Hideaki Morikawa

Physical properties and dyeability of silk fibers degummed with citric acid.

Silk fibers from Bombyx mori silkworm was degummed with different concentration of citric acid, and the physical properties and fine structure were investigated to elucidate the effects of citric acid treatment. The silk sericin removal percentage was almost 100% after degumming with 30% citric acid which resulted in a total weight loss of 25.4% in the silk fibers. The surface morphology of silk fiber degummed with citric acid was very smooth and fine, showed perfect degumming like traditional soap-alkali method. The tensile strength of silk fiber was increased after degumming with citric acid (507MPa), where as the traditional soap-alkali method causes to decrease the strength about half of the control silk fiber (250MPa). The molecular conformation estimated by Fourier transform infrared spectroscopy and the crystalline structure evaluated from X-ray diffraction curve stayed unchanged regardless of the degumming with citric acid and soap. The dye uptake percentage of silk fiber degummed with citric acid decreased slightly, about 4.2%. On the other hand, the dye uptake percentage of silk degummed with soap was higher which indicates the disordering of the molecular orientation of the laterally ordered structure, accompanied with the partial hydrolysis of silk fibroin molecules by the alkali action of soap. The thermal properties were greatly enhanced by soap and citric acid degumming agents. Dynamic mechanical thermal analysis showed silk degummed with citric acid is more stable in higher temperature than that of soap. With heating at above 300 degrees C, the silk degummed with citric acid shows an increase in storage modulus and an onset of tan delta peaks at 325 degrees C and the melt flow of the sample was inhibited. The degumming of silk fibers with citric acid is safe and the results obtained are quite promising as a basis for possible future industrial application.

Structural characteristics and properties of Bombyx mori silk fiber obtained by different artificial forcibly silking speeds

To study the spinning condition of natural biopolymer silk, the silk fibers were directly acquired from Bombyx mori silkworm, N140 x C140 by a simple artificial forcibly silking method at the speed of 60, 120, 180 and 240 cm min(-1), respectively and its microstructure and physical properties were evaluated. The fine silk fibers (about 8 microm) were obtained at faster spinning speed, 240 cm min(-1). The tensile properties of silk fibers were remarkably increased with raising the forcibly spinning speeds. The beta-sheet structure contents of silk fibers obtained at higher speed were considerably increased. The fibers obtained by different spinning speeds exhibited a fairly similar X-ray crystallinity, while the degree of molecular orientation increased with decreasing the fiber diameter. The fine silk fibers obtained at higher speed (240 cm min(-1)) exhibited a slightly higher thermal stability, as shown by the upward shift of differential scanning calorimetry (DSC) decomposition temperature.

Fabrication of silk sericin nanofibers from a silk sericin-hope cocoon with electrospinning method.

In this study, silk sericin nanofibers from sericin hope-silkworm, whose cocoons consist almost exclusively of sericin were successfully prepared by electrospinning method. Scanning electron microscopy (SEM) was used to observe the morphology of the fibers. The effect of spinning conditions, including the concentration of sericin cocoon solution, acceleration voltage, spinning distance and flow rate on the fiber morphologies and the size distribution of sericin nanofibers were examined. The structure and physical properties were also observed by Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The optimum conditions for producing finely thinner fibrous sericin nanofibers without beads were the concentration of sericin solution above 6-8 wt%, acceleration voltage ranging from 25 to 32 kV, spinning distance above 9 cm, and flow rate above 0.06 cm min(-1). The mean diameter of as spun sericin fibers varied from 114 to 430 nm at the different spinning conditions. In the as-spun fibers, silk sericin was present in a random coil conformation, while after methanol treatment, the molecular structure of silk sericin was transformed into a β-sheet containing structure. Sericin hope nanofiber demonstrated thermal degradation at lower temperature than the sericin hope cocoon, which probably due to the randomly coiled rich structure of the sericin hope nanofiber.

Production of silk sericin/silk fibroin blend nanofibers

Silk sericin (SS)/silk fibroin (SF) blend nanofibers have been produced by electrospinning in a binary SS/SF trifluoroacetic acid (TFA) solution system, which was prepared by mixing 20 wt.% SS TFA solution and 10 wt.% SF TFA solution to give different compositions. The diameters of the SS/SF nanofibers ranged from 33 to 837 nm, and they showed a round cross section. The surface of the SS/SF nanofibers was smooth, and the fibers possessed a bead-free structure. The average diameters of the SS/SF (75/25, 50/50, and 25/75) blend nanofibers were much thicker than that of SS and SF nanofibers. The SS/SF (100/0, 75/25, and 50/50) blend nanofibers were easily dissolved in water, while the SS/SF (25/75 and 0/100) blend nanofibers could not be completely dissolved in water. The SS/SF blend nanofibers could not be completely dissolved in methanol. The SS/SF blend nanofibers were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and differential thermal analysis. FTIR showed that the SS/SF blend nanofibers possessed a random coil conformation and ß-sheet structure.

Nanocomposite of silk fibroin nanofiber and montmorillonite: Fabrication and morphology

The purpose of our research is creating a new nanocomposite material. Generally silk fibroin (SF) is regarded as a promising base material for biomedical uses. The incorporation of montmorillonite (MMT) into SF fibers would improve physical properties of the SF fibers. We investigated a new method of combining electospun SF with MMT. Specifically, electrospun silk nanofibers were treated with methanol and dipped in a MMT suspension. We could obtain a nanosheet composite of silk nanofibers and MMT. Their ultrastructures were successfully visualized by high resolution transmission electron microscopy. This compound was comprised of individual silk nanofibers surrounded by thin layers of MMT, each with a thickness of about 1.2 nm. This structure was confirmed by elemental analysis. We also performed IR, NMR and X-ray diffraction analyses in conjunction with morphological data. Conclusively we obtained a new composite of silk nanofiber and MMT, which has never been reported. Using this unique nanocomposite biological tests of its application for a scaffold for tissue engineering are under way.

Thermal characteristics and physical properties of silk fabrics grafted with phosphorous flame retardant agents

The production of flame retardant silk fabrics is very challenging and there is limited technology available on fire retardant silk applications. In this study, two flame retardant monomers having phosphoric groups, phosmer M and phosmer CL, were applied onto silk fabrics by a graft copolymerization technique. The grafted silk fabrics showed a high level of flame retardancy as evaluated by Japanese Industrial Standard micro-burner test method. It was shown that grafting techniques using phosmer CL are more effective than those using phosmer M to enhance the flame retardant functional properties of the silk fabrics. The differential scanning calorimetry, thermogravimetric analysis and thermomechanical analysis showed that the thermal stability of silk fibroin molecules was greatly enhanced by graft copolymerization with the used phosmers. The position of thermal decomposition for silk fabric shifted toward higher temperature after graft copolymerization with phosmer CL and M. Fourier transform infrared spectra showed evidence of the reaction between the used phosmers and silk. However, the surface morphology of silk fiber was very smooth and fine, and the tensile strength was not significantly affected regardless of the graft copolymerization with phosmer M and CL.

Electrospinning of silk fibroin from all aqueous solution at low concentration

Non-woven mats of Bombyx mori silk fibroin were fabricated using electrospinning with an all aqueous solution at <10wt% without any co-existing water soluble polymer such as PEO. The fibroin aqueous solution electrospinnability was affected by the fibroin molecular weight and the spinning solution pH. Hot-water treatment without any alkaline reagent or soap produced higher molecular weight fibroin than the typical degumming process did. The higher molecular weight fibroin provided good electrospinnability. Results show that the basic solution (pH10-11) is important for electrospinning at low concentrations of 5wt%. Evaluation of structural and mechanical properties of the non-woven mat fabricated with water solvent revealed that it is safe for use in the human body. It is anticipated for wider use in medical materials such as cellular scaffolds for tissue engineering.

Design and characterization of self-cleaning cotton fabrics exploiting zinc oxide nanoparticle-triggered photocatalytic degradation

Self-cleaning surfaces are functional structures with application in smart textiles. In this study, self-cleaning cotton fabrics were fabricated by coating photocatalytic zinc oxide nanoparticles (ZnO NPs) on cotton surfaces, using a traditional dip-pad-dry-cure coating process. The coatings and ZnO content-dependent self-cleaning properties of the coated fabrics were investigated to evaluate their potential in practical application. The ZnO NP-coated cotton fabrics were characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, and thermogravimetric analysis. Methylene blue was used as a test contaminant to qualitatively assess the self-cleaning properties of the fabrics. The removal efficiency was determined for fabrics with different ZnO contents, under different solar irradiation times. Consecutive photocatalytic degradations were carried out to investigate the self-cleaning durability of the fabrics. This involved repeatedly contaminating the same fabric position and subsequent cleaning by photocatalytic degradation. The self-cleaning properties of the fabrics depended on their ZnO NP content. A higher wt% of ZnO NPs in the coated fabric resulted in more pronounced photocatalytic degradation than fabrics with a lower wt%. The self-cleaning performance of the higher wt% ZnO NP fabric decreased slightly after the third consecutive photocatalytic degradation. Results of wash fastness showed color removal after 10 times washing under light irradiation. Moreover, the ZnO NP-coated fabrics exhibited excellent ultraviolet blocking properties. These findings provide a potential model for the practical application of self-cleaning textiles.

Development of combination textile of thin and thick fiber for fog collection bioinspired by Burkheya purpurea

Fog collection is getting to be known as an important technology all over the world. Textiles and fibrous materials have been used and investigated as fog collectors. Plants and animals need to collect water from air in an arid area. We focused on Berkhera purpurea which is one of the African thistles collecting moisture or fog by hairs. This plant captures fog droplets using finer and comparatively hydrophilic hairs supported by thicker and hydorophobic hairs. Mimicking these fibers’ system of thicker fibers and thinner fibers, hydrophobic and comparatively hydrophilic, we made a thinner fiber created by electrospun cellulose acetate on a thicker fiber of Nylon mesh as a supporting material. In the experiment, fine fibers of cellulose acetate are electrospun for 1 min which gave the superior fog capturing property.

Mechanics of water collection in plants via morphology change of conical hairs

In an arid area like the Namib Desert, plants and animals obtain moisture needed for life from mist in the air. There, some plants have hairs or fibrous structures on their leaf surface that reportedly collect fresh water from the air. We examined the morphology and function of leaf hairs of plants during water collection under different circumstances. We studied the water collecting mechanics of several plants having fibrous hairs on their leaves: tomato, balsam pear, Berkheya purpurea, and Lychnis sieboldii. This plant was selected for detailed investigation as a model because this plant originated from dry grassland near Mount Aso in Kyusyu, Japan. We found a unique feature of water collection and release in this plant. The cone-shaped hairs having inner microfibers were reversibly converted to crushed plates that were twisted perpendicularly in dry conditions. Microfibers found in the hairs seem to be responsible for water storage and release. Their unique reciprocal morphological changes, cone-shaped...