Paper07-Reinforcement efficiency of multi-walled carbon nanotube-epoxy nano composites

1. Introduction In the last few decades, material scientists and engineers have focused a huge research activity on carbon nanotube (CNT) based nano-composites due to the extraordinary mechanical and functional properties shown by this particular kind of nano-additives of the family of fullerene. This form of carbonaceous nanostructure represents an ideal candidate as advanced filler material not only in a neat hosting system but also as advanced matrix in traditional fiber reinforced composites. In fact, the combination of this nanoloaded system and other more traditional reinforcement leads to the potential development of a new generation of hybrid composite materials with exceptional behaviour for both applications and fundamental science mechanisms. Several studies have sought to verify the reinforcement effect of CNT on the mechanical properties of polymer matrices [1–4]. Generally, these studies found that the mechanical moduli of the CNT/ polymer composites improved by adding only few percentages of nano-particles. Although many scientific works have been carried out or still are on progress, conflicting results about improvement in strength or fracture toughness [5,6] appear, whereas a common tendency is recorded for the enhancement effect on Young’s modulus. Coleman et al. [7] have published a systematic review comparing different studies regarding Young’s modulus enhancement by adding carbon nanotubes. The author has introduced a magnitude parameter to quantify the reinforcement effect, gE
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Mechanical reinforcement of polymer matrices loaded by carbon nanotubes is expected to benefit by both the high aspect ratio and the very high modulus of such nanofillers and, consequently, it depends not only by their content within the hosting system but also by the state of dispersion. This work analyses the effect on the bending modulus of dispersed multi-walled carbon nanotube (MWCNT) into an epoxy system. Results indicate that reinforcement efficiency is characterised by two limiting behaviours whose transition region coincides with the development of a percolative network of nanotubes. Well below the percolation threshold, the carbon nanotubes, contribute to the composite modulus with their exceptional modulus (in this case a value of 1.780 TPa was found), whereas it dramatically decreases above this limit due to the reduction of the effective aspect ratio and the micron sized cluster formation. An estimate of the maximum reinforcement induced by carbon nanotubes has been proposed based on percolation and stress transfer theory for large aspect ratio fillers. Ó 2010 Elsevier Ltd. All rights reserved.
Reinforcement efficiency of multi-walled carbon nanotube/epoxy nano composites
A. Martone a,b, C. Formicola b, M. Giordano b,*, M. Zarrelli b
a b
University of Naples ‘‘Federico II” DIMP, P.le Tecchio 80, 80125 Naples, Italy IMCB – Institute of Composite and Biomedical Materials, CNR – P E. Fermi 1, Granatello, Portici 80055, Italy
* Corresponding author. Tel.: +39 081 7758823; fax: +39 081 7758850. E-mail address: gmichele@unina.it (M. Giordano). 0266-3538/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2010.03.001
ARTICLE IN PRESS
Composites Science and Technology xBiblioteka Baidux (2010) xxx–xxx
Contents lists available at ScienceDirect
Composites Science and Technology
journal homepage: www.elsevier.com/locate/compscitech
Article history: Received 2 December 2009 Received in revised form 1 March 2010 Accepted 3 March 2010 Available online xxxx Keywords: A. Carbon nanotubes B. Mechanical properties D. Optical microscopy
gE ¼
ðE C À Em Þ Vf
ð1Þ
defined as the composite modulus, EC, change respect to the modulus of the hosting matrix Em, per volume unit fraction of CNT, Vf. According to this review, the highest efficiency value achieved on nano-composite modulus by adding CNT, is due to Xu et al. [8]. This author reports a significant increase for the modulus, from 4.2 GPa to 5.0 GPa, measured by shaft loaded blister method at only 0.1% w/ w of MWCNT, with an efficiency parameter of approximately 1200 GPa. The reinforcement effect of carbon nanotube in polymeric matrix depends not only by their content within the hosting system according to traditional micro-mechanics of composites but also by the level of dispersion within the final nano-composite. In a CNT/polymer composite, aggregation or networking of CNT may become a defect causing a deterioration of mechanical properties for the final nano-composite material [9,10]. Dispersion process of carbon nanotubes represents a very complex phenomenon since their natural tendency to aggregate due to inter-molecular van der Walls interactions and to form entanglements. A non uniform dispersion can lead to many defect sites and reach resin area limiting not only the efficiency of CNT as reinforcement filler [11–14] but also the electrical properties of the final nano-composite [15–17]. Efficient dispersion and possibly, the alignment of CNTs within a matrix is still a challenge and it could play the main role driving the diffusion of CNT or MWCNT as nano-reinforcements on industrial scale [18,19].