[The properties of natural silk fibers: deformation study and NMR data].

Natural silk (Bombyx mori) fibers with low humidity (0.07 g H2O/g dried silk) after temperature influence were studied for mechanical longitudinal deformation. On the basis of the stress-strain curves, some estimates of tensile properties for silk fibers were obtained. It was found that the maximal tension (sigma(max) in tensile-linear field of deformation of silk fibers decreases with increasing fiber diameter. The results showed that the heating of fibers (100 degrees C) results in a diminishing of the sigma(max)-value. Scanning electron microscopy pictures for cross section and longitudinal fiber surface were obtained. Natural silk fibers were studied by the NMR relaxation method (free induction decay curves) and the second moments of NMR-line shape in silk samples were calculated. The intra- and intermolecular contributions into the second moment were analyzed. The results showed a strong interaction of water molecules with macromolecules and a low molecular mobility. Some characteristics of interactions between silk macromolecules and water molecules as well as the role of intermolecular links in the change of the structure-function properties of natural silk under the action of external factors are discussed