A Preliminary Study On Topochemical Changes During Enzymatic Hydrolysis Of Plant Fiber

Cellulose is the most abundant polysaccharide resource in the world, recent yesrs, using plant fiber as raw material to develop renewable products has become a global hot research topic. As a novel nano-cellulose material, cellulose microfibril(CMF) has excellent mechanical properties, transparency and barrier properties, but the CMF can not successfully commercialized now, mainly because the high mechanical energy consumption when dissociate the fibers into CMF, while the enzymatic pretreatment can help the dissociation and reduce the energy consumption. Although there is a large number of enzymatic hydrolysis research works, the preparetion technology of CMF by enzymatic pretreatment still has some limitations. This paper focuses on the topochemical changes during the enzymatic hydrolysis of cellulose fiber. Using cellulase, endo-cellulase and exo-cellulase to hydrolysis the bleached softwood fibers, then separate the fiber cell wall and study the different layers of fiber morphological parameters, sugars and degree of polymerization, to strengthen a depth study of enzymatic pretreatment mechanism, optimize the pretreatment process, provides a theoretical basis for the practical application, and promote the CMF preparation technology has a further breakthroughs in industrial applications.The fiber cell wall was separated by ultrasound technology and DDJ (Dynamic Drainage Jar) screening effect. The ultrasound treatment can significantly fluff the fibers, and then the DDJ screen was used to peel off the primary wall(P layer) and the second wall outer layer(S1 layer). The fiber morphology analysis showed that ultrasound can not cut fibers, after DDJ sieved, the fiber length is essentially the same as the control sample, but because of the P layer and the S1 layer have been peeled off, the fiber width has reduced 0.4?m, the degree of polymerization and the FTIR analysis showed that the fibers did not produce the new functional groups.High performance liquid chromatography analysis method was established. Selected the Sugar Pak-I column to separate sugars on Waters-1525 high performance liquid chromatography for the simple separation process. The separation conditions are:column temperature:90?, mobile phase:ultrapure water, flow rate:0.5mL/min, injection volume:20?L. The five standard sugars: glucose, xylose, mannose, galactose and arabinose have achieved a better separation under this condition, the standard curve of five standard sugars showed a good linear relationship, and its reproducibility was good, the coefficient of variation of each sugar was less than 3%, meet to the requirements of measurement.The fiber morphology was analyzed after enzymatic hydrolysis, the microscopic examination showed that the three cellulase all can cut fibers, and the fiber were cut for many times. Under the action of three enzymes, the average fiber length of bleached softwood fiber and long fibers of separated sample was progressively shorter, but did not change significantly in fines peeled from the fiber surface. The scanning electron microscopy (SEM) analysis showed that the complex cellulase and exo-cellulase were able to significantly peel the fibers, but the endo-cellulase did not, its main role was cut fibers.The fiber morphological parameters analysis showed that after the enzymatic hydrolysis, the number average length and the weight average length of bleached softwood fiber were gradually reduced, decreased 86.3%,76.62% and 86.85% when the complex cellulase, endo-cellulase and exo-cellulase enzyme dosage reached the maximum. The curl and kinked fibers have the same downward trend with the fiber average length. The average width first decreased and then increased. Under the complex cellulase and exo-cellulase action, the fines were first decreased and then increased, but it increased under exo-cellulase action. In the separated samples, the average length of long fibers were gradually decreased, average width first decreased and then increased, and the fines was increased. The average length of fines peeled from the fiber surface was decreased, but the decline was small, at this length, the average width and the fines were measured too large.The fiber cell wall were separated after the enzymatic hydrolysis, then completely hydrolysed by the acid, and then measured the glycans of different layers, the HPLC analysis showed that, the bleached softwood fiber mainly contains glucose, xylose, mannose, galactose and arabinose, and the glucose content is more than 80%. Under the three enzymes, the glucose was first increased and then decreased, but the other four sugars were first decreased and then increased. In the separated samples, the long fibers contain more glucose, but less xylose, mannose, galactose and arabinose, so the outer layer has more hemicellulose and can be hydrolysised faster. The degree of polymerization showed that with the increasing of enzyme dosage, the degree of polymerization were gradually decreased, and at the beginning of the reaction, the degree of polymerization decreased rapidly, especially in the fines of separated sample, but with the hydrolysis of the amorphous region, the degree of polymerization decreased slowly. The topochemical analysis showed that the complex cellulase and the exo-cellulase have a stronger hydrolytic.