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Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites
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Original Article
Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites Vivekanandhan Chinnasamy a,∗ , Sampath Pavayee Subramani b , Sathish Kumar Palaniappan c , Bhuvaneshwaran Mylsamy d , Karthik Aruchamy e a
Department of Mechanical, Energy and Industrial Engineering, Botswana International University of Science and Technology, Palapye, Botswana b Department of Mechanical Engineering, K. S. Rangasamy College of Technology, Tiruchengode, Tamil Nadu 637 215, India c Department of Mining Engineering, Indian Institute of Technology Kharagpur, West Bengal 721 302, India d Department of Mechanical Engineering, K. S. R. College of Engineering, Tiruchengode, Tamil Nadu 637 215, India e Department of Mechanical Engineering, SSM College of Engineering, Komarapalayam, Tamil Nadu 638 183, India
a r t i c l e
i n f o
a b s t r a c t
Article history:
Scores of modern applications have the presence of composite materials. As such, scientists
Received 17 December 2019
worldwide started considering fabrication of a new composite and attempting to have more
Accepted 17 January 2020
applications using these materials. Fabricating composite materials newly has become the
Available online xxx
genuine considerations of scientific community worldwide and hence, serious attempts are continuously being taken in-order to improve the application of these materials. Due to
Keywords:
this vast development and research in this field, conscious attempt has been made in this
Epoxy
present work that studies the effect of nanoclay content with reference to structural and
Cloisite 30B
morphological behavior of epoxy composites. In this process, epoxy materials get reinforced
Kevlar fiber
with different particulate fractions of chosen nanoclay and investigations were carried out
Glass fiber
on the specimens. Composite laminate with varied layers of glass fiber and kevlar fiber
Nanoclay
and modified epoxy with 2 wt.% of Cloisite 30B and hardener are used, and strips are fabri-
Thermal properties
cated and tested for their mechanical properties. Also, sheets with 14 layers of glass without and with nanoclay and likewise sheets with 14 layers of kevlar without and with nanoclay were fabricated. The fabricated kevlar/glass fiber reinforced composites were subjected to various tests to evaluate the thermal properties. All specimens were prepared under the specifications of ASTM standard. Thermal testing of composites (glass transition temperature, thermo gravimetric analysis and dynamic mechanical analysis) has been conducted and the properties have been evaluated. © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
∗
Corresponding author. E-mail: [email protected] (V. Chinnasamy). https://doi.org/10.1016/j.jmrt.2020.01.061 2238-7854/© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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1.
Introduction
Developing new composite materials from existing materials is the real challenge for most of the material engineers. So, there are huge research endeavors emerging in the field of composites to develop new materials with upgraded mechanical, electrical and thermal properties. Among these composites, fiber reinforced polymer (FRP) is the most charming as a result of its enough utilization in different applications which incorporate numerous mechanical, automotive and structural components. Since improved composite materials have vast applications in modern science, it has become imminent for the scientists worldwide to consider fabrication of composite materials and have improved application of these materials. Fibers possess special reinforcement which has continuity with diameter from the range 120–7400 pin. Fibers generally remain linear elastic or perfectly plastic and become stronger and stiffer material than the same when in bulk form. Glass, carbon and aramid (kevlar) are the most used fibers. There is a continuous change in the fiber and whisker technology [1]. These are composite materials made from polymer matrix strengthen with fibers and the fibers may be carbon, glass, basalt or aramid. Other fibers like paper or wood or asbestos are rarely in use. The polymer is usually an epoxy, vinyl ester or polyester thermosetting plastic while phenol formaldehyde resin is used currently. Addition polymerization and step growth polymerization are the techniques used to manufacture a polymer. When merged with different agents so as to improve or change the properties of polymers, the result obtained is plastic after the bonding of two or more homogeneous materials bond with various properties in order to obtain the resultant product that can have mechanical properties as well as good material. [16] Fiber-reinforced plastic is a group of composite plastic which uses fiber materials to improve mechanically the strength and elasticity of plastics. Matrix is originally a plastic material that remains with no fiber reinforcement. They are reinforced using stronger and stiffer reinforcing filaments or fibers, thus making them tougher but relatively weaker. Mechanical properties of both the fiber and matrix with respect to their fiber orientation and length in the matrix [2] decide the extent of strength and elasticity that can have improvement in a fiber-reinforced plastic. Reinforcement of matrix takes place when the FRP materials exhibit additional strength or elasticity related to their elasticity and strength of the matrix [3]. FRP permits the arrangement of glass fibers in thermoplastics into consistent specific design programs. Indicating the strengthing fibers orientation, the strength and the deformation resistance of a polymer can be increased. Composite materials with synthetic fiber reinforcement have become significant and popular nowadays and got invariably many applications as it possesses high quality mechanical properties, light weight, uniqueness in flexibility, resistance to effects of corrosion, easy fabrication and more when it is compared to other metallic materials [4,14]. While comparing all synthetic fibers, poly aramid fiber (kevlar fiber) has more properties which are unique. [15] Further, as it has increased stiffness, it is also identified as nylon which has extra benzene rings in the polymer chain [5]. Thus, it finds more applications in various industries and advanced
technology like armor, ballistic, helicopter blades, pneumatic reinforcement and sporting goods. When it is compared with other man-made fibers, it has long elongation and high tensile strength and modulus [6–8]. Epoxy resin has become the most frequently used polymer matrix in composite materials. In the past years, researchers made deliberate attempts in order to change the properties of epoxy with the inclusion of rubber [9,10] or fillers [11,12] to increase the matrix-dominated composite properties. The addition of rubber particles further improves the fracture toughness of epoxy but decreases its modulus and strength. The results proved that adding rubber particles could improve the fracture toughness of epoxy but reduced the modulus and strength, while after the addition of fillers the modulus and strength of epoxy improved, and fracture toughness decreased. Further, fillers also increased the heat deflection temperature of epoxy [13]. Most recently, micro and nanoscaled particles are being considered as filler material for epoxy so that it can produce composites which have enhanced properties and improved performance. In view of this development in the research field, the present work attempts to study the result of nanoclay content on the thermal behavior of glass fiber and kevlar fiber with epoxy composites. Epoxy materials were reinforced with different particulate fractions of chosen nanoclay with glass fiber and kevlar fiber and the specimens were investigated.
2.
Experimental procedure
Composite laminate with varying the number of layers of glass fiber and kevlar fiber and modified epoxy with 2 wt.% of cloisite 30B and hardener is used, and strips are fabricated and tested for their mechanical properties. Epoxy and hardener are taken in the ratio of 10:1 for this study. Epoxy is taken in the double headed flask and heated up to 65-70 C until epoxy is changed to liquid state. Take 2% of nano clay in a separate beaker and add acetone to it. Mix thoroughly and pour this mixture to the epoxy in the double headed flask. The double headed flask is then placed in the heater and the mechanical stirrer is kept inside the double headed flask. Stirring is continued until the total weight is reduced to gross weight of epoxy and nanoclay (45% of weight ratio to the fiber). After weight reduction, the beaker is kept in the sonicator for 30 min. The content in the beaker is cooled to 30 C and then 10% weight ratio of hardener is added and mixed for 2 min. Sheets were prepared by varying layers of glass fiber and kevlar fiber while the hybrid epoxy along with hardener kept in the beaker is used as matrix. Also, sheets with 14 layers of glass without and with nanoclay and likewise sheets with 14 layers of kevlar without and with nanoclay were fabricated. The sheets are dried and cut according to ASTM standards and tested. The sheets are cut as per ASTM standards in various stacking inclination of 0◦ /90◦ , −45◦ /+45◦ , +30◦ /−30◦ , −60◦ /+ 60◦ . All the specimens were tested for various mechanical tests and thermal test results were summarized. The test results of composite laminates with varying layers of glass and kevlar and glass fiber laminates with and without nanoclay and kevlar fiber laminates with and without nanoclay were compared and results were studied for their mechanical behaviour.
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 1 – DSC curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 35:65.
Fig. 2 – DSC curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 40:60.
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 3 – DSC curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 45:55.
3. Thermal properties of kevlar/glass fiber reinforced composites The fabricated kevlar/glass fiber reinforced composite had been subjected to various tests to evaluate its thermal properties. All specimens were prepared under the specifications of ASTM standard. Thermal testing of composites (glass transition temperature, thermo gravimetric analysis and dynamic mechanical analysis) was conducted and its property was evaluated.
3.1.
Table 1 – Layer arrangements of glass fiber (G) and kevlar fiber (K) layers. Sheet name
No. of glass fiber layer
No. of kevlar fiber layer
G7K7 G6K8 G5K9 G4K10 G8K6 G9K5 G10K4
7 6 5 4 8 9 10
7 8 9 10 6 5 4
DSC analysis
DSC (differential scanning calorimetry) analysis has been carried out on the samples with TA instrument Q10 model. The test was done with nitrogen atmosphere and the flow rate was at 50 ml/min to analyze the glass transition temperature (Tg ). Each specimen weighing 5−6 mg was taken in aluminum pan and kept in the instrument. The dynamic measurements were noted when the heating rate constantly remained 10 ◦ C/min from 25 to 580 ◦ C. Tg of laminates made with epoxy matrix with varied concentrations of hybrid fiber was determined using midpoint method of the epoxy composites. DSC curves of kevlar and glass fiber composites are depicted in Figs. 1–4. In the hybrid curves, when the temperature was at 122.5 ◦ C for kevlar, one brand endothermic peak was noticed. The Tg of textured woven kevlar was almost near to 112.3 ◦ C. DSC curves of kevlar woven also indicated a sharp endothermic peak
with the minimum at 122.5 ◦ C,139.7 ◦ C, 131.1 ◦ C and 127.7 ◦ C, respectively. Then from 122.5 ◦ C to 580 ◦ C, DSC curves have shown endothermic peak at 10 ◦ C min−1 rate of heating at a nitrogen atmosphere. The DSC curves of kevlar fibers recorded endothermic peak at 472.0 ◦ C, 511.9 ◦ C and 536.0 ◦ C respectively well prior to melting point of kevlar fiber. As result, only the kevlar fiber could possess glass transition temperature around 122.5 ◦ C after the decomposition of the kevlar and glass fiber, immediately while melting. The DSC/TG curves of kevlar fiber are obtained under a static air atm nitrogen atmosphere and at a heating rate of 0.3–2.6 ◦ C/min. The kinematic parameters have been arrived at based on the peak temperature – program rate relation, or the so called non – isothermal techniques (Table 1).
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 4 – DSC curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 50:50.
Fig. 5 – TG-DTA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 35:65.
3.2.
Thermogravimetric analysis
During thermogravimetric analysis (TGA), test sample experienced weight loss and the loss percentage was observed when the sample was heated uniformly in an appropriate environment. The loss of weight thus observed during specific temperature range has provided indication on sample composition which includes volatile inert filler and its ther-
mal stability. TGA has been preferred and followed to observe the behaviour as it best represents the composites weight loss (mainly due to matrix loss) with temperature. The hybrid composites which have various fractions had been subjected to thermal degradation using TGA furnace in nitrogen atmosphere so that it can remain away from effects of any oxidation and record respective thermograms. During the experiment, the test material is kept in specimen holder, furnace is raised, and the initial readings are set to 100% before initiating
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 6 – TG-DTA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 40:60.
Fig. 7 – TG-DTA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 45:55.
heating. Also, the gas environment had been preselected for decomposition (insert nitrogen gas), oxidation decomposition (air/oxygen) or a thermal-oxidative combination. A sample weight of 10−15 mg is enough to test. Figs. 5–8 show TG-DTA (differential thermal analysis) curves for kevlar and glass fiber. TG curve shows that weight loss starts at 300 ◦ C. In addition, there is a great weight loss between 550 and 650 ◦ C which is related to the pyrolysis of the materials and between 600 and 800 ◦ C, another weight loss occurs which is smaller than the other ones. Finally, if fiber is subjected to temperatures close to 800 ◦ C, the weight loss will be near to 68.8% from the initial mass. The TGA values for various composition and neat epoxy resin are shown in Tables 2 and 3.
3.3.
Dynamic mechanical analysis
Dynamic mechanical analysis (DMA) calculates force and deflection when the temperature and/or frequency varies. TA
Table 2 – DTA results of onset and peak temperature of weight loss. Sample ratio Onset (o C) Peak (o C)
35:65
40:60
45:55
50:50
526.4 ◦ C 592.4 ◦ C
546.6 ◦ C 540.5 ◦ C
556.3 ◦ C 597.3 ◦ C
355.9 ◦ C 530.8 ◦ C
Table 3 – TG results of residual mass and temperature of weight loss. Sample ratio Residual mass (%) Temperature (o C)
35:65
40:60
45:55
50:50
27.14% 798.1 ◦ C
32.22% 798.1 ◦ C
31.59% 796.1 ◦ C
50.26% 796.0 ◦ C
instrument Q800 DMA is used in calculating loss modulus, storage modulus and damping coefficient when temperature range is from 150 ◦ C to 600 ◦ C. Using these mentioned curves, glass transition temperature could be determined. In
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 8 – TG-DTA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 50:50.
Fig. 9 – DMA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 35:65.
the present-day industry, these modern instruments have multiple applications in material characterization. The test specimen with strip 22.5 mm long, 6.25 mm width with a minimum thickness of 5 mm has been analyzed with the help of constant specimen geometry. As a result, the test specimens become stiff enough that it would not deform easily during the experimental process. Figs. 9–12 shows DMA curves for kevlar and glass fiber. The variation of tan ␦ and storage modulus value of the hybrid composites at a frequency of 10 Hz showed that storage modulus decreases with increase in temperature. At a temperature, storage modulus experiences slight increase with increase in volume fractions of glass fiber and decrease with increasing temperature. It is found that kevlar and glass fiber melting peak shifts to a high temperature region of 92 ◦ C – 98 ◦ C. It can also be
noted that a slight increase in loss modulus is observed with add to volume fraction of glass fiber at temperature range (0−160 ◦ C).
4.
Conclusion
This present research work has attempted in synthesizing advanced nano composite material to be applied in applications like structural, aerospace and other areas. Also, much attention was paid towards reinforcing efficiency of nanoclay particles on the polymer composites. Composite laminates with varying number of layers of glass fiber (G) and kevlar fiber (K) and modified epoxy with 2 wt.% of cloisite 30B and hardener were used, and strips were fabricated and tested for their
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 10 – DMA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 40:60.
Fig. 11 – DMA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 45:55.
mechanical properties. Sheets were prepared with varying layers of glass fiber and kevlar fiber and the hybrid epoxy along with the hardener being used as matrix. Also, sheets with 14 layers of glass without and with nanoclay and sheets with 14 layers of kevlar without and with nanoclay were fabricated. The thermal properties of kevlar and glass fiber epoxy hybrid composites were investigated. Hybrid composites were used as a modifier to alter the properties of epoxy resin. Kevlar fibers recorded endothermic peak at 472.0 ◦ C, 511.9 ◦ C and 536.0 ◦ C
respectively well prior to melting point of kevlar fiber. If fibers are subjected to temperatures close to 800 ◦ C, the weight loss will be near to 68.8% from the initial mass. Dynamic mechanical analysis and burn off test can be combined with various ratios such as 35:65, 40:60, 45:55 and 50:50. From the results, it can be concluded that the hybridization of based composites with modified kevlar/glass fiber improved the thermal properties and increased the glass transition temperature without affecting the thermal stability.
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 12 – DMA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 50:50.
Conflict of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. The author (s) provides no conflict of interest for publishing this manuscript.
Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j. jmrt.2020.01.061.
references
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[8] Young RJ, Lu D, Day RJ, Knoff WF, Davis HA. Relationship between structure and mechanical properties for aramid fibres. J Mater Sci 1992;27:5431–40, http://dx.doi.org/10.1007/BF00541602. [9] Imanaka M, Nakamura Y, Nishimura A, Iida T. Fracture toughness of rubber-modified epoxy adhesives: effect of plastic deformability of the matrix phase. Compos Sci Technol 2003;63:41–51, http://dx.doi.org/10.1016/S0266-3538(02)00175-6. [10] Chikhi N, Fellahi S, Bakar M. Modification of epoxy resin using reactive liquid (ATBN) rubber. Eur Polym J 2002;38:251–64, http://dx.doi.org/10.1016/S0014-3057(01)00194-X. [11] Xian GJ, Walter R, Haupert F. Friction and wear of epoxy/TiO2 nanocomposites: influence of additional short carbon fibers, aramid and PTFE particles. Compos Sci Technol 2006;66:3199–209, http://dx.doi.org/10.1016/j.compscitech.2005.02.022. [12] Vasconcelos PV, Lino FJ, Magalhaes A, Neto RJL. Impact fracture study of epoxy-based composites with aluminium particles and milled fibres. J Mater Process Technol 2005;170:277–83, http://dx.doi.org/10.1016/j.jmatprotec.2005.05.006. [13] Zhou Y, Pervin F, Biswas MA, Rangari VK, Jeelani S. Fabrication and characterization of montmorillonite clay-filled SC-15 epoxy. Mater Lett 2006;60:869–73, http://dx.doi.org/10.1016/j.matlet.2005.10.042. [14] Zegaoui Abdeldjalil, Derradji Mehdi, Dayo Abdul Qadeer, Medjahed Aboubakr, Zhang Hui-yan, Cai Wan-an, Liu Wen-bin, Ma Rui-kun, Wang Jun. High-performance polymer composites with enhanced mechanical and thermal properties from cyanate ester/ benzoxazine resin and short kevlar/glass hybrid fibers. High Perform Polym 2019;31(6):719–32, http://dx.doi.org/10.1177/0954008318793181. [15] Ghouti Hamid Abdelhafid, Zegaoui Abdeldjalil, Derradji Mehdi, Cai Wan-an, Wang Jun, Liu Wen-bin, Dayo Abdul Qadeer. Multifunctional hybrid composites with enhanced
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mechanical and thermal properties based on polybenzoxazine and chopped kevlar/carbon hybrid fiber. Polymers 2018;10:1308, http://dx.doi.org/10.3390/polym10121308. [16] Tang Lin, Dang Jing, He Mukun, Li Junyou, Kong Jie, Tang Yusheng, Junwei Gu. Preparation and properties of
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Available online at www.sciencedirect.com
www.jmrt.com.br
Original Article
Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites Vivekanandhan Chinnasamy a,∗ , Sampath Pavayee Subramani b , Sathish Kumar Palaniappan c , Bhuvaneshwaran Mylsamy d , Karthik Aruchamy e a
Department of Mechanical, Energy and Industrial Engineering, Botswana International University of Science and Technology, Palapye, Botswana b Department of Mechanical Engineering, K. S. Rangasamy College of Technology, Tiruchengode, Tamil Nadu 637 215, India c Department of Mining Engineering, Indian Institute of Technology Kharagpur, West Bengal 721 302, India d Department of Mechanical Engineering, K. S. R. College of Engineering, Tiruchengode, Tamil Nadu 637 215, India e Department of Mechanical Engineering, SSM College of Engineering, Komarapalayam, Tamil Nadu 638 183, India
a r t i c l e
i n f o
a b s t r a c t
Article history:
Scores of modern applications have the presence of composite materials. As such, scientists
Received 17 December 2019
worldwide started considering fabrication of a new composite and attempting to have more
Accepted 17 January 2020
applications using these materials. Fabricating composite materials newly has become the
Available online xxx
genuine considerations of scientific community worldwide and hence, serious attempts are continuously being taken in-order to improve the application of these materials. Due to
Keywords:
this vast development and research in this field, conscious attempt has been made in this
Epoxy
present work that studies the effect of nanoclay content with reference to structural and
Cloisite 30B
morphological behavior of epoxy composites. In this process, epoxy materials get reinforced
Kevlar fiber
with different particulate fractions of chosen nanoclay and investigations were carried out
Glass fiber
on the specimens. Composite laminate with varied layers of glass fiber and kevlar fiber
Nanoclay
and modified epoxy with 2 wt.% of Cloisite 30B and hardener are used, and strips are fabri-
Thermal properties
cated and tested for their mechanical properties. Also, sheets with 14 layers of glass without and with nanoclay and likewise sheets with 14 layers of kevlar without and with nanoclay were fabricated. The fabricated kevlar/glass fiber reinforced composites were subjected to various tests to evaluate the thermal properties. All specimens were prepared under the specifications of ASTM standard. Thermal testing of composites (glass transition temperature, thermo gravimetric analysis and dynamic mechanical analysis) has been conducted and the properties have been evaluated. © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
∗
Corresponding author. E-mail: [email protected] (V. Chinnasamy). https://doi.org/10.1016/j.jmrt.2020.01.061 2238-7854/© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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1.
Introduction
Developing new composite materials from existing materials is the real challenge for most of the material engineers. So, there are huge research endeavors emerging in the field of composites to develop new materials with upgraded mechanical, electrical and thermal properties. Among these composites, fiber reinforced polymer (FRP) is the most charming as a result of its enough utilization in different applications which incorporate numerous mechanical, automotive and structural components. Since improved composite materials have vast applications in modern science, it has become imminent for the scientists worldwide to consider fabrication of composite materials and have improved application of these materials. Fibers possess special reinforcement which has continuity with diameter from the range 120–7400 pin. Fibers generally remain linear elastic or perfectly plastic and become stronger and stiffer material than the same when in bulk form. Glass, carbon and aramid (kevlar) are the most used fibers. There is a continuous change in the fiber and whisker technology [1]. These are composite materials made from polymer matrix strengthen with fibers and the fibers may be carbon, glass, basalt or aramid. Other fibers like paper or wood or asbestos are rarely in use. The polymer is usually an epoxy, vinyl ester or polyester thermosetting plastic while phenol formaldehyde resin is used currently. Addition polymerization and step growth polymerization are the techniques used to manufacture a polymer. When merged with different agents so as to improve or change the properties of polymers, the result obtained is plastic after the bonding of two or more homogeneous materials bond with various properties in order to obtain the resultant product that can have mechanical properties as well as good material. [16] Fiber-reinforced plastic is a group of composite plastic which uses fiber materials to improve mechanically the strength and elasticity of plastics. Matrix is originally a plastic material that remains with no fiber reinforcement. They are reinforced using stronger and stiffer reinforcing filaments or fibers, thus making them tougher but relatively weaker. Mechanical properties of both the fiber and matrix with respect to their fiber orientation and length in the matrix [2] decide the extent of strength and elasticity that can have improvement in a fiber-reinforced plastic. Reinforcement of matrix takes place when the FRP materials exhibit additional strength or elasticity related to their elasticity and strength of the matrix [3]. FRP permits the arrangement of glass fibers in thermoplastics into consistent specific design programs. Indicating the strengthing fibers orientation, the strength and the deformation resistance of a polymer can be increased. Composite materials with synthetic fiber reinforcement have become significant and popular nowadays and got invariably many applications as it possesses high quality mechanical properties, light weight, uniqueness in flexibility, resistance to effects of corrosion, easy fabrication and more when it is compared to other metallic materials [4,14]. While comparing all synthetic fibers, poly aramid fiber (kevlar fiber) has more properties which are unique. [15] Further, as it has increased stiffness, it is also identified as nylon which has extra benzene rings in the polymer chain [5]. Thus, it finds more applications in various industries and advanced
technology like armor, ballistic, helicopter blades, pneumatic reinforcement and sporting goods. When it is compared with other man-made fibers, it has long elongation and high tensile strength and modulus [6–8]. Epoxy resin has become the most frequently used polymer matrix in composite materials. In the past years, researchers made deliberate attempts in order to change the properties of epoxy with the inclusion of rubber [9,10] or fillers [11,12] to increase the matrix-dominated composite properties. The addition of rubber particles further improves the fracture toughness of epoxy but decreases its modulus and strength. The results proved that adding rubber particles could improve the fracture toughness of epoxy but reduced the modulus and strength, while after the addition of fillers the modulus and strength of epoxy improved, and fracture toughness decreased. Further, fillers also increased the heat deflection temperature of epoxy [13]. Most recently, micro and nanoscaled particles are being considered as filler material for epoxy so that it can produce composites which have enhanced properties and improved performance. In view of this development in the research field, the present work attempts to study the result of nanoclay content on the thermal behavior of glass fiber and kevlar fiber with epoxy composites. Epoxy materials were reinforced with different particulate fractions of chosen nanoclay with glass fiber and kevlar fiber and the specimens were investigated.
2.
Experimental procedure
Composite laminate with varying the number of layers of glass fiber and kevlar fiber and modified epoxy with 2 wt.% of cloisite 30B and hardener is used, and strips are fabricated and tested for their mechanical properties. Epoxy and hardener are taken in the ratio of 10:1 for this study. Epoxy is taken in the double headed flask and heated up to 65-70 C until epoxy is changed to liquid state. Take 2% of nano clay in a separate beaker and add acetone to it. Mix thoroughly and pour this mixture to the epoxy in the double headed flask. The double headed flask is then placed in the heater and the mechanical stirrer is kept inside the double headed flask. Stirring is continued until the total weight is reduced to gross weight of epoxy and nanoclay (45% of weight ratio to the fiber). After weight reduction, the beaker is kept in the sonicator for 30 min. The content in the beaker is cooled to 30 C and then 10% weight ratio of hardener is added and mixed for 2 min. Sheets were prepared by varying layers of glass fiber and kevlar fiber while the hybrid epoxy along with hardener kept in the beaker is used as matrix. Also, sheets with 14 layers of glass without and with nanoclay and likewise sheets with 14 layers of kevlar without and with nanoclay were fabricated. The sheets are dried and cut according to ASTM standards and tested. The sheets are cut as per ASTM standards in various stacking inclination of 0◦ /90◦ , −45◦ /+45◦ , +30◦ /−30◦ , −60◦ /+ 60◦ . All the specimens were tested for various mechanical tests and thermal test results were summarized. The test results of composite laminates with varying layers of glass and kevlar and glass fiber laminates with and without nanoclay and kevlar fiber laminates with and without nanoclay were compared and results were studied for their mechanical behaviour.
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Fig. 1 – DSC curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 35:65.
Fig. 2 – DSC curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 40:60.
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Fig. 3 – DSC curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 45:55.
3. Thermal properties of kevlar/glass fiber reinforced composites The fabricated kevlar/glass fiber reinforced composite had been subjected to various tests to evaluate its thermal properties. All specimens were prepared under the specifications of ASTM standard. Thermal testing of composites (glass transition temperature, thermo gravimetric analysis and dynamic mechanical analysis) was conducted and its property was evaluated.
3.1.
Table 1 – Layer arrangements of glass fiber (G) and kevlar fiber (K) layers. Sheet name
No. of glass fiber layer
No. of kevlar fiber layer
G7K7 G6K8 G5K9 G4K10 G8K6 G9K5 G10K4
7 6 5 4 8 9 10
7 8 9 10 6 5 4
DSC analysis
DSC (differential scanning calorimetry) analysis has been carried out on the samples with TA instrument Q10 model. The test was done with nitrogen atmosphere and the flow rate was at 50 ml/min to analyze the glass transition temperature (Tg ). Each specimen weighing 5−6 mg was taken in aluminum pan and kept in the instrument. The dynamic measurements were noted when the heating rate constantly remained 10 ◦ C/min from 25 to 580 ◦ C. Tg of laminates made with epoxy matrix with varied concentrations of hybrid fiber was determined using midpoint method of the epoxy composites. DSC curves of kevlar and glass fiber composites are depicted in Figs. 1–4. In the hybrid curves, when the temperature was at 122.5 ◦ C for kevlar, one brand endothermic peak was noticed. The Tg of textured woven kevlar was almost near to 112.3 ◦ C. DSC curves of kevlar woven also indicated a sharp endothermic peak
with the minimum at 122.5 ◦ C,139.7 ◦ C, 131.1 ◦ C and 127.7 ◦ C, respectively. Then from 122.5 ◦ C to 580 ◦ C, DSC curves have shown endothermic peak at 10 ◦ C min−1 rate of heating at a nitrogen atmosphere. The DSC curves of kevlar fibers recorded endothermic peak at 472.0 ◦ C, 511.9 ◦ C and 536.0 ◦ C respectively well prior to melting point of kevlar fiber. As result, only the kevlar fiber could possess glass transition temperature around 122.5 ◦ C after the decomposition of the kevlar and glass fiber, immediately while melting. The DSC/TG curves of kevlar fiber are obtained under a static air atm nitrogen atmosphere and at a heating rate of 0.3–2.6 ◦ C/min. The kinematic parameters have been arrived at based on the peak temperature – program rate relation, or the so called non – isothermal techniques (Table 1).
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Fig. 4 – DSC curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 50:50.
Fig. 5 – TG-DTA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 35:65.
3.2.
Thermogravimetric analysis
During thermogravimetric analysis (TGA), test sample experienced weight loss and the loss percentage was observed when the sample was heated uniformly in an appropriate environment. The loss of weight thus observed during specific temperature range has provided indication on sample composition which includes volatile inert filler and its ther-
mal stability. TGA has been preferred and followed to observe the behaviour as it best represents the composites weight loss (mainly due to matrix loss) with temperature. The hybrid composites which have various fractions had been subjected to thermal degradation using TGA furnace in nitrogen atmosphere so that it can remain away from effects of any oxidation and record respective thermograms. During the experiment, the test material is kept in specimen holder, furnace is raised, and the initial readings are set to 100% before initiating
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 6 – TG-DTA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 40:60.
Fig. 7 – TG-DTA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 45:55.
heating. Also, the gas environment had been preselected for decomposition (insert nitrogen gas), oxidation decomposition (air/oxygen) or a thermal-oxidative combination. A sample weight of 10−15 mg is enough to test. Figs. 5–8 show TG-DTA (differential thermal analysis) curves for kevlar and glass fiber. TG curve shows that weight loss starts at 300 ◦ C. In addition, there is a great weight loss between 550 and 650 ◦ C which is related to the pyrolysis of the materials and between 600 and 800 ◦ C, another weight loss occurs which is smaller than the other ones. Finally, if fiber is subjected to temperatures close to 800 ◦ C, the weight loss will be near to 68.8% from the initial mass. The TGA values for various composition and neat epoxy resin are shown in Tables 2 and 3.
3.3.
Dynamic mechanical analysis
Dynamic mechanical analysis (DMA) calculates force and deflection when the temperature and/or frequency varies. TA
Table 2 – DTA results of onset and peak temperature of weight loss. Sample ratio Onset (o C) Peak (o C)
35:65
40:60
45:55
50:50
526.4 ◦ C 592.4 ◦ C
546.6 ◦ C 540.5 ◦ C
556.3 ◦ C 597.3 ◦ C
355.9 ◦ C 530.8 ◦ C
Table 3 – TG results of residual mass and temperature of weight loss. Sample ratio Residual mass (%) Temperature (o C)
35:65
40:60
45:55
50:50
27.14% 798.1 ◦ C
32.22% 798.1 ◦ C
31.59% 796.1 ◦ C
50.26% 796.0 ◦ C
instrument Q800 DMA is used in calculating loss modulus, storage modulus and damping coefficient when temperature range is from 150 ◦ C to 600 ◦ C. Using these mentioned curves, glass transition temperature could be determined. In
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Fig. 8 – TG-DTA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 50:50.
Fig. 9 – DMA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 35:65.
the present-day industry, these modern instruments have multiple applications in material characterization. The test specimen with strip 22.5 mm long, 6.25 mm width with a minimum thickness of 5 mm has been analyzed with the help of constant specimen geometry. As a result, the test specimens become stiff enough that it would not deform easily during the experimental process. Figs. 9–12 shows DMA curves for kevlar and glass fiber. The variation of tan ␦ and storage modulus value of the hybrid composites at a frequency of 10 Hz showed that storage modulus decreases with increase in temperature. At a temperature, storage modulus experiences slight increase with increase in volume fractions of glass fiber and decrease with increasing temperature. It is found that kevlar and glass fiber melting peak shifts to a high temperature region of 92 ◦ C – 98 ◦ C. It can also be
noted that a slight increase in loss modulus is observed with add to volume fraction of glass fiber at temperature range (0−160 ◦ C).
4.
Conclusion
This present research work has attempted in synthesizing advanced nano composite material to be applied in applications like structural, aerospace and other areas. Also, much attention was paid towards reinforcing efficiency of nanoclay particles on the polymer composites. Composite laminates with varying number of layers of glass fiber (G) and kevlar fiber (K) and modified epoxy with 2 wt.% of cloisite 30B and hardener were used, and strips were fabricated and tested for their
Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061
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Fig. 10 – DMA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 40:60.
Fig. 11 – DMA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 45:55.
mechanical properties. Sheets were prepared with varying layers of glass fiber and kevlar fiber and the hybrid epoxy along with the hardener being used as matrix. Also, sheets with 14 layers of glass without and with nanoclay and sheets with 14 layers of kevlar without and with nanoclay were fabricated. The thermal properties of kevlar and glass fiber epoxy hybrid composites were investigated. Hybrid composites were used as a modifier to alter the properties of epoxy resin. Kevlar fibers recorded endothermic peak at 472.0 ◦ C, 511.9 ◦ C and 536.0 ◦ C
respectively well prior to melting point of kevlar fiber. If fibers are subjected to temperatures close to 800 ◦ C, the weight loss will be near to 68.8% from the initial mass. Dynamic mechanical analysis and burn off test can be combined with various ratios such as 35:65, 40:60, 45:55 and 50:50. From the results, it can be concluded that the hybridization of based composites with modified kevlar/glass fiber improved the thermal properties and increased the glass transition temperature without affecting the thermal stability.
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Fig. 12 – DMA curve of epoxy resin reinforced kevlar/glass fiber composites with the ratio of 50:50.
Conflict of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. The author (s) provides no conflict of interest for publishing this manuscript.
Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j. jmrt.2020.01.061.
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Please cite this article in press as: Chinnasamy V, et al. Characterization on thermal properties of glass fiber and kevlar fiber with modified epoxy hybrid composites. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.061