ABHIMANYU REDDY
Carbon Fiber Manufacturing from PAN and its Adhesion to Vinyl Ester Matrices
Carbon Fibers
1. Background o...
2.0 Carbon Fibers Manufacturing Process from PAN
Manufacturing Carbon Fibers by PAN process is discussed below [8].
Figure...
3.0 Fiber- Matrix Adhesion
For achieving desired composite properties, Fiber- Matrix adhesion is looked upon as a necessar...
3.1 Key factors influencing interface compatibility
Mechanical interlocking: adhesion can be improved by increasing the su...
4.2 Role of coupling agent
The coupling agent serves as chemi-bridge between the carbon fiber and Vinyl Ester resin. The c...
References
[1] Fitzer, E.; Edie, D.D.; Johnson, D.J. Carbon fibers-present state and future expectation; Pitch and
mesopha...
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Carbon fibers Manufacturing

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Carbon fibers Manufacturing

  1. 1. ABHIMANYU REDDY Carbon Fiber Manufacturing from PAN and its Adhesion to Vinyl Ester Matrices Carbon Fibers 1. Background of Carbon Fibers Carbon fiber is defined as a fiber containing at least 92 wt % carbon, while the fiber containing at least 99 wt % carbon is usually called a graphite fiber [1]. Carbon Fiber is a relatively new and sophisticated material that has found many uses in the field of sports, automobiles, aviation, construction and even medical devices. It’s light and supple, yet very strong, boosting performances. Several thousand carbon fibers are bundled together to form a tow, which may be used by itself or woven into a fabric .The thickness varies according to use giving the object strength and flexibility suitable for its purpose. Carbon fiber composites are generally preferred in applications where strength, stiffness, low weight, and outstanding fatigue characteristics are essential requirements. They also can be used in operations where high temperature, chemical inertness and high damping are demanded. They are usually combined with other materials to form a composite. When combined with a plastic resin and wound or molded it forms carbon fiber reinforced polymer which has a very high strength-to-weight ratio, and is extremely rigid although somewhat brittle. However, carbon fibers are also composed with other materials, such as with graphite to form carbon-carbon composites, which have a very high heat tolerance [2]. Currently, the United States of America uses nearly 60% of the world production of carbon fibers and the Japanese account for almost 50% of the world capacity for production. The largest producer of this fiber is Toray Industries of Japan. The world production capacity of pitch-based carbon fiber is almost totally based in Japan [3]. The estimated global carbon fiber consumption is shown in Table 1 [4, 5]. Industry 1999 ( tons) 2004 ( tons) 2006 ( tons) 2008 ( tons) 2010 ( tons) Aerospace 4000 5600 6500 7500 9800 Industrial 8100 11,400 12800 16,600 17,500 Sporting goods 4500 4900 5900 6700 6900 1,1 Polyacrylonitrile (PAN) Organic polymers are used to manufacture carbon fiber which consist of long strands of molecules held together by carbon atoms. A large variety of fibers called precursors are used to produce carbon fibers of different standards and different specific characteristics. Polyacronitrile (PAN) process is the most dominating method of manufacturing carbon fibers (about 90%). Also a small amount (about 10%) are manufactured from rayon or the petroleum pitch process. To impart specific effects, qualities and grades of carbon fiber, different types of liquids and gases are mixed with the precursor. The highest grade carbon fiber with the best modulus properties are used in demanding applications such as aerospace [6]. Figure 1. Polyacrylonitrile Polymer [7]
  2. 2. 2.0 Carbon Fibers Manufacturing Process from PAN Manufacturing Carbon Fibers by PAN process is discussed below [8]. Figure 2.1: Manufacturing Carbon Fibers by PAN process 1.Spinning 2.Stabilizing 3.Carbonizing 4.Treating surface 5.Sizing Acrylonitrile plastic powder is mixed with another plastic, like methyl acrylate and is reacted with a catalyst in polymerization process to form a polyacrylonitrile plastic. The plastic is then spun into fibers through tiny jets into a chemical bath. The spinning step is important because the internal atomic structure of the fiber is formed during this process. The fibers are later washed and stretched to the desired fiber diameter. Stretching helps aligning the molecules within the fiber. Fibers are heated in air to about 390-590° F for 30-120 minutes before carbonizing to alter its chemical structure from linear to thermally more stable ladder bonding. Hence the fibers absorb oxygen molecules from the air and undergo rearrangement. After stabilizing, the fibers are heated to a temperature of about 1,830-5,500° F in absence of oxygen for several minutes in a furnace. This facilitates in formation of tightly bonded carbon crystals to each other by expelling oxygen and other non-carbon atoms in the form of water vapor, ammonia gas, nitrogen etc. temperatures are used to better control the rate of heating during carbonization. In order to improve the bonding properties with epoxies and other materials, the carbonized fiber surface is slightly oxidized in air. The surface is etched with nitric acid to create microspores which help in improving mechanical bonding properties. The surface treatment process must be carefully controlled to avoid forming tiny surface defects, such as pits, which could cause fiber failure. Coating materials such as epoxy, polyester, nylon are used to coat the treated carbon fibers to protect them from any further damage due to winding or weaving. The coated fibers are wound onto cylinders called bobbins. The bobbins are loaded into a spinning machine and the fibers are twisted into yarns of various sizes. Crude Acrylonitrile
  3. 3. 3.0 Fiber- Matrix Adhesion For achieving desired composite properties, Fiber- Matrix adhesion is looked upon as a necessary condition. A composite material is a combination of two or more constituent materials. The material with better mechanical properties is usually the reinforcement while the other material is the medium in which this reinforcement is suspended or dispersed to transfer load from reinforced fiber to fiber. The resultant composite formed is a material whose properties are close to the properties of the reinforcement material but in a form which can be easily fabricated into structural component. The reinforcement materials are particulate, fiber, flake, and sheet reinforcements. Matrices may be ceramic, metallic, polymeric and cementitious [9]. Adhesion in fiber reinforced polymer composites is influenced by multiple chemical and physical factors. We can observe the formation of chemical and physical bonds at the interface where reinforcement and the matrix come in contact. Usually the surface energy of reinforcement must be greater than that of the matrix to ensure firm adhesion. Hence chemical groups can react with the chemical groups in the matrix to form chemical bonds such as Van de Waals, hydrogen bonds and electrostatic bonds depending on the system [10]. Figure 3.0.1: Fiber-Matrix adhesion
  4. 4. 3.1 Key factors influencing interface compatibility Mechanical interlocking: adhesion can be improved by increasing the surface area of the fiber or by increasing the roughness of the surface by chemical surface treatment. Presence of defect: removal of the weakly boundary layers located at the surface of the fibers by thermochemical surface treatment Physical interactions (polar, dispersive): increase of the surface energy of the fiber and its polar component due to the creation of oxycarbonated functionalities (-OH, -COOH mainly) by thermochemical surface treatment, better wetting [11]. Chemical interactions: In order to increase the chemical bonding force between fiber and resin, several kinds of organometallic coupling agent (such as titanate, zirconate, and zircoaluminate) are chosen [12]. 4.0 Carbon Fiber Adhesion to Vinyl Ester Matrix Free radical cured thermosetting vinyl ester resins have greater toughness and chemical resistance in comparison to unsaturated polyester. The use of vinyl ester composites reinforced with carbon fibers requires an improvement in the fiber-matrix adhesion levels. Vinyl ester undergo as much as 10% volume shrinkage when cured [13, 14, and 15]. The shrinkage can develop significant instability in the fiber/matrix interphase and hence reduces the adhesion to a great extent between the carbon fiber and vinyl ester resin. Vinyl esters (matrix) is a solid chunk in its raw form and is supposed to be turned into a liquid form to be able to be usable by the composite manufacturers. So a monomer is added which is most commonly styrene. Once in the liquid polymer resin state, the matrix and carbon fiber (reinforcement) are mixed in the presence of a coupling agent to create a chemical reaction which cross-links the polymer molecules thereby forming a strong reinforced composite material. 4.1 Surface Modification Strategies Carbon Fibers have an inert and unreactive surface due to formation of the basal plane of graphite which is very stable and unreactive. Hence, to make the carbon fiber more adhesive to matrix material, they undergo chemical treatments to remove the native defective fiber surface leaving a structurally sound surface for bonding .However the reaction generally occurs at the corners of these planes of the resulting crystallites. The amount of reactive sites depends upon the fiber modulus and polymer precursor added. For the intermediate modulus fibers used in the highest number of applications, only 20% of the fiber surface contains mostly oxygen that can be reacted with other molecules under most conditions [16]. However increasing the concentration of functional group, oxygen results in the failure of the carbon fiber due to formation of pits and flaws which are greater than the critical size. Etching the carbon fiber surface with nitric acid and other etchants help in creating micropores on the native fiber surface formed during carbonization which can withstand higher shear loadings and hence is responsible for greater adhesion between the matrix and the reinforcement material [17]. Surface “finishes” are commonly used with surface chemical treatment for carbon fibers. Finishes are usually a matrix component applied from solvent to the fiber surface to create a layer about 0.1 microns in thickness [18].
  5. 5. 4.2 Role of coupling agent The coupling agent serves as chemi-bridge between the carbon fiber and Vinyl Ester resin. The chemical interaction between the carbon fibers and the matrix is strengthened. At the same time, the coupling agent coating may prevent nitrogen-containing groups on the carbon fiber surface from interfering the cationic polymerization of the matrix resin near the carbon fiber surface. For the carbon fiber with sulfuric acid etching treatment could catalyze the Vinyl Ester ring open [19]. COOH Covalent bonding, functional group reactive with –OH and COOH. OH Covalent bonding, Functional group reactive with C=C Vinyl ester monomer Carbon Fiber Figure 4.2.1: Role of coupling agent when coating Vinyl Ester Matrices [11] Coupling Agent
  6. 6. References [1] Fitzer, E.; Edie, D.D.; Johnson, D.J. Carbon fibers-present state and future expectation; Pitch and mesophase fibers; Structure and properties of carbon fibers. In Carbon Fibers Filaments and Composites, 1st ed.; Figueiredo, J.L., Bernardo, C.A., Baker, R.T.K., Huttinger, K.J., Eds. [2] http://en.wikipedia.org/wiki/Carbon_(fiber) [3] Composites Edge; 1992 http://www.engr.utk.edu/~mse/Textiles/CARBON%20FIBERS.htm [4] Roberts, T. The Carbon Fiber Industry: Global Strategic Market Evaluation 2006–2010; Materials Technology Publications: Watford, UK, 2006; pp. 10, 93–177, 237. [5] Red, C. Aerospace will continue to lead advanced composites market in 2006. Composites Manuf. 2006, 7, 24–33. [6] Fabrication and Properties of Carbon Fibers, ISSN 1996-1944 www.mdpi.com/journal/materials [7] http://www.pslc.ws/macrog/images/carfs01.gif [8] http://www.zoltek.com/carbonfiber/how-is-it-made [9] Interfaces and Interphases, Lawrence T.Drzal, Michigan State University [10] L.T Drazl, Advances in Polymer Science II, Vol 75 K.Dusek, Ed., Springer-Verlag, 1985 [11] CF/thermoplastic composite interface bond:Composites Part A 28A (1997) 587-594 – 4.3 to 6.8ksi IM7-TP 2005 SPE Automotive Composites Conference & Exposition, Troy, Mich., USA. 4.7 To 8.1ksi, PA6- AS4 COMPOSITES 2006 October 18-20, 2006, 6.7 to 7.1ksi, PA6-carbon fiber Managed by UT-Battelle for the U.S. Department of Energy. http://www.cfcomposites.org/PDF/Breakout_Soydan. [12] Effects of the organometallic coupling agents on adhesion of the carbon fiber–BMI composites, S.Chou* , H.-C. Chen, K.-S. Lee 10 MAR 2003, DOI: 10.1002/app.1992.070450416 [13] M. B. Launikitis, “Vinyl Ester Resin”, Hand Book of Composite, pp.38-49 [14] L. S. Penn and T. T. Chiao, “Epoxy Resins”, Hand Book of Composite, pp.57~88 [15] Xu, L. and Drzal, L., “Influence of Matrix Cure Volume Shrinkage on the Adhesion between Vinyl Ester and Cardon Fiber”, Proceedings of the 2003 Adhesion Society, pp.415-417, (2003) [16] G.Hammer and L.T Drzal, Appl.Surf.Sci., Vol 4, 1980, pg 340-355 [17] L.T Drzal, M.Rich, and P. Lloyd, J.Adhes,. Vol 16, 1983, p 1-30 [18] E.A. Plueddemann, Silane Coupling Agents, Plenum Press, NY 1982 [19] The effect of carbon-fiber surface properties on the electron-beam curing of epoxy-resin composites, Zhiqian Zhanga, Yuwen Liua,*, Yudong Huanga, Li Liua, Jianwen Baob, Department of Applied Chemistry, Harbin Institute of Technology, bInstitute of Aeronautic Materials Beijing, 100095, People’s Republic of China.

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