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Silk fibroin, a biodegradable component of silk, is increasingly used for various applications and studied intensively. Recently, a technique for preparing nanofibers without using chemicals has been gaining attention from the environmental impact and safety perspectives. This study focuses on the structure observation of ground silk fibroin (GF) prepared using a grinding method, which is a physical nanofibrillation method. The fabricated nanofiber samples were examined in detail using the X-ray diffraction (XRD), differential scanning calorimetry (DSC), micro Raman spectroscopy, and atomic force microscopy (AFM) techniques. The nanofibrillated structures were observed in both GF and regenerated silk fibroin (RF) samples prepared using the conventional method. As results, AFM images showed that the nanofibril diameter of GF was about 1.64 nm and that of RF was about 0.32 nm. Methanol treatment induced a structural transition from a random coil to a β-sheet for the RF film, but it had no effect on the GF film. Thus, it is suggested that the grinding method provides not only ultrafine silk fibroin nanofibers without using toxic reagents but also resistance to reagents such as methanol.

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The potential of termite (Coptotermes formosanus Shiraki) and fungal attacks [Fomitopsis palustris (Berkeley et Curtis) Murrill (FFPRI 0507) and Trametes versicolor (L. ex Fr.) Quel (FFPRI 1030)] against moso bamboo (Phyllostachys pubescens Mazel) were evaluated with regard to the seasonal and height-dependent changes of the free glucose and starch contents, which were measured by a newly developed method. The free glucose contents were generally lower in autumn and winter than in spring and summer, whereas the lowest starch contents were obtained in August, and the contents increased almost linearly up to February and March. In terms of the heightdependent fluctuation, the free glucose contents tended to decrease as the sampling heights increased. There was no special correlation between the free glucose or starch contents and the consumption by termites, even though higher mortalities were obtained in the bamboo-fed termites than in the wood-fed termites. However, a positive correlation between the free glucose contents and mass losses of the samples at 4-m and 8-m heights from the bottom by the decay fungi was observed. For starch, no influence on fungal attack was found.