Wednesday, March 12, 2008

Nanotubes Show Their Strengths in Polymer Fibres

Researchers at Queen Mary, University of London and Nanoforce Technology Ltd. in the UK, have successfully produced single-walled nanotube reinforced polymer fibres and tapes that are as strong as theory predicts.

The work shows for the first time the true reinforcing potential of single-walled carbon nanotubes (SWNTs) with effective properties of nanotubes in composites, which are close to their theoretical values.

Prof. Ton Peijs, who heads the research team said: "The problem with carbon nanotubes has always been that despite their amazing potential of becoming the ultimate reinforcing fibre for the next generation of high-performance composites, their success in actually delivering these mechanical properties when embedded in polymer composites has been limited. Despite promises of tensile strengths of 100 GPa or more – 15 to 40 times higher than carbon fibres – their efficiency after embedding them in polymer matrices has often been poor with effective reinforcing properties not far better than those of carbon fibres”.

Dr. Zhujuang Wang, who processed and characterized the new nanocomposite fibres and tapes during her PhD study at QMUL, says that in order to get the most out of nanotubes the composite need to exhibit a good dispersion as well as good interfacial interaction of the nanotubes with the hosting matrix. Moreover, similar to polymer molecules the excellent intrinsic mechanical properties of nanotubes can only be expected if they are all fully aligned. The QMUL team has explored many different nanotube/polymer combinations but the best results were obtained for a system based on poly(vinyl alcohol) (PVA) and SWNTs. Using solid-state drawing technology the team showed that they can effectively align nanotubes along the polymer fibre axis and triple the tensile strength of the PVA fibre or tape with the addition of only 1 wt.% of SWNTs. Further analysis of the materials showed that the stress carried by the SWNTs in these oriented PVA composites was very close to the theoretical tensile strength of nanotubes, indicating the exceptionally high reinforcing efficiency of the SWNTs in these materials.

In order to make the research a commercial success still some significant further developments are needed. Peijs said: “Although our work shows that indeed the impressive mechanical properties of nanotubes can effectively be translated into high-performance composites, the challenge is still to make a nanocomposite fibre of record breaking strength. We expect that in order to make such a fibre we will need to incorporate at least 5 wt.% of perfectly aligned and dispersed SWNTs in a highly oriented PVA fibre. So far we have only achieved good dispersions up to 1 wt.% of nanotubes, which makes that our current nanocomposite fibres and tapes have still significantly lower strengths than ultra-strong carbon fibres possessing strengths up to 7 GPa. If dispersion problems at high nanotube loadings can be overcome, nanocomposite fibres with strengths exceeding those of the strongest carbon fibre are possible. Such fibres can find their way in a large range of advanced composite materials, ranging from structural materials in sports equipment and aircraft to anti-ballistics.

The researchers published their work in Nanotechnology in a paper entitled “Extraordinary reinforcing efficiency of single-walled carbon nanotubes in oriented poly (vinyl alcohol) tapes”.

Publication Date: 11/03/2008

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