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The present study focused on the effects of the addition of lithium salts such as LiI, LiBr and LiCl on the rheological properties of aqueous solutions containing 15 wt% poly(vinyl alcohol) (PVA). There was a plateau in the shear storage modulus in the low frequency region, demonstrating that such solutions have a network structure attributed to hydrogen bonding of the PVA. The value of the plateau modulus evidently decreased with temperature and with the addition of lithium salts. The experimental results also demonstrated that the anion species in the salt plays an important role in determining the rheological properties, including the magnitude of the plateau modulus. The iodide anion, which is classified as a “water-structure-breaker” ion in the Hofmeister series, effectively decreased both oscillatory shear moduli including the plateau modulus. However, the effect of adding LiI decreased at high temperatures, owing to the reduced extent of hydrogen bonding.

The effect of lithium bromide (LiBr) on the structure and properties of poly (vinyl alcohol) (PVA) fibers obtained by wet-spinning was studied. The tensile modulus and strength of a PVA fiber were greatly enhanced irrespective of the post-spinning hot-stretching process. The high degree of molecular orientation arose from the reduction in the crystallinity and hydrogen bonding between PVA chains in the solution resulting from the addition of LiBr, which was revealed by the rheological properties of aqueous solutions. The LiBr was removed from the fiber during the spinning process in the coagulation bath, and during the washing process. This ensures strong hydrogen bonding in the fibers, and results in excellent mechanical properties.