Direct Preparation of a Novel Membrane from Unsubstituted Cellulose in NaOH Complex Solution

An environmentally acceptable cellulose dissolution procedure was employed to prepare a membrane directly from an unsubstituted cellulose. The effects of coagulants and coagulation conditions on the structure and properties of regenerated cellulose membrane prepared from cellulose in a NaOH complex solution (8 wt% NaOH/6.5 wt% thiourea /8 wt% urea/77.5 wt% H2O) are discussed. A series of cellulose membranes are prepared from cellulose solutions by coagulation with 5 wt% H2SO4, 5 wt% HCl ,5 wt% HAc, CH3CH2OH (abs.), 5 wt% H2SO4/5 wt% Na2SO4, 10 wt% Na2SO4, 10 wt% (NH4)2SO4 and 10 wt% NH4Cl, respectively. Moreover, the membrane coagulated at relatively low temperature possessed better mechanical properties compared to those coagulated at relatively high temperatures. The results indicated that in the coagulation bath of 7 wt% HAc aqueous solution, with coagulation temperature at 10؛C for duration of 5 min, the tensile strength of novel cellulose membrane could reach 134 MPa, which was much higher than the commercial cellophane and those of the membranes prepared from NaOH/urea and NaOH/thiourea aqueous solutions. The CP/MAS 13C NMR, WAXD and FTIR spectra indicate that the regenerated membrane possesses a specific cellulosic crystal type. The novel cellulose membrane showed dense structure and the crystallinity which was higher than that of a viscose fiber, was an indication that it possessed much more stable structure. The coagulation mechanism can be described as a two-phase separation. Cellulose in the gel was precipitated and regenerated with the coagulation process to form a cellulose membrane. This work provides a potential promising way to prepare novel cellulose membrane with excellent physical properties by controlling the coagulation conditions.