Study On Quaternary Ammonium Cellulose Based Functional Materials Via Electrostatic Interactions

Quaternary ammonium cellulose is a class of polyelectrolytes with quaternary ammonium cationic groups,which has the structural characteristics of both cellulose and electrolytes.It has a wide application prospect in biomedicine and waste water treatment.The traditional preparation method of quaternary ammonium cellulose mainly involves etherification of the hydroxyl group on cellulose,which has strict requirements on the functional group structure of the modified reagent,and the degree of substitution（DS）of the product is low.Tertiary amine compounds are a kind of good quaternary ammonium modification reagents,but most of them could react with cellulose to synthesize quaternary ammonium cellulose after multi-step complex modification.In order to solve the problems of complicated reaction steps and low DS,cellulose ester derivatives containing terminal bromine functional groups were prepared by modification of cellulose in this study,which could directly react with tertiary amine compounds of different structures to produce quaternary ammonium cellulose with high DS.Then quaternary ammonium cellulose was used as cationic compound,which was electrostatic combined with various types of anionic compounds to prepare functional materials with different structures,including nanoparticles,films,hydrogels and microcapsules.The main research results are as follows:（1）Synthesis of quaternary ammonium cellulose.Cellulose 6-bromohexanoyl ester（CBE）containing terminal bromine functional group was prepared by esterification reaction using microcrystalline cellulose with 6-bromohexyl chloride as esterification reagent.The terminal bromine functional group is universal and can react with tertiary amine compounds of different structures to form quaternary ammonium cations.N,N-dimethylbutylamine（QA₄）,N,N-dimethyloctylamine（QA₈）,N,N-dimethyldecylamine(QA₁₀),N,N-dimethyldodecylamine(QA₁₂),N,N-dimethyltetradecylamine(QA₁₄),N,N-dimethylhexadecylamine(QA₁₆),1-methylpyrrolidine（MP）,1-methylimidazole（MI）and pyridine（PY）were selected as quaternary ammonium reagents to prepare quaternary ammonium cellulose,and obtained product were named CBE-QA₄,CBE-QA₈,CBE-QA₁₀,CBE-QA₁₂,CBE-QA₁₄,CBE-QA₁₆,CBE-MP,CBE-MI and CBE-PY,respectively.Based on the two-step reaction,microcrystalline cellulose and 6-bromohexyl chloride were dispersed in pyridine system to prepare cellulose 6-（N-pyridinium）hexanoyl stere（CPHE）in one step.By means of FTIR,NMR,XPS and EA,the existence of quaternary ammonium cations in products was proved,and the DS of products was high.（2）The antibacterial nanoparticles（CBE-QA_n/CA_x）were prepared through electrostatic interaction by using quaternary ammonium cellulose with long alkane chain structure as cation and CA as anion.CBE-QA_n/CA_x nanoparticles were prepared through nanoprecipitation method by combining CBE-QA₈,CBE-QA₁₀,CBE-QA₁₂,CBE-QA₁₄,CBE-QA₁₆ with CA,respectively.The chemical structure,morphology and antibacterial properties of the complex nanoparticles were analyzed.The complex nanoparticles were spherical with average diameters of 70–145 nm.When the amount of complex nanoparticles was 0.2 mg/m L,the antibacterial rates against S.aureus and E.coli reached 100%.CBE-QA₁₆/CA₃₅ nanoparticles were added to polyvinyl alcohol（PVA）matrix by solvent casting method to prepare PVA-based composite films,and the antibacterial and mechanical properties were tested.The antibacterial properties of PVA-based composite membrane against S.aureus and E.coli were significantly enhanced,and the highest antibacterial rates were increased to 100%.With 5 wt.%of CBHE-QA₁₆/CA₃₅nanoparticles,the tensile strength of the PVA-based composite films increased to 53.40 MPa which was 47.27%higher than that of the pure PVA film.With 1 wt.%of CBHE-QA₁₆/CA₃₅nanoparticles,the elongation at break of the PVA-based composite films increased to 252.04%which was 46.92%higher than that of the pure PVA film.（3）The film materials with separation function were prepared through electrostatic interaction by using quaternary ammonium cellulose with short alkane chain or ring structure as cation and SA as anion.CBE-QA₄,CBE-MP,CBE-PY and CBE-MI were combined with SA and the film materials with dye or inorganic salt filtration performance were prepared by layer self-assembly method.The surface potential and morphology of the complex films were analyzed.The complex films were negative charged and their surface structure is dense.The filtration performance of the complex films was tested.The results showed that,compared with SA films,the filtrate permeation flux decreased,but rejection rates increased,among which the rejection rate for anionic dye methyl orange reached 98.08%.In addition,the complex films maintained good stability in a long-time filtration process.（4）The hydrogels with dye-adsorption function were prepared through electrostatic interaction by using CPHE as cation and polyacrylic acid as anion.The swelling properties of the complex hydrogels were analyzed.After being treated with sodium hydroxide solution and distilled water,the volume of the complex hydrogels became larger,and the network structure of complex hydrogel was loose,resulting in enhanced water absorption capacity,and the maximum swelling ratio was 382.86 g/g.The swelling complex hydrogels were used as adsorbent to adsorb methylene blue.The maximum adsorption capacity for the cationic dye methylene blue was 2864.13 mg/g,and the adsorption process was consistent with the pseudo-second-order adsorption kinetics model and Freundlich adsorption model,indicating that the adsorption process was mainly electrostatic adsorption,and there was multi-molecular layer adsorption.（5）The microcapsules with encapsulation function were prepared through electrostatic interaction by using CPHE as cation and carboxymethyl cellulose as anion.The morphology of complex microcapsules was analyzed.The complex microcapsules owned a core-shell structure,and the outer shell of complex microcapsules displayed a dense structure with unevenly distributed micro-nanopores.The internal structure was loosely constructed by a flaky or filamentous network.The PEG-based phase change energy storage capsules were prepared by encapsulating PEG into porous complex microcapsules through vacuum impregnation method.The thermal energy storage performance,shape stability and thermal cycle stability of the PEG-based phase change energy storage capsules were tested.The complex microcapsules exhibited excellent PEG encapsulation ability with an extremely high PEG loading up to 34.33 g/g after impregnation.The PEG-based phase change energy storage capsules showed high thermal energy storage ability with the melting latent heat up to 142.2J/g,which was 98.5%of pure PEG.According to the anti-leakage test and 200 heating-cooling cycles,the PEG-based phase change energy storage capsules demonstrated good form-stable property.In conclusion,the quaternary ammonium cellulose with different properties and high DS were synthesized by a two-step or one-step reaction using tertiary amine compounds as quaternary ammonium modification reagents.Based on electrostatic interaction,quaternary ammonium cellulose was combined with various types of anionic compounds to prepare functional materials with different structures,which have important potential applications in packaging materials,wastewater treatment and phase change energy storage filed.