Preparation Of Polymeric Microspheres And Porous Materials Stabilized By Cellulose Nanocrystals

Pickering emulsion is a kind of emulsions stabilized by solid particles.Compared with the emulsions stabilized by surfactants,Pickering emulsion has the advantages of higher stability,lower toxicity and less amount of stabilizer,which has aroused the interest of researchers.Cellulose nanocrystals(CNCs)are green,biodegradable and low cost rod nanoparticles.Because of its unique properties,CNCs have become an ideal Pickering emulsion stabilizer and have shown good ability to stabilize Pickering emulsion.In this thesis,hydrophobic modification of CNCs were carried out to improve amphiphilicity property of CNCs and enhanced ability of CNCs to stabilize the emulsion.The modified CNCs were used to stabilize the Pickering emulsion of styrene and high internal phase emulsion of acrylic acid respectively.Then polystyrene microspheres and poly(acrylic acid)porous materials were prepared by Pickering emulsion polymerization reaction.The specific research contents include the following two parts:1.Polyphosphoester-modified cellulose nanocrystals for stabilizing Pickering emulsion polymerization of styreneThe structure and properties of functional nanoparticles are important for stabilizing Pickering emulsion polymerization.Recently,cellulose nanocrystals(CNCs)are increasingly favored as a bio-based stabilizer for Pickering emulsions.In the first part of this thesis,we reported a novel functionalized polyphosphoester-grafted CNCs for the stabilization of oil-in-water Pickering emulsions and the emulsion polymerization of styrene.First,polyphosphoester containing an amino at one end of the chain,abbreviated as PBYP-NH2,was prepared by ring-opening polymerization(ROP)and hydrolysis reaction,wherein PBYP represents poly[2-(but-3-yn-1-yloxy)-2-oxo-1,3,2-dioxaphospholane].Subsequently,CNC-COOH was obtained via TEMPO oxidation of CNCs.The functionalized nanocrystals with carboxyl groups and polyphosphoester on the surface were obtained by the reaction of PBYP-NH2 with CNC-COOH.Finally,we used CNC-PBYP-COOH as sole nanoparticle surfactant to stabilize styrene-in-water Pickering emulsions and studied its effects on the emulsions in details by using dynamic light scattering(DLS).The results showed that the performance of the emulsions relied on the concentration of the stabilizer,the oil-water ratio and the change of pH in the medium.The modified CNCs had higher ability to stabilize the styrene-in-water emulsions relatived to the unmodified CNCs,and a stable oil-in-water(o/w)Pickering emulsion with diameter of hundreds of nanometers could be obtained.The resulting emulsions could be polymerized to yield nanosized latexes.The polyphosphoester-modified CNCs as green solid surfactants can efficiently stabilize nanoemulsions and latexes.2.Preparation of polymer porous materials by cellulose nanocrystalline modified with hexadecyl trimethylammonium bromidePolymers prepared from high internal phase emulsions stabilized only by solid particles often have a closed-cell-like structures,but with the addition of a small amount of surfactant will lead to the formation of more open-cell structures.In the second part of this thesis,porous poly(acrylic acid)(PAA)materials were prepared via oil-in-water(o/w)Pickering high internal phase emulsion(HIPE)templates stabilized by CNCs modified with hexadecyl trimethylammonium bromide(CTAB).The amphiphilicity of CNCs was adjusted by slight modification with CTAB.The effects of stabilizers at different concentrations or CTAB contents on the particle size of high internal phase emulsions were observed by optical microscopy(OM).The morphologies and inner structures of the PAA gels were observed by scanning electron microscope(SEM).The results showed that the internal structure and pore size of PAA porous gels could be regulated by changing the concentration of stabilizer and the content of CTAB.Experiments have proved that the prepared PAA gels had selective adsorbability for cationic dye methylene blue(MB),and its adsorption capacity was affected by internal structure of the PAA gels.The PAA gels with open-cell structure had good adsorption performance for MB.The study on the cyclic adsorption properties of MB showed that the prepared PAA porous gel had good reusability.The porous PAA gels prepared in this study have potential application value for the treatment of cationic dyes in wastewater.