Preparation Of Cellulose Based Hydrogels By Ethylenediamine/Potassium Thiocyanate (ED/KSCN) Solvent

Cellulose is the most abundant renewable biomass resource in the earth. Thanks to its biocompatibility and biodegradability, cellulose based materials have been widely used in fields of chemical engineering, biological engineering, medical materials and food, etc. Cellulose based hydrogels, a new kind of biomass material has attracted more and more attention.In this study, cellulose hydrogel were prepared by ethylenediamine/potassium thiocyanate (ED/KSCN) solvent under methanol as regeneration bath. The light transparency, equilibrium swelling ratio, compression properties, rheological properties morphology, structure, crystallinity and thermal properties of the hydrogels were explored. Single factor analysis was used to investigate the effect of three selected factors (dissolution concentration, dissolution time, dissolution temperature) on the mechanical properties of hydrogels. The optimal condition through single factor analysis was 4%,4h and 90℃, respectively. The results showed that cellulose hydrogel presented high light transparency. With the cellulose concentration increasing, the light transparency and the equilibrium swelling ratio of the hydrogels decreased, while the reswelling water uptake, the storage modulus and the stress increased with the cellulose concentration increasing. SEM showed that cellulose hydrogels presented a spherical-like particle structure with the diameter ranging from lOnm to 50nm and uniform pore structures composed of fibrillar networks. FTIR suggested that bamboo pulp was directly dissolved in ethylenediamine/potassium thiocyanate(ED/KSCN) solvent. The XRD pattern indicated that the form of cellulose crystalline transformed from I to cellulose Ⅱ during the process of dissolution, with the crystallinity decreasing from 84.64% to 43.23%. TGA revealed a slight loss of thermal stability of cellulose hydrogel.Different mass ratios of starch/cellulose composite hydrogels were prepared with ED/KSCN solvent under methanol as regeneration bath. The light transparency, equilibrium swelling ratio, tensile properties, compression properties, rheological properties, morphology, structure, crystallinity and thermal properties of starch/cellulose composite hydrogels were explored. The results showed starch/cellulose composite hydrogels presented lower light transparency and higher mechanical properties than cellulose hydrogel. The light transparency and the equilibrium swelling ratio first decreased with the increase of the starch concentration, then with the starch concentration increasing continuously, both of them increased. The tensile strength, storage modulus and the compression modulus showed a trend of increasing and then decreasing with the starch concentration increasing. Meanwhile, the reswelling water uptake increased with the starch concentration increasing. When the mass ratios of cellulose and starch was 1:3, composite hydrogels could get a maximum of mechanical strength. SEM showed that starch dispersed in the cellulose matrix evenly and hydrogel presented a more compact network structure than cellulose hydrogel. FTIR analysis indicated that the interactions of starch/cellulose hydrogel were achieved through physical crosslinking instead of chemical reactions. XRD showed that the crystallinity increased from 36.73%to 40.68%, compared to cellulose hydrogels, and TG presented a higher thermal stability than cellulose hydrogel.The prepared starch/cellulose composite hydrogels was used to remove methylene blue(MB) from aqueous solution. The effects of time, temperature, initial concentration and pH value on the adsorption were studied. The adsorption isotherm and kinetics are also investigated. The morphology, structure, crystallinity were characterized by scanning electron microscopy (SEM), fourier transformation infrared spectroscopy(FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results showed that the adsorption process was exothermic, which could reach equilibrium state in 120min. The effect of adsorption proceeded well under high pH value. The adsorption isotherm and kinetic could be well fitted by the Langmuir model and the persudo-second-order model, respectively. When the desorption time was 160 min, desorption reached the highest desorption rate on the basis of the optimum adsorptive saturation conditions. SEM showed that the pores of starch/cellulose composite hydrogels were filled up with MB, which indicated that methylene blue had already absorbed into the hydrogels successfully. In the FTIR spectra, a new peak appeared at 886cm-1 belonging to N-H bond stretching of MB. There was no difference of the crystalline between before and after adsorbing MB characterized by XRD. TG presented a lower thermal stability after adsorbing MB.