Effects of Carbon Nanotube Dispersion on the Material Properties of Polymer Matrix Composites

The combination of extraordinary mechanical and physical properties makes CNTs prospective candidates for reinforcement of polymer matrix composite systems. Besides their extraordinary small size, CNTs are half as dense as aluminum, with a density of 1.33-1.4 g/cm3. CNTs have Young’s modulus of about 1TPa and tensile strength 20 times that of steel alloys. Tensile strength of single–walled carbon nanotubes (SWCNTs) is as high as 2GPa, which is much higher than that of high strength steels [1,2]. Models were developed based on the method presented in [3,4] to determine nanocomposite effective mechanical properties. the results of nanocomposite reinforced with randomly distributed nanotubes in the FEM model presented in Figure 1 and Table 1 & 2.

Table 1:Computed Young’s moduli of randomly distributed CNT-reinforced nanocomposite.

Table 2:Poisson’s ratios of randomly distributed CNTreinforced nanocomposite.

Figure 1:Schematic of the elastic interface model. A part of each component is shown.

The ratio of nanocomposite modulus to matrix modulus in the longitudinal direction, Ez/Em, is equal to 1.310 in this case for the matrix with modulus of 3.2GPa. This is about 20% lower than the uniformly distributed CNT reinforced nanocomposite longitudinal modulus [3-5]. A comparison of the results with those obtained for the uniform distribution of straight CNTs indicates that strengthening is much more homogeneous in the randomly distributed CNT case. That is, the ratios of nanocomposite longitudinal and transverse moduli to matrix modulus are close in this case (at equal Em values). These results suggest that the random distribution of the CNTs reinforces the matrix in all three directions. In fact, in case of transverse moduli, the portions of CNTs that are oriented along the x- and y-directions contribute to the nanocomposite moduli in those directions.

Figure 2:Variation of Ez/Em with matrix modulus for randomly oriented CNT-reinforced nanocomposite.

Nanocomposite longitudinal modulus decreases with increasing CNT inclination angle, thus limiting the overall effective modulus of the nanocomposite. The variation of nanocomposite longitudinal modulus to matrix modulus, Ez/Em, with matrix modulus is shown in Figure 2. Note that the ratio of nanocomposite longitudinal modulus to matrix modulus decreases as the matrix modulus increases in this case as well.

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