formed. An example is formation of nylon by reacting hexamethylene diamine and adipic acid. Contrary, chain growth process involves addition of monomer to link at a time (David et al 2012). This process must be initiated by a chemical compound. Compounds which are formed by chair step process include polyethylene and polystyrene. Other polymers do not require laboratory or industrial process to be made but are synthesized biologically. They include polysaccharides and cellulose. This usually occurs in enzyme catalyzed reaction in living organism. The characteristics of polymers are determined by factors like the type of monomer and the arrangement of the monomers. Polymers made from only one kind of monomer are called homopolymer while, those containing different type of monomers are called copolymer. For example polystyrene and ethylene-vinyl acetate are homopolymer and copolymer respectively. Other polymer consists of ionized units and therefore referred to as polyelectrolyte. Although polymers may be composed of one kind of monomer the arrangement may completely alter the physical characteristics. The arrangement can be isotactic, syndiotactic or atactic. Isotactic means the sub units are found on the same side of polymer chain. Syndiotactic refers to an arrangement where polymer chair is made or alternating sub units. Finally atactic refers to an arrangement where sub units are randomly combined. The other factor that dictates the physical characteristics or polymers is chain length. The longer the length of chain, the greater the mechanical profile. Hence, a polymer with extended chairs is likely to have higher melting and boiling point, viscous and stress resistant. Long chain length means great interaction between the sub units (Bharagava 2004). Hence, there are magnified intermolecular forces such as Vander Waals and big entanglement. The chain length can be determined by the number of monomers like to a chair. This is also called degree of polymerization. Most polymers cannot be used in their synthesized forms for structural purposes. They need some modifications. The modification can be done through addition of oxygen, cross linking and fiber reinforcement. The later is the most commonly used method in engineering. It involves combining a polymer matrix with a fiber such as carbon, glass or metals like copper. Buoyed by various inventions and innovations in nanotechnology, the fiber reinforcements are becoming popular technology in modern world. The technology is expected to replace conventional methods of building using steel rods that are expensive and heavy. However, the technology is not still accepted and serious research is being carried out. Nevertheless, fiber composites have a serious potential of revolutionizing entire construction industry. One such composite is Carbon Fiber Reinforced Polymer (CFRP). The following diagram shows the mechanical characteristics of some of the polymers. CARBON FIBER REINFORCED POLYMER The need for light and strong materials in aerospace engineering fueled the research and development of fiber composites. Fiber such as glass and carbon are used to reinforce polymer matrix. A fiber composite in which carbon makes up the fiber phase is called Carbon Fiber Reinforced Polymer (C F R P). This is formed by embedding carbon fibers into polymer matrix. The following diagram shows the comparison of the characteristics of fiber composites with other materials. It important to note carbon fiber are very expensive than glass fibers. However, it provide excellent properties such as high strength to weight ratio, low density, good corrosion resistance, high tensile strength, low density, low coefficient of thermal expansion, high modulus of elasticity and viscosity (Donald, Pradeep & Bhattacharya 2010) .Although the composite are anisotropic, meaning their properties are unidirectional, they have a higher modulus of elasticity than steel which is isotropic in longitudinal direction. Thus provide great reinforcement and can be used to construct more durable structures with light weight. Carbon fiber is made of mainly carbon element. There are various types of carbon fibers with varying tensile stress. The fibers are classified according to the amount of stress they can withstand. These include: ultrahigh modulus (430Gpa), high modulus (360-430Gpa), intermediate (180-360Gpa), intermediate high tensile (100Gpa) and super high tensile (4.8Gpa). Carbon fibers can be manufactured by two processes, PAN based method and pitch based method. The PAN based is the most commonly used process. It involves the conversion of polyacrylenitrile (PAN) through a process called pyrolysis. The filaments from PAN are made stronger and oxidized by heat at a temperature of about 200oC. This is followed by carbonization process which involves heating in presence of nitrogen at 1200o C for many hours. This enables non carbon elements such as oxygen; nitrogen and hydrogen to evaporate thus the filaments are enriched. Finally the filaments undergo graphitization at a temperature of about 250oC. The pitch based method involves extracting the filaments from tar (asphalt). They are then spun and cured at temperature of about 315 degrees. This is followed by carbonization process. THE MANUFACTURE PROCESS There are several processes used to manufacture C F R P. These include: a) Open mold process. b) Closed mold process. c) Pultrusion The pultrusion process is the most popular, means of producing C F R Ps. This is because of the following reasons: a) It is automated b) High productivity c) Produces C F R Ps with constant dimensions d) Minimized use of manual labour e) Produces C F R Ps of high fiber concentrator f) Produces C F R Ps of high physical quality Pultrusion process In the manufacturing process by pultrusion, the polymer matrix used was polyester resin and fiber was carbon filaments. These two components were combined to produce C F R P strips of circular cross-section area of diameter 15mm and length 4m. The mass of a single strip was 1272 grams each batch consisted 24, 000 filaments. The following procedure was followed; 1. The 24, 000 carbon filaments were pulled from storage tank. 2. The fibers were collected into bundled and directed through a resin bath which contained catalyst, thermosetting polymer (polyester) and pigment. 3. The fiber went through a performer where extra resin was removed, and fiber reshaped. 4. The fiber (performed) entered a heated die where the final dimension of composite was determined. 5. The final product was then cut into rods of 4m in length. 6. The manufactured C F R Ps strips were used to produce aircraft, automobile and marine parts. ENGINEERING FIBER COMPOSITES Fiber composites can be engineered to form three types (a) Particulate composite (b) Fibrous composite (c) Laminate composite Particulate composite It is a composite made of matrix reinforced with particle fibers. The size of the particle affects the mechanical properties of the composite. Particles of small sizes of about 0.25 micros, when disposed in matrix hinder movements and dislocation thus boost strength. Contrary, big particles embedded in the matrix lowers the mechanical strength. However, the particles distribute the load placed on the material thus improves stiffness. The arrangement of fibers in a matrix dictates whether a composite is isotropic or anitropic. In carbon fiber reinforced polymer, the fibers are placed parallel to each other thus exhibit anitropy .In such a case, the physical properties of the material depend on the plane in which the stress is applied. A material that exhibits equal mechanical properties in any direction is called isotropic. Fibrous composites This consists of carbon filaments dispersed in polymer matrix. This enhances the strength of the materials. When long fibers are used, the material profile increases; the composite becomes stronger. For smaller fibers (discontinuous) the strengthening effect is reduced. This is because short fibers have reduced ability to share load. Laminate composites Consist of sheets or layers with various fiber orientations (Tsu-Wei 2005). It is also referred to as multi-layer composite. The matrix binds those layers keeping them in right position and shape thus protecting them from damage. Hence laminate composites have enhanced mechanical strength. Volume fraction of reinforcement fiber Composites with high concentration of fiber tend to possess high strength properties. CHANGES IN MATRIX COMPOSITES Apart from carbon fiber, glass fiber can also be used to reinforce polymer matrix. The glass fiber is obtained from melting silica sand into liquid form. The liquid is treated to form S glass or E glass which forms the raw material in the manufacturing process. There is no change in the manufacturing process by pultrusion only that instead of carbon fiber glass fiber is used. The manufacturing facility having a speed of 1 minute to manufacture 10m of 24,000 batches of carbon filaments used will definitely be affected by reduction in speed of production. If the bath is increases tenfold, the speed is likely to reduce by up to 80% standing at 2m per minute. If the batch is decreased to one tenth of the initial value the speed will probably increase by up to 60% standing at 16m per minute. In conclusion, the fiber composites present a suitable alternative to metallic rods which have been used in construction industry for many. Given that metals are non renewable, the development of better composites should be given a priority in this sector. This will help bridge the existing in the use of these two materials. References Bhargava, A. 2004. Engineering materials: Polymers, ceramics and composites. New Delhi: Prentice-Hall. David, J. et al. 2012. Organic chemistry: A short course. Belmont: Cengage Learning. Donald, R., Pradeep, P. and Bhattacharya. 2010. Essentials of Material Science. Stamford: Cengage Learning. Tsu-Wei, C. 2005. Microstructural design of fiber composites: Cambridge: Cambridge UP. Read More