| Lignin,as the second largest natural polymer in plants,is abundant in yield,low in cost and biodegradable.The annual production of industrial lignin in pulp and paper industry and biorefinery industry is up to 80 million tons.It is of great research significance and economic value to make high value utilization of industrial lignin.Lignin is an ideal precursor of functional materials because of its three-dimensional network structure,rich aromatic skeleton and active functional groups.Lignin/inorganic oxide nanoparticles have attracted more and more attention for their controllable preparation and application due to their properties of both organic polymer materials and inorganic materials.ZnO nanoparticles have excellent UV absorption properties and good biocompatibility,which have great application value in the field of sunscreen and anti UV aging agent.However,pure ZnO nanoparticles have high surface energy,easy agglomeration and poor compatibility with the substrate,which greatly limits the practical application value.Lignin/ZnO nanocomposites were constructed by self-assembly of lignin and ZnO nanoparticles based on the molecular structure characteristics of lignin.The dispersion and interfacial compatibility of lignin/ZnO nanocomposites were improved,and the synergistic ultraviolet absorption and antibacterial properties were given.Lignin/ZnO nanocomposites have broad application prospects as functional additives of polymer materials.In this paper,sodium lignosulfonate(LS),which originated from the field of pulp and paper making,was grafted and modified to obtain a kind of amphoteric quaternary ammonium lignosulfonate(QLS),so that its molecular structure is rich in negative functional group sulfonate and positive functional group quaternary ammonium.Then lignin/ZnO composite particles with different morphology and excellent dispersion were prepared by a simple hydrothermal process.SEM,TEM,XRD,FT-IR,XPS,UV Vis and PL were used to characterize the microstructure and optical properties of lignin/ZnO composite particles.The effects of process parameters such as concentration,time and raw material ratio on the morphology of lignin/ZnO Composite particles were systematically studied,and the formation mechanism of lignin/ZnO composite particles was revealed.The results show that the lignin/ZnO composite particles can significantly enhance the UV aging resistance and mechanical properties of waterborne polyurethane composite films,and endow them with antibacterial properties.The conclusions are as follows:(1)A kind of lignin limited pancake-like lignin/zinc oxide nanocomposite(QLS/ZnO-P)composed of two-dimensional lamellar structure units was synthesized by dynamic hydrothermal method.The surface of QLS/ZnO-P was covered by a layer of lignin with a thickness of nanometer.The ZnO nanocrystals were uniformly dispersed in the three-dimensional network structure of lignin.The particle size of QLS/ZnO-P is about 200 nm,and there is a strong bond between lignin and ZnO,which gives it excellent UV absorption properties.In addition,QLS/ZnO-P has good interfacial compatibility with waterborne polyurethane(WPU).The composite film not only has good mechanical properties and excellent UV aging resistance,but also has antibacterial activity.The tensile strength at break and elongation at break of WPU + QLS/ZnO-P composite films are 44% and22% higher than those of pure WPU films,respectively.After the composite film was placed in the UV aging and exposed to strong UV for 14 days,the composite film still had good mechanical properties and showed excellent UV aging resistance.(2)A litchi-like lignin/ZnO composite material(QLS/ZnO-L)with good dispersion and uniform particle size was synthesized by static hydrothermal method,and the surface was covered with a layer of ZnO nanocrystals with a particle size of 5-10 nm grain.Compared with ZnO,QLS/ZnO-L exhibits enhanced antibacterial activity.This is due to the positive charge of QLS,which can effectively trap bacteria under the action of static electricity;in addition,the ZnO nanorods on the surface of QLS/ZnO-L can further damage the bacterial cell membrane.The sterilization rate of QLS/ZnO-L against E.coli and S.aureus reached97.54% and 99.55%,respectively.The inhibitory concentrations(MICs)were all 100 ?g/m L and the minimum bactericidal concentrations(MBCs)were 100 ?g/m L and 200 ?g/m L.The composite waterborne polyurethane film incorporated with QLS/ZnO-L not only showed stronger tensile strength and enhanced UV barrier performance,but also had good antibacterial activity Compared with the pure WPU film,the tensile strength and elongation at break of the composite film are increased by 61% and 26%,respectively.In addition,the sterilization rates of the composite film against E.coli and S.aureus were 97.35% and 60.48%respectively.In this paper,the hydrothermal self-assembly mechanism of lignin/ZnO nanocomposites was revealed,and the mechanism of lignin/ZnO nanocomposites as anti UV aging agent and antibacterial agent was elucidated.The research results are of great significance for the development of lignin nanocomposites,provide process reference and theoretical guidance for the controllable construction of lignin/inorganic oxide nanocomposites,and have important theoretical and economic significance for the high value utilization of industrial lignin and the doping modification of traditional polymer materials. |
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