Preparation Of High-adsorbed Regenerated Cellulose Materials Using NMMO/H₂O

Cellulose is the most abundant nature macromolecule in the world, known as the most promising resources to replace fossil fuel. However, the complexity of cellulose morphology and aggregation structure and high crystallinity, make it very difficult to react with reagents, which confine the application of cellulose. Dissolution is able to destroy the hydrogen bonds of cellulose effectively. Regenerated cellulose from dissolution and pore-forming had a low degree of crystallinity, high accessibility and high chemical activity, therefore expanding the scope of application of cellulose. This project aimed at preparing cellulose which has low crystallinity, high accessibility and high chemical activity by dissolving and regenerating process. Therefore, in this thesis, adsorption regenerated cellulose materials were prepared by using NMMO·H2O as solvent and cotton pulp as raw material through physical pore-forming method and chemical pore-forming method. The main contents are listed as follows:The cellulose was dissolved and regenerated by using NMMO·H2O as solvent and water as coagulation bath. Observing cellulose dissolving in NMMO·H2O by polarized light microscopy (PLM), X-ray diffractometion (XRD), fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) were used to characterize cellulose before and after treatment. The results showed that Cellulose solubility is high and fast in the NMMO·H2O. The regenerated cellulose crystallinity was decreased obviously without changing the morphology.In this thesis, adsorption regenerated cellulose materials were prepared by using physical pore-forming agent as pore-forming system firstly. The structure and properties of cellulose materials were characterized by XRD, method of specific surface area, SEM, etc. The effects of cellulose concentration and the amount of the pore-forming agent on the structure and properties of the cellulose materials were investigated. The results showed that with the increase of the cellulose concentration, cellulose materials prepared by using Na2SO4 as physical pore-forming agent exhibited thicker wall of the pore and higher crystallinity with the decreased porosity, water absorption, moisture retention capacity. In addition, with the increasing amount of the pore-forming agent in a certain range, the pore structure of cellulose materials was further improved, and water absorption and moisture retention capacity were significantly improved, the specific surface area of materials increased firstly and then decreased with the further addition of the mixed forming agent. By comprehensively considering the difficulty of mixing, forming process and other factors, the cellulose concentration was selected to be 5wt% and the amount of pore-forming agent was set as the 2 times of the mass of NMMO·H2O/cellulose solution.In order to get larger pore structure in the cellulose materials and thereby increase the porosity and water absorption of cellulose materials, the physical-chemical pore-forming method was explored in the preparation of cellulose materials. NMMO·H2O/cellulose solutions were foamed at 110℃ and vacuum conditions by using sodium bicarbonate as chemical forming agent. The results showed that by adding chemical foaming agent larger pore structure was formed in the cellulose materials, and the water absorption, moisture retention capacity and the softness of materials were improved. Compared with the single pore forming agent, sodium bicarbonate chemical forming agent was relatively stable during foaming process. And the prepared cellulose materials exhibited much more uniform and smaller pores as well as better water absorbability and moisture retention capacity. Therefore, the pore forming agent and chemical forming agent were mainly used in this thesis.The effects of the mixed forming agent content on the morphology and properties of cellulose materials were further investigated in this thesis. The results showed that with the increasing content of the mixed foaming agent, the water absorption and moisture retention capacity and the specific surface area of materials increased firstly and then decreased with the further addition of the mixed forming agent, while the crystallinity of materials had a decreasing tendency. Under the conditions of this thesis, when the amount of pore forming agent was two times the mass of the NMMO·H2O/cellulose solutions and the content of chemical pore-forming agent was 4wt%, the cellulose materials exhibited the optimal comprehensive performance with a porosity of 87.1%, the crystallinity of materials of 27% and the specific surface area of materials of 5.3892m2·g-1.In addition, the grafting experiments were carried out with regenerated cellulose and water-soluble monomer of acrylamide (AM) in water medium, Cu2+ adsorption of graft materials were tested subsequently. Experimental results showed that Cu2+ adsorption improved with increasing the initial solution Cu2+ concentration and adsorption time. An adsorption equilibrium can be obtained within 90minutes with the loading of regenerated cellulose grafted acrylamide 30mg/L. Meanwhile, the temperature is 45℃, pH=5, and the initial concentration of Cu2+ is 30 mg/L. Adsorption kinetics study showed that the process of Cu2+ adsorption of regenerated cellulose grafted acrylamide was classified as Freundlich adsorption isotherm model, which was a non-uniform surface adsorption.