The structure–property relationships of artificial silk fabricated by dry-spinning process

Regenerated silk fibroin (RSF) fibers were dry-spun from RSF aqueous solution and then post-treated in ethanol aqueous solution. In order to prepare artificial silk which are tougher and stronger than their natural counterpart, the structure–property relationships of the RSF fibers and natural silkworm silks were investigated by using synchrotron radiation X-ray microdiffraction technology, birefringence measurements and Raman spectroscopy. The as-spun RSF fibers with poor mechanical properties exhibited a strong diffraction peak of the [021] lattice plane and a weak diffraction peak of the [020]/[200] lattice plane. However, both the natural silk and the post-treated RSF fibers with exceptional mechanical properties showed weak diffraction peaks of the [021] lattice plane and strong diffraction peaks of the [020]/[200] lattice plane. Nevertheless, the two crystalline peaks are attributed to the silk II structure of silk fibroin. By deconvoluting the one-dimensional wide-angle X-ray microdiffraction pattern, the crystallinity and the degree of crystalline orientation were obtained. The as-spun fibers showed low crystallinity and low crystalline orientation, but the microstructure of the RSF fibers could be improved greatly and even become similar to that of degummed cocoon silk by post-treatment. When the as-spun RSF fibers were first drawn 3 to 4 times with a draw rate of 0.9 mm s−1 in ethanol aqueous solution and then immersed in the same solution for another hour, the breaking strain and breaking energy of the post-treated fibers were significantly greater than those of degummed cocoon silk.