A facile approach to epoxy/graphene platelets nanocomposites Authors - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS Leave as it is. A facile approach to epoxy/graphene platelets nanocomposites Author’s Initials I. Zaman 1, 2 , T. M Lip 1 , Q. H Le 1 , L. Luong 1 , J. Ma 1 followed by Surname 1 School of Advanced Manufacturing & Mechanical Engineering, University of South Australia, Mawson Lakes, SA 5095, Australia 2 Faculty of Mechanical Engineering and Manufacturing, University of Tun Hussein Onn Malaysia, 68400 Batu Pahat, Malaysia * Corresponding author(Jun.Ma@unisa.edu.au) Keywords : Epoxy, fracture, graphene, electrical conductivity, nanocomposites with good electrical conductivity still remains a 1 General Introduction challenge. Since 1859, extensive research has been conducted Therefore, this study will develop a facile method to concerning graphite and graphite modification [1-4]. synthesizing epoxy/GP nanocomposites, and Graphite comprises layers of interconnected investigate their mechanical and electrical hexagonal carbon rings arranged in parallel, where properties. The method mainly comprises expanding each sheet of carbon atoms is offset by one-half of a graphite by thermal shock and dispersing graphene unit such that alternate sheets are in the same in epoxy by sonication. The investigation is carried position [5]. In the basal plane, each sp 3 carbon atom out using tensile test, fracture toughness and forms covalent bonds along internuclear axis with electrical conductivity test. one distributed bonding that resides above and below the graphite atoms. This distributed bonding 2 Preparation and Submission gives rise to delocalized electrons that make graphite 2.1 Materials electrically conducting. Along the basal plane, Acid-treated Graphite, Asbury 3494, was provided graphite possesses an exceptionally high modulus by Asbury Carbons, Asbury, NJ. Epoxy resin, (~1TPa), excellent electrical and thermal diglycidyl ether of bisphenol A (DGEBA, Araldite- conductivities, and a low coefficient of thermal F) with epoxide equivalent weight 182–196 g/equiv, expansion. Graphene is just a single layer of was purchased from Ciba-Geigy, Australia. Two graphite. When graphite is modified and mixed with types of hardeners, namely polyoxyproppylene polymers by appropriate routes, it is able to disperse (J230) and 4,4-diaminodiphenyl sulfone (DDS), as graphene platelets (GP). These characteristics of were used to mix with epoxy at 100:33 and 100:30, graphite drive new approaches to fabricating high- respectively. performance, functional polymer nanocomposites. 2.2 Synthesis of epoxy/graphene nanocomposites Epoxy is widely used in various engineering fields 1 g of acid-treated graphite was first expanded in a from structural composites to microelectronic, due to their excellent bonding strength, chemical resistance, furnace at 700°C for 1 minute to produce expanded graphite (GP) which was then suspended at 1 wt% in and electrical, mechanical and thermal properties. 100 g tetrahydrofuran (THF) using a metal However, the high crosslink density makes these materials inherently brittle, leading to poor container. The container was covered and treated in an ultrasonic bath (200 watts and 42 kHz) below resistance to crack propagation [6–9]. Nowadays, 30°C for 2 hours to obtain a uniform suspension of toughening epoxy by graphene has become an interesting method due to the amazing properties of GP. DGEBA dissolved in acetone was added to the mixture and mixed by a mechanical stirrer for 30 graphene. Potential applications for this type of minutes, followed by sonication under 30°C for 1 material include electromagnetic shielding, hour. The solvent was evaporated through electrochemical capacitors, light emitting devices, mechanically mixing at 110°C for 1 hour. Then the antistatic, corrosion resistance, etc [10,11]. Epoxy/graphene composites have already showed mixture was highly degassed in a vacuum oven at 120°C to remove trace of solvent and air bubbles. potential in application in thermoelectric power Stoichiometric amount of hardener D230 or DDS generation [12]. However, composites associated

was added and mixed using the mechanical stirrer at A similar behavior has also been observed for 50°C for 2 min or at 130°C for 20 min, respectively. nanoclay-toughened epoxy [14]. The reduction of The resultant mixture was then highly degassed in tensile strength was caused by the incorporation of the oven for 5 min. The mixture was poured into a graphene platelets which actually work as defects rubber mould, followed by curing (i) at 80°C for 3 under tensile loading. hrs and at 120°C for 12 hrs for D230-cured system and (ii) at 140°C for 14 hrs for DDS-cured system. 2.3 Characterization techniques Tensile testing was performed at 0.5 mm/min at room temperature using an Instron 5567. An Instron extensometer 2630-100 was used to collect accurate displacement data for modulus which were calculated using 0.005–0.2 % strain. Fracture toughness testing was carried out using an instantly propagated crack, which was introduced to each sample by a razor blade tapping method [13, 14]. Six specimens were tested for each set of data at 0.5 mm/min. The Plane-strain fracture toughness ( K 1c ) and Critical strain energy release rate ( G 1c ) of CT specimens were calculated and verified according to ISO13586. Electrical conductivity measurement was obtained at room temperature through a conventional two-point- probe conductivity measurement device (Agilent). The test was conducted according to ASTM D257- 99 and five average values were taken to measure volume resistivity at 5 V. 3 Results and discussion 3.1 Tensile properties Figure 1 Variation of (a) Young’s modulus and (b) Figure 1 shows the Young’s moduli and tensile tensile strength for epoxy/graphene nanocomposites strength of neat epoxy and its nanocomposites. In 3.3 Fracture toughness Figure 1(a), Young’s modulus increases obviously Figure 2 illustrates the fracture toughness and with the fraction of graphene platelets (GP). At 4 fracture energy release rate of the two systems. In wt%, the modulus increases 17% for DDS-cured Figure 2(a), fracture toughness increases steadily system and 13% for J230-cured system. The with graphene fractions until 2 wt%, and then modulus improvement is attributed to (i) the decreases slightly. The fracture toughness of DDS- exceptionally high modulus 1TPa of GP compared cured system increases from 0.46 to 1.13 MPa·m ½ at to epoxy matrix, and (ii) the possibly good 4 wt%, while for J230-cured system, it increases dispersion of graphene platelets in matrix, which from 0.66 to 1.09 MPa·m ½ . The maximum fracture imposes restriction on the molecular motion of toughness values, 1.23 MPa·m ½ for DDS-cured epoxy upon tensile loading. DDS cured-system system and 1.17 MPa·m ½ for the other system, were shows the higher modulus improvement compared observed at 2.0 wt% for both systems. to J230 cured-system, because the DDS backbone contains benzene and sulfone groups which provide The fracture energy release rates for both systems the network with rigidity [15, 16]. show a similar trend in Figure 2(b): increasing steadily from 0–2 wt%, followed by a slight In contrast to Young’s modulus, tensile strength reduction. The energy release rate increases from decreases with filler content as shown in Figure 1(b).