Preparation And Properties Of Sodium Alginate/Hydroxyapatite Composite Adsorption Fiber

In this study, sodium alginate and hydroxyapatite were used for preparation of composite adsorption fiber. The preparation process, structure and properties of sodium alginate/hydroxyapatite composite adsorption fiber were studied. Stable dispersion of nanoscale hydroxyapatite was obtained via Microfluidizer and the addition of surfactants and the dispersion stability was discussed. The sodium alginate was modified using epichlorohydrin and polyurethane prepolymer. The preparation process of sodium alginate/hydroxyapatite composite adsorption fiber was optimized using orthogonal and single factor analysis method. The adsorption properties, breaking strength and elongation at break were analyzed. The kinetics and thermodynamics were studied. Moreover, the structure of fibers was characterized using Fourier transform infrared spectroscopy and scanning electron microscopy.The optimum dispersion process of nanoscale hydroxyapatite was that the surfactant type was sodium hexametaphosphate, the pH value was8-10, the dosage of the surfactant was0.5%, dispersion temperature was25℃, the mechanical stirring time of the surfactant was60min, and the dispersion of hydroxyapatite suspension solution was performed via ultrasonication for10min and via Microfluidizer for2times under15000PSI.The large specific surface area of sodium alginate/hydroxyapatite composite adsorption fiber benefited physical adsorption of cadmium ions. Chemical adsorption occurred between hydroxyl group, phosphoric acid group and carboxyl group of fibers and cadmium ions.The CH2group of cyclopropane at2971.77cm"’after modification of sodium alginate indicated that sodium alginate was crosslinked with polyurethane prepolymer via epichlorohydrin.The preparation process of sodium alginate/hydroxyapatite composite adsorption fiber with good adsorption properties was set up as follow:mass fraction of sodium alginate of3%, mass fraction of CaCl2solution of3%and coagulation temperature of15℃in the first coagulation bath, minus spinneret draw ratio, CaCl? as the second coagulant and mass ratio of sodium alginate and hydroxyapatite of7:3. The process for good breaking strength and comprehensive performance (breaking strength and adsorption property) was determined: mass fraction of sodium alginate of3%, mass fraction of CaCl2solution of5%and coagulation temperature of15℃in the first coagulation bath, minus spinneret draw ratio, water as the second coagulant and mass ratio of sodium alginate and hydroxyapatite of7:3.Fast adsorption appeared in the initial stage and the adsorption amount reached92%of equilibrium at60min and reached equilibrium at8h. The optimum adsorption was found at pH of6-7. High removal percent of more than83.03%at low concentration of Cd(ⅡⅡ) and90%at high concentration of Cd(Ⅱ) was obtained at the bath ratio of1:1000and1:100, respectively. The pseudo-second-order model and Freundlich isotherm described the adsorption behaviors of sodium alginate/hydroxyapatite composite adsorption fiber well. The pseudo-second-order model was suitable for modified sodium alginate/hydroxyapatite composite adsorption fiber. Both Langmuir isotherm model and Freundlich isotherm model fit Cd(Ⅱ) adsorption data of onto modified sodium alginate/hydroxyapatite composite adsorption fiber. The maximum adsorption capacity of modified sodium alginate/hydroxyapatite composite adsorption fiber at25℃,35℃and45℃were256.4,357.1,344.8mg·g-1respectively. Both physical and chemical sorption existed in adsorption. The adsorption process is spontaneous, endothermic in nature.