• Journal of Sericultural and Entomological Science
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• v.34 no.2
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• pp.41-51
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• 1992

In this thesis, both soap and enzymatic degumming method were adopted and the optimum degumming conditions were obtained. Difference between the two degumming methods in silk fiber state was investigated and analyzed on the basis of the results of physical testings, polarizing microscopy, scanning electron microscopy, viscosity measurement, (${\alpha}$＋$\varepsilon$) amino group contents measurement, birefringence measurement, amino acid analysis, thermal analysis, infrared spectroscopy and x-ray diffraction analysis. The results obtained were summarized as follows; Physical test results of the degummed silk fiber showed that the tenacity and the elongation of enzymatic degummed silk fiber were lower than those of soap degummed fiber. But SEM observation and amino acid analysis showed almost the same tendency in the two degumming methods. The viscosity of enzymatic degummed silk fiber was lower than that of soap degummed fiber, but (${\alpha}$＋$\varepsilon$) amino group contents was higher in the enzymatic degummed fiber. It can be suggested that the enzymatic degummed silk fibroin was more degraded than the soap degummed fibroin. The birefringence, endothermic temperature of DSC spectrum, IR crystallinity and X-ray lateral order factor of enzymatic degummed silk fiber were higher than those of soap degummed fiber. It seems that the enzymatic degummed silk fiber has the higher crystallinity than that of soap degummed one according to the above results. However, it can be inferred that these differences between soap and enzymatic degummed fiber would be lessened if pretreatment and aftertreatment were included in the enzymatic degumming process.

• Fashion & Textile Research Journal
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• v.4 no.2
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• pp.198-202
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• 2002

Degummed silk from Bombyx mori was dissolved in 9.3M lithium bromide solution. The regenerated silk fibroin films were completely ${\alpha}$-randomcoil type as shown by x-ray diffraction and infrared spectroscopy. The structural changes in silk fibroin induced by immersion into methanol and dilute hydrochloric acid and its photo-yellowing effect was studied. The changes of crystallinity were measured by infrared spectrometer. Yellowness index caused by ultraviolet irradiation were observed as a function of the structural change on silk fibroin. On treatment with methanol, ${\alpha}$-randomcoil silk film is converted to the ${\beta}$-form structure. After the treatment of hydrochloric acid on ${\beta}$-form structure in silk induced by immersion into methanol, ${\beta}$-form in silk fibroin is partially decreased. Crystallization owing to ${\beta}$-form transition reduced the initial yellowness index by ultraviolet irradiation. A little ${\beta}$-form structure in silk fibroin increased the initial yellowness in comparison with more ${\beta}$-form structure.

• International Journal of Industrial Entomology and Biomaterials
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• v.43 no.1
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• pp.16-21
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• 2021

The silkworm cocoon has recently attracted the attention of researchers because of its usefulness as a biomedical material (e.g., usage in the development of the membrane for guided bone regeneration and usage as a starting material for the fabrication of natural silk nonwoven fabric). The silkworm variety and strain have been reported as one of the important factors affecting the structure and properties of silk materials. This study examines the morphology and the molecular conformation of the silkworm cocoon at different cocoon measurement points, as well as the effect of the silkworm strain and rearing season on the morphology and crystallinity of the silkworm cocoon. The results show that the morphology of the outside of the cocoon does not differ depending on the cocoon measurement points, but that of the inside does. The silkworm cocoon crystallinity is not affected by the cocoon division. Interestingly, the crystallinity of the outside of the Jam101 cocoon differs depending on the rearing season, whereas it does not in other silkworm strains.

• International Journal of Industrial Entomology and Biomaterials
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• v.38 no.1
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• pp.18-23
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• 2019

Bombyx mori silkworm has many silkworm varieties and the structure and properties of silk can be varied depending on the silkworm variety. Therefore, the choice of proper silkworm variety can be an effective way to control and improve the performance of silk materials in biomedical and cosmetic applications. As a preliminary study, in the present study, thirty nine Bombyx mori silkworm cocoons were prepared and their molecular conformation and crystallinity were examined. Molecular conformation and the crystallinity of silkworm cocoons were different depending on the silkworm variety. Interestingly, the crystallinity index of outside of cocoon was different from that of inside of cocoon and the difference between the crystallinities of outside and inside of cocoon was varied depending on the silkworm variety. In this study, the silkworm variety cocoons were classified into three groups (Group 1, Group 2, and Group 3) based on the difference of crystallinities between outside and inside.

• International Journal of Industrial Entomology and Biomaterials
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• v.40 no.1
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• pp.6-15
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• 2020

Silk has attracted the attention of numerous research groups because of its unique properties as a biomedical material. Recently, studies on the biomedical application of silk cocoon, such as membranes for guided bone regeneration, have been conducted. As a preliminary study on silkworm cocoons, the morphological structure and crystallinity of cocoon of nine silkworm varieties with different sides are examined in this study. The morphological structure of the silkworm cocoon is shown to be dependent on silkworm variety and the cocoon layer (i.e. outside or inside). It is also shown that the silk filaments of the out layer are more bent and twisted compared to those of the inner layer. Furthermore, the crystallinity of the outer surface of all silkworm cocoons is found to be higher than that of the inner surface, regardless of the silkworm variety. Lastly, it is shown that the crystallinity index of the cocoon depends on the silkworm variety, implying that the structure of the cocoon varies with silkworm variety.

• International Journal of Industrial Entomology and Biomaterials
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• v.37 no.2
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• pp.36-42
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• 2018

Recently, silk sericin has attracted attention because of its unique properties as a biomaterial, including its UV resistance, moisturizing effect on skin, and wound-healing effect. Therefore, the preparation of sericin in various forms such as gel, film, fiber, and sponge is studied for cosmetic and biomedical applications, and the effect of the preparation conditions on the structure and properties of sericin forms is examined to maximize its performance. In this study, silk sericin films were prepared under different preparation conditions and heat-treated at high temperatures ($100-250^{\circ}C$) to examine the effect of heat treatment on the film structure. The order of the crystallinity index of the untreated sericin film is as follows: F25 (sericin film cast from formic acid) > WE25 (ethanol treated sericin film cast from water at $250^{\circ}C$) > W25 (sericin film cast from water at $250^{\circ}C$) > W100 (sericin film cast from water at $100^{\circ}C$). As the heat-treatment temperature was increased, the color of the sericin films changed gradually from colorless to yellow, brown, and black depending on the temperature. The crystallinity of the sericin film changed after the heat treatment, depending on the preparation condition. Whereas a sericin film cast from formic acid (F25) started to lose its crystallinity at $200^{\circ}C$, thus undergoing the highest loss of crystallinity among the sericin films studied, the rest (W25, WE25, and W100) showed a decrease in crystallinity at $250^{\circ}C$, owing to the disruption of the ${\beta}$-sheet crystallites due to heat.

• International Journal of Industrial Entomology and Biomaterials
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• v.38 no.2
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• pp.51-55
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• 2019

The structure and properties of silk polymers (fibroin and sericin) can be satisfactorily controlled by choosing a suitable silkworm variety and, hence, this parameter (i.e., silkworm variety) has attracted increasing attention. A previous study reported that the crystallinity of white colored silkworm cocoons depends on the silkworm variety. In the present study, sixteen yellow colored silkworm variety cocoons were produced and their molecular conformation and crystallinity were investigated. The conformation of the silkworm cocoons varied with the silkworm variety. Most cocoons exhibited ${\beta}$-sheet conformation, although random coil and ${\beta}$-sheet conformations co-existed in some cocoons (e.g., 21 and D90). The crystallinity of the silkworm cocoons varied with the silkworm variety and the measurement position of the cocoon (i.e., outer surface or inner surface). However, the difference in the crystallinity indices of the outer and inner surfaces comprising the cocoons varied with the silkworm variety, but was <2% for all cocoons, except for MAL.

• Journal of Sericultural and Entomological Science
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• v.35 no.1
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• pp.60-68
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• 1993

It has been known that the silk degumming treated by hot alkali solution is easy to handle but is liable to yield poor-quality silk due to the degree of degumming loss, incomplete-degumming or over-degumming. Therefore, many studies have been carried out on the silk degumming by enzyme in order to improve the quality of silk. However, no attention has been paid to the physicochemical analysis of enzymatic degummed silk. In this paper, two different degumming methods, soap and enzymatic, are compared in aqueous solution state of silk fibroin. The results can be summarized as follows: There was no significant difference between two solutions on the bases of polarizing microscopy, TEM observation and SDS-PAGE. Spherulite of silk fibroin was not observed in polarizing microscopy, however the leaf-shape fibril structure was developed upon solidification. The size of spherulites of silk fibroin in TEM observation were 30~120nm with a wide range of size distribution. The intrinsic viscosity of enzymatic degummed fibroin solution was lower than that of soap degummed solution. This can be explained that the silk fibroin was more degraded by enzymatic degumming method compared with the soap degumming method. SDS-polyacrylamide gel electrophoresis showed that the fibroin molecule was composed of large component of molecule weight above 50 kd and small component of molecule weight about 20 kd. There was no difference in crystallinity between two degumming methods on the bases of results of DSC thermograms and IR spectra.

• International Journal of Industrial Entomology and Biomaterials
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• v.26 no.2
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• pp.81-88
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• 2013

Wet-spun silk fibers have attracted the attention of many researchers because of 1) the unique properties of silk as a biomaterial, including good biocompatibility and cyto-compatability and 2) the various methods available to control the structure and properties of the fiber. Cellulose nanofibrils (CNFs) have typically been used as a reinforcing material for natural and synthetic polymers. In this study, CNF-embedded silk fibroin (SF) nanocomposite fibers were prepared for the first time. The effects of CNF content on the rheology of the dope solution and the characteristics of wet-spun CNF/SF composite fibers were also examined. A 5% SF formic acid solution that contained no CNFs showed nearly Newtonian fluid behavior, with slight shear thinning. However, after the addition of 1% CNFs, the viscosity of the dope solution increased significantly, and apparent shear thinning was observed. The maximum draw ratio of the CNF/SF composite fibers decreased as the CNF content increased. Interestingly, the crystallinity index for the silk in the CNF/SF fibers was sequentially reduced as the CNF content was increased. This phenomenon may be due to the fact that the CNFs prevent ${\beta}$-sheet crystallization of the SF by elimination of formic acid from the dope solution during the coagulation process. The CNF/SF composite fibers displayed a relatively smooth surface with stripes, at low magnification (${\times}500$). However, a rugged nanoscale surface was observed at high magnification (${\times}10,000$), and the surface roughness increased with the CNF content.

• Textile Coloration and Finishing
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• v.13 no.5
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• pp.1-1
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• 2001

As the basic study to investigate the mechanism of improvement in the dyeing fastness of natural dyes on silk fabrics the optical behavior of tannin solution, the optimal condition of tannin treatment and the changes of the physical structure of silk fabrics were studied in the treatment of tannin. Results obtained were as follows ; 1.The K/S values of tannin-treated silk fabrics were not changed by tannin content on silk fabrics but yellowing of tannin in treatment condition. 2. As the concentration of tannin was increased in its treating condition, the tannin content and K/S vague of tannin-treated silk fabrics were increased. 3. Because tannin gave rise to yellowing by hydrolysis and oxidation at high temperature, the higher tannin-treating temperature was, the lower the tannin content and K/S values of silk fabrics 4. The tannin content of silk fabric was higher in acidic treating condition and the highest K/S value was showed at pH 5. 5. As the tannin content of silk fabric was increased, the value of ζ -potential of it became negative. 6. As the tannin content of silk fabric was increased, the crystallinity and crystallite size of it were decreased. This meant that the fraction of amorphous region in the fibers increased. And the degree of orientation of it was decreased with the tannin treatment.