Yutaka Kawahara

Influence of swelling of noncrystalline regions in silk fibers on modification with methacrylamide

The degrees of swelling of noncrystalline regions of domestic and tussah silk fibers were investigated by measuring the small-angle X-ray scattering intensity of the fibers in wet conditions and analyzing the scattering intensity based on a two-phase model, i.e., crystalline regions and water-swollen noncrystalline regions. The influence of the degree of swelling of noncrystalline regions on the graft treatment of these fibers with methacrylamide was investigated. The changes in the structure caused by the graft treatment were also analyzed using the wide-angle X-ray diffraction measurements. As compared with the tussah silk fibers, the domestic silk fibers showed a larger degree of swelling of the noncrystalline regions, and gained a larger amount of resin by the graft treatment. The crystallites with smaller sizes in the tussah silk fibers were destroyed preferentially by the graft treatment. For the domestic silk fibers, the crystallites were destroyed more seriously and rather homogeneously independent of the crystallite sizes.

Characterization of microvoids in mulberry and tussah silk fibers using stannic acid treatment

To investigate the volume, size, and number of microvoids in mulberry and tussah silk fibers, stannic acid gel was used as a contrasting medium to the small-angle X-ray scattering (SAXS). The influence of the stannic acid treatment on the structure of silk fibers was first investigated by using the wide-angle X-ray diffraction prior to characterization of the microvoids. The changes in crystallite size and degree of orientation with increasing stannic acid gel fraction in fibers are investigated, and it was found that the stannic acid treatment does not cause serious changes in crystallite size and degree of orientation. The changes in crystallinity indices were observed when the volume fractions of stannic acid gel in the fibers exceeded about 10%. Thus, it was confirmed that the structure of silk fibers was retained in the region of the stannic acid gel fraction less than 10%. SAXS measurements revealed that the number and the fraction of the microvoids are larger, while the sizes of the microvoids are smaller, for the mulberry silk fibers compared with the tussah silk fibers. The fraction macrovoids, however, is considered to be larger for the tussah silk fibers.

Enzymatic degradation of bacterial homo-poly(3-hydroxybutyrate) melt spun fibers

The effect of the higher order structure on the degradation behavior of bacterial homo-poly(3-hydroxybutyrate) (PHB) melt spun fibers by a PHB depolymerase from Commamonas testosteroni was investigated. After the enzymatic degradation, fibrillar structure remained at the surface of the drawn and annealed fibers, while a spongy structure appeared in the as-spun fiber. Similar spongy structure to the degraded as-spun fiber was observed in the core part of some drawn and annealed fibers after the fibrillar surface disappeared. The mechanical properties deteriorated as enzymatic degradation proceeded. After the amorphous region was degraded, β-form crystal, which seems to have less ordered structure, degraded in advance to the α-form crystal as revealed by WAXS measurements. However, these tendencies were less pronounced for the fiber annealed at high temperature under high tension. This result suggests that the β-form crystal in the fiber annealed at high temperature under high tension would have more ordered crystalline structure, which withstands against the attack by the enzyme.

DYEING BEHAVIOR OF HIGH-SPEED SPUN POLY(ETHYLENE TEREPHTHALATE) FIBERS IN SUPERCRITICAL CARBON DIOXIDE

The dyeing behaviors for several types of high-speed and normal speed spun poly (ethylene terephthalate) fibers were compared in supercritical CO2 fluid. At lower temperature and pressure, the high-speed spun fibers, which had inherently larger crystallite sizes and lower birefringence, showed a larger dye uptake than the other fibers. However, when the supercritical conditions were elevated to 125°C and 230 bar, the dye uptake of both types increased markedly and the difference in dye uptake between the fibers became small. This suggests that the swelling of fibers in supercritical CO2 fluid exceeded a certain degree and then the diffusion of dye molecules was promoted. The swelling also promoted the rearrangement of molecular chains and permitting cold crystallization to occur. The modification of fiber structure through the dyeing in supercritical CO2 fluid was serious especially for the fibers whose inherent structure was not so well developed.

Chemical Finishing of Bast Fibers and Woods Using Hydrolyzed Keratin from Waste Wool or Down

Chemical treatments using hydrolyzed keratin from waste wool or down are effective for enhancing the tensile properties of bast fibers. Treatment with hydrolyzed down keratin is also useful for suppressing shrinkage in the course of drying waterlogged archaeological wood excavated from sites. This novel treatment shows some degree of probable use for conservation treatments of such waterlogged woods.

Mechanical Properties and Structure of Methacrylamide (MAA) Grafted Silk Fibres

Graft copolymerizalion was performed on silk fibres by using methacrylamide (MAA), and changes in the mechanical properties and structure were investigated. Youngs modulus of the MAA grafted silk fibre was analysed by applying the law of mixture by regarding the MAA grafted silk fibres as a composite comprising silk fibres and a MAA polymer resin. Youngs modulus of the MAA polymer in the MAA grafted fibres was calculated to be approximately 4.6 GPa, which was larger than the value of a MAA polymer film. The MAA polymer in the MAA grafted silk fibres was oriented with respect to the fibre axis. When the volume fraction of the fibre in the MAA grafted silk fibres was more than 0.8, the tensile strength of the MAA grafted silk fibres agreed with the strength calculated by assuming that the failure of the MAA grafted silk fibres was caused by the failure of silk fibres and the MAA polymer was strained to the same extent as the silk fibres. The wide-angle X-ray diffraction measurements showed that crystallit...

Diffusion of Organometallic Compounds into High-Speed Spun Poly(Ethylene Terephthalate) Fiber in Supercritical Carbon Dioxide Fluid

High-speed spun poly(ethylene terephthalate) (PET) fibers that had higher crystallinity, larger crystallite sizes, and lower birefringence than ordinarily spun PET showed higher penetrability to Fe3(CO)12 and its derivatives in supercritical carbon dioxide fluid at a temperature of 50°C–80°C and a pressure of 18.2–19.3 MPa. The sizes of the channels caused by the fibrillation of PET fibers in supercritical CO2 fluid influenced the penetrability of these organometallic compounds.

Morphology of high-speed spun poly(ethylene-2,6-naphthalene dicarboxylate) fiber and its structural changes by the treatment in supercritical carbon dioxide fluid

An alkaline etching for high-speed spun poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) fibers revealed that these fibers have a well-developed fibrillar structure. From a comparison between the morphologies for PEN and poly(ethylene terephthalate) (PET) fibers, the high-speed spinning technique is useful to develop the fibrillar structure in both fibers. Treatment with supercritical carbon dioxide fluid promoted local rotation of the molecular chains for PEN and caused the crystal transition from β- to α-form more markedly as compared with the pressurized hot water treatment.

Transmission Electron Microscopic Investigation of the Morphology of High-Speed Spun Poly(Ethylene Terephthalate) Fibers

Permanganic etching was performed on high-speed spun (HSS) and regular fibers of poly(ethylene terephthalate) (PET), and their surface morphologies were investigated via the two-stage carbon replica method using a transmission electron microscope (TEM). The HSS PET fibers, with disordered amorphous regions, showed peculiar surface morphology; many small warts corresponding to the pits of etched disordered amorphous regions were observed. Such unevenness, however, was hardly observed on the surface of the permanganic-etched regular PET fibers, with well-oriented amorphous regions, or on the surface of alkali-etched HSS PET fibers. The permanganic etchant removed the disordered amorphous regions more preferentially compared with the alkali etchant.

Influence of steam treatment on crystalline regions of silks

aea pernvi ), and Japanese oak silk (Antheraea yamamay) were steamed and structural changes investigated by measuring the wide-angle x-ray scattering ( wAxs ) . The samples used for waxs were prepared by forming the fibers into a bundle. By adjusting the mass of the sample, the volume of the fibers irradiated by the x-rays was kept approximately constant. The wAxs intensity distributions were measured with an imaging plate (type R-axis DS3, Rigakudenki Ltd.) using CuKa x-rays monochromatized by graphite and collimated by two pinhole slits. Crystallinity was calculated by using the peak separation method from the equatorial wAxs intensity distribution. The degree of orientation was calculated from the full width at half maximum of the azimuthal intensity distribution of 201 diffraction. Shrinkage of raw silk fibers after steaming without tension is shown in Table I, and crystallinity and degree of orientation for raw silk fibers are shown in Table II. The WAXS pattern for raw mulberry silk fibers was modified when the fibers were steamed without tension control at I 15’C for 3 hours, but the wAxs pattern was unchanged when the fibers were steamed under a tension of 0.05 gf/d at 1 15°C for 3 hours. In contrast. the wAxs patterns for raw wild silk fibers were unchanged when these fibers were steamed without tension control