Study On The Redispersion Properties And Application Of Lignocellulose Nanofibrils

Nanocellulose have attracted broad attention due to their favorable properties such as large specific surface area,several remark mechanical properties,good biocompatibility,degradation and so on.In addition,nanocellulose also has a high viscosity and usually can only exist stably in the form of a low concentration suspension.The transportation cost will be increased and the large-scale application of nanocellulose will be limited if the drying process is not be carried out.Therefore,the dehydration and drying of nanocellulose become particularly important.However,the process of dehydration and drying is accompanied by hornification which leads to the decreasing of water retention and mechanical properties,and the agglomeration of nanocellulose.In order to promote the large-scale utilization of nanocellulose,in this paper,the effect of lignin content on the structure properties of lignocellulose nanofibrils(LCNFs)before and after drying and their redispersibility were discussed,respectively,and the dried-redispered LCNFs(DLCNFs)was applied to the PVA-based composite films,the results are as follows:(1)The pulps with lignin content of 16.9%,10.4%,9.6%,6.2 wt%were prepared from high lignin content(22.1 wt%)of Bleached-Chemi-Thermo-Mechanical-Pulp(BCTMP)by bleaching with sodium chlorite,and the lignocellulose nanofibrils(LCNFs)were prepared from bleached pulp by mechanical method.The effect of lignin content on the physical properties of LCNFs was discussed by characterizing the morphology,static rheological and film-forming properties of LCNFs.The results indicated that the pulp fibrillation and film-forming properties of LCNFs were greatly affected by lignin content.The average diameter was reduced by the high content of lignin when the lignin content was 22.1%and16.9%,and the size of LCNFs decreased with the content of lignin decreasing from 16.9%to6.2%.The entanglement of LCNFs was weakened by lignin leading to the decreasing of static rheological property of LCNFs suspensions.The data of film formation of LCNFs indicated that the number of crystalline region of LCNFs films was reduced by lignin when the content of lignin was 6.2%?9.6%and 10.4%.The surface roughness and hydrophobic properties of LCNFs films were improved and the tensile strength was decreased by lignin.The results of pyrolysis kinetic analysis showed that the thermal stability of the films had a reduction when the lignin content was 16.9%and 22.1%.(2)The LCNFs suspensions were treated by freeze drying,oven drying,evaporation combined with vacuum drying(EV),centrifugal dehydration combined with vacuum drying(CV),and the properties of thermal stability,crystallinity index(Cr I),specific surface area(SSA),pore volume of LCNFs after drying were studied in order to discuss the effect of different lignin content on the structure properties of dried LCNFs.The results showed that when the lignin content was 22.1%,the pore volume of the samples obtained by four drying methods were small,and the Cr I of the sample obtained by freeze drying was lowest(37.5%).The sample with the lignin content of 16.9%after freeze drying had the largest SSA(14.04m~2/g).The thermal stability of the sample with lignin content of 22.1%was generally higher for the samples treated by same drying method.Compared with other three drying methods,the agglomeration of nanocellulose in drying process was effectively alleviated and a more complete structure of fibril can be maintained by freeze drying.In addition,the structural stability of LCNFs after drying can be maintained by the high content of lignin.(3)The freeze-dried LCNFs with different lignin content was redispersed by a high pressure homogenizer,and the effect of different lignin content on the redispersion characteristics of the DLCNFs was explored.The results showed that the size of DLCNFs was increased by hornification phenomenon during the drying process,and when the lignin content was 6.2%,the value of increase of average diameter of DLCNFs-6.2 was largest(86.1%),indicating their lowest redispersion properties.The water retention performance of DLCNFs,the hydrophobic property and mechanical properties of DLCNFs films was reduced by hornification phenomenon,while the hornification can be alleviated by the present of lignin.(4)DLCNFs with different lignin content were applied to film materials of PVA as reinforcing agents,and the pratical application value of DLCNFs with different lignin content in PVA-based composite membrane materials was discussed.The results indicated that the thermal stability,hydrophobicity and mechanical strength of composite films was improved by DLCNFs:when the lignin content was 9.6%,the thermal stability of composite films was the highest;the contact angle of the composite films with the lignin content of 22.1%increased by 164.5%,and the tensile strength of composite films had a increase of 335.2%when the lignin content was 16.9%.