Thermally stimulated current (TSC) spectra of polyacrylonitrile were measured for temperatures ranging from 10 to 170°C. The TSC spectrum obtained with the polarization in a low polarizing field is characterized by two peaks at 110°C (αI peak) and at 150°C (αII peak). In the case of the high field polarization, a current reversal phenomenum was observed near at the αII peak temperature. It is considered that the αI and αII peaks are due to the dipolar relaxations in the amorphous and paracrystalline phases, respectively. The activation energies for these two dipolar relaxations were determained by thermal sampling method. The values obtained were 36 kcal/mol for the αII relaxation and 43 kcal/mol for the αI relaxation. The degree of crystallinity, which was calculated as a percentage of the polarization charge responsible for the αII relaxation against the total polarization, was 32%.
Molecular conformation and crystal structure of poly-O-benzyl-L-serine (POBLS) and poly-L-serine (PLS) as model compounds related to silk sericin were investigated by means of an infrared spectrometer, an x-ray diffractometer, a differential scanning calorimeter and a polarized scope. A cross β molecular conformation was found in both POBLS and PLS. Crystals were presumed to be made up by stacking of, β-sheets, which were formed by cross β molecular chains. Since the side chains were interposed by the sheets, hydrogen bonds were formed between the side chains or between the side chain and the main chain. A needle-like crystal was observed in POBLS. In contrast, a spherulite was found in PLS. However, the molecular alignment in both crystals was similar, i.e. polypeptide chains were folded perpendicular to the direction of crystal growth, while the side chains oriented paralled to it.
In order to estimate the effect of yarn density of fabric on breaking behaviour, five kinds of the fabrics with different yarn densities were prepared. The warp and weft yarns of these fabrics were composed of 20 denier polyester mono-filaments. The fabric, into which a sharp notch had been introduced, was fractured under a dynamic loading condition. The fracture process was monitored using a load cell and a streak camera. Moreover, the effects of the sample extension rate and the initial crack length on the fracture were investigated. As a result, it is found that the breaking behaviour of the fabrics can be explained to some extent in terms of an energy-balance concept.
Conformational change of silk fibroin coagulated from the aqueous solution by the mechanical stirring was examined by means of infrared spectroscopy, circular dichroism and x-ray diffractometry. The silk fibroin obtained by flow-induced crystallization showed unoriented molecular form “silk II” structure, nevertheless of the applying of shears with various rates and time intervals. In contrast, the silk fibroin obtained by the casting from the supernatant solution and/or the residual silk fibroin in the solution exhibited β-structure, of which content increased with increasing shear rate.