Study on Green Preparation of Micro/Nano-fibrils Cellulose and Its Application in Paper Sheets

Author:Wang Sheng Dan

Supervisor:chen ke fu


Degree Year:2019





Micro/nanofibrillar cellulose(M/NFC)has been obtained increased attention because of their desirable properties.In this study,M/NFC with different structural characteristics was prepared by enzyme in conjunction with mechanical disintegration.The effects of enzyme pretreatment on the microstructure and deconstruction of cellulosic fibers,energy consumption of mechanical disintegration,and M/NFC morphology were discussed in detail.The M/NFC was used to enhance the strength properties of paper handsheets.The distribution and retention of M/NFC in paper handsheets were elucidated.The results provide theoretical support for the green preparation of M/NFC and the realization of industrial applications.Provide theoretical support for green preparation of M/NFC and industrial application of industrial words.The bleached softwood pulp was pretreated by commercial endoglucanase(Banzyme2900).The conditions of endonuclease pretreatment were optimized.The changes of microscopic properties of cellulose fibers during endonuclease pretreatment were explored.The adsorption and dissociation of endonuclease on the substrate were analyzed.And the degradation kinetics of the substrate were also analyzed.The results showed that:the preferred enzyme treatment condition was obtained at the enzymatic pretreatment temperature of 50℃,the solid concentration of 5%(w/w),and pH of 5.5.A highly fibrillated and fractured surface of pretreated fibers was observed after 0.5 h of pretreatment compared to native fibers.The progressive deconstruction of cellulosic fibers was occurred with the enzymatic pretreatment time prolongation.The binding force of cellulose intra-chains was strengthened.However,the binding force of cellulose inter-chains and inter-fibrils was weakened.Meanwhile,and the celluloseβ-1,4 glucosidic linkages were randomly cleaved,the crystallite size of the cellulosic fibers was decreased.The cellulose fiber cannot be completely recovered at endoglucanase usage higher than 9.0 mg/g(substrate)and pretreatment time of greater than 3.0h.Banzyme 2900 was rapidly adsorbed by the fibers at the initial 1 h.In this stage,the degree of polymerization of cellulose decreases rapidly and the surface of the fibers becomes loose.Then,the Banzyme 2900 dissociate gradually from the cellulose substrate.and the desorption rate was slow.The equilibrium state was obtained at the pretreatment time of 35 h.There are two forms of cellulose degradation:rapid degradation and slow degradation.The initial degradation was mainly rapid degradation.When the pretreatment time exceeds 0.25 h,the slow degradation was dominant,and the apparent activation energy of the slow degradation was 12.25 kJ·mol-1.The relationship between enzyme dosage(LE,mg/g(substrate)),reaction time(t,h)and combined enzyme treatment factor(CHFE,h·mg/g(substrate))was:CHFE=exp(0.2413-0.0378·LE)·t·LE,whenCHFE<5,the degree of polymerization(DP)of the fiber changes rapidly,and it is difficult to control the degradation of cellulose fiber at this stage;WhenCHFE>35,the prediction model was not applicable.These discoveries provide new insights into a more efficient and economic pretreatment methods for the disintegration of fibrils from cellulosic fibers.The effect of pretreatment of endoglucanase on the refining energy consumption of M/NFC was investigated,and the morphological differences of M/NFC obtained by different pretreatment were compared.The results show that:If the beating degree of BSKP was between 32 oSR45 oSR,there was possibility to save 94%of the beating energy consumption with theCHFEhigher than 4;Further deep refining for preparation of M/NFC,the total energy consumption of mechanical disintegration could be saved up to 75%.Higher enzyme dosage and two-stage enzyme treatment resulted in a significant reduction in energy consumption during the mechanical treatment stage,but the length of M/NFC was relatively low;Moreover,the M/NFC treated by enzyme and without enzyme pretreatment showed a highly differentiated tree structure and a smooth network structure.With the prolongation of the pretreatment time,the average diameter of the M/NFC showed adecreasing.With the enzyme dosage of 9 mg/g(substrate))and the pretreatment time for 1 h,3 h,and 24 h,the average diameter of M/NFC was in the range of 1723 nm,1418 nm and 1015 nm,respectively.This result provides theoretical support for the green,efficient preparation of M/NFC.The effects of endoglucanase,cellulose complexase and xylanase on the performance of MFC/NFC were explored.The results showed that:the M/NFC prepeared by celluase treatment has lower crystallinity and better transparency,compared with endocellulase pretreatment and xylanasepretreatment.The M/NFC has higher polymerization degree and better mechanical properties by endonuclease pretreatment,compared with cellulase pretreatment and xylanasepretreatment.The M/NFC prepeared by xylanase and celluase pretreatment has lower decomposition temperature and poor thermal stability.These result provide theoretical support for the application of M/NFC in different fields.The effects of different types of M/NFC on the strength properties of paper handsheets was explored.The M/NFC was labelled by a traditional Congo red dye labeling method.The distribution and retention of labelled-M/NFC in paper handsheets were analyzed using a residual ink analyzer and an UV-Vis spectrophotometer,respectively.The results show that:the higher of fibrillation on the surface of M/NFC,the more significant the enhancement on the paper handsheets;In the process of paper forming,M/NFC was combined with pulp fibers in a bridging manner.M/NFC not captured by the fiber network evenly deposited on the wire side of paper handsheets.With the increase of M/NFC addition,the deposition amount of M/NFC in the wire increase.When the addition amount of M/NFC was more than 10%,the distribution amount of M/NFC on wire side and the felt side of paper handsheets was different;The retention of M/NFC in paper handsheets increased as the loading of M/NFC increases.When the loading of M/NFC added increases from 1%to 40%,the retention of M/NFC increases from 24.5%to 68.5%.The result provides a theoretical basis for the application of M/NFC in the papermaking field.