Study and Application of Nanocellulose Based on Fluorescence Technologys

Author:Ding Qi Jun

Supervisor:zeng jin song chen ke fu


Degree Year:2019





Fluorescent labeling technology had become the most widely used labeling technology due to its low cost,simple operation technology and high sensitivity.The most critical issue was the preparation of fluorescent nanomaterials with excellent properties and the development of appropriate analytical tools for their applications.Nanocellulose had been widely used in food,cosmetic and paper reinforcement industries due to its high mechanical strength,large aspect ratio and excellent barrier properties.In the field of pulp and paper industry,the application of fluorescence technology is a very novel analytical detection method.This paper first analyzes the fluorescence properties of nanocellulose itself.It is then combined with an organic fluorescent dye to prepare a fluorescent nanomaterial with excellent fluorescence properties.It has been successfully used to characterize the retention of nanocellulose in the keratinization and paper sheeting process of nanocellulose during dehydration.Finally,the dynamic characterization of nanocellulose was achieved by fluorescence and microfluidics using a Micro-nano Pulp Fiber Analyzer(FTA).This work provides a new analytical technology for the application of nanocellulose in the field of pulp and paper industry,with certain practicality and reference value.Nanocellulose was prepared from different material(dissolved pulp and bleached chemical pulp)using acid hydrolysis,mechanical refining,and TEMPO oxidation.The effects of physical and chemical structures of nanocellulose on its autofluorescence properties were investigated.The microstructure,biochemistry and spectral properties of nanocellulose were characterized by Atomic Force Microscopy(AFM),Fourier Transform Infrared Spectroscopy(FTIR),Laser Scanning Confocal Microscopy(LSCM),Raman Spectroscopy and fluorescence spectroscopy.The results showed that all samples showed a distinct emission peak at 574 nm.The autofluorescence properties of nanocelluloses were found by FTIR and Raman spectroscopy due to the presence of glycosidic bonds and aliphatic C=O absorption(n→π* transition).The fluorescence intensity of nanocellulose was significantly reduced compared to the raw material.Increasing the excitation wavelength(510-530 nm)caused a red shift of the fluorescence emission peak(570-582 nm),but the fluorescence intensity did not change.Changing the acid/base conditions(pH 7 to 1 or 7 to 13)resulted in an increase in fluorescence intensity but no changed in the position of the emission peak.Finally,the interaction between functional groups in the system affected by external factors was studied by generalized two-dimensional correlation fluorescence spectroscopy.The CNCs were fluorescently labeled by electrostatic adsorption and covalent bonding and the labeling efficiency.The fluorescence performance of the two fluorescent composites were analyzed and compared.The results showed that the labeling efficiency of fluorescent CNCs labeled by electrostatic interaction was about 94.76%,and the amount of dye molecules adsorbed by each CNCs was about 208.The efficiency of fluorescent labeling for covalently bonded CNCs was about 95.51%,and the number of dye molecules adsorbed per CNCs was about 1038.It was found that the quenching modes of the two fluorescent CNCs were dynamic quenching.The fluorescence lifetime and quantum yield of fluorescent CNCs increased by a factor of 1-2 compared to free dyes.In the dehydration process of nanocellulose,hornification usually occured in cellulose fibers and nanocellulose fibrils.First,cellulose nanocrystals(CNCs)and cellulose nanofibers(CNF)with different solid contents were prepared by a rotary evaporation technique and then redispersed in water.In order to avoid the effects of drying,the morphology and size of the nanocellulose in the suspension were characterized using the AFM liquid mode.Quantitative study of different water components on the surface of nanocellulose was carried out by differential scanning calorimetry(DSC).The study found that redispersed nanocellulose showed significant radial assembly,resulting in a significant decrease in the aspect ratio of nanocellulose.And during dehydration,the amount of free water,frozen bound water,and non-icing combined water is gradually reduced.And completely removed in order.Finally,the effect of the dehydration process on its hydroxyl accessibility was investigated by fluorescently labeling the redispersed nanocellulose.The experiment found that the hydroxyl accessibility of redispersed CNCs and CNF decreased by 83.33% and 81.96%,respectively.Nano-cellulose with large aspect ratio was prepared by enzymatic pretreatment plus mechanical method and added as a reinforcing agent to the pulp to improve the performance of the paper.In order to study the retention and loss rate of nanocellulose during sheet preparation,it was fluorescently labeled prior to addition.The retention rate was characterized by elemental analysis of the fluorescent dye in the paper,and the rate of loss was characterized by analysis of the fluorescence intensity in white water.The experiment found that with the increase of the amount of CNF added,the retention and loss rate of nanocellulose decreased gradually.The retention aid had a positive effect on the retention rate of CNF during the papermaking process.The CNF could be evenly distributed in the paper up to 8% with a lower addition amount.In addition,retention aids help to improve the mechanical properties of papers with higher CNF content.The tensile index,TEA,elongation,and Young’s modulus of the paper were increased by about 296%,752%,103%,and 156%,respectively,compared to the blank paper.Highly efficient and accurate dynamic measurement of nanocellulose is achieved by fluorescence and microfluidics.This method allowed online analysis of a large number of samples,avoiding the disadvantages of traditional methods being time consuming,labor intensive and complicated to operate.In this method,scattered light of nanocellulose in water was captured by a high resolution CCD,and then image analysis techniques were used to calculate data such as size and velocity of the nanoparticles.The number of pixels occupied by the circumscribed rectangle and the inscribed circle of each fiber profile in the image was taken as its length and diameter,respectively.A large amount of sample size data was consistent with AFM image statistics.This new method can statistically analyze various information of a large number of samples in a short time.This is of great significance for the effective and controllable preparation of micro-nanocellulose.