Construction Of Controllable Gelation Films And Lysozyme Adsorption Gell Beads Based On The Sol-gel Transition Of Alginate

Alginate has been widely used in the field of functional materials because of its excellent features,such as mild gel condition,biodegradability,biocompatibility,low toxicity,low price,and easy modification.Based on the sol-gel transition induced by divalent cations,sodium alginate?SA?can be used to prepare many kinds of functional materials,such as films,beads,hydrogels,fibers,etc.However,the rapid and poorly controlled sol-gel transition is extremely unfavorable for the properties of alginate based films.Until now,there is not an effective external coagulating bath which can be used in the controllable preparation of alginate based films.From another point of view,the rapid sol-gel transition is the basis of the preparation of alginate-based gel beads.The presence of negative carboxylate functions along the alginate chains ensures its high affinity and binding capacity for charged species,which has been utilized as a naturally available low-cost adsorbent for removing dyes or heavy metal ions from wastewater.However,few attempts have been made to the adsorption of proteins by alginate-based materials.In addition,how to use industrialized natural polymers to replace synthetic polymers in more fields has become an urgent problem to be solved.In this dissertation,firstly,we developed a new type of controllable coagulation bath system to inhibit the rapid gelation rate during the preparation of alginate based films.And we used this system to prepare alginate films with improved properties.Secondly,we prepared gel beads based on the rapid sol-gel transition of alginate and the feasibility of the protein adsorption application was evaluated.Calcium alginate?Ca-SA?films were prepared by ionic crosslinkage in a calcium chloride?Ca Cl₂?water solution containing different proportions?0–40%?of ethanol as the co-solvent.It was found that the addition of ethanol to the coagulation bath could significantly reduce the shrinkage,surface roughness,and opacity of the films,while the visual appearance and mechanical properties?in dry and wet states?of the films were improved.In addition,the incorporation of ethanol into the coagulation bath did not detract the gel reaction and homogeneity of the films.Furthermore,the gel degree would not be decreased when the ethanol proportion did not exceed 30%.Ethanol can decrease the hydration process?swelling?of films during the crosslinking process,which reduces the infiltration rate of Ca²⁺ into alginate film matrix and the contact probability with the carboxyl group?-COO-?in the SA chains.Therefore,the sol-gel transition rate of alginate can be inhibited and sol-gel transition process can be controlled.In addition,this Ca Cl₂/H₂O/C2H5 OH crosslinking system can be used to prepare calcium alginate/konjac glucomannan based blending films?Ca-SA/KGM?and deacetylation modified Ca-SA/DKGM films.It was found that the mechanical properties and thermal stability of Ca-SA/KMG films could be improved by blending modification and deacetylation.Calcium alginate?Ca-SA?gel beads were prepared by crosslinking with by Ca²⁺ and glutaraldehyde?GA?,and the adsorption properties of positive lysozyme in aqueous solution were investigated.With the increase of Ca²⁺ concentration in the coagulation bath,the pore volume and particle size of Ca-SA gel microspheres were decreased,but the particle size distribution,sphericity,and compressive properties were improved.In addition,with the increase of Ca²⁺ concentration in the coagulation bath,swelling degree was increased and then reached a stable minimum value In response to this,the Ca²⁺ content in the beads was increased first,then reached a saturation value.The variation trend of calcium content was in synchrony with the changing trend of swelling degree,indicating that with the increase of Ca²⁺ concentration in the coagulation bath,the content of-COO-in Ca-SA gel beads was decreased gradually and then remained unchanged.Taking advantage of the abundant negative carboxyl groups,the prepared Ca-SA gel beads exhibited a well-integrated adsorption performance towards positive lysozyme,including a superior adsorption capacity of 213.63 mg/g,fast adsorption equilibrium within 12 h at a p H value of 6.The adsorption process can be described by the pseudo-second order kinetic equation and fitted well with the Langmuir isotherm model.In addition,Ca-SA gel beads have good reusability,and the adsorption/desorption process does not affect the structure and conformation of lysozyme.The as-prepared Ca-SA gel beads achieved a comparative adsorption capacity compared to other cation exchange adsorbents.The high performance is mainly attributed to the naturally possessed abundant active carboxyl groups on alginate chains,which can spontaneously and efficiently adsorb lysozyme without any modification.Three water-soluble polysaccharides with different molecular structure and performance,carboxymethylcellulose?CMC?,xylan and chitosan?CS?,were used to prepare gel beads by blending and crosslinking with alginate.It was found that different properties of the three alginate based blending gel beads were related to their different interactions.The Ca²⁺ crosslinking and GA covalent crosslinking turned out to be the dominant factor that existed in all the three kinds of blending gel beads.In the case of Ca-SA/CMC,there is a weak crosslinking between CMC and Ca²⁺ as well as a strong hydrogen interaction.Furthermore,there is a side chain rigid effect in the Ca-SA/Xylan gel beads and an electrostatic interaction in the Ca-SA/CS gel beads.These different interactions made the performance of the blending beads vary with the blending ratio.In general,the results indicate that it is possible to improve and tune the properties of alginate based blending gel beads by varying the kinds of polysaccharides and blending proportions.Ca-SA/CMC gel beads showed better comprehensive properties and were used to investigate the lysozyme adsorption performance.The introduction of CMC increased the adsorption capacity of Ca-SA gel beads to 236.34 mg/g and shortened the adsorption equilibrium time to 8h.Moreover,the introduction of CMC had no effect on the adsorption mechanism and adsorption selectivity of the gel beads.This is mainly due to the fact that the CMC itself contains a lot of-COO-,but its crosslink ability with Ca²⁺ is weak,so the introduction of CMC can improve the content of-COO-for adsorption in Ca-SA/CMC gel beads.