Fully hydrolyzed ultra-high-molecular-weight polyvinyl alcohol (PVA) electrospun fibers with uniform diameters of about 200 nm were fabricated by reducing the viscosity of PVA in aqueous solution. A novel viscosity-modifier (hydrazine monochloride, HMC) gradually reduces the viscosity of PVA aqueous solution over a period of several days. This phenomenon is counter to the usual effect of ionic salt addition. After being stored for several days, the viscosity decreased by up to 60 % compared to that of an equivalent pure PVA solution. Using HMC to control the viscosity of the PVA solution made it possible to fabricate ultrafine electrospun fibers. In addition, the hot water resistance of the fibers was obviously improved by annealing.
The scientific identification of excavated bast fibers (mainly hemp and ramie) is one of the important procedures for the conservation of textile cultural properties. In this paper, the new procedure to distinguish the kind of excavated bast fibers was proposed. Though excavated bast fibers are usually degraded by the long-term preservative environment, it was confirmed that they show still dichroism in infrared spectroscopy. Since the allowed amount of sampling for scientific analysis is severely limited in archaeology or in cultural properties, the authors used polarized synchrotron FT-IR Micro-spectroscopy. All of the bast fibers showed peaks at 1160, 1110, 1060, 670, 620 and 560cm-1 . The corresponding modern reference bast fibers also show similar dichroism in polarized FT-IR Micro-spectroscopy. Though SEM images of excavated bast fibers indicate the degraded appearance, the results of polarized FT-IR spectrum show that a part of the molecular orientation of cellulose and hemicelluloses are still remained in fiber structure. The authors are continuing the research for the identification of excavated bast fibers using polarized FT-IR Micro-spectroscopy.
To preserve excavated archaeological textile fibers, a preliminary investigation of materials and the degraded state of samples is indispensable. The excavated samples are valuable because the remaining amounts are usually scarce and often heavily degraded. In the past, infrared microscopic analysis has been used to overcome the above-mentioned limitation and has sufficient sensitivity for the analysis. However, the identification of bast fibers, such as hemp and ramie, using FT-IR, is rather difficult because their infrared spectra resemble each other. In this report, we investigated a procedure using a polarized radiation beam for the FT-IR microscope at JASRI (SPring-8) Beamline BL43IR for the identification of bast fibers. A minute amount of sample fibers was pressed by diamond plates to make a flat thin layer. The polarized absorbance spectrum of the sample on the diamond plate was measured. The polarizer was rotated from 0o to 90o, measuring the spectrum at 15o intervals. Both of the bast fibers, hemp and ramie, showed a decrease in the absorption peaks at 1428,1371,1160,1110, and 1060cm-1 with increase in the rotation angle of polarizer. Since the absorption peak intensity at 2900cm-1 of both fibers remained constants, the decreases were expressed as the ratios to the 2900cm-1 values of hemp and ramie. The plotted curves showing the relation between peak intensity versus polarizer angle are distinctly different between hemp and ramie. The infrared dichroism could be due to the difference in molecular orientation of the fiber components (cellulose and hemicelluloses) of hemp and ramie.
Bis maleimide-terminated poly-L-lactide (M-PLLA-M) and bis furan-terminated poly-D-lactide (F-PDLA-F) were synthesized by isocyanate coupling reactions of mono maleimide-terminated PLLA (M-PLLA) and mono furan-terminated PDLA (F-PDLA) that had been prepared by the ordinary ring opening polymerization of L- and D-lactides with N-(2-hydroxyethyl)-maleimide and furfurylamine as the initiators, respectively. Both the M-PLLA-M and F-PDLA-F were dissolved in CH2Cl2 in 1:1 ratio and subjected to the ordinary electrospinning where the initial polymer concentration was increased up to 20 wt% because of the prepolymer state of the solute and the fiber diameter could be retained in nanometer to submicron size. The molecular weight of the polymers was found to have increased from 1.0 × 104 to 2.5 and 4.5 × 104 after the electrospinning and post annealing, respectively, due to the spontaneous chain extension taking place by the terminal Diels-Alder reaction of M-PLLA-M and F-PDLA-F to form a stereoblock polylactide. The as-spun fibers were amorphous or partially semi-crystalline, whereas the annealed fibers become fully crystalline due to the formation of the stereocomplex showing a melting temperature above 200oC.