Preparation, Structure And Properties Of Modified Polymers Based On Chitosan And Sodium Alginate

With the pollution caused by industrialization, water pollution has become a globalproblem. Therefore, water treatment has become an important facet of protecting environmentfor every country. Chitosan has good environmental compatibility, reproducibility, richresources and high biodegradation. It has aroused more and more attention in water treatmentfield. Sodium alginate has low toxicity, good biocompatibility, thickening property, the filmforming ability, gel performance, high biodegradation and cheap. These unique propertiesmake sodium alginate have wide applications in many fields, and its internal porous structuremakes it a good adsorption material.There are a large number of amino group on chitosan molecular chains, and there areplenty of carboxyl group on sodium alginate molecular chains. After blending andcrosslinking modification of the two natural polymers, the obtaining modified polymer basedchitosan and sodium alginate as a flocculant will have broad molecular weight distribution,many of active group points and structural diversity. It can be completely biodegradable andhas good "environmental acceptability". It will be a kind of "green flocculant ". Howeverthere is no report of chitosan/sodium alginate modified polymer as flocculant till now.Using chitosan and sodium alginate as main raw materials, chitosan/sodium alginatepolymer （M-CS/SA） was prepared via electrostatic interaction between chitosan and sodiumalginate. The product was characterized with FTIR, SEM, X-RD and TGA. It was showed thatthe introduction of SA destroyed the regularity of CS molecular chains; M-CS/SA became apolymer with amorphous porous structure. Its thermal stability is better than CS. TheM-CS/SA was used for dyeing wastewater treatment and Cu²⁺and Cr2O72-adsorption. Theeffects of adsorption time, pH value and M-CS/SA dosage on the adsorption Cu²⁺and Cr2O72-were investigated. The adsorption of Cu²⁺on M-CS/SA was followed the pseudo-first-orderdynamics, And the adsorption of Cr2O72-on M-CS/SA was followed the pseudo-second-orderdynamics. M-CS/SA is good for turbidity removal rate, but it is not ideal on the COD removalrate. M-CS/SA is better than CS to Cu²⁺and Cr2O72-adsorption.In order to optimize the performance of chitosan/sodium alginate polymer flocculant,chitosan/sodium alginate polymer （E-CS/SA） was synthesized using the etherification method.Its structure and properties were investigated by using FTIR, SEM, X-RD, TGA, The resultsshow that: chitosan has obvious chemical reaction with sodium alginate. The structure ofM-CS/SA is amorphous and porous, and is more fine than CS. Taking decoloring rate, CODremoval rate and turbidity as evaluation indexes, the optimal conditions were found. At thesame time, the effects of the reaction conditions on the yield were investigated. The effects of deacetylation degree, solution pH value, polymer dosage, sedimentation time, different watersoluble dyes on the flocculation performance were also investigated. The product wasexplored to use for printing and dyeing wastewater treatment. It was found that the producthas a good adsorption effect on printing and dyeing wastewater. Under the optimum reactionconditions, E-CS/SA yield can reach more than80%. To the actual dye wastewater,decolorizing rate of E-CS/SA reached86%, COD removal rate reached92%, and turbidityremoval rate reached97%.The effect of E-CS/SA on Cr₂O₇^2-,Pb²⁺,Cd²⁺,Cu²⁺,Zn²⁺adsorption rate and the adsorptioncapacity was investigated. The adsorption dynamics was studied. The adsorption of E-CS/SAto heavy metal ions has quicker dynamic speed. In the best conditions, the adsorption rate ofE-CS/SA to Cr2O7^2-,Pb²⁺,Cd²⁺,Cu²⁺,Zn²⁺were88%,94%,95%,80.43%and58.33%respectively. The adsorption capacity to Pb²⁺,Cd²⁺were56.6mg/g and47.0mg/g. Dynamicsresearch showed that: the adsorption mechanism of E-CS/SA to Cu²⁺and Zn²⁺ismonomolecular layer adsorption mechanism in which chemical adsorption is primarily. Andadsorption speed is obviously faster than CS, which proved once again that E-CS/SA withmore active groups can increased chelating ability to metal ion. Scanning electron microscopyimages showed that the surface of E-CS/SA after adsorption Cu²⁺was no longer smooth.In order to improve the polymer stability and flocculation performance, a new kind ofcrosslinked chitosan/sodium alginate flocculant（C-CS/SA） was prepared usingepichlorohydrin as the crosslinking agent. With degree of crosslinking as evaluation index,using the orthogonal experimental design to analyze the influence factors of crosslinkingprocess （CS: SA ratio, epichlorohydrin dosage, reaction temperature, reaction time）, the bestpreparation conditions of the crosslinking process were obtained.The structure of the product was characterized by means of FTIR, SEM, X-RD and TGA.The results showed that the reaction was according to the path of the set, the introduction ofSA destroyed CS crystal structure, C-CS/SA formed better spatial structure, the surface has alarge number of holes, which is beneficial to the improvement of the performance of theadsorption.Using the polymer （C-CS/SA） to adsorption Cu2+, influence of adsorption time, thesolution pH value, flocculant dosage and degree of cross-linking on the adsorptionperformance were discussed. At the same time adsorption dynamics and adsorption isothermwere discussed, and the polymer was applied to the actual printing and dyeing wastewatertreatment. The results showed that C-CS/SA was the best in C-CS/SA, M-CS/SA andE-CS/SA on the actual printing and dyeing wastewater treatment.To obtain the best swelling conditions, the relationships of the polymer swelling degree with swelling time, solution pHand temperature were investigated, and the relationships of adsorption performance of thepolymer with degree of cross-linking were discussed. In the best conditions of crosslinkingand swelling, the decolorizing rate of C-CS/SA to printing and dyeing wastewater can reach96.5%, COD removal rate was95.2%, the turbidity removal rate is99.5%.Finally, three methods of the preparation of CS/SA polymer and the adsorptionperformance of the products were compared. Three preparation methods have theiradvantages and disadvantages, and the products performance is not the same, which can bechosen in practical applications. In the printing and dyeing wastewater treatment, C-CS/SAwas the best.