Polysaccharide Beads Via Polymer Complexation: Formation,Properties,and Applications

Polysaccharide based polyelectrolyte complex have attracted much attention due to the growing demand for sustainable materials and a wide range of applications.Derived from the two most abundant polysaccharides,carboxymethyl cellulose(CMC)and chitosan(CHI)have been widely researched.Meanwhile,spherical beads made of naturally derived polymers can be widely used as promising matrices for adsorption,releasing and protection of sensitive and active compounds.However,the poor mechanical properties of the pure CMC/CHI beads hindered their applications.This work focused on the fabrication of spherical beads with just CMC and CHI as materials via polymer complexation,improving their mechanical performance without adding any other chemicals,and investigation of their possible application in selectively loading and releasing of charged molecules,with dye molecules as example molecules.In the first part of the thesis,the optimal parameters for fabrication of CMC/CHI core-shell beads via an extrusion-drop method were established based on systematical investigations on working distance,solution pH and polymer concentrations.Spherical beads only could be obtained when the working distance and polymer concentration were in certain ranges.The beads prepared at pH 4.5 were the strongest and could resist a force of up high to 0.071 N,suggesting a more efficient complexation was achieved at pH 4.5.The FTIR was used to demonstrate the electrostatic interactions between CMC and CHI.The concentrations of CMC and CHI solutions played important roles in determining the shape and size of beads.A shape map was created to provide the information of critical concentrations required for effective fabrication of beads with certain shapes.In the second part,we managed to improve the beads stability by a simple thermal treatment during the bead preparation.The effects of the temperature,changing from 25 ℃ to 75 ℃,on the stability of the formed beads were investigated.The changes in morphology,diameter,shell thickness and structure of the beads before and after the thermal treatment were analyzed using SEM,XPS and FTIR.The stability of the beads was studied by mechanical test and swelling experiments,which showed that heat treatment enhanced the bead’s ability to withstand pressure and resist swelling.The beads treated at 75 ℃ showed the best pressure resistance,while the beads treated at 55 ℃ exhibited the highest swelling.This method is simple and easy to implement,not only improves the stability,but also can control the swelling capacity and mechanical properties of the beads,which are important for their potential applications in adsorption and controlled release.More importantly,the work provides an intuitive study and characterization of the effects of heating on the complexation process of two polysaccharide molecular chains.The CMC/CHI complex beads have a core-shell structure composed of a thin skin layer and a 3D entangled internal structure,which endows the beads with adsorption possibilities toward anionic and cationic molecules via electrostatic interaction.Thus,in the third part,the loading and releasing behavior of such a system was studied systematically.The influences of beads physical state,adsorbent dosage,agitation speed,solution pH and temperature on the loading behavior were investigated.The CMC@CHI beads demonstrated different loading efficiency to three typical dyes of methylene blue(MB),acid blue-113(AB),and methyl orange(MO)with different charge status.The adsorption rate followed an order of MB ﹥ AB ﹥ MO,giving 97.4%,73.3% and 20.2%,respectively.The releasing of three dyes from CMC@CHI beads also exhibited different rates,and MB release was found to be prolonged compared to AB and MO.The loading mechanism of dyes was further investigated via X-Ray photoelectron spectroscopy.These CMC@CHI beads may have possible applications in the mixed dye removal and selective adsorption of molecules with different charges,as well as encapsulating systems of drugs or sensitive chemicals with different charges.In the last,the adsorption ability of CMC@CHI core-shell beads were also evaluated via kinetic and isotherm studies.The results showed that the loading equilibrium was reached in 3 h for MB and 4 h for AB dyes.The analysis of the adsorption kinetics highlighted that all the data could be fitted by a pseudo-second order model,and the adsorption isotherm could be sufficiently described by Langmuir isotherm model for MB and AB dyes.Further,the maximum adsorption capacity determined by Langmuir model matched well with the experimental data,giving 42.3 and11.5 mg/g for MB and AB dyes,respectively.In addition,the releasing process of AB dye could be sufficiently defined with the Korsmeyer-Peppas model based on the R2 value(0.98),while the value of n,0.35,suggested the AB dye was released by Fickian diffusion owed.