Study Of Properties Of Cellulose/Naoh/Urea Aqueouse Solution And Structure Of Cellulose Materials

Gel is spatial reticulated structure interconnected by colloidal particles in sol or by macromolecules in solution under certain conditions. Properties of the solution change sharply when gel appears. Gelation is of vital importance for theory research and material preparation. The thermally induced gelation of cellulose/NaOH/urea aqueous solution, the influence of gelation on the extensional properties, morphology of as-spun fibers and mechanical properties of regenerated hydrogel membranes were investigated in this paper.Influence of the concentration of cellulose on the shear rheology properties, and effect of the concentration and extension rate on extensional breakup of the thread of cellulose solution were investigated. It was found that extensional properties of the solution were improved with increasing concentration. The extensional properties of the solution firstly increased and then decreased with the enhanced gelation degree of cellulose solution at low extension rate. The capillary breakup time of gel-formed solution plunged dramatically with the increase of extension rate. Results showed that a certain degree of gelation was helpful to improve the extentional properties of the solution and it was expected to improve the processing performance of the solution system.Influence of gelation on the morphological structure of as-spun fibers was investigated. The fibers were prepared by injecting the pre-gelled solution heated in the syringe needle at50℃into coagulation. Results showed that pre-gelation was helpful to prepare as-spun fibers with round section without changing the pore structure obviously. Compact fibers were obtained by decreasing the temperature of coagulation bath. Grooves on the skin of the fibers could be eliminated effectively by pre-gelation of the solution. Fibers with macroporous structure on the skin and relatively compact structure in the core were prepared.Regenerated cellulose hydrogel membranes were prepared by introducing pre-gelation of the solution into the typical preparation procedure of immersion precipitation phase inversion of cellulose solution. Results showed that mechanical properties of the hydrogel membranes could be improved by pre-gelation of the cellulose solution. This method overcame the shortcoming of low efficiency in original method. Additionally, influence of the pre-gelation temperature, the sulphuric acid concentration and temperature of the coagulation bath on the structure and properties of the regenerated cellulose hydrogel membranes were investigated. It was found that pre-gelation could effectively improve the mechanical properties of the resultant cellulose hydrogel membranes without obviously changing in the pore structure. Both the increase in the temperature and the sulphuric acid concentration of the coagulation bath resulted in the formation of larger pores in the membranes accompanied with decrease in the mechanical properties. Results showed that the double diffusion of solvent and solidifier of the solidification process was the key factor in determining the mechanical properties of regenerated hydrogel membranes. All of the factors which could accelerate the rate of double diffusion were beneficial to form membranes with relatively larger pores.The cellulose solution was coagulated in water after heating at60℃for different time. It was found that less wrinkles were on the surface of the membrane and transparency was improved. With the heating time increased, the strength of the membrane was climbed up and then declined.