Preparation And Properties Of Cellulose-based Antimicrobial Composites

Combined with the advantages of the cellulose and inorganic antibacterial materials, the cellulose-based antimicrobial nanocomposites were synthesized by using cellulose as the matrix, and silver, silver chloride, titanium dioxide, other inorganic antimicrobial materials as the reinforcing phase, which had potential applications in the field of tissue engineering and biomedical owing to its unique properties such as biodegradation, biocompatibility, and antibacterial activities. Currently, there had been problems about the cellulose-based antimicrobial nanocomposites, such as the tedious preparation method and poor dispersion of the reinforcing phase in the matrix. This thesis focused on the above scientific issues, used green method to fabricate series of cellulose-based antimicrobial nanocomposites, characterized their phase, shape, dispersion, and explored the mechanism of the composites.The cellulose/silver nanocomposites were in-situ synthesized by fast microwave-assisted heating method by using microcrystalline cellulose (MCC) as the matrix, ethylene glycol as the solvent, microwaves absorbers and reducing agent, and silver nitrate as reactant. The results showed that cellulose-silver nanocomposites were synthesized by microwave heating at140℃for only10min. By optimized the preparation parameters, it can be achieved uniform and stable distribution of silver nanoparticles on the cellulose matrix. Compared to the monomer-MCC, the thermal stability of the cellulose/silver nanocomposites had significantly improved. The prepared composites had obvious antibacterial properties against Escherichia coli and Staphylococcus aureus.The cellulose/AgCl-Ag nanocomposites and cellulose/Ag nanocomposites were synthesized via microwave-assisted heating method by LiCl/DMAc pretreatment of cellulose using MCC as the matrix, DMAc as the solvent, and ascorbic acid as a reducing agent. The results indicated that series of cellulose/AgCl-Ag, cellulose/Ag-AgCl, and cellulose/Ag nanocomposites were synthesized by adjusted the concentration of ascorbic acid. Compared with the oil bath heating, microwave-assisted heating method was much more favor of the phase transition from silver chloride to silver and also conducive to improve the proportion of silver in nanocomposites. Compared to the cellulose/Ag nanocomposites, the antibacterial experiment demonstrated that the cellulose/AgCl-Ag nanocomposites had better antimicrobial effect against Escherichia coli and Staphylococcus aureus.The cellulose/AgCl nanocomposites were synthesized via microwave-assisted heating method by LiCl/DMAc pretreatment of cellulose without any reducing agent using MCC as the matrix and DMAc as the solvent. The novel preparation method was based on the simultaneous formation of the AgCl nanoparticles and precipitation of the cellulose. The high heating temperature and long heating time are favorable for the complete formation of AgCl nanoparticles in the cellulose/AgCl nanocomposites. The cellulose/AgCl nanocomposites had good antibacterial activities against both E. coli (Gram-negative) and S. aureus (Gram-positive).The holocellulose/Ag nanocomposites were synthesized via hydrothermal method by NaOH/urea pretreatment of holocellulose using holocellulose as the matrix from cotton stalk. Compared with the reductants of sodium borohydride and glucose, there had been a large number of silver nanosheets dispersed on the surface of composites prepared using fructose as reducing agent by hydrothermal method. The long hydrothermal reaction time is conducive to the crystallization of silver, but not favorable for the uniform distribution of silver nanoparticles. Holocellulose from cotton stalk as the carrier for silver nanoparticles, are much more conducive to improve the dispersion of silver nanoparticles in the cellulose matrix compared with the composites prepared by MCC. It has been well distributed for cotton stalk holocellulose fiber by NaOH/urea pretreatment, which were much more conducive to improve the dispersion of silver nanoparticles.The cotton stalk fiber/Ag nanocomposites were synthesized via ultrasonic treatment by NaOH/urea pretreatment of cotton stalk fiber. It was generated linear nano-silver on the surface of the composites by using sodium borohydride as reducing agent via ultrasonic treatment for40min. It was much more conducive to the generation of the chip-like nano-silver using glucose as reducing agent. The crystallinity of cotton stalk fiber decreased with the increasing ultrasonic treatment time. The thermal stability was greatly improved by using sodium borohydride as reducing agent.The cellulose/TiO2nanocomposites were synthesized via hydrothermal method by LiCl/DMAc pretreatment and NaOH/urea pretreatment of Cellulose, respectively, which were used MCC as the matrix. The morphology of the composites was different by using different cellulose dissolution systems. The composites prepared by NaOH/urea pretreatment were superior to the composites pretreated by LiCl/DMAc solution either in phase, thermal stability and antibacterial properties. The TiO2crystals were obtained by calcination the composites.The cellulose/manganese oxide nanocomposites were synthesized via microwave-assisted heating method using MCC as the matrix, manganese acetate and hexamethylenetetramine (HMT) as raw materials, dimethylformamide (DMF) as a solvent. The crystallinity of cellulose decreased with the increasing microwave heating time. The Mn2O3materials were obtained by calcination the nanocomposites. The cellulose/Mn3O4nanocomposites were synthesized via ultrasonic treatment using MCC as the matrix, manganese acetate as manganese source. The particle morphology of the manganese tetroxide on the matrix of composites synthesized by ultrasonic treatment for90min were different using four kinds of alkalis——urea, HMT, sodium hydroxide and potassium hydroxide. Sodium hydroxide is conducive to the formation of inorganic particles having a long thin sheet-like morphology. Compared with urea and HMT, the thermal stability of the cellulose/Mn3O4nanocomposites prepared by sodium hydroxide and potassium hydroxide were much better. The Mn3O4materials with spinel structure were obtained by calcination the nanocomposites.