Construction And Properties Research Of Nanocellulose Film Modified By Lanthanide Complexes

With the aggravation of environmental pollution and fossil energy consumption,a wide range of natural polymers have become the focus of research.Nanocellulose(NC)is a high value-added product extracted from plant fibers by physical or chemical methods,showing good biocompatibility,low toxicity,renewable,rich hydroxyl for modification and self-assembly.In addition,NC films show the characteristics of high transmittance and low molar absorptivity,so it is practical significance to develop NC based fluorescent materials.Lanthanide complex as a kind of typical inorganic fluorescent material has shown a series of advantages such as low toxicity,better biocompatibility,sharp characteristic emission peaks,high luminescence purity,wide Stokes shift,and fluorescence types that involve the all visible light wavelength.In this paper,two kinds of NC(TEMPO oxidized cellulose nanofibrils(tCNFs)and cellulose nanocrystals(CNCs))were modified by lanthanide complexes to prepare composite films and to investigate fluorescent properties.The preparation methods adopted are all based on the self-assembly properties of NC.The tCNFs fluorescent film is prepared by vacuum filtration co-assembly and the CNCs fluorescent film is evaporation induction co-assembly.There are core research contents and conclusions as shown follow:(1)Investigation on the film-forming performance of tCNFs and CNCs.The tCNFs was prepared with cotton pulp board as raw material by using TEMPO oxidation system pretreatment assisted high pressure homogenization method,and then the film was formed by vacuum filtration assisted self-assembly(VASA)process.Similarly,with cotton pulp board as raw material,CNCs was prepared via sulfuric acid hydrolysis method,and then the film was formed evaporation induced self-assembly(EISA)process.Both films showed dense layer-layer structure,which is due to the abundant hydroxy-hydrogen bonding in the two NC.The transmittance of tCNFs film and CNCs film at 600 nm is 90.5%and 90%,respectively.The reason was that the wavelength of incident light is larger than the size of two kinds of NC,so scattering is not carried out inside the film but direct penetration.The tCNFs film showed considerable tensile strength(12.5 MPa)and certain flexibility,which can be used as the base material for composite films.Although CNCs film shows high tensile strength,it is fragile and can't be used in practical applications,so it should be modified further with plasticizer.(2)Construction and properties of three(2-benzimidazolidylmethyl)amine lanthanide complexe(Ln(NTB)Cl3)modified tCNFs films.The soft fluorescent emission films were prepared via vacuum filtration assisted co-assembly,and the chosen Ln3+was Tb3+ and Eu3+.The main results show that Ln of Ln(NTB)Cl3 can form coordination bonds with the carboxyl O on the surface of tCNFs,so as Ln(NTB)Cl3 to load on tCNFs steadily.The three kinds of composite films(NTB-Tb3+-tCNFs,NTB-Eu3+-tCNFs,NTB-Tb3+/Eu3+-tCNFs)showed high transmittance and haze value in the wavelength range of light.With the increase of Ln(NTB)Cl3 content,the transmittance of films decreased gradually and the haze value corresponding increased.Under specific UV excitation,NTB-Tb3+-tCNFs,NTB-Eu3+-tCNFs,NTB-Tb3+/Eu3+-tCNFs film emits soft green,red,and orange light,respectively.This is because the introduction of lanthanide complexes will lead to the generation of cavities in the films,in which UV light was scattered and refracted for many times,resulting in soft light effect,which also improves the absorption capacity of the films to ultraviolet light.The films can be used as anti-counterfeiting,optical signal enhancement devices and so on.(3)Construction and properties of hydrosoluble lanthanide polymer(Poly-Ln)modified CNCs film.A block polymer Poly-Ln was designed to be used as"plasticizer" and "fluorescer" to solve the brittle problem of CNCs films and to introduce the properties of circular polarized luminescent(CPL)emission.The selected Ln3+ was Tb3+and Eu3+.The main results showed that the hydroxyl group between Poly-Ln and CNCs form a stable 3D reticular structure.The transmittance of CPL-Eu NP film at 600 nm reached 86%.With the increase of Poly-Ln content,hydrogen bonding enhanced and transmittance remained unchanged significantly.The films have chiral nematic helical structure and CPL emission.By adjusting the mixing ratio of Poly-Tb and Poly-Eu,a variety of CPL emission from red to green light was realized.The introduction of Poly-Ln will enhance the plastic performance of the film,and elongation at break was improved up to 36.8%,but excessive Poly-Ln can break the chiral nematic structure,resulting the reduction of CPL signal strength.The films have potential applications in circular polarization fluorescence devices and 3D fluorescence imaging.