Study On Extraction And Application Of Sodium Alginate

Sodium alginate(NaAlg) is a kind of polysaccharide carbohydrate extracted from kelp or sargassum which belongs to brown algas. NaAlg has a good biodegradability and biocompatibility, and its demand has been largely ascending on the international market. The production of NaAlg can't meet the need of market at present because of its low extraction rate and poor derivatives. It is obvious that further improving the extraction technology and developing its derivatives have important practical value.The contrast experiments on the extraction methods with the acid agglomerating-acidification, calcium agglomerating-acidification and calcium agglomerating-ion exchange were carried on. In the acid agglomerating-acidification method, sedimentation rate of acid agglomerating is very slow and the particle of gel deposit is small, which makes filtering difficult and causes the extraction rate dropdown. In the calcium agglomerating-acidification method, even though the calcium agglomerating speed is comparatively rapid and sediment particle is relatively big, the medium product, alginic acid, is not stable and easy to be degraded which makes the extraction rate not high. In the calcium agglomerating-ion exchange method, calcium-agglomerating speed is faster, deposited particle is bigger and the extraction rate is higher than in other methods. The results of the contrast experiments show that it is valuable to further study the process of the calcium agglomerating-ion exchange method. The systematically studies of the calcium agglomerating-ion exchange method indicated that while digesting, the concentration of the alkali liquid, digesting temperature and time were main factors affecting on the extraction rate of NaAlg. The orthonogal experiments show that the extraction rate can be up to 42.6% and the viscosity can reach 2.84 Pa.s in the condition of digesting 3h at 50℃ with 3%Na2CO3. The detection of the products showed that the quality is up to the GB1976-80. The process has an obvious industrialization advantage because it has a lower material cost.The complexing ability between alginate radical (Alg- ) and some typical ions such as Pb2+, Ca2+, Zn2+ and Mn2+ was determined in the applied research on alginate. The complexing constants and relationship are K(6.4×106)>K(4.5×105)>K(1.11×104)>K(3.2×102), which indicates that the ability of Alg- complexing with Pb2+ is the strongest and is the weakest with Mn2+. A composite of polyvinyl alcohol(PVA)-calcium alginate was prepared from polycondensation and cross-linking of NaAlg and PVA. The experiment shows that the water sorption increases firstly and then decreases with increasing of the dosage of polycondensate agent glutaraldehyde , cross linker CaCl2 and PVA proportion in the composite. Based on water sorption, the most optimum preparing conditions are glutaraldehyde content 0.85%, the mass ratio of PVA and NaAlg 8:1, CaCl2 concentration 2.0% which is optimized by L9 (33). Under this condition, the water sorption of the product is up to 80.6%, the tensile strength reaches 9.08MPa and the tensibility reaches 400%, all of which are higher than that of the single material NaAgl or PVA.