山田 由佳子

Two kinds of cotton fibers cultivated by different methods were measured and the mechanical properties of these fibers were compared with the mechanical properties of cotton yarns made of organic cotton fiber and non-organic cotton fiber. In this study, the mechanical properties of single cotton fibers and cotton yarns the authors measured and the moduli were calculated by assuming that the cross-section of the cotton fiber is elliptical. It was also found that the strains and stresses of breaking point of organic cotton fibers were larger than those of non-organic cotton fibers. Cotton fibers cultivated in different areas were then examined and it was found that the moduli of cotton fibers cultivated in the northern or southern hemisphere (USA and Australian cottons in this study) were very similar, and the yarn properties for yarns made from cotton fibers from both areas were also very similar. However, the yarn consisting of a mixture of cottons in the northern and southern hemispheres had larger strain, torsional stiffness and hysteresis. It was concluded that the deterioration of fibers consisting of a mixture of cotton contributes to the yarn properties, because the rules of surface orientation differ for cotton fibrils cultivated in the northern and the southern hemisphere as shown in Onogi's study (Textile Res. J 66, 406-410 (1996)).

In this study, we investigate the relationship between the UVR-shielding rate and the moisture regain of plain woven fabrics. Samples are 8 cotton fabrics and 4 polyester filament fabrics each of which have different porosity. In the case of cotton fabrics, the moisture cause fiber swelling in the wet condition and the porosity decrease with increase of the moisture regain. However, the UVR-shielding rate decrease with the increase of the moisture regain. It is assumed that the result is caused by the increase of the UVR transmitting through a fiber by the fiber swelling. The relationship between the moisture regain and the UVR-shielding rate result in linearity up to 80% of the moisture regain, and besides, significant difference on the inclination of each sample is not found. Therefore, we can estimate the UVR-shielding rate by using porosity under the standard condition and the moisture regain. In the case of polyester filament fabrics, it is found that we can estimate the UVR-shielding rate by the same way as the cotton fabrics. However, the range of the moisture regain in which the UVR-shielding rate can be estimated is smaller than that of cotton fabrics.