Research On The Redispersibility And Application Of Lignocellulose Nanofibrils Based On Enzymatic Pretreatment

Cellulose is the most abundant renewable resource on the earth,which has great potential to replace traditional fossil resources with the advantages of environmental protection,green degradability and good biocompatibility.As a new type of nano-material,nanocellulose is favored by researchers because it not only continues the advantages of cellulose,but also has many excellent properties,such as high specific surface area,high mechanical properties,high crystallinity and unique nanostructure.However,the influence of hydroxyl groups of polar groups on nanocellulose can only be stable in the form of low concentration suspension,which greatly increases the cost of storage and transportation.Moreover,nanocellulose is easy to agglomerate in the process of dehydration,which hinders its large-scale utilization.In this paper,lignocellulose nanofibrils(LCNF)suspension were prepared by mechanical method and enzymatic pretreatment / mechanical method,and the concentration,drying and redispersion of LCNF were researched.At the same time,LCNF as well as dehydrated and redispersed LCNF were applied to barrier membrane materials,the results are as follows:(1)The pulp with lignin content of 11.51% was obtained from Bleached-Chemi-ThermoMechanical-Pulp by treating with sodium chlorite.And LCNF was prepared by mechanical method,endoglucanase pretreatment / mechanical method and xylanase pretreatment /mechanical method,respectively.The results showed that the LCNF(N-LCNF)prepared by mechanical method showed tree structure with an average diameter of 48.19 nm,a large distribution span and poor dimensional uniformity;LCNF(E-LCNF)prepared by endoglucanase pretreatment / mechanical method and LCNF(X-LCNF)prepared by xylanase pretreatment / mechanical method showed intertwined network structure with average diameters of 27.80 nm and 38.33 nm,respectively,the distribution was relatively concentrated,and the size uniformity was better.In addition,compared with N-LCNF,the water retention,specific surface area,crystallinity and Zeta potential of E-LCNF and X-LCNF were improved.Among them,the Zeta potential of E-LCNF was-45.43 mv,indicating that it had good stability and dispersion.(2)Centrifugal concentration and freeze drying were used to treat E-LCNF suspension,and their redispersibility were researched.The results showed that when concentrated to the solid content was 5.90%(E-LCNF-C6),16.29%(E-LCNF-C16)and 25.99%(E-LCNF-C26),the average diameter after mechanical redispersion by emulsifier was 63.56 nm,67.10 nm and88.53 nm,respectively,the size increased but still in the nano dimension.Compared with the E-LCNF suspension without dehydration,the water retention and specific surface area of the redispersed E-LCNF-C6 and E-LCNF-C16 suspensions decreased by less than 7.5%,and the static suspensions had no obvious settlement phenomenon,indicating that when the centrifugal degree was not high,the redispersed suspensions can maintain better microscopic properties.The addition of lignosulfonate can effectively alleviate the agglomeration of fibers in the process of freeze-drying,But when the addition of lignosulfonate was 15 wt%,after fiber adsorption saturation,the excess lignosulfonate covered the fiber and made it bond together,which had an adverse effect on redispersion.(3)Films were made of suspensions E-LCNF without dehydration,suspensions E-LCNFC16 with concentrated redispersion,suspensions E-LCNF-D0 with freeze-dried redispersion without added lignosulfonate,and suspensions E-LCNF-D10 with freeze-dried redispersion added 10 wt%(based on absolute dry E-LCNF)lignosulfonate,and the properties of films were tested.The results showed that with the increase of the quantity of the film,the porosity decreased and the structure became more compact.The water absorption of the film decreased with the decrease of porosity.At the same time,the denser structure of the film improved the hydrophobicity and barrier performance to water vapor and oxygen of the film.The quantitative increase can improve the mechanical properties of the film to a certain extent.After fiber agglomeration,the hydrophobicity improved after film formation,but the porosity increased,the water absorption increased,and the mechanical properties and barrier properties to water vapor and oxygen decreased.In particular,lignosulfonate can improve the barrier property of the film after fiber agglomeration.In addition,the film had a strong shielding ability to UV(up to 97%)regardless of whether the fiber was agglomeration or not.