Surface analysis of novel fibroin films based on well-preserved crystalline structures.

We recently reported that a highly homogeneous aqueous suspension of fibroin nanofiber (FNF) can be simply obtained by mechanical water-grinding a heterogeneous aqueous fibroin slurry and that the FNF in the suspension preserves the native ß-sheet secondary structure during this mechanical treatment. The current study reports the surface properties of well-preserved crystalline structure novel FNF film from water-grinding preparation as compared with those of typical, conventionally prepared regenerated fibroin (RF) film. RF film was not treated with alcoholic solutions and was verified to be amorphous from a WAXD diffraction diagram. The air-side surfaces of the FNF semi-crystalline and RF amorphous films were studied to clarify differences using scanning electron microscopy (SEM), atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), static water contact angle, and X-ray photoelectron spectroscopy (XPS). The well-preserved crystalline in the FNF film was found to exist near a slightly deep surface region and to act as a physically cross-linking domain, governing the molecular motions of the amorphous polypeptide chains at the very shallow surface region.

Characterization of Ground Silk Fibroin through Comparison of Nanofibroin and Higher Order Structures.

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 ß-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.

Comparison of cellulose nanofiber properties produced from different parts of the oil palm tree.

Cellulose nanofibers (CNFs) were obtained from three types of oil palm wastes, mesocarp, empty fruit bunch (EFB), and palm kernel shell (PKS), as well as the trunk of the oil palm tree, to compare their morphological, thermal, and mechanical properties. Despite large differences in the chemical components of cell walls in the raw materials, the production of CNFs from all parts of the oil palm were achieved in this work. The morphology and mechanical properties of the CNF sheets obtained from the trunk had advantages over the CNF sheets from wastes, while the thermal degradation properties showed no advantage. Cellulose crystallinity of the CNF sheet from the mesocarp and PKS had lower crystallinity (69.1 and 71.1%), and the highest crystallinity of 77.0% was exhibited by the sheet from the trunk. The value of specific tensile strength and specific Young's modulus were highest in the CNF sheet of the trunk, and lowest mechanical properties shown in the CNF sheet from the mesocarp. These results strongly suggested that the CNF could be obtained from all parts of the plants, but their properties may vary.