Nano-magnetite decorated carbon fibre for enhanced interfacial shear strength

Accepted Manuscript Nano-magnetite decorated carbon fibre for enhanced interfacial shear strength Seyed Mousa Fakhrhoseini, Quanxiang Li, Vishnu Unnikrishnan, Minoo Naebe PII:

S0008-6223(19)30302-1

DOI:

https://doi.org/10.1016/j.carbon.2019.03.078

Reference:

CARBON 14069

To appear in:

Carbon

Received Date: 18 September 2018 Revised Date:

21 March 2019

Accepted Date: 24 March 2019

Please cite this article as: S.M. Fakhrhoseini, Q. Li, V. Unnikrishnan, M. Naebe, Nano-magnetite decorated carbon fibre for enhanced interfacial shear strength, Carbon (2019), doi: https:// doi.org/10.1016/j.carbon.2019.03.078. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Nano-magnetite decorated carbon fibre for enhanced interfacial shear strength Seyed Mousa Fakhrhoseini1, Quanxiang Li1, Vishnu Unnikrishnan1, Minoo Naebe1,2* 1

2

Institute for Frontier Materials, Carbon Nexus, Deakin University, Geelong, Victoria 3216, Australia

School of Engineering, Edith Cowan University, 270 Joondalup Drive, Joondalup, Perth, WA 6027, Australia

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Abstract: The modification of carbon fibres surface has been achieved by high temperature (1000oC) growth of Fe3O4 magnetic nanoparticles (MNPs) on the surface of carbon fibres using ammonium iron (II) sulphate as a single precursor of the nanoparticles. As a consequence, the formation of MNPs on the surface of unsized carbon fibres increased the

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interfacial shear strength by 84.3%, as measured by single fibre fragmentation test. Further investigation on interfacial reinforcing mechanism confirmed an increase in average total surface energy of carbon fibres from 58.81 for unmodified carbon fibre to 64.31mJ/m2 for fibres. Fundamental analysis revealed a 12.44% increase in average

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MNPs decorated

dispersive and no significant reduction in average specific surface energy of carbon fibre after MNPs surface decoration. This led to an increase in interlaminar shear strength from 46.9 to 63.3 MPa due to the strong mechanical interlocking at the MNPs decorated-carbon fibre/epoxy interface which can be described by improve in the dispersive component of the

1. Introduction

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surface energy.

Extensive studies have been carried out on carbon fibre surface treatment to gain a stronger

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interaction with the matrix in a composite structure. However, there is no consensus on the best surface modification of fibres as it is strongly dependent on many factors, such as surface treatment, sizing and the chemical structure of the matrix. Besides the very high

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mechanical strength to weight ratio of carbon fibre [1, 2], its poor interfacial adhesion with the matrix remains a challenge [3, 4]. Carbon fibres are thermally treated above 1500oC to form a highly resistance graphitic-like structure [5]. Therefore, the lack of chemically activated sites on their surface results in a poor interaction with resin and reduces the fibrematrix adhesion [6, 7]. The weak interfacial bonding and the poor load transfer between fibres and matrix can potentially lead to the composite delamination and fibres de-bonding under tension load, leading to poor performance of composite [8, 9].

*

Tel: +61 3 52271410 E-mail: [email protected]

ACCEPTED MANUSCRIPT In order to enhance fibre-matrix interfacial adhesion, the surface of carbonised fibres is partially oxidised in an electrochemical treatment bath to generate active oxygen related functional groups [10]. Subsequently, in a sizing bath, a thin layer of sizing agent adheres to these functional groups and increases the number of chemically activated sites on carbon fibres [3, 5, 11].

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Although the electrochemical oxidation of carbon fibres decreases their mechanical properties, it roughens the surface of fibres and increase the surface area and energy of fibres, which results in a higher interfacial shear strength (IFSS) with polymer matrix [4, 7]. As a result, weak compression behaviour and inter-laminar properties of carbon fibre composites

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are eliminated by increasing the adhesion force between fibres and matrix [5, 12, 13]. Increasing the surface polarity of carbon fibres by plasma oxidation in different gases such as

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air, oxygen and carbon dioxide [4, 6, 7] have been reported as a solution to increase the interfacial interaction between fibre and matrix and assist in the effective stress transfer in composite. Surface roughening of carbon fibres by chemical treatment in HNO3 [6], grafting amines on the surface of carbon fibres [12] or depositing nanoscale structures such as YbF3 [6], carbon nanotubes (CNT) [6, 7, 13, 14], graphene oxide (GO) [15], Nano-silica [8, 16] or carbon Nano-fibres [17] have been reported as alternative approaches to improve the

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interaction between fibres and matrices. However, lack of a continuous surface modification or deposition approach calls for further research efforts in this field. Magnetite Nano-Particles (MNPs) has attracted considerable research interests due to their

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unique properties such as decent magnetic, electric, catalytic, biocompatibility and low toxicity properties [18-20]. Growing Fe3O4 Nano-particles onto fibre not only provides a rough surface that can increase fibre-matrix physical interaction, but also increases the

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surface area of carbonaceous materials [18], which increases the fibre-matrix physical interaction. However, previously reported synthesis methods for magnetic nanoparticles (known as co-precipitation with hydrothermal treatment, solvo-thermal and sol-gel methods) are time-consuming and require at least two precursors, followed by acid and base treatment to terminate the Fe3O4 formation reaction [21-23]. The multi-steps and slow nature of these approaches make them less attractive for industrial application and production at large scale. In this work, we have successfully developed a continuous one-step approach to grow Fe3O4 nanoparticles on surface of a 24k carbon fibre bundle using a single precursor material. The aim of this large scale surface modification is to increase the surface area and energy of

ACCEPTED MANUSCRIPT carbon fibres and subsequently, enhance the fibre-matrix interfacial shear strength. To better understand the mechanism involved in enhancement of the interfacial sheer strength of the MNPs modified carbon fibres in epoxy matrix Raman spectroscopy, surface energy measurements and elemental analysis were employed. The significant difference of this study with previous reports is that; in current study 24k commercial carbon fibre bundle/tow (i.e.

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24000 filaments) was used for the proposed surface modification. Since the main aim of this investigation is to develop an industrial scale method for surface modification of carbon fibre, we have focused on the interfacial interaction between the surface decorated carbon fibres in epoxy matrix. Inclusion of magnetic nanoparticles not only reinforced the carbon fibre

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composites but also provided electromagnetic interference (EMI) shielding functionality to the composite. The EMI shielding capability of magnetic nanoparticles in composites has

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been already reported in literature [24, 25]

It is worth to note that the used carbon fibre in this study is the unsized fibre bundle obtained from Carbon Nexus at Deakin University. Existing reports on surface modification of carbon fibres are often conducted on desized fibres i.e sized fibres that has undergone solvent treatment; and therefore are not a true representative of carbon fibres which has never undergone a sizing treatment. Desizing of fibres using solvents are likely to damage the

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surface of fibres which in turn undermine the potential of any surface treatment on mechanical performance and interfacial interaction of fibres. 2. Material and methods Materials

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2.1.

Pristine unsized 24k carbon fiber bundle was obtained from Carbon Nexus, Waurn ponds,

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Australia and used as the reference sample. Further chemical modification on the unsized sample was conducted using ammonium iron (II) sulphate, which was purchased from Chemsupply.

2.2.

Surface modification of fibres

The formation of Fe3O4 magnetic nanoparticles on the surface of carbon fibres were carried out by immersion of the unsized carbon fibre tow in an aqueous solution of ammonium iron (II) sulphate followed by a heat treatment of fibres at 1000oC. Ammonium iron (II) sulphate is a unique double salt, which contains Fe (II) species however, during thermal decomposition at 230oC, Fe (III) species appears as presented in below reaction [26, 27]: 2(

)

(

) ⇄(

)

(

) +(

)

ACCEPTED MANUSCRIPT Since the presence of both iron species is required to form magnetite nanoparticles, application of this unique double salt simplifies the complex Fe3O4 MNPs preparation method. H2O molecules are formed by dehydration of the compounds and at 450oC, Fe2(SO4)3 and FeSO4 are formed by decomposition of the salt [26, 27]. Ferrous sulphate and the other Fe-included chemicals are converted to Fe2O3 at ~640oC [28, 29] and Fe3O4

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nanoparticles are formed by thermal conversion for Fe2O3 in nitrogen [30]. Figure 1 shows the simplified schematic of preparation of MNPs deposited onto carbon fibres. To remove any contamination from the surface of carbon fibres, the unsized fibres were washed with

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acetone several times and dried in vacuum oven at 70oC for 24 hrs.

Figure 1 Schematic of formation of Fe3O4-magnetic nanoparticles on surface of carbon fibre

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A 20gr/lit aqueous ammonium iron (II) sulphate solution was prepared, and carbon fibres were immersed in the chemical treatment bath for 10min. Then, the wetted fibres were placed into an oven and dried at 100oC for 12 hrs. Dried samples were directly placed in an alumina crucible and placed into the tube furnace. The furnace was vacuumed and purged three times with nitrogen to remove any traces of oxygen and before heating up to 1000oC with a heating rate of 10oC/min under nitrogen flow. 2.3.

Electron microscopy and elemental analysis

To investigate the effect of thermochemical reaction on the surface morphology of carbon fibres, the surface-modified samples were immersed in ethanol and sonicated for 30min. a

ACCEPTED MANUSCRIPT scanning electron microscope (SEM) (ZEISS Supra 55 SEM VP) with a 5kV accelerating voltage was used for the non-coated carbon fibre samples. Elemental and crystallographic analyses of Fe3O4 MNPs was conducted by a transmitting electron microscope (JEOL2100 FEGTEM at 200KV) and bright field (BF), selected area electron diffraction (SAED), scanning tunnelling electron microscopy (STEM) and electron dispersive spectroscopy (EDS)

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analyses. To prepare TEM samples, modified fibres were gently hand-milled, immersed in ethanol and sonicated for 90min in a sonication bath to separate the strongly bonded Fe3O4 MNPs. Milled carbon fibres and Nano-particles were collected by passing a lacey formvar TEM grid in the dispersion. Single fibre tensile testing

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2.4.

Linear density, elongation data and tensile properties of control and modified fibres were

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measured by FAVIMAT + Air Robot2 single fibre testing instrument (Textechno. Germany). A minimum of 75 randomly selected filaments were picked from each sample to achieve a statistically meaningful data. 2.5.

Chemical analysis of fibres and MNPs

The surface of carbon fibres was analysed with Renishaw inVia Raman microscope and change in disordered sp3 and graphitic sp2 carbon atoms (D- and G- bands, respectively) were

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investigated. Three random spots on three different fibres from each sample were picked to calculate change in D/G ratios of samples. Moreover, separated Fe3O4 MNPs were dispersed in water, dropped on an aluminium foil, dried and analysed with Raman laser and their

2.6.

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Raman spectra was collected and compared with the reference spectrum. Single fibre fragmentation test

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The influence of surface modification on the interfacial bonding of carbon fibres with epoxy matrix was assessed by a single fibre fragmentation test (SFFT). To prepare the test coupons, six filaments (longer than 80mm length) from control and modified carbon fibres were picked and placed in the centre of a dog bone shaped cavity. Two light clips were attached to each side of each filament to keep the fibres straight. A 10:3 weight ratio of RIM935/RIM936 epoxy resin/hardener was mixed, degassed under vacuum and poured into the mould to entirely cover the fibre. The samples were cured at room temperature for 1 days, post-cured in the oven at 100oC for 6 hours and finally polished carefully for further testing. To obtain the fragmented carbon fibre samples, each testing coupon was placed in an Instron 5967 tensile tester and strained more than 6% with 0.05mm/min crosshead speed to ensure

ACCEPTED MANUSCRIPT crack saturation stage. At this stage, carbon fibres were broken, cracks propagated in the sample however, coupons remained in their original shape. Fragmentation of each single fibre at its all length was monitored using AD-4113ZT Dino-Lite digital microscope during the test, and the number of fibre fragments were counted within 20mm gauge length. The length of each fragment was measured using an Olympus DP70 digital camera couples to an

2.7.

Interlaminar shear strength test (ILSS)

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Olympus SZX12 long stereo zoom cross-polarisation microscope.

The interaction between fibre and matrix at tow level was investigated based on ASTM D2344 for short-beam strength of polymer matrix composite materials [31, 32]. Carbon fibre-

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epoxy composite samples were prepared by wetting eleven layers of 24k carbon fibre tows in a 10:3 weight ratio of RIM935/RIM936 epoxy resin/hardener. Based on the standard, the

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specimen was cut into 18mm length beams using Accutom machine. The span length between two supports was 12mm and the moving speed of loading nose was 1mm/min. 2.8.

Surface area and surface energy analysis

Specific surface area and energy of control and modified carbon fibres were measured by the Inverse Gas Chromatography-Surface Energy Analyser (IGC-SEA) instrument (Surface Measurement Systems, Alperton, Middlesex, UK). To prepare SEA samples, approximately

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1.0g of each sample was measured and individually placed into L 300mm× Φ 4mm glass column. Relative humidity of samples was removed by two hours heating and purging by helium gas at 30oC. Then, the conditioned sample were exposed to a different n –alkanes (n-

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hexane, n-heptane, n-octane and n-nonane) and polar probes (chloroform, ethyl acetate, acetone, ethanol and dichloromethane) with different surface coverage, and their retention times were measured. Finally, the value of surface energy of different fibres was calculated

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based on the standard method described by Jones [7]. 2.9.

Fractographic analysis

After SFFT measurement, each single fibre composite sample was stretched to break in the middle region of the dog bone. SEM was used to observe the cross-section of the broken samples, and fractographic analysis was employed to provide detailed information and understand the sequence of failure process.

ACCEPTED MANUSCRIPT 3. Results and discussion 3.1.

Surface morphology of Fe3O4 MNPs decorated carbon fibres

Surface morphology of carbon fibres after the growing of MNPs on its surface were analysed with SEM, and two changes in surface characteristics were observed: (i) higher surface roughness of modified fibres and (ii) growth of nano-particles onto the carbon fibres surface.

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Figure 2-a shows the smooth surface of as-received carbon fibre sample. Chemical treatment with ammonium iron (II) sulphate and thermal reaction resulted in a uniform growth of MNPs on the surface of carbon fibres as presented in Figure 2-b. Moreover, the smooth surface of control fibre is converted to a rough surface after thermal reaction, which increases

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surface area and physical interlocking at the interface of fibre-epoxy resin. Figure 2-c shows the roughened surface of carbon fibre with one attached MNP to its surface. The rough surface is due to the multiple reactions during the thermal conversion of (

)

(

) ,

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which releases H2O, SO2, SO3, NH3 and etc. [26, 27, 30, 33] and magnetite reduction reaction, which occurs above 800oC and converts formed magnetite particles into FeO, hydrogen, carbon monoxide and dioxide [34]. As fibre samples were sonicated prior to SEM imaging, the remained Nano-particles are strongly attached to the body of carbon fibres and cannot be removed easily. Figure 2-d shows the attachment of a MNP to the surface of

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carbon fibre and the HRTEM image of separated nanoparticles are presented in Figure 2-e.

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2µ

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Figure 2 Surface morphology of control and modified carbon fibres; (a) surface of unsized control fibre, (b) surface of MNPs modified carbon fibre, (c) high magnification images of

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modified carbon fibre, (d) TEM image shows attachment of MNP to carbon fibre, (e) HRTEM image of MNP, (f) SAED pattern of particles on modified fibre, (g) STEM image and EDS map for (h) iron and (i) oxygen elements on separated MNPs Figure 2-f shows SAED pattern of MNP in which Fe3O4 diffraction patterns is clearly visible.

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To characterise the Nano-particles, the remaining particles in ethanol solution were diluted and placed on a TEM grid and then subjected to imaging and EDS analysis. Figure 2-g, -h

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and -i show STEM image, iron and oxygen elemental maps, respectively, which confirms the chemical composition of the Nano-particles. Using aqueous solution of ammonium iron (II) sulphate as the precursor material followed by the heat treatment at high temperature, MNPs were grown onto the surface of carbon fibres. Electron microscopy images and elemental analysis confirmed an attachment between Nano-particles and fibres, which can lead to enhanced physical interlocking at the interface of carbon fibre and epoxy matrix. 3.2.

Chemical analysis of fibres and particles

Raman spectroscopy was conducted for the carbon fibres and carbon fibre decorated with MNPs to investigate the effect of second thermal reaction on the graphitic structure of fibres. As shown in Figure 3-a, Raman spectra of both samples revealed the same trend which

ACCEPTED MANUSCRIPT suggest non-detrimental MNPs growth process for the chemical structure of carbon fibres. Moreover, Raman spectroscopy on particles (Figure 3-b) showed a major peak around 680cm-1 and a minor peak around 520 cm-1 which are two identical peaks of Fe3O4 nanoparticles [35]. Raman analysis provided further evidence for the formation of MNPs which

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were investigated by EDS elemental analysis, previously.

Control CF MNPs modified

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1200

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1600

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Raman shift (cm-1)

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Raman shift (cm-1)

Figure 3 Raman spectra of (a) carbon fibres and MNPs decorated carbon fibre and (b) spectrum of Fe3O4 Nano-particles

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Although thermal treatment and MNPs growth onto the surface of unsized carbon fibres led to a rough surface, Raman data did not show any change in the graphitic structure of the

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modified carbon fibres.

3.3. Influence of MNP deposition on mechanical performance of Fibres Since the surface modification of carbon fibres with MNPs includes a high temperature thermal treatment, it can potentially affect the mechanical properties of carbon fibres. SEM images in Figure 2 showed increased surface roughness of carbon fibres due to the chemical treatment and thermal reactions. To further determine the effect of surface treatment on the mechanical properties of carbon fibres, tensile strength and Weibull modulus of control and modified carbon fibres were evaluated.

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Control MNPs Modified

50

10 5

1 0.5 Control Modified

Tensile strength (GPa) 3.64±0.63 3.16±0.64

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Weibull Modulus 6.73 5.47

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Weibull Percentiles

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Tensile Strength (GPa)

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Figure 4 Weibull plots for control and modified carbon fibres, both samples are unsized fibres

As shown in Figure 4, the high temperature treatment of unsized carbon fibres after chemical treatment with ammonium iron (II) sulphate decreased the tensile strength of fibres from 3.64 to 3.16 GPa. This 13% reduction in tensile strength of MNPs modified carbon fibres is

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described by high temperature treatment of fibres and reduction of magnetite nanoparticles in the presence of carbon atoms on the surface of carbon fibres as described before [34]. Moreover, the Weibull modulus was reduced after MNPs growth, which means the distribution of material strength of MNPs modified fibres was uneven, compared to the

modification.

Effect of MNPs deposition on composite interfacial bonding

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3.4.

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control sample. This could be due to the surface defects appearing after the surface

Interfacial shear strengths of control and MNPs modified carbon fibres in epoxy matrix were measured to assess the influence of surface modification on fibre interface performance. The calculation of IFSS was carried out using the presented method by Li et al. [4] and results are given in Figure 5.

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20

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Modified CF

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IFSS/MPa

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Figure 5 Interfacial shear strength of control and modified carbon fibres Surface modification of carbon fibres with MNPs resulted in a fairly significant increase in IFSS value from 46.96MPa for control carbon fibres to 76.72MPa (63.37%). Although chemical and thermal treatment step reduced the tensile strength of carbon fibres, the formation of bud-like Nano-particles improved the IFSS significantly as t-Test evaluation proved a significant difference between results. As shown in SEM images, a rougher surface

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of modified samples resulted in a higher interaction between fibre and matrix and subsequently improved the IFSS. 3.5.

Interfacial reinforcing mechanism

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Since Fe3O4 Nano-particles do not interact chemically with epoxy matrix, therefore the reinforcing mechanism in current study can be due to the strong physical interlocking, fibre surface roughness, higher surface area, higher surface energy and a possible new interphase

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with higher mechanical property formed by bud-like MNPs and epoxy matrix. 3.5.1. Single fibre fragmentation test results Cured epoxy dog-bones were stretched more than 6%, and fragment images are presented in Figure 6. As shown in Figure 6-a, the average length of fragments in control carbon fibre is about 416um, while after growing Fe3O4-MNPs on its surface, the mean length of fragments is reduced to about 221um. The formation of smaller fragments means stronger interaction and stress transfer between carbon fibre and epoxy matrix. The interaction mechanism between carbon fibre and epoxy matrix is shown in Figure 6-c. As shown in the schematic, the formation of strongly bonded MNPs at the surface of modified carbon fibres resulted in

ACCEPTED MANUSCRIPT physical interaction at the interphase of fibre-matrix, which ensures highly effective stress transfer from the matrix to carbon fibre. However, due to the smooth surface of control carbon fibre, the load cannot be transferred effectively from matrix to fibres, and a de-

b

a

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bonding phenomenon occurs at the interface under low load, as shown in Figure 6-d.

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Figure 6 Birefringent stress patterns observed for single fibre composite: (a) control, (b) MNP modified carbon fibres; (c) Proposed interfacial failure mechnism; Fracture morphology of single fibre composite fragmentation tests: (d) control fibre and (e) surface modified carbon fibre.

ACCEPTED MANUSCRIPT Figure 6-d and -e show fracture morphology of broken SFFT samples in which de-bonding of control carbon fibre from epoxy matrix is clearly demonstrated. In comparison, stronger interaction between MNPs modified carbon fibre and epoxy matrix was found without obvious de-bonding or pull-out which is beneficial for stress transfer within composite. Shorter fragment length in MNPs modified carbon fibre composite is an evidence of stronger

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interaction between carbon fibre and epoxy matrix. Effective load transfer between MNPs modified fibre and matrix is interpreted by observing SEM images at the surface of carbon fibres and cross-section of broken SFFT samples however, whether the higher load transfer is because of an enhanced chemical or physical interfacial interaction requires further

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investigation.

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3.5.2. Flexural and ILSS test Despite the importance of single fibre fragmentation test in understanding of the fibre-resin interface, however, the results cannot be used as a representative for the composite behaviour as it only involves an individual fibre. Therefore, we have conducted the short beam testing of composites comprising the surface modified carbon fibres tow. To investigate the influence of surface modification of carbon fibre tows on the flexural strength of the

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composite specimen, the prepared samples were tested under an axial force.

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Figure 7 ILSS results of prepared composite parts from control and modified carbon fibre tows

As it is shown in Figure 7, the ILSS value was increased from ~ 46MPa to 63MPa for surface modified carbon fibre tows. This 31.1% increase could be due to the mechanical interlocking at the fibre-resin interface as a result of magnetic nanoparticles presence.

ACCEPTED MANUSCRIPT 3.5.3. Surface area and surface energy Surface area and energy of carbon fibre samples were measured using Inverse Gas Chromatography (IGC) technique at ambient temperature and using the organic probe molecules [4, 16]. The BET surface area of carbon fibre samples was calculated from octane adsorption isotherms, and the results are shown in Figure 8-a. BET surface area of MNPs

interaction between fibre and epoxy matrix effectively.

BET=1.25 m2/g R^2: 0.9978

Method: Elution PeakMax

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Parameter: PeakMax P/P0 Range: 0.05 - 0.35

BET=4.26 m2/g R^2: 0.9986

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0.25

120 100

80

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0.8 0.9 1.0

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Dispersive energy [mJ/m^2]

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Coverage [n/nm]

Specific energy [mJ/m^2]

P/[n*(P0-P)] [g/mMol]

a

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modified carbon fibres was increased from 1.25 to 4.26 m2/g, which can improve the

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d

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Coverage [n/nm]

Figure 8 (a) BET surface area of control and modified fibres and (b) specific, (c) dispersive and (d) total surface energies of control and MNPs decorated carbon fibres

Adhesion and cohesion phenomena are usually used to describe the interactions among fibres and polymer matrix. Both properties depend on surface energy of materials. In this study surface energies of carbon fibres before and after MNPs growth have been determined by IGC (Figure-8 b-d and Table 1). It is found that all samples exhibit surface heterogeneity over 30% (0.3 n/nm) of the fibre surface. But from these results it is clear that MNPs growth

ACCEPTED MANUSCRIPT affected the surface energy of fibre remarkably. The variation of total surface energy of control carbon fibre sample is from 58.8 to 130.5 mJ/m2, while the total surface energy value of MNPs modified carbon fibre increased with a range from 64.3 to 201.6 mJ/m2 which indicates that the resulted carbon fibres are energetically more active. Analysis of dispersive surface energy revealed similar trend. The whole profile of dispersive energy for MNPs

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modified carbon fibre is higher and 12.8% increase of average energy and 48.8% increase of maximum energy were measured for MNPs modified carbon fibres.

Table 1 Parameters from fitting the exponential decay function, y = y0 + Aex/t, to the surface energy data of carbon fibres with and without Fe3O4 MNPs, conditioned at 120oC.

Dispersive

Specific

Modified 162.10 Control

21.41

Modified 38.22 Control

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108.97

130.49

Modified 201.64

Decay Constant (t)

61.56

47.41

0.052

108.79

53.31

0.054

10.31

11.10

0.050

27.67

10.55

0.042

71.68

58.81

0.051

137.33

64.31

0.050

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Total

Control

Maximum Range (A) Average y(1)

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Energy Type Sample

Energy (mJ/m2)

In comparison, specific surface energy of MNPs modified carbon fibres did not show significant difference with that of control sample. However, it is found that more than 10%

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surface of MNPs modified carbon fibre has obviously higher specific energy than that of control sample. Based on the SEA graphs and calculated energy values in Table 1, the

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increase in IFSS is the main result of higher physical interlocking between roughened surface of MNPs modified carbon fibres and epoxy matrix. Moreover, more than 10% surface of MNPs modified carbon fibres may also contribute to improve the interaction due to the higher specific surface energy. 4. Conclusion: Fe3O4 magnetic nanoparticles were successfully and uniformly grown onto the surface of a 24k carbon fibre tow by thermal treatment of carbon fibre in the presence of ammonium iron sulphate as a single precursor material.

The surface modified carbon fibres have been

carefully characterised by means of SEM, TEM, SAED, EDS and Raman. SFFT images showed a significant reduction in fragment length, which indicates an effective load transfer

ACCEPTED MANUSCRIPT between modified fibres and epoxy matrix. More importantly, 84.3% increase in IFSS was calculated for MNPs modified carbon fibres which confirms the positive influence of the proposed surface modification on the interfacial performance of carbon fibre composite. The ILSS test results also revealed 31.1% increase in interlaminar shear strength of the surface modified carbon fibre tows. To investigate the reinforcing mechanism, surface energy

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analysis was conducted which suggested that the increase in IFSS is mainly due to the stronger physical interaction between modified carbon fibres and epoxy matrix. Additionally, the higher specific surface energy of the MNPs modified carbon fibre improved the interaction between the modified carbon fibres and the epoxy matrix. Nano-decoration of

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carbon fibre during its formation in the carbonisation furnace provides higher IFSS in the composite and reduce cost of manufacturing by eliminating surface treatment and sizing

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steps. Acknowledgement

Authors would like to thank Deakin University’s Advanced Characterization team for use of the Electron microscopy facility. This research was supported by the Australian Research Council World Class Future Fibre Industry Transformation Research Hub (IH140100018)

(ATLAS). 5. References:

[3]

[4]

[5] [6] [7] [8]

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