Preparation Of Cellulose Sponge By Using N-Methylmorpholine-N-Oxide (NMMO)as Solvent

Sponge, also known as flexible foam, is a porous elastic material, which is widely used in daily life as the porous absorbent materials as well as packaging and cushioning materials. Currently, most of the commercially available sponges are prepared from synthetic polymers such as polystyrene (PS) and polyurethane (PU), etc. Although the production technology of this kind of sponge is quite mature and the output and consumption of the sponge are huge, there are still many disadvantages:its raw materials is from non-renewable petroleum resource and the production process is not environmentally friendly. Moreover, the waste sponge is very difficult to be degraded. Therefore, the production, consumption and discard of this kind of sponge without restrictions will bring serious harm to the ecological environment and human health.Cellulose is an inexhaustible resource because it is the most abundant natural materials and can be easily degraded under natural conditions. Therefore, in face of the declining oil reserves and anabatic environmental pollution continuing to highlight nowadays, the study on the preparation of the cellulose sponge draws widespread attention of researchers. In addition to the advantages in source of raw material and degradation of the waste, cellulose sponge shows other characteristics such as higher hydrophilicity, better water absorption and air dry property, etc. Therefore, good ecological benefit and application value can be achieved by using cellulose sponge. However, the present study on cellulose sponges is still at an early stage at home and abroad. N-methylmorpholine-N-oxide (NMMO) is a new environmentally friendly solvent for cellulose dissolution with advantages better solubility and recyclability. Cellulose sponge with a pollution-free production process is expected to be prepared by using NNMO as solvent. But the related research reports are still rare till now.Therefore, in this thesis, cellulose sponges were prepared by using NMMO as solvent and cotton pulp as raw material through physical pore-forming method and physical-chemical comprehensive pore-forming method, respectively. And the different factors which may affect the structure and properties of cellulose sponges were investigated. On this basis, the structural and properties of our own cellulose sponges by using NMMO as solvent were compared with several kinds of commercial sponges and cellulose sponges using ionic liquids as solvent prepared by our laboratory. Then the market application prospect of cellulose sponge by using NMMO as solvent was analyzed and proposed.In this thesis, cellulose sponge was prepared by using physical pore-forming agent as pore-forming system firstly. The structure and properties of cellulose sponges were characterized by SEM, WARD, sclerometer, universal material testing machine, etc. The effects of cellulose concentration and the amount of the pore-forming agent on the structure and properties of the sponge were investigated. The results showed that with the increase of the cellulose concentration, cellulose sponge prepared by using Na2SO4as physical pore-forming agent exhibited thicker wall of the pore and higher tensile strength with the decreased porosity, water absorption, moisture retention capacity and softness. In addition, with the increasing amount of the pore-forming agent in a certain range, the pore structure of cellulose sponge was further improved, and water absorption, moisture retention capacity and softness were significantly improved while the tensile strength was decreased. By comprehensively considering the difficulty of mixing, forming process and other factors, the cellulose concentration was selected to be7%and the amount of pore-forming agent was set as the3times of the mass of cellulose/NMMO-H20solution.To prepare cellulose sponges with higher strength, two kinds of natural fibers, flax and absorbent cotton, were selected to enhance the strength of sponge, respectively. The results showed that compared with flax, absorbent cotton played a more significant role on the enhancement of the mechanical property of cellulose sponges and the resultant sponges had the original pore structure, water absorption and moisture retention capacity. Therefore, absorbent cotton was chosen as the reinforcing fiber for follow-up study. Subsequent studies found that with the increase of absorbent cotton content, the strength of the sponge was enhanced significantly in a certain range, but the effect of enhancement slowed down when the content of absorbent cotton was more than50%. Accordingly, the reinforcing fiber content was set to be50%of the cellulose concentration..In order to get larger pore structure in the cellulose sponge and thereby increase the porosity and water absorption of sponge, the physical-chemical comprehensive pore-forming method was explored in the preparation of cellulose sponge. Cellulose/NMMOH2O solutions were foamed at110℃and vacuum conditions by using p-toluenesulfonhydrazide, sodium bicarbonate and their mixture as chemical forming agent, respectively. The results showed that by adding chemical foaming agent larger pore structure was formed in the cellulose sponge, and the water absorption, moisture retention capacity and the softness of sponge were improved. Compared with the single chemical foaming agent, p-toluenesulfonhydrazide/sodium bicarbonate mixed chemical forming agent was lower-cost and relatively stable during foaming process. And the prepared cellulose sponge exhibited much more uniform and larger pores as well as better water absorbability, moisture retention capacity and softness. Therefore, the mixed chemical forming agent was mainly used in this thesis.In addition, the effects of the mixed forming agent content on the morphology and properties of cellulose sponge were further investigated in this thesis. The results showed that with the increasing content of the mixed foaming agent, the water absorption, moisture retention capacity and softness of sponge increased firstly and then decreased with the further addition of the mixed forming agent, while the tensile strength of sponge had a decreasing tendency. Under the conditions of this thesis, when the amount of pore forming agent was three times the mass of the cellulose/NMMO-H2O solution and the content of chemical pore-forming agent was4%, the cellulose sponge exhibited the optimal comprehensive performance with a porosity of97.7%. Compared with the cellulose sponge without chemical foaming agent, its water absorption was increased by about84%and the hardness was reduced by about18%.Based on the above results, the structure and properties of sponges prepared by using NMMO as solvent were compared with four kinds of commercial sponges and cellulose sponge by using ionic liquids as solvent prepared by our laboratory. The results showed that cellulose sponges prepared by using NMMO as solvent through physical pore-forming method and physical-chemical comprehensive pore-forming method met the relevant requirements of performance including morphological structure, water absorption, moisture retention capacity, tensile strength and the thermal properties.Moreover, the porosity and moisture retention capacity of the cellulose sponges prepared in this work were significantly better than the market commercial sponges. Compared with the cellulose sponges prepared by using ionic liquid solvent, the cellulose sponges prepared by using NMMO showed better water absorption and higher tensile strength. Therefore, it can be predicted that cellulose sponge prepared by using NMMO as solvent may have a good market prospect.