Research Of Enzymatic Cellulose Nanofibrils (CNF) And Its Fluorescent Composite Film

In view of the current research on the preparation of cellulose nanofibrils(CNF)by mechanical treatment or acid hydrolysis,there are some problems such as low yield,long preparation time,large energy consumption,and serious environmental pollution.In this study,enzyme treatment and ultrasonic cavitation was combined to prepare cellulose nanofibrils(CNF)in a green and efficient way.By the cellulase pretreatment,the fiber surface was corroded,and the fiber chain was cut and shortened,which leads to the degradation of the cellulose macromolecule into the segment of low degree of polymerization.Cellulose nanofibrils(CNF)were obtained by further ultrasonic cavitation treatment.And then,the enzymatic cellulose nanofibrils(CNF)was highlyoxidized by sodium periodate to prepare 2,3-dialdehyde-based cellulose nanofibrils(DNF),which provided an active site for the subsequent grafting of amino groups.Carbon dots(CDs)were prepared by hydrothermal method using chitosan as a carbon source.Based on Schiff's base bond,the high-intensity fluorescent composite film was prepared by crosslinking aldehyde groups of dialdehyde-based cellulose nanofibrils and amino group of gelatin,using CDs as light-emitting source.The main contents and results of this paper are as follows:(1)Cellulase pretreatment combined with ultrasonic cavitation was used to prepare cellulose nanofibrils(CNF)under mild conditions.By controlling the factors of enzyme dosage,enzymolysis temperature,enzymatic hydrolysis time and ultrasonic time,the optimal preparation conditions of nanocellulose were obtained.Under the optimal conditions,cellulase dosage of 8%w/w(the mass ratio of cellulase and cellulose raw material),enzymolysis temperature of 50?,enzymolysis time of 10h,ultrasonic time treatment of 6h,the yield of cellulose nanofibrils(CNF)could reach to 62.6%.(2)The prepared cellulose nanofibrils(CNF)have a diameter of 2-24 nm,a length of 50-450 nm.The XRD results revealed that the prepared cellulose nanofibrils(CNF)still belongs to cellulose of type I,with the crystallinity of 73%,which indicates that under cellulase pretreatment combined with ultrasonic cavitation the preparation conditions of cellulose nanofibrils(CNF)were mild and the damage to the crystalline area was low.The TG analysis showed that the residual mass fraction of the cellulose nanofibrils(CNF)still up to 15.3%even at temperature of 700?,which has potential applications in the field of biocomposites with high heat resistance requirements.(3)Dialdehyde-based cellulose nanofibrils(DNF)was prepared by highly specific oxidation of sodium periodate.When the reaction condition was mass ratio of sodium periodate to cellulose nanofibrils(CNF)of 2:1,reaction time of 12h,oxidation temperature of 45?,the aldehyde content of DNF was 5.326 mmol/g,the oxidation degree was 42.6%.(4)The chitosan carbon dots were prepared by hydrothermal method.Under the conditions,hydrothermal temperature of 200?,hydrothermal time of 9h and chitosan dissolved concentration of 2%,the quantum yield of carbon dots was 32.86%.The study of the metal ions selectivity showed that the carbon dots have a higher selectivity for Fe3+ compared to other metal ions.(5)The DNF/gelatin/CDs fluorescent composite film based on Schiffs base bond was prepared by one-pot method.The analysis results showed that when the DNF content of 1%(The mass ratio of DNF to gelatin),the tensile strength Up to 70.5MPa,which was two times higher than that of the fluorescent film without DNF added(tensile strength was 35.1 MPa).The fluorescence composite film showed good fluorescence stability and linear response to the fluorescence quenching efficiency of Fe3+(0-150 p.M)within a certain concentration range.