Density estimations and comparisons of a fragmented single fiber using X-ray computed tomography.

A commercial X-ray computed tomography (CT) apparatus using a quasi-monochromatic beam was utilized for density estimations and comparisons of a fragmented single fiber. The validation of quasi-monochromaticity of the X-ray source was investigated by radiograph measurements. For the case of a transmittance higher than 50%, the contribution of Cu Kα characteristic X-rays was dominant. To realize a sufficient statistical quality, an attempt to increase the number of averaged voxels was demonstrated using the neighboring slices of the 3D-CT image. A minimum value of the coefficient of variation (CV) was achieved using multiple images rather than using a single image. The observed values of the inverse of the transmitted X-ray intensity (CT value) of the polymers showed a fairly good relationship with their density. An analytical curve derived from measurements of reference samples of known densities could provide the relative density of an unknown fragmented fiber down to the size of 30 µm in diameter and 35 µm in length. The CV of the estimated density was from 1.5 to 2%, which was estimated from the CV of CT values. Moreover, the correlation of CT values was improved with the linear absorption coefficient than the density. A better performance of discrimination of polymers including fibers might be realized with the difference of linear absorption coefficients for X-rays.

Non-destructive analysis of hollow-shaped single fibers using X-ray computed tomography.

A commercial high-resolution X-ray computed tomography (CT) was utilized for non-destructive analysis of single fibers. The micro-CT apparatus was employed because it is applicable to both colored and colorless fibers. A sample preparation using adhesive sheets was demonstrated, and the method is similar to typical tape-lift sample collection method in crime cases. Different cross-sectional shapes of nylon and polyester single fibers were non-destructively distinguished, and the method is applicable to all types of fibers. Cross-sectional areas, aperture ratios, and volumes of individual fibers were directly and automatically measured using the open-source software. The observed parameters were within a coefficient of variation of 3%. In addition, a mass of a single fragment of a fiber can be estimated when the local density is given.

Feasibility Studies of X-Ray Computed Tomography for Forensic Examination of Single Fibers.

Non-destructive observations of cross-sectional shapes of acrylic single fibers using X-ray computed tomography (CT) were performed. A commercial X-ray CT apparatus (Rigaku nano3DX) was employed because of its micrometer-scale spatial resolution and remarkable image contrast for soft matter. We assessed two types of sample support, a paraffin strip and a nylon string, for single fiber samples in terms of easy handling and sample recovery. Fixed individual single fibers were loaded into a narrow polyimide tube in both cases, and the tube ensured that the sample remained in the field of view during the CT measurements. In both cases, the cross-sectional shapes of individual single fibers could be distinguished, with a circular shape for one sample and a triangular shape for the other. However, the support using a nylon string was found to be more suitable for further analysis. The cross-sectional profile of the obtained tomographic image showed a clear difference between polyimide and nylon. The intensity ratio or the image contrast corresponded to that of the local densities. It was also found that the effect of the artifact appeared at around the boundaries of the objects, but the local density could still be utilized for examining individual single fibers.