Influence Of Enzymatic Hydrolysis On Sturctures And Properties Of Wheat Straw Fibers And The Preliminary Preparation Of Cellulose Microfibril

Cellulose microfibril(CMF) is such a cellulosic material obtained from cellulose by the action of repeatedly homogenization treatment. This paper main used bleached wheat straw fiber as raw material, by the analys is and comparison the affecting of fiber morphology, structure, performance about composite cellulose, endo-glucanase and exo-glucanase in a different degree of hydrolysis, studying the mechanism of the enzymatic modification of fiber material, the general laws of the changes about the enzymatic modification to fibers in the structure and performance, to provide theoretical guidance for the industrial application of enzymatic hydrolys is of the modified plant fiber raw materials. Meanwhile, the subject through the study application of enzymatic modification in the paper production process, the different effects of enzyme depth hydrolys is and acid hydrolysis to the fiber structure and properties, in order to provide the enzyme pretreatment technology as the oretical basis for practical application in the preparation of CMF, promote further breakthrough of CMF preparation technology and process of industrial application.First of all, enzyme activity was detected. The enzyme activity of composite cellulase was 88FPU/m L under the reaction conditions of p H=4.8, temperature=50℃ with Whatman1 filter paper as the reaction substratum; The enzyme activity of endo-glucanase was 115CMCU/g under the reaction conditions of p H=6, temperature=55℃ with CMC as the reaction substratum; The enzyme activity of exo-glucanase was 94MCCU/g under the reaction conditions of p H=4.8, temperature=40 ℃ with MCC as the reaction substratum.A series of changes of bleaching wheat straw fiber like "pitting", "stripping" and "tearing" of fiber happened after enzyme treatment. With the increase of the enzyme dosage, the average length and width of fiber gradually decreased while the content of fines increased; for compound cellulase treatment, with the increase of the compound cellulase dosage, the fiber specific surface area increased first and then decreased, and the fiber specific surface area reached a maximum of 2.26m2/g when the dosage of compound cellulase was 0.5FPU/g; for endo-glucanase treatment, with the increase of the endo-glucanase dosage, the fiber specific surface area had a periodic change which increased first and then decreased; for exo-glucanase treatment, with the increase of the exo-glucanase dosage, the fiber specific surface area gradually decreased.After enzyme treatment of bleaching wheat straw fiber, fiber still had the basic chemical structure of cellulose.Cellulose basically kept the crystalline form of natural fiber, still existing in the crystal form of celluloseⅠ.The aggregation structure of cellulose changed. For compound cellulase treatment, with the increase of the compound cellulase dosage, the crystallinity of cellulose had a periodic change which increased first and then decreased, then increased and then decreased, and the average degree of polymerization and the average molecular weight of cellulose reduced. For endo-glucanase treatment, with the increase of the endo-glucanase dosage, the crystallinity of cellulose had a periodic change which decreased first and then increased, then decreased and then increased, and the average degree of polymerization and the average molecular weight of cellulose reduced gradually and finally tended to be stable. For exo-glucanase treatment, with the increase of the exo-glucanase dosage, the crystallinity of cellulose increased first and then decreased, and reached a maximum of 56.02 when the dosage of exo-glucanase was 10MCCU/g, and the average degree of polymerization and the average molecular weight of cellulose reduced sharply.After enzyme treatment of bleaching wheat straw fiber, fiber properties also changed a lot. For compound cellulase treatment, with the increase of the compound cellulase dosage, fiber yield decreased gradually while pulp beating degree increased, and the absolute value of Zeta potential on the surface of the fiber had a periodic change which decreased first and then increased, reaching the minimum of 22.8m V when the dosage of compound cellulase was 5FPU/g. Besides, the water retention value of fiber also decreased first and then increased, reaching the minimum of 192.67% when the dosage of compound cellulase was 5FPU/g. For endo-glucanase treatment, with the increase of the endo-glucanase dosage, fiber yield decreased gradually finally tended to be stable, and pulp beating degree decreased first and then increased, reaching the minimum of 24oSR when the dosage of endo-glucanase was 2CMCU/g. The absolute value of Zeta potential on the surface of the fiber had a periodic change which increased first and then decreased, and then increased the decreased. Besides, the water retention value of fiber had a periodic change which decreased first and then increased, then decreased and increased. For exo-glucanase treatment, with the increase of the exo-glucanase dosage, fiber yield decreased gradually while pulp beating degree increased.The absolute value of Zeta potential on the surface of the fiber increased first and then decreased, reaching the maximum of 27.2m V when the dosage of compound cellulase was 2MCCU/g. Besides, the water retention value of fiber decreased gradually. The thermal stability of bleaching wheat straw fiber decreased after enzyme treatment.The cellulose microfibril(CMF) products were synthesized after enzyme pretreatment of bleaching wheat straw fiber with high pressure homogenization. Through the preliminary study, we found that the yield of CMF was very high, the diameter of which was about 30~50nm and the length was about a few microns between dozens of microns. The specific surface area and the cationic demand of CMF reached up to 39m2/g and 48μmol/g respectively, which was significantly higher than ordinary plant fiber raw materials, and CMF suspension had better dispersibility and stability.