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摘要
In order to analyze and explore the changes of deformation, mechanical behavior and structure of spider major ampullate gland silk (abbr: Mas) during repetitive stretching and their relationship, the mechanical behavior of spider Mas and the changes of protein secondary structure after repetitive stretching were tested and investigated through the design of different combinations of loading elongation and the interval relaxation between the two stretching via electronic universal testing machine and laser Raman spectrometer. The results show that spider Mas presents excellent repetitive stretching characteristics with the gradual increase of the initial modulus but the a marginal variation in yield stress; When two groups of spider Mas fibers were stretched in the condition of gradual increase of the set stretching length and the set time intervals as 15~25 s and 5 min respectively, as a result, the acquired tensile curves of the two groups overlapped fairly well, even for the samples were stretched over the yield point, or even over the yield zone and into the strengthening zone as well; It reveals that in case the stretching test of the above two groups of samples has been interrupted for a long time interval of ≥23 min in between two stretching tests, the mechanical behavior of samples may be reproduced as soon as only one stretch again independent from the previous loading history. In other word, the above findings show that the mechanical behavior of spider Mas is similar to those of rubber's viscoelasticity. The results of Raman spectra showed that with the increase of the number of repetitive stretching and the set stretching length, the hydrogen bond between the random coils was broken. The interval after stretching seems to allow some structures to recover and contribute to the formation of the new β-turn or β-bend and PGⅡ β-sheet structure, After repetitive stretching for many times, the primitive β-sheet structure will be gradually destroyed, and almost all of it will be destroyed when Mas breaks. These findings may be helpful to guide the biomimetic design of novel fiber materials.
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