Dissolution And Solution Properties Of Cellulose In NaOH/Thiourea/Urea Aqueous Solution

Cellulose is the most abundant resource in nature, and is renewable, biodegradable, and biocompatible. But cellulose has not reached its potential applications because it cannot be melted to fabricate into a desired form or to be dissolved in a common solvent, attributing to the strong inter- and intra- molecular hydrogen bonding. In this paper, NaOH /Thiourea /Urea Aqueous Solution was used as a solvent of cellulose. The dissolution of cellulose in this novel solvent system was investigated. Also the dissolution mechanism and the rheological properties of cellulose solution were studied. The behavior of the gel-formed cellulose solution was discussed, too.In this paper, the permutation and combination experiments were designed to obtain an optimal dissolution condition. The effects of the temperature of solvent and the speed of stirring were discussed. Then the optical dissolution condition was established.To understand the dissolution mechanism, double component solvents including NaOH aqueous solution, thiourea aqueous solution, and urea aqueous solution, tripartite component solvents including thiourea/urea aqueous solution, quadruple solvents including NaOH/ thiourea/urea aqueous solution were used to dissolve cellulose accompanied with POM, SEM, X-Ray, FT-IR, CP/MAS-¹³C-NMR, ¹³C-NMR. It was found that double component couldn’t dissolve cellulose both at atmosphere temperature and low temperature. But the surface of cellulose was destroyed in a certain extent in NaOH aqueous solution, while cellulose was only swelled in thiourea aqueous solution and urea aqueous solution in low temperature condition. Also cellulose couldn’t be dissolved in thiourea/urea aqueous solution in low temperature. The cellulose couldn’t be conversed to cellulose II in these solvents mentioned above.But the NaOH/thiourea/urea aqueous solution could completely dissolve cellulose I at -10℃. The dissolution behavior and mechanism of cellulose were studied. The experiment results showed that the regenerated cellulose membranes were conversed to cellulose II. There was no peak for cellulose derivatives in ¹³C-NMR spectra of cellulose in the solution, indicating an absence of derivatives. It could be concluded that a complex structure compound was formed between NaOH, thiourea, urea and water at -10°C.It could quickly penetrate into the amorphous regions of cellulose, and then destroy the neighboring crystalline regions and create new amorphous ones. At last the amorphous regions dissolved in the solvent.The viscosity experiments revealed that cellulose dissolved much better in NaOH/thiourea/urea aqueous solution than in NaOH/thiourea aqueous solution or NaOH/urea aqueous solution.The reological behavior of polymer has great impact on the processing engineering. The rheological properties showed that all the solutions were pseudoplastic fluid. Under the same solid content, the shearing stress and structure index rise with increasing the temperature. Viscosity flow activation energy changed little with the increasing of the concentration of cellulose solution.The solution wasn’t stable while the temperature was too high or low. The dynamic rheology experiments and FBM（Falling Ball Method）experiments showed that 6wt% cellulose solution with （DP）|—= 558 would gelled at 37℃. When the gelation happened, the cellulose molecules approached towards each other.