Influence Of Enzymatic Pretreatment On Structures And Performances Of Masson Pine Fibers And The Preliminary Preparation Of Cellulose Microfibril

As a novel nano-cellulos e mater ial, cellulos e microf ibril(CMF) with a bright mar ket pros pect offers excellent mechanical performance, barrier property and trans mittance. But the high mechanical cons umption in gr ind ing preparat ion is the main reas on to hinder the s uccess ful commercializat ion of CMF, while the enzymat ic pretreatment has a great potent ial in t he as pect of reducing the d is s ociat ion energy cons umption. Domes tic and foreign res earches on the preparation of CMF by enzymat ic pretreatment ar e more focus ed on the applicat ion and characterizat ion of phys ical properties, but there ar e few res earches on the mechanis m of enzymat ic pretreat ment and the effect of enzymat ic pretreat ment on fiber morphology and aggregat ion s tructure. Due to the complexit y of cellulos e and hydrolys is s ubs trate, the analys es on the changes of fiber morphology and aggregat ion s tructure after enzymat ic hydro lys is are not cons is tent. Therefore, this paper focus es on enzymat ic pretreat ment as the key point of pre paration of CMF by enzymat ic pretreat ment. The mas s on pine f ibers wer e pretreated by complex cellulas e, endo-cellulas e and exo-cellulas e, ut ilizing t he high pres s ure homogeneous to prepare CMF. The gener al rules of the effects of enzymat ic hydrolys is on th e fiber morphologies and s tructures and performances were s tudied to reveal the mechanis m of enzymat ic pretreatment. It will provide a theoret ical bas is for the s elect ion of cellulas es and the practical applicat ion of enzymat ic pretreat ment in preparat ion process of CMF. And it can promote the development of nanocellulos e.The cellulas e loading and pretreat ing t ime wer e changed to s tudy the hydrolys is yield of fibers. The res ults s howed that increas ing loading and prolonging pretreat ing t ime can increas e t he hydrolys is degree of f ibers. Compared with complex cellulas e and exo-cellulas e, endo-cellulas e has a weaker ab ilit y to hydrolys is fibers.The morphology of fibers pretreated by cellulas es were analyzed, the res ults s howed that 3 kinds of cellulas es pref erent ially hydrolyzed the f ines on the s urface of the fibers and the s pecif ic s urface area of the fibers decreas ed. Fibers were cutted off and did not have obvious peeling aft er being pretreated by endo-cellulas e. But the phenomena of peeling, s tripping and cutt ing were gradually aggr avated with the loading increas ing of complex cellulas e and exo-cellulas e. As the loading of 3 kinds of cellulas es increas ed, the f ines content increas ed and the average length of fibers decreas ed gradually, the specific s urfac e area and crys tallinity changed oppos itely.The res ults of FTIR, XRD and TGA s howed that molecular s tructure, crys tal s tructure and thermal s tability of cellulos e could not be changed by enzymat ic pretreat ment. The polymer izat ion degree went down and crys tallinity integrally went up with t he increas ing loading of cellulas e. Endocellulas e had a greater contribut ion to decreas ing the polymer izat ion degree. The crys tallinity of corresponding cellulos e changed as a M type with increas ing the complex cellulas e loading. When the loading of exo-cellulas e increas ed, crys tallinity changed as a wavy line. When the endo-cellulas e loading was greater than 0.5CMCU/g, crys tallinit y was s table f rom 80% to 82%. Endo-cellulas e mainly hydrolyzed the amorphous region of cel lulos e. When the loading of complex cellulas e and exo-cellulas e was s mall, the amorphous region was hydrolyzed and crys tallinit y increas ed. When the loading of complex cellulas e and exo-cellulas e was larger, the crys talline and amorphous region were hydro lyzed at the s ame t ime. As the hydrolys is degree of amorphous region was large, t he crys tallinity went up. On the contrary, the crys tallinity went down.When the loading of complex cellulas e and exo-cellulas e increas ed, the water r etent ion value, beat ing de gree and s urface charge of f ibers decreas ed originally, then increas ed. When the loading of complex cellulas e was 20.0FPU/g, the water r etent ion value, beat ing degree and Zeta potent ial res pectively increas ed to 196.57%, 56°SR and 68.5m V from 153.23%, 11°S R and 64.9m V. When the load ing of exo-cellulas e was 10.0FPU/g, the wat er ret ent ion value, beat ing degree and Zet a potential res pectively increas ed to 200.13% 、 34°SR and 66.4m V. When the loading of endo-cellulas e increas ed, the wat er retent ion value and Zeta potent ial gradually decreas ed. While the beat ing degr ee s light ly decreas ed originally and then increas ed. When the loading of endo-cellulas e was 10.0FPU/g, the water retent ion value and Zeta potential res pectively decreas ed to 103.92% and 23.6m V, and beat ing degree increas ed to 35°SR.The preparation of CMF was inves t igated that the pretr eat ed fibers with 1.5% concentrat ion wer e circulated for 30 times in high pres s ure homogenizer. The diameter of CMF ranged from 20 nm to 60 nm. CMF s uspens ion appeared s emitrans parent gelat iniform and offers good trans mis s ion and s tability. The cat ionic demand of CMF was ten t imes as much as that of blank f ibers. The res ult of FTIR, XRD and TGA s howed that molecular s tructure, crys tal s tructur e and thermal s tabilit y of CMF were s ame wit h that of natural cellulos e. The crys tallinity of CMF was between the blank f ibers and enzymat ic pretreated f ibers.