Mechanical Analysis of Nickel Particle-Coated Carbon Fiber

3Materials Group, Bhabha Atomic Research Centre, Mumbai 400085, India .... 2 (a-e) indicate the SEM micrographs of nickel coated carbon fibers as a fu...
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Mechanical Analysis of Nickel Particle-Coated Carbon FiberReinforced Epoxy Composites for Advanced Structural Applications Amit Kumar Yadav, SOMA BANERJEE, Ravindra Kumar, Kamal K Kar, Janakarajan Ramkumar, and Kinshuk Dasgupta ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b01193 • Publication Date (Web): 30 Jul 2018 Downloaded from http://pubs.acs.org on August 4, 2018

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Mechanical Analysis of Nickel Particle-Coated Carbon Fiber-Reinforced Epoxy Composites for Advanced Structural Applications Amit K Yadav,1,$ Soma Banerjee,1,$ Ravindra Kumar,1 Kamal K Kar1,2,* J. Ramkumar,2 and Kinshuk Dasgupta3 1

Advanced Nanoengineering Materials Laboratory, Materials Science Programme, Indian

Institute of Technology Kanpur, Kanpur-208016, India 2

Advanced Nanoengineering Materials Laboratory, Department of Mechanical Engineering,

Indian Institute of Technology Kanpur, Kanpur-208016, India 3

Materials Group, Bhabha Atomic Research Centre, Mumbai 400085, India

$

Equal contributions, *Corresponding Author: Email: [email protected], Phone:91-512-

2597687, Fax:91-512-2597408

Abstract Nickel particles were deposited on carbon fiber (CF) via a facile electroless coating method at various coating time intended for advanced structural application. Scanning electron microscopy demonstrates that with progressive coating, particle size and density of Ni over the CF surface increase. The influence of electroless surface modification and coating time on static and dynamic mechanical properties of CF reinforced epoxy hybrid composites were investigated by short beam, flexural test and dynamical mechanical analysis. Results summarize that composite reinforced with CF and a layer of Ni particle exhibits significant improvement in static and dynamic mechanical properties compared to unsized CF. Presence of Ni on CF surface improves mechanical interlocking of CF through the polymer and greatly enhances the interfacial adhesion between CF and epoxy. Study reveals that static and dynamic mechanical properties of the composites are strongly dependent on coating time. Keywords: Carbon fiber; electroless coating; dynamic mechanical properties; epoxy composites; nickel particles; interlaminar shear strength, advanced structural application

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1. Introduction Carbon fiber (CF) has long been used as a reinforcement material due to lightweight and exceptional mechanical properties. At microscopic level, the carbon atoms of CF are bonded with each other in a direction parallel to fiber axis which favours unidirectional alignment of the fibers. The unidirectional orientation of fiber contributes to excellent tensile strength and low coefficient of thermal expansion with an added advantage of light in weight. Carbon fiber reinforced polymer (CFRP) would exhibit desired performance for various structural and mechanical applications. However, matrix to fiber load transfer has been facilitated by bonding at the interphase region and hence, governing mechanical characteristics of the composites.1 CF, when reinforced with polymer without surface modifications, exhibits low out-of-plane mechanical and viscoelastic properties due to poor bonding with the polymer matrix.2-4 To overcome these drawbacks, matrix has been modified with Nano-materials.5-8 Another approach is to grow/attach Nano-materials (CNT, CCNT, metallic oxide, metal, etc.) directly over the fiber surface followed by fabrication of composites to avoid the agglomeration of nanoparticles and induce local stiffness at fiber/matrix interface.9-11 Carbon fiber reinforced polymer composites are extensively utilized in number of advanced application areas such as aerospace, military, sport, etc. The mechanical improvement of the composite material is essential for advanced structural applications.12,13 The matrixreinforcement interface is a crucial region of a polymer composite deciding the properties of a composite. A proper tailoring is required to minimize lack of wettability and degradation of the reinforcement. Several methods are implemented to obtain desired interfacial bonding and hence final properties of the composites such as by modification of matrix, chemical treatment of reinforcement, coating of reinforcement as well as controlling the process parameters. Among all, coating of reinforcement is the widely accepted one. Various types of coating techniques such as physical vapour deposition, electrolytic techniques, thermal spraying, sol-gel synthesis, electroless and cementation methods, etc. have been practiced to obtain uniform surface coverage. 14 Coating of nano particles over the CF surface is advantageous due to large surface to volume ratio, good electrical and magnetic properties, and ease of tailoring morphology of the particles as per property requirement. The interfacial bonding and strength of the CFRP have been improved through surface wettability and surface roughness by introduction of various nanomaterials such as metal particles, carbon nanotubes and graphene, etc. over the fiber surface.15,16 A controlled growth of metal particles is essential due to strong correlation

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between size, shape and structure of metal nanoparticles determining electrical and mechanical properties of the final composites.17 Nickel and copper are the most common metals used for coating purpose. Nickel, a transition metal, possesses high strength, corrosion resistance, toughness, and conductivity and it has been utilized to form alloy with several metals. Various methods are available to coat fiber with nickel particles of nano-scale dimensions. Electroless coating is a low cost, highly efficient coating process that provides uniform coverage of nickel particles continuously over the CF surface. The coating process is mainly affected by the composition of chemicals used, temperature and pH of coating bath.18,19 There remains a parabolic relation between coating thickness with coating time. Electroless Ni has been extensively used in numerous applications e.g. computers and electronic devices, aircraft and automotive sectors, valves, parts of copy machines and typewriters, etc. Ni coated CF composites have improved properties such as tensile strength, wear and corrosion resistance, and are of good conductivity.20,21 Nickel coating on CF surface has been studied by several researchers as well.22,23 However, the effect of coating time on surface morphology, interfacial bonding and mechanical properties as a function of coating time has not been explored yet. In this work, we have synthesized Ni coated CF by using electroless method at various coating time. The mechanical and viscoelastic properties of the multiscale composite obtained from Ni-coated carbon fibers have been optimized by simply varying the coating time. The effect of interfacial bonding among the three components on the mechanical properties of the composites has been correlated by analysing possible bonding mechanism of the fracture surface. The coating time is expected to be decisive in improving the static and dynamic mechanical properties of the composites by providing efficient bonding at the interphase region. 2. Experimental Ni particles were coated on CF (continuous bi-woven 0o/90o polyacrylonitrile (PAN) based CF supplied by M/S ZOLTEK Corporation Inc. USA) using electroless method (for composition see Table S1 in supporting information). Ni particles have been coated over CF for different coating time say 5, 10, 15, 20, and 25 min. Ni coated and unsized CF were soaked with epoxy (PG 100, Resinova Chemie, India) resin by hand layup technique and pressed subsequently in a hot press at a temperature and pressure of 60 oC and 1.0 MPa,

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respectively for 8 hours. For curing of epoxy resin, hardener (PHY861, Resinova Chemie, India) was added in 1:10 ratio to epoxy. The test samples were prepared according to the specified ASTM standards. The complete fabrication procedure of the composite is represented in Scheme 1.

Scheme 1: Fabrication of composite 3. Characterization The growth of Ni particles on CF substrate was examined in X-ray diffraction (XRD) at a scanning angle of 10 to 60 degree and speed of 30º/min in M/S Rich Seifert diffractometer, England model: ISO Debyeflex-2002. The X-ray tube was operated at 30 kV and 20mA. Cu Kα radiation of wavelength λ= 1.54184 Å was used to obtain the diffraction patterns. The surface morphology of nickel coated CF was examined by scanning electron microscopy (SEM, model no.: EVO, MA15, ZIESS; beam voltage: 10keV, probe current: 100mA, pressure: ≤ 10-5 torr). Short beam tests were carried out to study the interlaminar properties of the composites. Rectangular specimens having thickness 3 mm, width 15 mm, total length 30 mm and span length of 15±3 mm were prepared according to ASTM D2344 standards.21 Span length to thickness ratio was kept as 5:1. The samples were tested in UTM machine (3point bending fixtures at a cross head speed of 2mm/min.). The interlaminar shear strength (ILSS) was calculated by using Eqn. 1 as given below ‫ ܵܵܮܫ‬ൌ

ଷ௉ ସ௕௛

(1)

The Flexural test was carried out in UTM at a cross head speed of 5 mm/min using 3 point bending fixture. Samples were prepared according to ASTM D790M. Span to thickness (l/h) ratio was kept 40:1. The flexural strength (fs) was determined by using Eqn. 2 as given below ݂‫ ݏ‬ൌ

ଷ௉௟ ଶ௕௛మ

(2)

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The thermo mechanical properties i.e., storage modulus (E′), loss modulus (E″), loss tangent and glass transition temperature (Tg) were measured by using dynamical mechanical thermal analysis (DMTA, Pyris Diamond Apparatus) under bending mode at a frequency of 1 Hz from 30 to 150 oC and heating rate of 10 oC/min. The fiber volume fraction was found to be in the range of 42-47 % and void volume fraction was in the range of 2.3-2.5 based on the general equations (Eqn. S1-S3 in supporting information) for the composite materials. 4. Results and discussion 4.1 X-ray diffraction: XRD pattern for Ni coated fiber shown in Fig. 1 confirms the deposition of Ni particles over the CF surface. The peak at 26.2º represents the graphitic carbon (200) plane which is in aggrement with JCPDS file (JCPDS 75-1621). The other major peak observed at 2θ of 45º corresponds to the (111) plane of nickel (JCPDS 88-2326). The XRD patterns reveal that the intensity of peak increases with increasing coating time, due to increase in coating thickness.

Fig. 1. XRD pattern of Ni coated carbon fiber at various coating time. 4.2 Morphology: Fig. 2 (a-e) indicate the SEM micrographs of nickel coated carbon fibers as a function of coating time. With an increase in coating time, density and size of Ni particle increase as well. A homogeneous distribution of nickel particles over the fiber surface has been evidenced. For coating time of 25 minutes, a layer of aggregated Ni particles has been

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observed. Fig. 2f shows the average particle size and density of loading of Ni particles (defined as % area covered by coated Ni particle) calculated by using image j software. Results reveal that the nickel particles cover up to 67 % of carbon fiber as the coating time approaches to 25 minutes and hence an aggregation of particles has been evidenced in the SEM micrograph (Fig. 2e). At about 20 minutes of coating time the coverage and distribution of nickel particles are optimum, the effect of which is also reflected in other characization techniques. The size of the nickel particle varies proportionally with the coating time as evidenced in Fig. 2f specifically in the range of around 145 nm to 1200 nm, i.e. from nano to micrometic size.

Fig. 2. (a-e) SEM images of Ni coated CF for different coating time, and (f) particle size and area coverage at various coating time.

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4.3 Static mechanical properties: The static mechanical properties for Ni-CF/epoxy and Unsized CF/epoxy composites are shown in Fig. 3. In this study we have examined the effect of Ni coating on unsized CF. The interlaminar shear strength (ILSS) of unsized and commercial sized CF are also tested and the values are nearly the same (33.8 and 34.1 MPa). The removal of sizing is advantageous in the sense that it helps better access of the Ni particles over the CF surface and the bonding or interfacial adhesion will be improved much more as compared to sized one. Hence, both flexural strength and ILSS of composites are related to CF surface characteristics and interaction with epoxy. For small coating time, i.e. 5 and 10 min, the increase in ILSS is also minimal (9 and 28 % with respect to unsized CF composite). With further increase in coating time (i.e. 15 and 20 min) more and more improvement in ILSS (56 and 69 %, respectively) has been observed. However, for a very high coating time say 25 min, ILSS got reduced further. A considerable drop in ILSS has been evidenced as the coating time increases from 20 to 25 minutes. This may be in correlation with SEM micrographs. Fig. 2e displays that at 25 minute of coating, aggregation of nickel particles over the CF surface has been evidenced and this bigger particles (Fig 2f) will adversely affect the ILSS of the composites. The ILSS enhancements of Ni-CF/epoxy composites are found to be comparable or more than the electrodeposited CNT-CF/epoxy (58 % improvements),24 Cu-CNT-CF/epoxy (10 % improvement),25 graphene nanosheets-CF/epoxy (max. 11 %),26 GNP/MWCNT/CF/epoxy (40 % improvements)27 and CF-g-POSS/epoxy composites (40 % improvements).28 A similar trend in flexural strength as a function of coating time has also been evidenced in this study. The flexural strength of the composites remains almost constant after 15 minutes of coating and did not increase further. The coating of CF has been continued up to 30 minutes which evidenced formation of bigger particles due to heavy agglomeration of nickel particles (See Fig. S1 in supporting information) hence providing no added advantage to the mechanical properties of the composites. Again prolonged coating affects the bath composition adversely due to lowering of effectiveness of bath stabilizer. Results reveal that the layer of Ni particles over CF surface contributes to enhance the static mechanical properties of the composites and a significant change has been observed with electroless coating time.

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Fig. 3. Flexural strength and ILSS of composites as a function of coating time.

4.4 Dynamic mechanical properties: DMA has been carried out to see the effect of Ni coating on CF composites. The effect of temperature and Ni coatings on the storage modulus (E′) of CFRP at a frequency of 1 Hz is shown in Fig. 4a. Curves for unsized and Ni coated CF composites show three distinctive regions i.e. a high modulus region where epoxy movement is extremely restricted, a transition zone where the storage modulus decreases steeply and a rubbery region where storage modulus attains a plateau. The incorporation of Ni over CF surface by electroless method alters the storage modulus of the CFRP. To understand the effect of coating time in the glassy region, storage modulus is plotted with respect to coating time over a range of temperature (40 to 60 °C) as shown in Fig. 4b. Results reveal that the viscoelastic properties in this region are mainly affected by the movement of the side chains or small groups adjacent to the backbone. Ni layer restricts the movement of these side groups and results in lower compliance. For small coating time, the changes in storage modulus are not much significant in glassy region possibly due to undercoating of nickel particles on CF surface. Significant improvement in storage modulus has been evidenced for Ni-coated CF/epoxy composites for 20 and 15 minutes of coating (1.72-1.64 times of unsized CF reinforced composite for the temperature range), indicating favourable stress transfer between epoxy and CF. These composites show maximum contact between CF/epoxy due to good density of nickel coating over the CF as well as high surface to volume

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ratio. However, with further coating, a decrease in storage modulus has been observed due to large aggregated particles which will result in possible decrease in interfacial interaction between CF and epoxy. The Effectiveness of Ni coating on the behavior of CF/epoxy composites is expressed in terms of C factor, which is defined as the change in storage modulus with temperature. The expression for C factor is given by Eqn. 329, 30  E 'g     E 'r  Ni −CF C=  E 'g     E 'r  Polymer

(3)

Where, E’g and E’r are the storage moduli in glassy and rubbery regions for Ni-CF composites and polymer, respectively. Fig. 4c shows the variation of C factor with coating time. C factor provides the information on the effectiveness of Ni coating for glassy to rubbery transition. A high value of C factor is undesirable due to decrement in reinforcing ability and vice versa.

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Fig. 4. (a) Storage modulus vs. temperature, (b) storage modulus vs. coating time at 40, 50 and 60 °C, (c) C factor with coating time, (d) degree of entanglement with coating time, and (e) mechanistic representation of interaction of Ni at CF/epoxy interface. Storage modulus in the rubbery region is mainly affected by large chain movement of the polymers. Measurement of degree of entanglement determines the effectiveness of the Ni coatings in rubbery region. Degree of entanglement of the composites can be calculated by using storage modulus data and the expression according to the theory of rubbery elasticity as given by Eqn. 431 V=

E' 6 RT

(4)

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Where, V is the degree of entanglement, R is the universal gas constant and E' is the storage modulus at the temperature above Tg. The expression signifies direct proportionality of degree of entanglement with storage modulus in the rubbery region. Hence, measures the effectiveness of Ni coatings in rubbery region. Fig. 4d shows the degree of entanglement as a function of coating time. With an increase in coating time, the degree of entanglement increases up to 15 minutes of coating and then after becomes less than CF/epoxy composites. At a very high loading of nickel particle, the degree of entanglement decreases further, as evidenced for coating time >15 minutes due to the presence of large aggregated Ni micro particles. These large particles consume more free space and reduce entanglement among the polymer chains. Small sized Ni coated samples remain more effective as compared to large Ni particle filled composites during glassy to rubbery transition. For small nickel particles, minimal movement of particles are observed owing to the coating at rough sites of CF (refer to Fig. 2a and b). For a high coating time (20 and 25 minutes), the degree of entanglement has been affected due to constrained slipping or rolling of nickel particles at the interphase region. This, in turn, lowers the storage modulus of the composites owing to the presence of large size Ni particles. Hence, the transition from glassy to rubbery region with a minimal movement of the particles, increases the C-factor values as compared to other composites. Fig. 4e shows the possible mechanism of interaction among the components of the composites at the interphase region. The bonding among the three components has been examined by SEM analysis at various coating times.

Fig. 5. SEM images of fractured specimens at coating time of (a) 10, (b) 15, and (c) 25 minutes

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Fig. 5 represents the SEM micrographs of fractured specimens of Ni/CF/epoxy composites at a low, optimum, and high coating time. SEM analysis of coated fiber exhibits that at a low coating time (Fig. 5a), a very few and isolated patches of nickel particles are formed over the CF surface. With an increase in coating time patches become more and more uniform leading to better surface coverage as evidenced in the micrograph (Fig. 5b). As the coating is continued longer (Fig. 5c), a massive growth of nickel particles has been evidenced leading to the formation of large agglomerated nickel particles over CF surface. The nickel particles are favourably deposited over the energetically favoured sites and the partial coating of CF by nickel particles might have taken place due to non-uniform activation of fiber surface prior to coating. A low concentration of metal ion in the coating bath is another possible reason for partial coating of the CF surface by nickel particles. The SEM micrograph of the composites with coating time is an evidence of its profound effect on the viscoelastic properties of the composites. At a very high coating time, the polymer will interact more with agglomerated nickel particles rather than with CF and hence, the mechanical interlocking will be less due to chipping away of the nickel particles from the fiber surface.

Fig. 6. (a) Loss modulus vs. temperature, (b) Cole-Cole plots, (c) tangent loss vs. temperature, and (d) Tg and peak height vs. coating time for different composites.

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The variation of loss modulus (E″) with temperature for all the composites is shown in Fig. 6a. Loss modulus indicates the ability of a material to dissipate mechanical energy in the form of heat. The result clearly shows that up to 20 min of coating, loss modulus value increases. The increment can be explained in terms of increase in friction between Ni coated CF and epoxy. The enhanced friction with an increase in particle size is attributed to the higher interfacial area due to a high surface to volume ratio of Ni coating. High loss modulus values are obtained for 15 and 20 min Ni coated samples due to high surface area as well as good density and distribution of coating. However, as the coating is continued further, the surface available for CF-epoxy interaction per unit volume reduces due to large particle size and aggregation of Ni particles. Hence, the loss modulus decreases and becomes even lower than unsized CF composite. The peaks shift to higher values compared to unsized CF epoxy composite with an increase in particle size up to 870 nm i.e. for a coating time of 20 minutes. The changes introduced by the reinforced CF and Ni-CF on the structural properties of composites are also examined by plotting loss and storage modulii at the same frequency, giving insights on mechanical relaxation phenomenon. Fig. 6b shows cole-cole plots of unsized CF and Ni-CF epoxy composites. The nature and shape of cole-cole plot define the homogeneity of the composite system. The deviation of the Cole-Cole curve from circularity is a qualitative measure of adhesion between epoxy and CF. The more is the imperfection and ellipticity, the better will be adhesion between the polymer and filler. From Figure 6b it is evidenced that the deposition of nickel by electroless coating leads to deviation from circularity and the curves shifted gradually towards ellipticity indicating better bonding between CF and nickel particles specifically upto a coating time of 20 minutes. Loss tangent vs. temperature graphs for all samples are represented in Fig. 6c. A shift in Tg to higher values (shown in Fig. 6d) has been observed for all composites compared to the unsized one. With an increase in particle size (870 nm) and density, the peak area under loss tangent curves (representing energy dissipated) decreases (except for 5 minutes), indicating a decrease in damping with an increase in coating time. At 5 minute of coating, the deposition of nickel over CF surface was not significant enough to show its effect in mechanical properties of the composites. Hence to achieve a significant improvement in mechanical porperties an optimum coating is essential. The investigatigation of morphological, static and dynamical mechanical characterization unfolds that an optimum coating time is essential to achieve good static and dynamic mechanical properties. High density or overcoating leads to agglomeration of nickel paricles

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and hence adversely affects the mechanical properties of the composites, whereas a low density or undercoating of Ni particles proved to be insufficient to bring remarkable changes in properties as well. Here, we have evidenced a good coverage of nickel particle for 15 and 20 min coating however, the particle size remains large than that of 5 and 10 min of the coating time. For higher coating time i.e. 25 min, one can observe aggerated phase and larger particle size as evidenced in Figs. 2e and f.

5. Conclusions In this study we have fabricated a hybrid multi-scaled Ni-coated CF-epoxy composite by simple electrloess coating technique and characterized for static and dynamic mechanical properties. Study reveals that the static and dynamic mechanical properties are greatly dependent on electroless coating time. About 70 % increment in storage modulus has been evidenced for Ni-CF composites for a coating of 20 min. The effect of Ni coating time on dynamic mechanical properties has been investigated in terms of degree of entanglement, Cfactor, and Cole-Cole plot. Static mechanical analysis shows 69 % improvement in ILSS for Ni coated CF composites. Flexural strength reaches a maximum of 330 MPa which about 20 % higher than the unsized CF/epoxy composites. This study concludes that the extent of nickel coating on CF surface plays a dominant role in enhancing the static mechanical properties of multiscaled composites by strengthening the mechanical interlocking between the fiber and matrix promoting a better bonding at the interphase region. Hence, the Ni coated CF-epoxy can be a promising and suitable composite material to be used in advanced structural applications.

Acknowledgements The authors acknowledge the financial support provided by Department of Atomic Energy, Bhabha Atomic Research Centre India for carrying out this research work.

References (1) Kar, K. K.; Pandey, J. K.; Rana, S. K. Handbook of Polymer Nanocomposites. Processing, Performance and Application: Volume B: Carbon Nanotube Based Polymer Composites, (Springer, 2014), pp. 13-59.

(2) Kar, K. K.;

Hozdic, A. Developments in Nanotechnologies, Research Publishing

Services, Singapore (2014).

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(3) Bekyarova, E.; Thostenson, E.; Yu, A.; Kim, H.; Gao, J.; Tang, J.; Hahn, H.; Chou, T.W.; Itkis M.; Haddon, R. Multiscale Carbon Nanotube−Carbon Fiber Reinforcement for Advanced Epoxy Composites. Langmuir 2007, 23, 3970-3974.

(4) Rahaman, A.; Kar, K. K. Carbon Nanomaterials Grown on E-Glass Fibers and their Application in Composite. Compos. Sci. Technol. 2014, 101, 1-10.

(5) Agnihotri, P.; Basu, S.; Kar, K. K. Effect of Carbon Nanotube Length and Density on the Properties of Carbon Nanotube-Coated Carbon Fiber/Polyester Composites. Carbon 2011, 49, 3098-3106.

(6) Siddiqui, N. A.; Woo, R. S. C.; Kim, J.-K.; Leung C. C. K.; Munir, A. Mode I: Interlaminar Fracture Behaviour and Mechanical Properties of CFRPs with Nanoclay-Filled Epoxy Matrix. Compos. A 2007, 38, 449-460.

(7) Tehrani, M.; Boroujeni, A. Y.; Hartman, T. B.; Haugh, T. P.; Case, S. W.; Al-Haik, M. S. Mechanical Characterization and Impact Damage Assessment of a Woven Carbon Fiber Reinforced Carbon Nanotube–Epoxy Composite. Compos. Sci. Technol. 2013, 75, 42-48.

(8) Yokozeki, T.; Iwahori, Y.; Ishiwata, S.; Enomoto, K. Mechanical Properties of CFRP Laminates Manufactured from Unidirectional Prepregs using CSCNT-dispersed Epoxy. Compos. Part A 2007, 38, 2121-2130.

(9) Jen, M.-H. R.; Tseng Y.-C.; Wu, C.-H. Manufacturing and Mechanical Response of Nanocomposite Laminates. Compos. Sci. Technol. 2005, 65, 775-779.

(10) Hage, E.; Costa S. F.; Pessan, L. A. Modification of the Carbon Fiber Surface with a Copper Coating for Composite Materials with Epoxy. J. Adhes. Sci. Technol. 1997, 11, 1491-1499.

(11) Wang, C.; Li, J.; Sun, S.; Li, X.; Wu, G.; Wang, Y.; Xie, F.; Huang, Y. Controlled Growth of Silver Nanoparticles on Carbon Fibers for Reinforcement of both Tensile and Interfacial Strength. RSC Adv. 2016, 6, 14016-14026.

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(12) Zhao, F.; Huang, Y. D.; Liu, L.; Bai Y. P.; Xu, L.W. Formation of a Carbon Fiber/Polyhedral Oligomeric Silsesquioxane/Carbon Nanotube Hybrid Reinforcement and its Effect on the Interfacial Properties of Carbon Fiber/Epoxy Composites. Carbon 2011, 49, 2624-2632.

(13) Ma, L.; Meng, L.; Fan, D.; He, J.; Yu, J.; Qi, M.; Chen, Z.; Huang, Y. Interfacial Enhancement

of

Carbon

Fiber

Composites

by

Generation

1–3

Dendritic

Hexamethylenetetramine Functionalization. Appl. Surf. Sci. 2014, 296, 61-68.

(14) Karthigeyan, R.; Ezhil vannan, S.; Ranganath, G.; Paul vizhian, S.; Annamalai, K. Effect of Coating Parameters on Coating Morphology of Basalt Short Fiber for Reinforcement Preparation of Al/Basalt Metal Matrix Composites. Int. J. Electrochem. Sci. 2013, 8, 10138 10148.

(15) Fan, W.; Wang, Y.; Chen, J.; Yuan, Y.; Li, A.; Wang, Q.; Wang, C. Controllable Growth of Uniform Carbon Nanotubes/Carbon Nanofibers on the Surface of Carbon Fibers. RSC Adv. 2015, 5, 75735–75745.

(16) Sharma, R.; Kar, K. K. Hierarchically Structured Catalyst Layer for the Oxygen Reduction Reaction Fabricated by Electrodeposition Of Platinum on Carbon Nanotube Coated Carbon Fiber. RSC Adv. 2015, 5, 66518–66527.

(17) Sun, Y. G.; Xia, Y. N. Shape-Controlled Synthesis of Gold and Silver Nanoparticles. Science 2002, 298, 2176–2179.

(18) Kar, K. K.; Sathiyamoorthy, D. Influence of Process Parameters for Coating of Nickel– Phosphorous on Carbon Fibers. J. Mater. Process. Technol. 2009, 209, 3022-3029.

(19) Sahoo, P.; Das, S. K. Tribology of Electroless Nickel Coatings – A Review. Mater. Des. 2011, 32, 1760-1775.

(20) Tzeng, S.-S.; Chang, F.-Y. Electrical Resistivity of Electroless Nickel Coated Carbon Fibers. Thin Solid Films 2001, 388, 143-149.

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(21) Lee, C. K. Structure, Electrochemical and Wear-Corrosion Properties of Electroless Nickel–Phosphorus Deposition on CFRP Composites. Mater. Chem. Phy. 2009, 114, 125133.

(22) Kumar, N.; Chittappa, H. C.; Bhat, V. Statistical Analysis of Electroless Nickel Coating on Carbon Fiber. Int. J. Mater. Sci. 2017, 12, 229-237. (23) Sunitha, J.N.; Rajesh, C.S.; Rai, S.K Electromagnetic Interference Shielding Effectiveness and Electrical Conductivity of Ni Coated PCABS/PPS Composites with Reinforcement of Carbon Fibre. Polym. & Polym. Compos. 2016, 24, 57-64. (24) Jiang, J.; Xu, C.; Su, Y.; Guo, Q.; Liu, F.; Deng, C.; Yao, X.; Zhou, L. Influence of Carbon Nanotube Coatings on Carbon Fiber by Ultrasonically Assisted Electrophoretic Deposition on its Composite Interfacial Property. Polymer 2016, 8, 302-(1-11).

(25) Choi, O.; Lee, S.; Byun, J.; Lee, W.; Yi, J.; Kim, B.; Thostenson, E. T.; Chou, T.-W. Coating Effects of Copper in CNT/Carbon Fabric Hybrid Composites using Electrophoretic Deposition,” Proceedings of the 17th International Conference on Composite Materials, Edinburgh, Scotland, July 27-31 (2009).

(26) Li, Y.; Zhao, Y.; Sun, J.; Hao, Y.; Zhang, J.; Han, X. Mechanical and Electromagnetic Interference Shielding Properties of Carbon Fiber/Graphene Nanosheets/Epoxy Composite. Polym. Compos. 2016, 37, 2494-2502.

(27) Wang, P.-N.; Hsieh, T.-H.; Chiang, C.-L.; Shen, M.-Y. Synergetic Effects of Mechanical Properties on Graphene Nanoplatelet and Multiwalled Carbon Nanotube Hybrids Reinforced Epoxy/Carbon Fiber Composites. J. Nanomater. 2015, 2015, 1-9.

(28) Wu, G.; Ma, L.; Wang, Y.; Liu, L.; Huang, Y. Interfacial Properties and ThermoOxidative Stability of Carbon Fiber Reinforced Methylphenylsilicone Resin Composites Modified with Polyhedral Oligomeric Silsesquioxanes in the Interphase. RSC Adv. 2016, 6, 5032-5039.

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(29) Pandey, A. K.; Kumar, R.; Kachhavah, V. S.; Kar, K. K. Mechanical and Thermal Behaviours of Graphite Flake-Reinforced Acrylonitrile–Butadiene–Styrene Composites and their Correlation with Entanglement Density, Adhesion, Reinforcement and C Factor. RSC Adv. 2016, 6, 50559-50571.

(30) Panwar V.; Pal, K. An Optimal Reduction Technique for rGO/ABS Composites Having High-End Dynamic Properties Based On Cole-Cole Plot, Degree Of Entanglement and Cfactor. Compoites. Part B 2017, 114, 46-57.

(31) Martin, M.; Hanagud, S.; Thadhani, N. N. Mechanical Behavior of Nickel + Aluminum Powder-Reinforced Epoxy Composites. Mater. Sci. Eng. A 2007, 443, 209-218.

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