In recent years, due to their high specific mechanical properties, polymer matrix composites have been widely used. In particular, carbon nanotubes have been used as reinforcement because of their exceptional properties. In this work, the degree of dispersion and alignment of multiwalled carbon nanotubes into polyvinyl alcohol was quantified, which is a key information to optimize the mechanical properties of composites. For the dispersion of the multiwalled carbon nanotubes into the solution, a magnetic stirring and ultrasonic agitation were used. Finally, the mixture was dried to obtain a multiwalled carbon nanotubes reinforced polymer. The composites were mechanically stretched to obtain sheets with multiwalled carbon nanotubes aligned in the stretching direction. The layers obtained were prepared for transmission electron microscopy analysis. A dispersion quantification method based on the statistical distribution of horizontal and vertical separation distance between carbon nanotubes was used; a lognormal distribution was obtained. The angle of carbon nanotubes with respect to the stretching direction was used to quantify the alignment degree of carbon nanotubes. The bulk mechanical properties of the composites were measured by nanoindentation test; tensile test allowed to measure the mechanical properties of the composites in both the stretching and perpendicular directions to the stretching direction. Multiwalled carbon nanotubes showed a good dispersion and alignment degree and this, in conjunction with stretching, produced a high increase of both the stiffness and strength in the stretching direction, which allowed an increment of the mechanical properties measured by nanoindentation test; the best properties of the composites were reached with 0.5 wt% of MWCNTs.

Recently, a new manufacturing process for the production of metallic matrix composite materials reinforced with carbon nanotubes, known as sandwich technique has been proposed. This technique produces a material comprised of a metallic matrix and a banded structures-layers of multi-walled carbon nanotubes. However, among other issues, the matrix-reinforcement interface and the reinforcement dispersion degree are still open questions. The present study uses field emission scanning electron microscopy and high resolution transmission electron microscopy to probe that the method is capable to achieve a good dispersion of the multi-walled carbon nanotubes with no evidence of carbon nanotubes’ damage. The mechanical properties were measured by tensile and nanoindentation tests; improvements in the elastic modulus, yield and ultimate strengths were found, with respect to the unreinforced material.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.