Research On Construction And Composite Mechanism Of Nanocellulose-based Luminescent Films

Wood-based nanofibrillated cellulose?NFC?is mainly derived from natural wood materials.Compared with the synthetic polymer and plastics,NFC has the advantages of high aspect ratio,high specific surface area,biodegradability,high mechanical strength,and easy modification.Furthermore,NFC after carboxylation modification?ONFC?has excellent suspension stability,film formation,and solution self-assembly characteristics.It is becoming one of the important raw materials for energy and chemical industry.With the rise of NFC and rapid development of functional materials,NFC has shown great potential in the fields of thermal insulated aerogel,superhydrophobicity,and hydrogel.Among them,NFC-based photoelectric device is a new type of functional materials,which is developed by using NFC as three-dimensional network and fluorescent materials as functional fillers.However,NFC is still in its infancy in the field of high-value materials such as afterglow luminescence,fluorescence,temperature sensing,and multi-functional integration materials.Therefore,in this study,functional films and coatings with stable and uniform structure were constructed with ONFC as three-dimensional network substrate,and modified long afterglow phosphors and fluorescent carbon dots as fillers.The main research contents and conclusions are as follows:?1?Construction of ONFC long afterglow luminescence system and composite films.ONFC was successfully self-assembled with modified Sr Al₂O₄:Eu²⁺,Dy³⁺phosphors?SAOED?to prepare long afterglow films,utilizing excellent dispersibility of ONFC in aqueous system,good film formation and three-dimensional reinforcement effect during drying.The core-shell coating on SAOED phosphors by introducing a silica/APTMS dual-modification system effectively avoided hydrolysis of SAOED in ONFC aqueous system.Additionally,the surface of modified phosphors formed a certain electrostatic adsorption and hydrogen bond with the ONFC,which ensured high compatibility of two-phase and good mechanical strength of films.After sol-gel modification,nano-scale Si O₂??20 nm?and APTMS amination coating were formed on surface of phosphors.The maximum emission intensity of spectrum decreased by3.46%and 9.71%,respectively.Howev er,emission peak remained unchanged at 512 nm.Compared with silica modified SAOED,ONFC-based composite film formed a denser interface structure and better tensile strength with aminated SAOED.When addition ratio of ONFC/SAOED reached 1/1,the tensile stress of composite film was 64.2 MPa,and 2920 MPa for the Young's modulus.The preparation of ONFC-based luminescent film provides a high-value utilization platform for ONFC in applications such as flexible illuminating devices and fluorescent indication.?2?Construction of ONFC luminescent/superhydrophobic dual-functional film.ONFC was applied as a three-dimensional network reinforcement skeleton,and the modified SAOED was added as functional fillers.Combining with suspension spraying and chemical vapor deposition,luminescent/superhydrophobic coating was constructed on the surface of PVA pretreated wood by a simple and effective method.After the cross-linked ONFC luminescent coating was subjected to chemical vapor deposition of low energy superhydrophobic treatment,functional wood material possessed both long afterglow luminescence and superhydrophobic characteristics.The afterglow brightness after 2 min was 315.8 mcd/m².Compared with the luminescent particles,when the doping ratio of ONFC/phosphor reached 1/1,the peak of emission spectrum of composite coatings showed a slight blue shift?2.8 nm?around 512 nm.Meanwhile,the hybrid coating had certain self-cleaning and wear-resisting properties.After 5times of sandpaper abrasion cycle,the coating still maintained superhydrophobic performance,the static water contact angle was 151.0°,and the rolling angle was lower than 8.5°.At the same time,the cross-linked ONFC dual-functional coating had good translucency,which resulted in little effect on the color of wood substrate after coating process.Furthermore,the apparent color difference?4.8?9.6?can be adjusted by different doping ratio of luminescent particles in coating.In general,ONFC and luminescent particles were used to develope a long-lasting luminescence and superhydrophobic bifunctional coating,which broadened the variety of wood materials and was expected to be applied to indoor decoration,smart ceilings,or night indications,etc.?3?Construction of ONFC-based SAOED/CDs dual fluorescent release system.A simple and effective core-shell coating strategy was introduced to modify SAOED phosphors with silica sol as a coating agent,and cellulose nanocrystals?CNCs?pre-dispersed CDs as functional fillers.The CNCs/silica coating can effectively inhibit CDs aggregation and enhance the light-capturing ability of SAOED,as well as improve water resistance of SAOED particles.The modified particles with dual fluorescence release were constructed and the optical signal of dual release can be adjusted by different doping ratio of CDs in SAOED system.In addition,APTMS amino-grafted modification further enhanced surface activity of SAOED,and the composite film obtained by self-assembly with ONFC had a good interface.The fluorescence spectrum of film had a strong temperature response?243?383K?,and the fluorescence signal intensity ratio has a good linear relationship with temperature.The ONFC-based dual fluorescence film with strong temperature response,light scattering,and good flexibility was expected to be applied as a flexible fluorescence temperature sensor device.?4?Development of biomass CDs and construction of ONFC fluorescent system.Based on the concept of biomass refining,the hot water extractions?120?180°C?of switchgrass?SG?was used as the precursor for the first time.Novel fluorescent CDs with adjustable quantum yield?11.75%?6.20%?were synthesized without carbonizing the entire lignocellulosic biomass.This method provided a platform for the high value utilization of biomass hydrothermal pre-extraction waste liquid.Furthermore,the ONFC/CDs flexible fluorescent composite film was prepared by using ONFC as a three-dimensional network reinforcement skeleton.The fluorescence response relationship under variable temperature conditions was analyzed.The results showed that the fluorescence ratio of the film had a good linear relationship and fluorescence-temperature cycling behavior in the temperature range of 243?343 K,which can be applied to fluorescence temperature monitoring,fluorescent labeling and anti-counterfeiting identification.