Fabrication And Application Of Functional Materials Through Chitosan-based Pickering Emulsion Template Method

Because the excellent properties of nontoxicity, biocompatibility, biodegradability andrecoverability of natural polymers, there are growing interests in design and preparation ofnovel natural polymers-based colloid particles to stabilize Pickering emulsions, and fabricaterelated functional materials. For the first time, this study discusses the stability mechanism ofPickering emulsions stabilized by pure chitosan nanoparticles (CNPs) or other colloidparticles modified by chitosan. Based on these emulsions, this thesis describes thedevelopment of new strategies for the preparation of hierarchical macroporous material ordegradable polymer microspheres, and studies the practical application of these materials. Theinnovative ideas of this study can be concluded as follows: we develop novel kinds ofparticulate emulsifiers to stabilize Pickering emulsions; the proposed approach for preparationof various functional materials based on Pickering emulsion stabilized by pH-responsivechitosan expands the application of a wide range of reversible emulsifiers or emulsionsystems, and has a potential application in green economy or environmental protection. Themain contents and results of this study are listed as follows:1. For the first time, a simple reversible Pickering emulsion system stabilized by pureCNPs without any hydrophobic modification is developed. Chitosan has a pH-tunable sol-geltransition due to free amino groups along its backbone. At pH6.0, chitosan is insoluble inwater. CNPs or micrometer-sized floccular precipitates are formed in situ. These chitosanaggregates can adsorb at the interface of oil and water to stabilize O/W Pickering emulsions.At pH6.0, chitosan is soluble in water. Demulsification happens. Four organic solvents(liquid paraffin, n-hexane, toluene, and dichloromethane) are chosen as the oil phase.Reversible emulsions are formed for all four oils. Chitosan-based Pickering emulsions canundergo five cycles of emulsification-demulsification with only a slight increase in theemulsion droplet size. They also have good long-term stability for more than2months. Whenthe salt concentration of chitosan aqueous solution is less than400mmol/L, the droplet size ofPickering emulsion increases with increasing of salt concentration.2. Pickering emulsion stabilized by pH-reversible chitosan is developed to preparedegradable polymer microspheres by emulsion photopolymerization, where chitosan acts as a green and recyclable particulate emulsifier. The thiol-ene photopolymerization oftrimethylolpropane tris(3-mercaptopropionate) and trimethylolpropane triacrylate is initiatedby UV irradiation. The property of excellent pH-reversibility of chitosan endows it to be usedfor recycles in emulsion polymerization at least three times. Pure microspheres are obtainedby dissolving the chitosan-coated microspheres in HCl aqueous solution to remove chitosan.Ibuprofen is loaded into the microspheres. The higher release temperature or pH value, thefaster release rate and higher release extent of IBU from the microspheres are found.Meanwhile, the resulting microspheres exhibit a good degradability in1M NaOH aqueoussolution, with a weight loss of about90wt%after35days. This study opens up a new routefor the green and recyclable application of chitosan in fabrication of degradable polymermicrospheres.3. Chitosan scaffolds with hierarchical macroporous structures for recyclable adsorptionof Cu2+are prepared by templating from Pickering high internal phase emulsions (HIPEs) forthe first time. The liquid paraffin-in-water HIPEs are stabilized by CNPs. The internal phasefraction can be up to90.0%, meanwhile the chitosan concentration only needs1.0wt%. Thechitosan scaffolds are obtained by crosslinking the dispersed CNPs, followed by removing theinternal phase. The resulting scaffold exhibits the average pore size of around15m andinterconnecting throat size of several micrometers. The adsorption capacities of thechitosan-glutaraldehyde (chitosan-GLA) scaffolds for Cu2+increase with increasing the molarratio of-NH2of CNPs to-CHO of GLA. At the optimized ratio of2:1, the adsorption capacityis60.2mg/g at room temperature and pH5.0. The adsorption capacity can be greatlyimproved by addition of carboxymethylated chitosan or adopting imprinting method, and theadsorption capacities are100.2,90.3mg/g, respectively. The adsorption isotherm of thechitosan scaffold closely follows Freundlich model. Furthermore, the adsorption capacity ofthe scaffold undergoing10consecutive desorption-adsorption cycles still maintains at a highlevel of90.3%, suggesting the chitosan scaffold is a green and recyclable biosorbent inpractical wastewater treatment.4. For the first time, chitosan acts as a new kind of weak polyelectrolyte modifier tomodify graphene oxide (GO), and Pickering emulsions are stabilized by the CS/GOnanocomposite colloid particles. When the mass ratio of chitosan and GO is in the range of 0.0625-0.25, no matter what the polarity and viscosity of oils are, besides, whatever the oilsare aromatic solvents or aliphatic solvents, the obtained CS/GO colloid particles can stabilizePickering eumulions, which have good long-term stability for more than two months. Thisstudy suggests that chitosan molecules can not only act as an effective particulate emulsifierto stabilize Pickering emulsions alone, but also as a kind of modifier to preparenanocomposite colloid particles with other particles, and preparation of Pickering emulsions.5. Nanocomposite polysaccharide microcapsules composed of biocompatiblepolyelectrolyte complex via electrostatic Layer-by-Layer self-assembly on Pickeringemulsions template method are firstly prepared. PEI/Laponite-based Pickering emulsions areobtained regardless of the polarity and viscosity of the oils at PEI/Laponite mass ratio of0.5and Laponite concentration of0.25wt%, and these emulsions show good long-term stabilityfor more than two months. Four bilayers sodium alginate-chitosan microcapsules with thedimension of about43.9μm and wall thickness of55nm were prepared by alternateadsorption of negatively charged alginate and positively charged chitosan on Pickeringemulsions. Hollow microcapsules are obtained after core removal at a mild condition ofwashing with excess2-propanol. IBU as a model drug is loaded into hollow microcapsules,and the release rate of IBU from the microcapsules at pH7.4is obviously faster than therelease rate at pH2.0. The more polyelectrolyte layers of IBU-loaded microcapsules, the moredifficult for IBU release.