Preparation And Properties Of Modified Sodium Alginate Adsorption Materials

In this study, the alginate was modified with epichlorohydrin. Then the modified sodium alginate fibers were prepared using wet spinning method. The modified sodium alginate fibers were dried at 100 ℃ for crosslinking reaction. After that the dried fibers were soaked in 0.4% NaCl solution for removing the calcium ions. Effects of drying time and soaking time in NaCl solution on breaking strength, elongation at break and adsorption properties were studied. The structure of modified sodium alginate fibers was characterized using FTIR, SEM and EDS.The results showed that the highest breaking strength of the modified sodium alginate fibers which were dried at 100 ℃(1 h)and soaked in 0.4% NaCl solution(15 min) was 15.9 c N/tex. 59% and 42.9% increment of the strength was obtained in comparison with the modified sodium alginate fibers without drying and soaking in Na Cl solution and pure sodium alginate fibers, respectively. The-C-O-C- group of epichlorohydrin at 1256 cm-1 and-C-Cl group of epichlorohydrin at 723 cm-1 in FTIR spectra indicated that crosslinking reaction happened. With the drying time extending, the-C-O-C- group of epichlorohydrin and-C-Cl group of epichlorohydrin disappeared, indicating further crosslinking reaction. Meanwhile, soaking in NaCl solution destroyed “egg-box” structure to a certain extent, leading to the shift of –CH and-COOH peaks. In the SEM images there were roughness and many grooves on the surface of both pure sodium alginate fibers and modified sodium alginate fibers without soaking in NaCl solution. More uniform and smooth surface was found for modified alginate fibers with extended soaking time in NaCl solution. The EDS results showed that after soaking in Na Cl solution, the ratio of carbon and oxygen atoms increased, while the ratio of calcium atoms decreased.In order to solve the brittleness of pure alginate fibers, the sodium alginate and Polyurethane(PU) was also modified with epichlorohydrin in the same condition. The results showed that the highest breaking strength of the modified sodium alginate –PU fibers was 16.0 cN/tex. Compared with modified sodium alginate fibers, the breaking strength was not obviously improved. Nevertheless, the elongation at break was improved. FTIR results showed that crosslinking reaction happened, SEM and EDS images demonstrated that after soaking in NaCl solution, Ca2+ ions were removed from the fibers and the surface of the fibers became smooth and even.The adsorption amount of modified sodium alginate fibers towards cadmium ions changed with different drying and soaking time in NaCl solution. The maximum adsorption amount of modified sodium alginate fibers was 253.83 mg/g, which were dried at 100 ℃ for 3 h and soaked in 0.4% NaCl solution for 1 h. 23.3% and 18.6% increment of adsorption amount was obtained in comparison with sodium alginate fibers and modified sodium alginate fibers without drying and soaking in NaCl solution, respectively. The adsorption thermodynamics and isotherms of modified sodium alginate fibers which had the best breaking strength were discussed. The result showed that the adsorption rate was fast within 90 min, then the adsorption approached equilibrium in a short time. The adsorption amount increased with the cadmium concentration increasing. Moreover, the equilibrium adsorption amount increased with the temperature increasing. The cadmium adsorption of modified sodium alginate fibers obeyed pseudo-second-order kinetic model and Langmuir isotherm model. The adsorption belonged to chemical adsorption and the adsorption process was spontaneous, endothermic in nature.