Effect Of Enzyme Pretreatment On Cell Wall Structure Of Masson Pine And Preparation Of Cellulose Microfibrils

Cellulose microfibril(CMF)was attracting much attention for the advantages of high strength,light weight,renewability,biocompatibility,biodegradability and barrier.Because it needed too much energy to disintegrate cell wall for cellulose microfibrils,and their size distribution was not uniform,the cellulose microfibrils were difficult to realize industrialization.Enzyme pretreatment was an effective way to solve these.Enzyme pretreatment could reduce the binding force between the microfibrils and helped to mechanical dissociation,therefore,it could greatly reduce the energy consumption.In this study,we focused on the effect of enzyme pretreatment on cell wall structure and mechanical dissociation for CMF.The structure of cell wall was changed by controlling enzyme pretreatment,and the influence of enzyme pretreatment on mechanical dissociation of cell wall for the preparation of CMF was explored.After enzymatic pretreatment,fibers had revealed different morphology changes,such as cutting,peeling,erosion,tearing.The cell wall surface of bleaching masson pine fiber exist a lot of pits which showed a linear distribution.Tearing occurred mainly in the pit connection region.Changes of broken ends and kinked fibers reflected the degree of fiber was cut.Each fiber was completely cut through after enzyme treatment for 2 hours by 5.0FPU/g cellulase,as the average fiber was cut 3~4 times.With the increase of enzyme dosage,specific surface area of cell wall took the changes of W-type,which was opposite to that of the cellulose crystallinity.The cellulase got into cell wall structure through their mesopores and macropores.With the increased of enzyme dosage,the mesopore volμme increased first and then remained stable,while the macropore volume increased first and then decreased,and the micropore volume decreased slightly.The change trend of the total pore volume was the same as that of the macropores volume.The microfibrillation was mainly confined to the cell wall surface,and spreaded to the edge along the cell wall,until the cell wall was completely dissociated to obtain CMF.Enzyme pretreatment could increase the specific surface area and fibrillation area,which contributed to dissociation.The more times of homogenization,the higher the degree of fibrillation and mechanical energy consumption.With the increase of the homogenization number,granularity and average polymerization degree of the fiber were decreased,while water retention value,thermal stability of the fiber and transmittance of the CMF film were on the rise.The energy consumption of high pressure homogenization mainly depended on the material volume and the homogenization number,the solid content of fiber suspension had little effect on it.The cellulase could destroyed the basic structure of the cell wall and form fragments with large specific surface area,the area of fibrillation was increased.Diameter distribution of CMF,energy consumption,degree of polymerization of cellulose and transmittance of CMF films were used as indicators to evaluate the effect of enzyme pretreatment on mechanical dissociation for CMF.The results showed that,after 30 times homogenization treatment under 100 MPa,the DP and diameter distribution of MFC obtained from raw fibers were 354 and 20~50nm,while the DP and diameter distribution of MFC obtained from enzymatic fibers which was hydrolyzed by 10FPU/g cellulase at 50℃ for 2h were 229 and 10~40nm.Compared with the CMF prepared by single mechanical dissociation,the diameter of CMF prepared by enzyme pretreatment combined with mechanical dissociation was smaller,the distribution was more uniform and the content of nanofibers was higher.Under the condition of the same homogenization condition,the enzyme pretreated fiber had less energy consumption and better dissociation effect than that of the raw material.