Degumming Treatment Research Articles

Isothermal crystallization kinetics of silk fibroin fiber‐reinforced poly(ε‐caprolactone) biocomposites

AbstractBACKGROUND: Poly(ε‐caprolactone) (PCL) has attracted great attention due to its wide applications for pharmaceutical controlled released systems and implanted polymer devices. In this study, silk fibroin fiber (SF) obtained from degumming treatment of silk was used to prepare novel reinforced PCL biocomposites. The isothermal crystallization behavior of these composites was investigated using differential scanning calorimetry measurements.RESULTS: With a decrease of isothermal crystallization temperature (Tc) and an increase of fiber filler, the crystallization time of the SF/PCL composites becomes shorter, the crystallization rate constant (K) increases and the Avrami exponent (n) gradually decreases (being between 1 and 2). The crystallization of PCL and SF/PCL composites occurs in the same regime. With the gradual addition of fiber, lateral surface free energy (σ) is nearly unchanged, but fold surface free energy (σe) decreases.CONCLUSION: Heterogeneous nucleation is dominant and different growth morphologies coexist during the isothermal crystallization process of the SF/PCL hybrid systems. Although the introduction of SF obviously increases the overall crystallization rate of PCL, the growth rate constant and nucleation constant of PCL are reduced because of the confinement effect of fiber network structures on the molecular mobility of polymer molecular chains. Copyright © 2009 Society of Chemical Industry

Mechanical Properties of Silk Yarn Degummed with Several Proteases

The silk filament spun by the silkworm (Bombyx mori) is composed of two fibroin filaments held together by a cementing layer of sericin. Fibroin and sericin account for about 75 wt% and 25 wt% of the raw silk, respectively. The degumming process consists in removing the sericin layer prior to dyeing using a solution of soap, synthetic detergents, or proteolytic enzymes. Silk yarn was degummed with different commercially available enzymes, two alkaline, a neutral, and an acidic proteases and the results were compared in terms of physical and mechanical properties. Proteases were used under optimum conditions of pH and temperature. The treatments were carried out with three different enzyme dosages, that is, 0.2, 1, and 5 U/g yarn. Soap was taken as the standard method of degumming and enzymatic treatments were compared with this method. The degree of polymerization of silk fibroin was assessed by measuring the intrinsic viscosity of the treated samples.

Silk sericin–insulin bioconjugates: Synthesis, characterization and biological activity

When silk fiber derived from Bombyx mori was subjected to degumming treatments twice in water and subsequent degraded processing in slightly alkaline aqueous solution under high-temperature and high-pressure, the water-soluble silk sericin peptides (SS) with different molecular mass from 10 to 70 kDa were obtained. The sericin peptides could be conjugated covalently with insulin alone with cross-linking reagent glutaraldehyde. The physicochemical properties of the silk sericin–insulin (SS–Ins) conjugates were determined by Enzyme-Linked Immunosorbent Assay (ELISA). The biological activities of SS–Ins bioconjugates were investigated in vitro and in vivo. The results in human serum in vitro indicated that the half-life of the synthesized SS–Ins derivatives was 2.3 and 2.7 times more than that of bovine serum albumin–insulin (BSA–Ins) conjugates and intact insulin, respectively. The pharmacological activity of SS–Ins bioconjugates lengthened to 21 h in mice in vivo, which was over 4 times longer than that of the native insulin. The immunogenicity of silk sericin and the antigenicity of SS–Ins derivatives were not observed in both rabbits and mice. The bioconjugation of insulin with silk sericin protein evidently improved both physicochemical and biological stability of the polypeptide.

Tensile behavior and morphology of differently degummed silkworm (Bombyx mori) cocoon silk fibres

Tensile tests have been performed on silkworm cocoon silk fibres degummed using five different methods: distilled water, boracic acid–sodium borate buffer, sodium carbonate, urea and succinic acid. Using an electronic single-fibre tensile instron, the force–displacement curves were obtained for each condition. Effects of degumming on silk include a decrease in the initial elastic modulus and a decrease in the proportional limit (i.e., yield point). These results suggest that degumming weakens at least one type of non-covalent interaction of core fibrion, such as hydrogen bonds and Van der waal's bonds. The stress–strain curve determined from a force–displacement curve as rescaled by the corresponding sample cross-sectional area failed to reproduce the actual mechanical properties of two fibroin core fibres because of variable degradation of the sericin coating. The two important factors associated with degumming could affect the tensile properties of silkworm silk: 1) the change in the microstructure of two core fibroin, and 2) the degumming ratio. SEM was used to observe visually the morphology and fractography of differently degummed cocoon silk fibres. Effects of different degumming treatments on the tensile behavior, mechanical properties, morphology and fractography of cocoon silk are clearly visible.

Reduction of mutagenicity of the fumes from cooking oil by degumming treatment

The fume of cooking oil has been reported to increase the risk of respiratory tract cancer. The influence of a degumming treatment of peanut oil on the contents of mutagenic compounds in fumes from heated peanut oil was investigated. The results indicate that the peanut oil prepared from roasted peanut kernels which underwent degumming treatment had a lower free fatty acid (FFA) content and a higher smoke point, was more clear in color, and produced less fumes when heated at smoke point. Moreover, when compared to untreated peanut oil, the mutagenicity of oil fumes of degummed peanut oil toward Salmonella typhimurium TA98 and TA100 was reduced to 81% and 73% ( p<0.05), respectively. The degummed peanut oil which was obtained by adding 3% water and heating at 60°C for 20 min produced the least amount of mutagenic fume. The contents of four mutagenic compounds, trans-trans-2,4-decadienal ( t-t-2,4-DDE), trans-trans-2,4-nonadienal ( t-t-2,4-NDE), trans-2-decenal ( t-2-DCA), and trans-2-undecenal ( t-2-UDA) in oil fumes of degummed peanut oils were drastically decreased ( p<0.05), especially the t-t-2,4-DDE. The results also indicate that the FFA content had a high linear correlation with mutagenicity ( r 2=0.9978) and content of t-t-2,4-DDE ( r 2=0.7685). Moreover, there was a correlation ( r 2=0.7816) between the content and the mutagenicity of t-t-2,4-DDE. The decrease of FFA by degumming might explain the reduction of mutagenic alkenal compounds and mutagenicity of fumes from heated peanut oil.

Effect of degumming on the tensile properties of silkworm (Bombyx mori) silk fiber

AbstractForcibly reeled silkworm (Bombyx mori) silk was used to study how exposure to a degumming treatment (boiling in distilled water for 30 min) affects tensile properties. Because forcibly reeled and naturally spun fibers exhibit comparable mechanical behavior, the results can be generalized to material obtained conventionally from cocoons. The effects of degumming include: a decrease in the initial elastic modulus, a decrease in the stress at the proportional limit (yield strength), a change in the qualitative shape of force‐displacement curves, and significant qualitative and quantitative variability in force‐displacement data from samples subjected to nominally identical degumming histories. Immersion in water at room temperature or heating in air at 100°C for 30 min are both qualitatively equivalent to a 30‐min degumming treatment in boiling water, in terms of the effect on silk tensile properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1431–1437, 2002; DOI 10.1002/app.10366

Tensile properties of silkworm silk obtained by forced silking

AbstractBave was acquired by the forced silking of three Bombyx mori silkworms, and its tensile properties were characterized. The material collected from any given silkworm yielded reproducible force‐displacement plots, which were qualitatively similar to the plots obtained from silk collected from the other silkworms. This uniformity contrasts with the highly variable properties exhibited by silk which had been reeled from degummed cocoons. Scanning electron microscopy images were used to obtain information about the sample cross‐sectional area, so that force‐displacement plots could be rescaled as stress–strain curves. Surprisingly, the scatter in the tensile properties increases after such rescaling. This finding can be explained in terms of the sericin coating of the bave (which contributes to the cross‐sectional area but not significantly to the load‐bearing capacity) having a variable thickness. When the sericin coating was eliminated by a degumming treatment, it was found that the fibers showed more consistent cross‐sectional areas. Therefore, stress–strain curves of forced B. mori silk are reproducible, provided that force‐displacement data are rescaled by the correct cross‐sectional area. Finally, the Weibull parameters of the forced silk were determined. The Weibull modulus, m, has a value of 13.0 ± 0.3, which is more than double the value obtained previously from silk reeled from a cocoon, demonstrating that the process of degumming cocoons has a detrimental effect on the distribution of defects in the silk microstructure. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 82: 1928–1935, 2001