The Fabrication And Properties Of Fluorescent Cellulose Film

Cellulose is one of the most abundant renewable resource in nature,which can be processed into various materials such as fiber,film and gel based on cellulose after physical or chemical modification.These materials are widely used in textile,clothing,packaging,food,household chemicals,medicine and coating etc due to many virtues,such as low cost and environmental protection.Cellulose is not suit to melt processing and can not been dissolved in common solvents owing to its multiple hydrogen bonded network.The traditional solvents have been gradually eliminated because of their pollution and toxicity.The reported new solvents still have some deficiencies such as low solubility,and strict requirements for environment.Fluorescent materials based on cellulose not only have special fluorescent properties,but also have the characteristics of environmental protection and biocompatibility,which can be used in many fields such as cell imaging and biosensor.But these materials are not promoted and applied because of its unstable structure and high cost.To solve the above problems,in this paper,we developed a new generation of solvent,tetra-butylammonium hydroxide（TBAH）/H₂O/DMSO ternary solvent system with mass ratio of 2:3:5,which can dissolve cellulose with high molecular weight rapidly at room temperature.Based on this,fluorescent cellulose film was fabricated via crosslinking reaction and chemical grafting,and the structure,properties and application of this kind of film were studied and explored in detail.The specific work is as follows:（1）TBAH/H₂O/DMSO ternary solvent can rapidly realize the non-derivative dissolution of cellulose.3 wt%solution of degreased cotton with polymerization degree of1300 was obtained via this solvent at room temperature in about 3 min.In this ternary solvent system,the OH^-could break down hydrogen bond of cellulose and establish new hydrogen bonded network,meanwhile,TBA⁺could reduce the hydrophobic binding force between cellulose molecules.Also,as a non-proton polar solvent,DMSO could stabilize the system through preventing the aggregation of cellulose molecular chains,and water could decrease the viscosity of solution and promote the dissolution process.All these factors collectively led to the good dispersion of cellulose molecules in the solution.（2）Based on this system,cellulose could be modified by cross-linking with epichlorohydrin（EPI）,thus affecting aggregation of cellulose molecules,so as to regulating the transmittance and mechanical properties of cellulose film.（3）9-（2,3-epoxypropyl）-carbazole was synthesized by nucleophilic substitution reaction between carbazole and EPI,then reacted with cellulose solution to obtain carbazole-substituted cellulose,and the carbazole-cellulose fluorescent film was fabricated by regeneration and drying.The structure of the film and the degree of substitution of carbazole group were characterized by FTIR,XRD,UV-Vis,elemental analysis and surface contact angle test respectively.The fluorescence properties of the film,especially in DMSO,were investigated by fluorescence spectra.The results showed that the carbazole-cellulose fluorescent films exhibited similar fluorescence properties compared with carbazole molecules,and possessed concentration self-quenching effect.DMSO can change the microenvironment of carbazole group by interacting with cellulose,and then affect the fluorescence properties of carbazole-cellulose films.（4）Fluorescein-substituted cellulose was synthesized through two reaction firstly introducing epoxypropyl group to fluorescein,and then react with cellulose solution.After regeneration and drying,the fluorescein-cellulose functional film was obtained.The structure,thermal stability and mechanical properties of film were characterized by FTIR,XRD,SEM,UV-Vis,TG and tensile test respectively.Fluorescence properties of fluorescein-cellulose functional film were measured,and results indicated that the film showed red-shifted emission compared with that of fluorescein solution because of the formation of excimer in solid state.The influence of p H on fluorescence intensity of fluorescein-cellulose functional film was researched.The results showed that owing to existing in various forms of fluorescent groups in environment with different p H,increasing p H could cause an increasing fluorescence intensity,which can be in used for p H detection of aqueous system.The results also showed that the film has a relatively high fluorescence anisotropy value because the fluorescent groups were fixed on the cellulose molecular chains and its mobility is limited.In addition,the effects of stretching on the structure and properties of the film were also studied.It was found that fluorescent cellulose functional film with permanent oriented structure can be prepared by stretching and drying the fluorescein-cellulose gel,and the strength and fluorescence anisotropy of film can be significantly improved.This work will provide critical information and scientific basis for comprehensive utilization of cellulose,design and preparation of new cellulose fluorescent materials.