Mechanical properties of Bombyx mori silk yarns studied with tensile testing method

Abstract

The mechanical properties of Bombyx mori silk yarns and baves were investigated with tensile testing method. After silk yarns were pre-extended at different strain levels and fixed for a while followed by recovery process, the tensile characteristics were examined in detail. It was commonly observed that low preliminary extensions up to 2-3% do not cause the changes of the mechanical properties and stress-strain curves because they result in small structural changes and distortions, which were recovered within relatively short time ($ 1 min) in recovery process. However, pre-extension values >3% strain lead to great changes of the mechanical properties and fibre structure, i.e., the changes of the shape of stressstrain curve where additional transition point was observed, increase in the rigidity and stress at rupture, but decrease in extensibility as a result of orientation and destruction of the fibre structure especially in the amorphous region. It was stated that silk fibre consists of two distinct deformation regions, namely first linear region extending up to 2-3% strain and the second region beyond 2-3% strain where the main reorganization processes of the fibre structure, that is, the straining of macromolecular chains especially in the amorphous regions, the orientation of structural units such as b-sheet microcrystals in stretching direction, and the destruction of macromolecules take place.

Secondary structure transformation and mechanical properties of silk fibers by ultraviolet irradiation and water

“…Meanwhile, the sericin still covers the surface of fibers and plays a protective role, so that the speed of photo-degradation of the inner fibers slows down. 44,45 With only 38℃ water, its influence equals the partial degumming effect, as shown in Figures 8(a)–(f). Comparing the breaking strength of silk fibers for UV irradiation and water ageing, we notice that the speed of water and light ageing is faster.…”

Stretching-Induced Conformational Transition of the Crystalline and Noncrystalline Domains of 13C-Labeled Bombyx mori Silk Fibroin Monitored by Solid State NMR

“…For example, shear-induced self-assembly of native silk fibroin into fibril was reported by atomic force microscopy. , He et al reported that the N-terminal domain of B. mori silk fibroin functions as a pH-responsive self-assembly module that could prevent β-sheet formation at neutral pH yet could initiate fibroin assembly as pH decreases . The pH-induced change in the rheological properties of B. mori silk fibroin was also examined. − The promotion of random coil to β-sheet structures has been induced by several ions such as K + or Ca 2+ . ,, The important role of water molecules during silk fiber formation was also discussed in detail. ,,,, Thus, NMR provides a great contribution to clarify these interactions during the formation of strong and tough fibers from aqueous solution. ,− The structural change of B. mori silk fibroin fiber by stretching has been intensively studied and the change in the noncrystalline region has been emphasized. ,− Thus, domain-specific information on the crystalline and noncrystalline domains is likely to be important in understanding the structural change during the fiber formation process and the origin of the strong and tough fibers in detail.…”

Effect of UV-light on the uniaxial tensile properties and structure of uncoated and TiO2 coated Bombyx mori silk fibers

“…Materials and UV-irradiation process Uncoated B. mori silk fibers Silkworm (B. mori) silk cocoons purchased from Koza Han in Bursa, Turkey were opened and degummed with the method described earlier [23]. Because the degummed silk fibers were obtained in the form of bave consisting of the two constituent brins of the cocoon fiber which could not be separated.…”