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The effects of carbon nanotubes (CNTs) on the mechanical and fracture properties of ramie fiber-reinforced epoxy composites were investigated. Three-point bending, short beam shear, single-edge-notch bending, and Charpy impact tests were employed to evaluate the properties of ramie fiber-reinforced composites without and with CNTs modification. The fracture mechanisms were revealed with the aid of the dynamic mechanical analysis, Fourier transform infrared, and X-ray photoelectron spectroscopy. It was found that the mechanical and fracture properties of ramie fiber-reinforced composites were enhanced by incorporating multiwalled carbon nanotubes, except the impact fracture toughness. The unique chemical compositions and the multiscaled nanosized microstructures of natural fibers brought into focus new mechanisms for the improvement of the mechanical properties of natural fiber-reinforced composites. [ABSTRACT FROM AUTHOR]

Abstract: Spinnable carbon nanotube (CNT) arrays with different CNT structures have been synthesized using different growth methods and carbon sources, and long and stable fibers have been produced. Parameters of the nanotubes such as tube diameter, wall thickness, tube length and level of defects were found to play a more important role in the mechanical properties of the fibers than did the initial tube arrangement. To improve the fiber strength, as well as the modulus, the tubes must be long and have a small diameter and thin walls. The strongest fiber from double- and triple-walled CNTs is 1.23GPa in strength, and 32% and 221% higher than those from CNTs with ∼6 and ∼15 walls (932 and 383MPa), respectively. The fiber strength can be improved by 25%, up to 1.54GPa, after poly(vinyl alcohol) infiltration with volume fraction of ∼20%. Our study also shows that C2H4 is superior to C2H2 as the carbon source for the growth of mainly double- and triple-walled CNTs, and therefore the spinning of high-strength fibers. [ABSTRACT FROM AUTHOR]

The performance of carbon nanotube (CNT) fibers is limited by the intertube characteristics. Here we report a direct method of curing to improve mechanical properties of poly(amic acid)-infiltrated fibers. After curing at 190 °C for 60 min the fibers composed of double- and triple-walled CNTs, their strength is stably improved by 30.3%, from 1.58 to 2.06 GPa. The enhancement arises from the increase in shear stress between tube surfaces, by measuring the static frictional force of CNT fibers. Due to the existence of CNTs, the imidization temperature of polyimide drops greatly from 218 to 157 °C. [ABSTRACT FROM AUTHOR]

Carbon nanofiber (CNF)/graphene oxide (GO) hybrid papers are prepared by vacuum filtration of mixed dispersion with varied CNF to GO weight ratios. The effects of GO content, precursor GO size and reduction on the structure, electrical conductivity and mechanical properties of hybrid papers are studied. The electrical conductivity of hybrid papers shows a decreasing trend before reduction, while it drastically increases after reduction with increasing GO content, a testament to the dominant role played by GO sheets. The tensile strength and Young's modulus of hybrid papers exhibit similar performance with respect to GO content, confirming the importance of GO sheets. The GO sheet size has a positive effect on mechanical properties of hybrid papers through better alignment and their role as the substrate. [ABSTRACT FROM AUTHOR]