a b s t r a c tDrawing, winding, and pressing techniques were used to produce horizontally aligned carbon nanotube (CNT) sheets from free-standing vertically aligned CNT arrays. The aligned CNT sheets were used to develop aligned CNT/epoxy composites through hot-melt prepreg processing with a vacuum-assisted system. Effects of CNT diameter change on the mechanical properties of aligned CNT sheets and their composites were examined. The reduction of the CNT diameter considerably increased the mechanical properties of the aligned CNT sheets and their composites. The decrease of the CNT diameter along with pressing CNT sheets drastically enhanced the mechanical properties of the CNT sheets and CNT/epoxy composites. Raman spectra measurements showed improvement of the CNT alignment in the pressed CNT/epoxy composites. Research results suggest that aligned CNT/epoxy composites with high strength and stiffness are producible using aligned CNT sheets with smaller-diameter CNTs.

a b s t r a c tAligned multi-walled carbon nanotube (CNT) sheets produced from aligned CNT arrays were used to develop high volume fraction CNT/epoxy composites. Stretching and pressing techniques were applied during CNT sheet processing to straighten the wavy CNTs and to enhance the dense packing of CNTs in the sheets. Raman spectra measurements showed better CNT alignment in the CNT sheets and the composites after stretching and pressing. Aligned CNT/epoxy composites with CNT volume fraction up to 63.4% were developed using hot-melt prepreg processing with a vacuum-assisted system. Stretching and pressing of the CNT sheets enhanced the mechanical properties of high volume fraction CNT/epoxy composites considerably. Stretching and pressing increased tensile strength of the composites by 32% and elastic modulus of the composites by 27%. Applying stretching and pressing is effective for production of superior CNT sheets with high alignment and dense packing of CNTs, thereby supporting the development of high-performance CNT composites.

Spinnable carbon nanotubes enable us to produce carbon nanotube assemblies such as yarn and sheet without binder. Untwisted carbon nanotube yarn is one of the assemblies. Untwisted carbon nanotube yarns are composed of unidirectionally aligned carbon nanotubes along with the yarn axis, and thus untwisted carbon nanotube yarns are an ideal preform for composite fabrication with high mechanical performance. In this study, untwisted carbon nanotube yarns with varied densities were prepared by using spinnable carbon nanotube forests, and the tensile properties were examined. Furthermore, an analytical model of tensile properties for untwisted carbon nanotube yarns was proposed based on the shear-lag model. The proposed model can predict the tensile behavior of an untwisted yarn from the tensile modulus and strength of a carbon nanotube, the volume packing fraction of carbon nanotubes for the untwisted yarn, and shear stress exerted on the slipped region of a carbon nanotube. Then, the proposed model was applied to estimate the elastic modulus and tensile strength of a carbon nanotube from the tensile properties of untwisted carbon nanotube yarns. In our case, the estimated tensile elastic modulus of a carbon nanotube was about 200 GPa, and the estimated tensile strength of a carbon nanotube was about 1.9 GPa.

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