RESUMEN
Cellulose nanofibers (CNFs) derived from oil palm trees were utilized to reinforce polyvinyl alcohol (PVA) films by either casting or impregnating. CNFs derived from trunks of the oil palm tree were dispersed well in a PVA film by the casting method. Using the impregnating method, however, a sandwich construction with CNFs and PVA was obtained, which was confirmed using attenuated total reflectance Fourier transform infrared spectroscopy. The thermal stability, tensile strength, and Young's moduli of the PVA/CNF nanocomposite films were increased by compounding CNFs at different concentrations using both the casting and impregnating methods. However, the impregnated nanocomposite films showed higher thermal melting temperature and higher tensile toughness than those obtained by the casting method. No obvious differences appeared in the X-ray diffraction patterns or thermal decomposition behavior between the impregnated and cast nanocomposite films. In addition, adding CNFs was confirmed to increase the crystallinity of PVA.
RESUMEN
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.
RESUMEN
An oligomaltose-carrying polystyrene "glycoconjugate polystyrene" was synthesized by the homopolymerization of 4-vinylbenzylamine oligomaltonic amides, derived from maltose, maltotriose, maltopentaose, and maltoheptaose. The resultant amphiphilic glycoconjugate polystyrenes were dissolved in 0.1 M aqueous urea, and their structures characterized by small-angle X-ray scattering and molecular modeling. "Glycoconjugate polystyrene" was found to behave as a "molecular bottle brush", composed of a large pseudo-helical polystyrene backbone and carbohydrate brushes. A large pseudo-helical polystyrene backbone is formed by a random sequence of TT, TG, and/or TTGG. The results indicate that the cross-section of a backbone chain with smaller oligosaccharide side-chains is obliged to expand more than that with longer side-chains. Even with rigid hydrophilic pendant oligosaccharide chains, the larger pseudo-helix of the main chain could orient the side-chains so as to envelop the hydrophobic backbone in aqueous solution. Thus the conformation of the main chain is determined not only by the chemical nature of an oligosaccharide chain but also by its length.