Preparation And Antibacterial Activities Of Lignin Nano-silver Composite

Nano-silver had the advantages of broad-spectrum antibacterial activity and low possibility of resistance,so it was widely used in medical,packaging,electronics and other fields as an inorganic antibacterial agent.However,there were still some problems limited the wider application of nano-silver in antibacterial polymer materials,such as the preparation process was complex and not green,the particles were easy to agglomerate and had poor biocompatibility with polymer materials.Lignin was a kind of natural biomass resource with reducing functional groups,three-dimensional network structure and environmental friendliness.As the carrier,reducing agent and dispersant of nano-silver,it could realize the green and controllable preparation and good dispersion of nanoparticles.However,the interaction between unmodified lignin nano-silver composites and bacteria was weak,and their antibacterial activities were limited,which hindered their wider application in polymer materials.In order to enhanced the interaction between lignin nano-silver and bacteria and antibacterial activities,polydopamine(PDA)and 3-chloro-2-hydroxypropyl trimethyl ammonium chloride(CHMAC)were used as modifiers for alkali lignin to prepare polydopamine-lignin(AL-PDA)with biological adhesion and quaternary ammonium-lignin(QAL)with positive charge.With AL-PDA and QAL being used as the carrier,reducing agent and dispersant of nano-silver respectively,the lignin nano-silver composites as antibacterial materials with well dispersed silver nanoparticles were prepared under microwave irradiation.The microstructure and morphology of the prepared materials were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).The antibacterial properties of the prepared materials were characterized by colony forming units(CFUs).The composite antibacterial films with excellent antibacterial activities,enhanced mechanical properties and UV shielding function were prepared by compounding the prepared materials with waterborne polyurethane(WPU).The main conclusions were as follows:(1)Using AL-PDA as dispersant and reducing agent,polydopamine-lignin silver nanoparticles(AL-PDA-Ag)with strong biological adhesion properties were prepared.The silver nanoparticles in AL-PDA-Ag were quasi spherical with particle size about 20-30 nm.Silver nanoparticles were distributed uniformly in AL-PDA in the form of single substance.The bactericidal rate of AL-PDA-Ag to Escherichia coli(E.coli)could reach 99.9 % and 100 %for only 10 min without or with infrared light,respectively.The antibacterial mechanism of AL-PDA-Ag could be attributed to the synergistic antibacterial effect of photothermal effect of complex and antibacterial activity of silver nanoparticles.The WPU film doped with 5 wt%AL-PDA-Ag had excellent antibacterial activity with bactericidal rate against E.coli reaching99.99% within 10 min under infrared light.Compared with pure WPU film,the tensile strength and elongation at break of WPU film doped with 1 wt% AL-PDA-Ag increased by 155% and61%,respectively.(2)Using QAL as dispersant and reducing agent,quaternized-lignin silver nanoparticles(Ag@QAL)with strong electrostatic capture ability were prepared.The silver nanoparticles in Ag@QAL were quasi spherical with particle size about 10-20 nm.Silver nanoparticles were distributed uniformly in the three-dimensional framework of QAL in the form of single substance.Ag@QAL exhibited excellent antibacterial activity with the bactericidal rates reaching 99.9% and 99.999% against E.coli and Staphylococcus aureus(S.aureus)respectively for only 5 min.Its antibacterial mechanism was the synergistic effect of the strong electrostatic effect of QAL to bacteria and enhancing the release of reactive oxygen species.The WPU film doped with 5 wt% Ag@QAL had excellent antibacterial activity with the bactericidal rate to E.coli reaching 99.9 % and 99.999 % for 3 h and 24 h,respectively.Compared with the pure WPU film,the tensile strength and elongation at break of the WPU film doped with 5 wt% Ag@QAL were increased by 54% and 45%,respectively.In conclusion,AL-PDA and QAL were used as carriers,dispersants and reducers of silver nanoparticles,which could strengthen the interaction between materials and bacteria and realize green and controllable preparation of lignin nano-silver composite with excellent antibacterial activity.Compared with WPU film,the films prepared by physical blending of lignin silver nanoparticles and WPU had excellent antibacterial activity with a wide application prospect in the field of antibacterial polymer materials.