Multiscale Composites
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Development and Characterization of Novel Carbon Nanomaterial Based Multi-scale Composites Sohel Rana 1 , Ramasamy Alagirusamy 2 , Raul Fangueiro 1 , Mangala Joshi 2 1 Fibrous Materials Research Group (FMRG), School of Engineering, University of Minho, 4800-058 Guimaraes, Portugal 2 Department of Textile Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India [email protected] INTRODUCTION One of the most recent developments in the field of high performance composite materials is the multi-scale multi- functional composites, which are developed through combining various functional nanomaterials with conventional fiber reinforced polymers (FRPs). This new class of advanced materials primarily originated to overcome the drawbacks of conventional composites, especially their poor properties in through-thickness direction such as interlaminar shear strength. Moreover, incorporation of a few nanomaterials with exceptional properties such as carbon nanotube (CNT) and carbon nanofiber (CNF) [1] led to considerable improvements in other important properties such as electrical and thermal conductivity, thermal stability, thermo-mechanical behavior, etc. with further possibility to add new functionalities such as strain and damage detection, electromagnetic shielding, etc [2]. However, the major concern in developing such multi-functional composites is the dispersion problem of these nanomaterials in polymeric matrices. Poor dispersion of CNF and CNT resulted in significant deterioration of in-plane mechanical properties of composites such as modulus and strength [3]. To address this issue, the present paper reports the development of carbon/epoxy multi-scale composites with very uniform dispersion of CNF and CNT within the matrix. The developed composites have been characterized for in-plane tensile and compressive properties as well as for thermal and electrical conductivity. MATERIALS AND METHODS Single-walled CNT (0.1 wt.%) and vapor- grown CNF (0.5 wt.%) were dispersed homogeneously in an epoxy resin using a combination of ultrasonication and high speed mechanical stirring at 2000 rpm. The effect of each treatment and their combination on the dispersion quality and nanomaterial damage was thoroughly investigated and accordingly the treatment durations were optimized. Multi-scale composites were then developed though impregnation of carbon fabrics with the nanomaterial dispersed resin, stacking 4 sheets of impregnated fabrics in the form of laminates and finally curing the laminates in a compression molding machine.
Transcript of Multiscale Composites
Development and Characterization of Novel Carbon Nanomaterial Based Multi-scale Composites
Sohel Rana1, Ramasamy Alagirusamy 2 , Raul Fangueiro1, Mangala Joshi2
1Fibrous Materials Research Group (FMRG), School of Engineering, University of Minho, 4800-058 Guimaraes, Portugal2Department of Textile Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
INTRODUCTIONOne of the most recent developments in the field of high performance composite materials is the multi-scale multi-functional composites, which are developed through combining various functional nanomaterials with conventional fiber reinforced polymers (FRPs). This new class of advanced materials primarily originated to overcome the drawbacks of conventional composites, especially their poor properties in through-thickness direction such as interlaminar shear strength. Moreover, incorporation of a few nanomaterials with exceptional properties such as carbon nanotube (CNT) and carbon nanofiber (CNF) [1] led to considerable improvements in other important properties such as electrical and thermal conductivity, thermal stability, thermo-mechanical behavior, etc. with further possibility to add new functionalities such as strain and damage detection, electromagnetic shielding, etc [2]. However, the major concern in developing such multi-functional composites is the dispersion problem of these nanomaterials in polymeric matrices. Poor dispersion of CNF and CNT resulted in significant deterioration of in-plane mechanical properties of composites such as modulus and strength [3].
To address this issue, the present paper reports the development of carbon/epoxy multi-scale composites with very uniform dispersion of CNF and CNT within the matrix. The developed composites have been characterized for in-plane tensile and compressive properties as well as for thermal and electrical conductivity.
MATERIALS AND METHODSSingle-walled CNT (0.1 wt.%) and vapor-grown CNF (0.5 wt.%) were dispersed homogeneously in an epoxy resin using a combination of ultrasonication and high speed mechanical stirring at 2000 rpm. The effect of each treatment and their combination on the dispersion quality and nanomaterial damage was thoroughly investigated and accordingly the treatment durations were optimized. Multi-scale composites were then developed though impregnation of carbon fabrics with the nanomaterial dispersed resin, stacking 4 sheets of impregnated fabrics
in the form of laminates and finally curing the laminates in a compression molding machine. The dispersion of CNF and CNT within epoxy matrix was characterized using Optical microscopy and phase imaging technique of Atomic Force Microscopy. Carbon/epoxy and multi-scale composites were characterized for in-plane mechanical properties in a Universal Testing Machine following ASTM standards. Fracture surface of failed specimens after tensile test was studied using Scanning Electron Microscopy. Thermal conductivity was measured in ALAMBETA instrument and bulk electrical conductivity was characterized using an impedance analyzer.
RESULTS AND DISCUSSION
Dispersion studyIt was observed from the dispersion study that a much longer dispersion route (combination of 6hr ultrasonication with 2hr mechanical stirring) was necessary to uniformly disperse 0.1% CNT as compared to the treatment required for 0.5% CNF (combination of 2hr ultrasonication with 1 hr mechanical stirring). The homogeneous distribution of CNF and CNT achieved through the optimized dispersion routes have been presented in Fig.1.
Fig.1: Distribution of CNF (a) and CNT (b) within epoxy matrix as observed by AFM phase imaging technique.
Mechanical PropertiesIn-plane mechanical properties of carbon/epoxy and multi-scale composites are listed in Table I. It can be noticed that multi-scale composites showed considerably higher mechanical properties as compared to neat
carbon/epoxy composites. Moreover, the improvement obtained with CNT was much higher than that obtained with equal or even higher concentrations of CNF.
Table I: In-plane mechanical properties of carbon/epoxy and multi-scale composites
Composites
Tensile Compressive
Modulus (GPa)
Strength (MPa)
Modulus (GPa)
Strength (MPa)
Carbon/epoxy
48.4 665.7 17.7 140.5
Multi-scale: 0.1% CNT
94.3 872.3 31.3 198.2
Multi-scale: 0.1% CNF
65.2 737.0 20.4 158.0
Multi-scale: 0.5% CNF
66.1 785.2 26.6 166.3
The improvement of mechanical properties in multi-scale composites was mainly attributed to the formation of a strong interface between carbon fiber and epoxy matrix in the presence of CNF or CNT, as can be realized from the strong adhesion between fiber and matrix in the fracture surface presented in Fig. 2(b) and (c). In contrast to that, the fracture surface of neat carbon/epoxy [Fig. 2(a)] showed poor adherence of matrix with carbon fibers indicating a weaker interface and lower mechanical properties.
Fig.2: Fracture surface of neat carbon/epoxy (a) and multi-scale composites:(b) CNF based and (c) CNT based.
The strong interface originated in case of multi-scale composites due to increased residual stresses or interface
pressure of nano dispersed epoxy on the surface of carbon fibers during composite curing.
Thermal and electrical conductivityThermal and electrical conductivity of CNF and CNT based multi-scale composites are listed as well as compared with neat carbon/epoxy composites in Table II.
Table II: Thermal and electrical conductivity of carbon/epoxy and multi-scale composites
Composites
Thermal Conductivity(Wm-1K-1 ×
10-3)
Electrical conductivity
(S.cm-1)
Neat carbon/epoxy 193 ± 5 1.4 × 10-4
Carbon/epoxy/0.1% CNT 278 ± 14 8.9 × 10-4
Carbon/epoxy/0.5% CNF 205 ± 2 2.6 × 10-3
It can be seen from Table II that both thermal and electrical conductivity of carbon/epoxy composites improved strongly due to presence of CNF and CNT. Presence of CNF or CNT thorough out the epoxy matrix formed a conductive network leading to better thermal and electrical conduction.
CONCLUSIONSThe present paper reports the possibility of dispersing CNF and CNT very uniformly within an epoxy matrix using a combination of ultrasonication and high speed mechanical stirring. Dispersion of very low concentrations of CNT (0.1%) and CNF (0.5%) led to strong improvements in the in-plane tensile and compressive properties of carbon/epoxy composites. Moreover, thermal and electrical conductivity also improved significantly. Although the improvement in mechanical properties was quite higher with CNT than equal or even higher concentrations of CNF, a much longer dispersion treatment was required for their homogeneous dispersion in epoxy matrix. REFERENCES
1. S. Rana, R. Alagirusamy, M. Joshi. (2009). A Review on Carbon Epoxy Nanocomposites. J Reinf Plast Compos 28: 461-87.
2. T. Chou, L. Gao, E. Thostenson, Z. Zhang, J. Byun. (2010). An assessment of the science and technology of carbon nanotube-based fibers and composites. Compos Sci Technol 70:1-19.
3. A. Godara, L. Mezzo, F. Luizi, A. Warrier, S.V. Lomov, A.W. van Vuure, et al. (2009). Influence of carbon nanotube reinforcement on the processing and the mechanical behaviour of carbon fiber/epoxy composites. Carbon 47:2914-23.
