Rotation and contraction of native and regenerated cellulose fibers upon swelling and dissolution: the role of morphological and stress unbalances

Upon swelling and dissolution, native cellulose fibers such as cotton hairs or wood fibers are rotating and contracting. Regenerated cellulose fibers are only contracting, not rotating. Cotton hairs show two rotation mechanisms, a well known untwisting, not seen in wood fibers, due to the unwinding of the twists initially induced by the desiccation that occurs at the end of the growth, and a microscopic rotation that can also be slightly observed in wood fibers. In addition to these rotation mechanisms, cotton hairs and wood fibers show a rolling up of their primary wall that is due to the higher elongation of the external layers as compared to the internal layers arising during the elongation phase of the cell. Contraction originates from the fact that the cellulose chains are in an extended conformational state due to the spinning process for the regenerated fibers and to the bio-deposition process for native fibers. The contraction is related to the relaxation of the mean conformation of cellulose chains from an extended state to a more condensed state. Physical as well as mechanical modeling will support the experimental observations.