Preparation And Properties Of Nanocellulose-Based Antibacterial Materials

As a kind of biomass natural polymer with a unique micro-nano structure（high aspect ratio and nanometer diameter）,nanocellulose-based functional materials have been widely studied in recent years because of their high specific surface area,abundant reactive groups（hydroxyl,carboxyl,etc.）and excellent biocompatibility.Among them,cellulose-based antimicrobial nanomaterials have promising applications in the fields of biomedical excipients and packaging materials because of their degradable and biocompatible properties.In this thesis,lignin-cellulose nanofibers with natural antimicrobial properties,which exist in nature,were prepared by a green and environmentally friendly hydrolysis method,and their antimicrobial properties were investigated.Based on the understanding of the antimicrobial properties and antimicrobial principles of nanocellulose and lignin composites,composite antimicrobial films with antimicrobial properties and thermal adhesion were prepared using nanocellulose and lignin as the main components and biodegradable polymer poly（adipic acid-butylene terephthalate）（PBAT）as the reinforcing material.In addition,their microscopic morphology,mechanical properties,antimicrobial properties,and thermal adhesion were investigated.The microscopic morphology,mechanical properties,antimicrobial properties,and thermal adhesion were investigated to provide a reference for the development of nanocellulose-based antimicrobial composites.The main studies are as follows:（Ⅰ）Preparation of antimicrobial cellulose composite nanofibers and its performance study:A cellulose-based nanofiber（P-CNF）with good antibacterial properties was successfully prepared by using pine cones,which have natural antibacterial properties in nature,with hydrogen peroxide as the hydrolysis solvent.The free radicals such as HOO^-,OH^·,O^2-generated by H₂O₂ under heating conditions（60°C）destroy the internal structure of pine cones as well as the amorphous region of cellulose.The nanocellulose prepared by this hydrolysis method was found to contain lignin and rosin with diameters of about 20-30 nm and lengths of about 1-2μm by FT-IR,UV-Vis,and SEM studies.Since the phenolic substances in lignin and rosin can inhibit biological enzyme activity and thus hinder bacterial reproduction,P-CNF can be found to have excellent inhibitory effects on Gram-negative Escherichia coli（E.coli）and Gram-positive Staphylococcus aureus（S.aureus）in antimicrobial experiments,with minimum inhibitory concentrations（MICs）as low as 1.5 and 2 mg m L^-1,respectively.In addition,P-CNF has good dispersibility in ethanol,and its ethanol dispersion（0.15wt%）can be used as a new disinfectant with both bactericidal and long-lasting bacterial inhibition,which can effectively resist the secondary invasion of bacteria.This provides new ideas for the application of antimicrobial cellulose-based nanofibers in the field of bactericidal disinfection.（Ⅱ）Preparation of antimicrobial nanocellulose-based composite film and its performance study:Based on the investigation of the antimicrobial properties and mechanisms of lignin and nanocellulose composites,antimicrobial composite packaging films can be prepared using nanocellulose and lignin as raw materials.To enhance the mechanical and thermal processing properties of the prepared composite films,this thesis utilizes poly（adipic acid-butylene terephthalate）（PBAT）as the reinforcing polymer to prepare antimicrobial composite films with thermal adhesion properties.Cellulose nanofibers（CNF）were dispersed in a DMAc solution of lignin to achieve the co-blending of CNF and lignin,and PBAT was added and reinforced by solution casting of nanocellulose-based composite membranes.The effects of different percentages of PBAT on the chemical structure,thermal stability,UV-blocking property,mechanical property,water resistance,heat sealing property,and antibacterial property of the composite films were investigated by infrared,thermogravimetric,and mechanical tests.It was found that PBAT could improve the compatibility between CNF and lignin and thus improve the mechanical properties of the composite films,with a maximum increase of 25.5%in tensile strength.In addition,PBAT improved the thermal stability of the nanocellulose-based composite film while its water resistance was significantly improved,and the film did not swell or diffuse the contents in an aqueous solution for 4 h.According to the antimicrobial results,the composite film showed good inhibition of E.coli and S.aureus,and thanks to the processability conferred by PBAT,the nanocellulose-based composite film is expected to be an ideal material for the antimicrobial packaging field.