The Impact Of Inorganic Salts On The Properties Of Cellulose/NMMO System

N-Methylmorpholine-N-oxide(NMMO)is used as a solvent for direct dissolution of cellulose Compared to the conventional viscose fibers,the regenerated cellulose have some unique properties,such as high degree of orientation,high crystallinity,long crystallites,thus possessing very high strength and modulus.Cellulose with a high degree of polymerization(DP)or 10wt%cellulose was used in the process of manufcacturing lyocell fiber.However,cellulose dissolved in the NMMO/water system need higher temperature or long time with increasing cellulose content,which hampered the process of spinning or casting as a result of high viscosity of the system.The addition of inorganic salts in the cellulose/NMMO/water could significantly affect on the properties of cellulose,such as the cellulose molecule and the forces acting between NMMO and cellulose,thus remarkably affect the quality of the regenerated cellulose.In this paper,the dissolving pulp produced form hardwood was dissolved by NMMO.The effects of different types of inorganic salts on the rheological properties of the cellulose/NMMO/water system were studied.The molecular weight and molecular weight distribution of cellulose in system were investigated by using dynamic rheological test.In addition,the mechanical properties and DP of the regenerated cellulose were also measured.The results showed that under the same ionic valence and concentration,the viscosity(ηa),the non-Newtonian exponent(n)and the critical shear rate(rcr)decreased with increasing the ionic radius while the viscosity coefficient(k),zero-shear viscosity(η0)and the structural viscosity exponent(△η)increased.For the dynamic frequency scanning,the cross point of storage modulus(G’)and loss modulus(G")shifted to zone of low frequency,the molecular weight and molecular weight distribution of cellulose in system increased with increasing the ionic radius.Moreover,the DP of regenerated cellulose and the tensile strength of the regenerated cellulose membrane increased with increasing the ionic radius.Compared to the control sample(without inorganic salts),the addition of Li+、Mg2+、Al3+have negative effect on the viscosity,the DP and the tensile strength of the regenerated cellulose membranes The DP and the viscosity decrease with the addition of Na+,Ca2+ and CI-while the mechanical properties of the membranes increased.It should be noted that the addition of K+,Br-and I-have positive effect on the properties of the membranes.