A. Martone, A. Petriccione, M.R. Ricciardi, V. Antonucci, M. Zarrelli, M. Giordano
IMCB-CNR Institute for Composite and Biomedical Materials- National Research Council Italy
mauro.zarrelli@imcb.cnr.it
Carbon nanotubes dispersed in polymer matrix has been studied extensively in the last two decade as they represent the ideal candidate as matrix for a new class of advanced systems: the multifunctional polymer composites. The continuous demand for new high performance polymers to use as matrix for composite systems with peculiar and specific property has lead many researchers to investigate the potential use of the carbon nanotubes (CNTs) as tailoring nanofillers of polymer matrix to manufacture of traditional laminate composite. The “tailored multifunctional”
matrix may represent the break-through of the new concept of laminate composites in which not only fibre arrangement and constituent coupling play a rule for the final performance of the manufactured composite but also the matrix could contribute significantly to add further peculiar features.
Final composite properties such as elastic modulus, fracture toughness, electrical, damping and rheology could be significantly
“tuned” and “altered” by adding nanotube to the bulk polymer with important effect on the overall behaviour of the final composite materials. A number of issue arise which need to be faced and analysed.
Experimental measurements of both mechanical moduli and electrical conductivity of nanocomposites [1-2] have highlighted the relevance of nanotubes networking in determining the effective macroscopic behavior of such nanocomposite systems. In particular, the reinforcement capability of carbon nanotubes in a polymeric matrix certainly depends by both their length and amount but, undoubtedly, their arrangement and contacting [3-4] within the hosting medium plays a fundamental role in the load transfer mechanism. In addition, experimental findings support the evidence that the clustering of the nanotubes implies a sensible decrease of the
effective mechanical efficiency of the carbon nanotubes in the polymer matrices reinforcement.
In literature the enhancing reinforcement of CNT loading for the Young‟s modulus is commonly reported [5-6]. However, at the same time, discrepancies among the different data are highlighted thus the overall “ratio” on using carbon nanotube filler is still to assess and a reliable database for this property is still misisng. Characterization and structure-properties of nano-mechanics modelling research have shown that enhancement in mechanical properties of nano- composites are strongly dependent upon the level of dispersion and the final morphology of the nano-fillersDispersion and homogenization stands as a very complex phenomenon due to the natural tendency of CNTs to bundle and to aggregate mainly due to Van der Walls interactions among nanotubes thus CNTs dispersion still represents a critical issue for the widely usage of these nano- structures as reinforcements. A mechanical property model can be build up to explicitly accounts for the reduction of the stress transfer efficiency between reinforcing nanotubes and hosting matrix via a reduction of the effective filler length with the increasing nanotubes content. This modeling approach which takes origin by the Philipse‟s Random Contact model [5] and it relates the excluded volume of a particle to the average number of contacts between an ensemble of such shaped particles, is hereafter described and tested with literature data and new experimental data, reporting a very good agreement.
As recently demonstrated, electrical property could be suitably modified not only by changing the CNTs concentration, but also and, for some features, primarily to the ability of tuning the formed network morphology to provide the optimization of the final nanocomposite properties [6]. Experimental results showed the existence of a multiscale dispersion state, where nanotubes form a hierarchical structured networks of micro aggregates and nanoelements which indeed play effect on the electrical performance of the system.
The combination of extremely large interfacial contact area and low mass density of nanofiller materials implies that frictional sliding of nanoscale particles within the matrix has the potential to cause
performance and experiments confirm the existence of an optimum nanofiller content related to the dispersion state.
Rheology behaviour of polymer matrix which represents a key factor for optimal manufacturing conditions is drastically effected by the presence of nanotube contents. In fact, pristine nanotube network increases the unreacted resin viscosity, as expected, and it gives arise to an elastic contribution of the dynamic mechanical modulus;
whereas upon reaction, the same effect is switched depending on the nanotube content. In the case of functionalised nanofiller, depending on the reactive group, the nanotube content atwhich the viscosity arise is significantly “amplified” allow the dispersion of an higher nanfiller content thus increasing the reinforcement effect of the nanoloads.
Different approaches to build an appropriate theory for predicting reinforcement efficiency of CNTs within an hosting matrix have been presented in the literature however a complete understanding of the overall effects of nanotube addition on different properties is still missing.
References
1. Martone, A.; Formicola, C.; Giordano, M.; Zarrelli, M. (2010).
Reinforcement efficiency of multi-walled carbon nanotube/epoxy nano composites. Composites Science and Technology, Vol. 70, Issue 7, pp.
1154-1160.
2. Tuning by process of the electrical percolation behavior of multiwalled carbon nanotubes/epoxy composites. Faiella, G.; Zarrelli, M.; Antonucci, V.; Giordano, M. AIP Conference Proceedings; 2010, Vol. 1255 Issue 1, p411
3. Martone, A.; Faiella, G.; Antonucci, V.; Giordano, M.; Zarrelli, M.
(2011). The effect of the aspect ratio of carbon nanotubes on their effective reinforcement modulus in an epoxy matrix. Composites Science and Technology, doi: 10.1016/ j.compscitech.2011.04.002.
4. Philipse, A.P. (1996). The Random Contact Equation and Its Implications for (colloidal) Rods in Packings, Suspensions, and Anisotropic Powders. ACS publications Langmuir, Vol. 12, N. 5, pp. 1127-1133.
5. Coleman, J.N.; Khan, U.; Blau, W.J.; Gun‟ko, Y.K. (2006). Small but strong: A review of the mechanical properties of carbon nanotube-based composites. Carbon, Vol. 44, pp. 1624-1652. doi: 10.106/j.carbon.02.038.
6. Carbon Nanotubes - From Research to Applications, ISBN: 978-953- 307-500-6, chapter contribution “Investigation of the Effective Reinforcement Modulus of Carbon Nanotubes in an Epoxy Matrix”, Alfonso Martone, Gabriella Faiella, Vincenza Antonucci, Michele Giordano and Mauro Zarrelli DOI: 10.5772/17551