Han Gi Chae

Making Strong Fibers

Research toward carbon nanotube fibers that are light yet extremely strong is progressing rapidly.

Polyethylene Crystallization Nucleated by Carbon Nanotubes under Shear

Polyethylene crystallization under shear has been studied in the presence of single-wall, few-wall, and multiwall carbon nanotubes (SWNT, FWNT, and MWNT). Polyethylene crystal d-spacings for (110) and (200) planes in polyethylene/carbon nanotubes (CNT) are smaller than in the control polyethylene without CNT and the polymer chain is oriented along the CNT axis. The single-wall carbon nanotube templated polyethylene crystals do not redissolve in boiling xylenes; instead, the chain morphology transforms to an amorphous conformation but remains oriented along the nanotube axis. SWNT crystal peaks were also observed in polyethylene/SWNT fibers.

Observations on Solution Crystallization of Poly(vinyl alcohol) in the Presence of Single-Wall Carbon Nanotubes.

PVA/SWNT dispersions yield aloe plant-like crystals, where the leaves are single crystals templated by PVA coated SWNT. Longer growth times (≈18 months) lead to hexagonal rod-like crystals. HR-TEM images show evidence that PVA molecules are aligned parallel to the SWNT axis. WAXD, electron diffraction, and HR-TEM observations of these aloe plant and hexagonal crystals suggests evidence for possible PVA-SWNT epitaxy. Wide-angle and electron diffraction data of these crystals also show that the structure seems to mimic the 2D hexagonal crystal packing of SWNT. PVA lattice images and moiré fringes were also observed in the leaf-like crystals.

Development of single filament testing procedure for polyacrylonitrile precursor and polyacrylonitrile-based carbon fibers

Single filament testing protocols for polyacrylonitrile precursor and polyacrylonitrile-based carbon fibers have been developed to ensure reliable tensile results that can be compared to the standard testing protocols used by the industry. Accurate carbon fiber linear density measurement by vibroscope was quite sensitive to the pre-stress applied to the fiber. Gauge length dependence testing of the commercial carbon fibers exhibited that tensile strengths obtained at 25.4 mm gauge length are comparable to those reported by the manufacturer using the standard strand testing results. On the other hand, experimental carbon fibers that have not been surface treated or sized, showed that single filament tensile strength values at 6 mm gauge length was comparable to the strand testing results. In addition, the compliance corrected tensile moduli of carbon fibers obtained by single filament tests were also comparable to the moduli obtained from the standard strand testing results. A modified Weibull analysis, which accounts for sample volume effects, has also been used to determine the Weibull modulus of both the commercial and experimental carbon fibers.