Md. Majibur Rahman Khan

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.

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.

Surface Morphology and Properties of Bombyx mori Silk Fibroin Fiber Treated with I-2-KI Aqueous Solution

The surface morphology, thermal and mechanical properties of Bombyx mori silk fibroin (SF) fiber treated with a 1.23 N iodine-potassium iodide (I2-KI) aqueous solution were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry, thermogravimetric analysis, and tensile measurements to clarify the effects of the iodine treatment. SEM and AFM analyses indicated that the SF fiber surface became rougher by the absorption of polyiodide ions. The mechanical properties of iodinated SF showed an increase in Young’s modulus, and strain remained constant although ultimate tensile strength slightly decreased. The thermal stability of SF molecules was greatly enhanced by iodine treatment. Iodinated SF fibers should be an attractive candidate for biomedical applications such as for producing antimicrobial filters, iodine containing wound-healing anion exchange fibers, etc.

Mechanical performance of wool fabrics grafted with methacrylamide and 2-hydroxyethyl methacrylate by the Kawabata Evaluation System for Fabric method

Wool fabrics were graft copolymerized with methacrylamide (MAAm) and 2-hydroxyethyl methacrylate (HEMA) in aqueous media, using a chemical redox system as an initiator. After grafting, the mechanical properties related to the hand evaluation, such as tensile, shearing, bending, compression and surface properties of wool fabrics, were evaluated by means of the Kawabata Evaluation System for Fabric. The surface morphology was examined by scanning electron microscopy. The results revealed that the surface morphology and low-stress mechanical properties of wool fabrics were remarkably changed after grafting with HEMA. The weight gain of the wool fabrics grafted with HEMA increased rapidly in the initial grafting stage and reached saturation level at 17 wt% after 20 minutes. Small deposits of oligomers were visible on wool surfaces and typical scale patterns were changed after grafting wool fabric with HEMA. The slope of the shearing hysteresis curves in the weft and warp directions for wool fabrics grafted with HEMA was increased compared with the control and wool fabrics grafted with MAAm. These results imply that the changes in tensile, shearing, bending and compression behavior of grafted wool fabrics are due to the reduction of the free internal volumes of the fabrics, leading to a tightening of its texture.

Structural and physical properties ofAntheraea pernyi silk fibroin fiber treated with I2-KI aqueous solution

Silk fibroin (SF) fiber from theAntheraea pernyi silkworm was treated with a 1.23 N iodine-potassium iodide (I2-KI) aqueous solution, and the structure and physical properties were investigated to clarify the effects of the iodine treatment. The noticeably high weight gain value of SF fiber, about 25 wt% was attributed to the absorption of polyiodide ions in the form of I3− and I5−. Fourier transform infrared spectroscopy and X-ray diffraction measurements suggested that polyiodide ions mainly entered the amorphous region. In addition, a new sharp reflection on the meridional direction, corresponding to a period of 7.0 Å, was observed and indicated the possibility of the formation of mesophase structure ofβ-conformation chains. Dynamic viscoelastic measurements showed that the damping tanδ peak at 270°C gradually shifted to lower temperature in the iodinated SF fibers, suggesting an enhancement of the molecular motion of the fibroin chains induced by the presence of polyiodide ions. With heating above 254 °C, the iodine component introduced intermolecular cross-linking of SF, and the melt flow of the sample was inhibited. The thermal decomposition stability of fibroin molecules was greatly enhanced by iodine treatment.