| The invasion of bacteria,active free radicals and ultraviolet rays has been interfering with human daily life.Lignin is a kind of green,non-toxic,renewable and degradable biomass material with abundant sources.It has attracted wide attention due to its antibacterial,antioxidant and UV shielding properties.However,as a natural antibacterial agent,lignin has weak antibacterial activity due to its complex structure and low effective antibacterial components,which limits its application as an efficient antibacterial material.In this study,lignin nanoparticles（LNP）were prepared by acid hydrolysis precipitation method using alkali lignin as raw material.Then,the antibacterial activity of LNP was improved by various modification methods,and it was uniformly dispersed in poly（butylene adipate-co-terephthalate）（PBAT）to prepare PBAT/lignin composites with excellent tensile properties and antibacterial,antioxidant,ultraviolet shielding properties.The specific work is as follows:First of all,LZn（LNP-Zn O）hybrid nanoparticles were prepared by one-step hydrothermal method using LNP and zinc acetate dihydrate（Zn（CH3CO2）2·2H2O）as raw materials.The morphology of LZn and the loading of zinc oxide（Zn O）were controlled by p H during the reaction.The structure of LZn were analyzed by infrared spectroscopy,thermogravimetric analysis and X-ray energy spectrum,and their antibacterial activities were tested,and the optimal reaction conditions were explored.LZn provided more effective antibacterial components for lignin,and enhanced the antibacterial activities of lignin.The antibacterial rates of LZn-9（p H=9）against Escherichia coli（E.coli）and Staphylococcus aureus（S.aureus）reached 91%and 51%,respectively,which were 194%and 155%higher than those of LNP,respectively.PBAT-G was prepared by grafting glycidyl methacrylate（GMA）onto PBAT.PBAT-G-x LZn composites were prepared by the reaction of PBAT-G and LZn catalyzed by triethylamine（TEA）.The tensile strength and elongation at break of PBAT-G-2LZn composite reached 32.1 MPa and 922%,respectively.The tensile modulus of PBAT-G-3LZn and yield strength were 82.3 MPa and 8.5 MPa,respectively,which were 35.2%and 28.6%higher than those of PBAT.In addition,PBAT-G-x LZn composites exhibit good antibacterial,antioxidant and ultraviolet shielding properties.The E.coli and S.aureus adhesion concentrations of PBAT-G-3LZn composite were only 18%and 19%of PBAT respectively,and the free radical scavenging rate（RSA）of PBAT-G-3LZn composite was 9.3%.Secondly,in order to further simplify the construction process of hybrid nanoparticles and optimize the compatibility of hybrid nanoparticles with PBAT,LZA（LNP-Zn O-CTAB）and LZM（LNP-Zn O-CMMB）hybrid nanoparticles were prepared by a simple self-assembly method using LNP,nano-Zn O,cetyltrimethylammonium bromide（CTAB）and 1-hexadecyl-3-methylimidazolium bromide（CMMB）as raw materials.The structure and composition of LZA and LZM were analyzed by infrared spectroscopy,thermogravimetric analysis and X-ray energy spectrum.The structure of LZA and LZM contains long-chain alkanes and cations,which destroy the membrane structure of bacteria when they contact bacterial cells,so they have excellent antibacterial activity.Their antibacterial rates aganist E.coli and S.aureus can reach 100%,which were further enhanced compared to the previous system.The long-chain alkane structure of LZM promotes its interfacial compatibility with PBAT,and PBAT/LZM composites with excellent tensile properties were prepared.The tensile strength and elongation at break of PBAT-1%LZM composite reached 37.1 MPa and 1188%,respectively.In addition,PBAT/LZM composites have good antibacterial,antioxidant and UV shielding properties.The E.coli adhesion concentration of PBAT-3%LZM composite was only 4%of PBAT,and no S.aureus adhered to PBAT-3%LZM composite.The RSA of PBAT-3%LZM composite reached25.5%.Finally,modified lignin（LNP-VB）with different contents of vitamin B1（VB1）were synthesized by mannich reaction using LNP and VB1 as raw materials.Compared with the first two systems,LNP-VB are safer and greener.The chemical structure and properties of LNP-VB were studied by infrared spectroscopy,gel permeation chromatography,nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy.LNP-VB had good antibacterial activity.The antibacterial rates of LNP-30VB against E.coli and S.aureus were 98%and 90%,respectively,which were 170%and 290%higher than those of LNP.The antibacterial mechanism of LNP-VB was explored from the molecular structure.The results showed that the phenolic hydroxyl groups were more likely to lose H·to form a stable phenoxy radical after LNP grafted VB1,and the phenoxy radicals could better attack the bacteria.At the same time,the hydrogen ions ionized by the phenolic hydroxyl groups would acidify the physiological environment of the bacteria.The cationic structure of LNP-VB enhanced their adsorption to bacteria,thereby enhancing the antibacterial activities of LNP-VB.In addition,the antioxidant activities of LNP-VB also increased simultaneously,and the RSA of LNP-30VB increased to82.4%compared with LNP（71.9%）.PBAT/LVB composites with good tensile properties,antibacterial,antioxidant and ultraviolet shielding properties were prepared by dispersing LNP-VB in PBAT.The tensile strength and elongation at break of PBAT-1%LVB composites reached38.2 MPa and 873%,respectively.The E.coli and S.aureus adhesion concentrations of PBAT-3%LVB composite were only 21%and 20%of PBAT respectively,and the RSA of PBAT-3%LVB composite was 99.9%.In this thesis,lignins were modified to improve their antibacterial properties and their antibacterial mechanism were analyzed.The modified lignin with good antibacterial properties,antioxidant properties and UV shielding properties were prepared,and the value-added of lignin was realized.The modified lignin were compounded with PBAT to prepare a composite materials with good tensile properties and antibacterial,antioxidant and ultraviolet shielding properties,which provided technical support for the application of PBAT/lignin composites in the field of medical and active packaging. |
