Study On The Sturcture And Performance Of Enzymatic Hydrolyzed Bleached Softwood Fiber

Fiber raw material is the most abundant renewable naturalresources on the earth， the effective use of it has a very importantsignificance to energy conservation and the protection of theenvironment. Using of cellulase or hemicellulase to hydrolyze the fibermaterials, on one hand, it could activate the fiber surface and internalstructure to a certain degree, and improve the fiber performance; on theother hand, it could obtain oligosaccharides and monosaccharidesdirectly, which can produce biomass fuels such as ethanol, methanol byfurther fermentation. So the enzymatic hydrolysis of fiber materials hasa wide value of application in farming, food, wine, textiles, washing,papermaking, energy and other industries. However, due to the widevariety of enzymes, the large difference of its composition, structure,catalytic mechanism, and coupled with the complex structure of thefiber material itself, in the process of enzymatic hydrolysis, thestructure and properties of fiber changed complexly, it would affect theapplication of fiber enzymatic modification technology. This taskmainly used bleached softwood fiber as the raw material, by analyzingand comparing the influence of the composite cellulase, endo-cellulaseand xylanase to the morphology, structure and performance of the fiberin a different hydrolysis degree, studied the general rule and mechanismof the changes of fiber structure and properties with enzymatichydrolysis. It aimed at strengthening the control of the change of thefiber structure and properties in the enzymatic hydrolysis, providingtheoretical guidance for the industrial application of fiber enzymatichydrolysis, and promoting the application of fiber enzymatic hydrolysisin full range effectively. The effect of enzymatic hydrolysis to fiber yield was investigated.The results showed that by the hydrolysis of complex cellulase namedas Celluclast1.5L, with the increasing of the enzyme dosage or thehydrolysis time, the fiber yield declined rapidly. Hydrolyzed in thedosage of10.0FPU/g for48h, the fiber yield was just55.34%. Itindicates that the complex cellulase has a strong hydrolysis on cellulose,and it can hydrolyze the cellulose both in amorphous region and incrystallization region. Endo-cellulase named as Novozym476had a farweaker hydrolysis on the fiber than Celluclast1.5L. Hydrolyzing for2hours with Novozym476in the dosage of50.0CMCU/g, only about5%cellulose was hydrolyzed. There was not essentially change in the fiberyield when hydrolyzed with xylanase named as Pulpzyme HC, itindicates that the function of xylanase on bleached softwood fiber isvery limited.The effect of enzymatic hydrolysis to fiber morphology wasinvestigated. The results showed that there are many tiny fibrils on fibersurface without enzymatic hydrolysis. both of Celluclast1.5L andNovozym476took role on these tiny fibrils firstly and made them behydrolyzed, thus the fiber surface became smooth, and the fiber specificsurface area reduced. With the increasing enzyme dosage of theCelluclast1.5L, there was peeling and stripping appeared on the fibersurface. While the enzyme dosage increased furthermore, the fiberappeared significant gaps and breaking. Thus the fiber specific surfacearea increased, average length of fiber declined sharply, the content offine increased significantly, and curl rate and kink index of fiberdecreased. The average length of fiber hydrolyzed with Novozym476was not changed significantly, but curl rate and kink index of fiberincreased. Pulpzyme HC had no significant effect on fiber morphology.The effect of enzymatic hydrolysis on molecular weight andaggregation structure of bleached softwood fiber were investigated. Theresults showed that hydrolyzed by Celluclast1.5L or Novozym476,with the enzyme dosage increasing, the degree of polymerization (DP)of the cellulose decreased gradually. When the dosage of Celluclast 1.5L was10.0FPU/g, the DP of cellulose declined to694, dropped by40.38%compared with the control sample; when the dosage ofNovozym476was50.0CMCU/g, the DP of cellulose declined to711,dropped by38.92%compared with the control sample. It illustrates thatin the function of complex cellulase or endo-cellulase, themacromolecular chain of cellulose would break in a high degree, andthe molecular weight of cellulose declined. It shows that in the processof enzymatic hydrolysis, it is endo-glucanase that mainly leads the DPand molecular weight of cellulose to decrease. Bleached softwood fiberhydrolyzed by Pulpzyme HC, the DP and the molecular weight ofcellulose was essentially unchanged.Shown from the results of X-ray diffraction (XRD) and FourierTransform infrared spectroscopy (FTIR), that the enzymatic hydrolysiswould not cause the change of macromolecule structure, and there hadno new functional groups generated during the hydrolysis process. Thecellulose crystal form was not changed, and it is still the cellulose I.However, the crystallinity of cellulose went through different variationswith the function of two cellulases. After hydrolyzing by Celluclast1.5L, the crystallinity presents a periodic variation with the increase ofthe enzyme dosage. It indicates that the celluloses in crystallizationregion and amorphous region are hydrolyzed at the same time in thefunction of Celluclast1.5L. With the function of endo-cellulaseNovozym476, the crystallinity decreased initially, but it would increaseand then decreased with the enzyme dosage increasing, but it showed agrowth trend as a whole. After hydrolyzing by xylanase Pulpzyme HC,the crystallinity gradually increased with the increase of the enzymedosage.The effect of enzymatic hydrolysis on the properties of bleachedsoftwood fiber was investigated. The results showed that with theincreasing dosage of Celluclast1.5L, the filtration performance of fibersuspension increased initially and then decreased, while the waterretention value (WRV) of fiber decreased first and then increased. In theenzyme dosage of20.0FPU/g, the WRV of fiber increased to204.19%, increased by47.73%compared with the control sample. With theenzyme dosage increasing, absolute Zeta potention of fiber surface firstdecreased and then increased, fiber surface free energy decreasedgradually, and the hydrophilicity of fiber decreased while thelipophilicity increased. After enzymatic hydrolysis with Celluclast1.5L,the thermal stability of fiber declined.With the increasing dosage of cellulase Novozym476, thefiltration performance of fiber suspension gradually increased while theWRV of fiber decreased. Absolute Zeta potention of fiber surfacedecreased and the surface free energy of fiber increased gradually whilethe enzyme dosage increased, and the hydrophilicity of fiber increased.After enzymatic hydrolysis with Novozym476, the thermal stability offiber declined.There had no significant effect to the filtration performance offiber hydrolyzed with xylanase Pulpzyme HC. While the enzyme dosageincreased, the WRV of fiber decreased slightly, the absolute Zetapotention of fiber surface decreased gradually, the surface free energyof fiber increased gradually and the hydrophilicity of fiber increased. Inaddition, the thermal stability of hydrolysis fiber was slightly higherthan the control sample.The effect of enzymatic hydrolysis to fiber refining performanceand paper sheet properties was investigated. The results showed thatpretreated by cellulase of Celluclast or Novozym476and then refinedby higher PFI revolutions, the pulp freeness decreased with theincreasing of the enzyme dosage. it indicates that the pretreatment withcomposite cellulase or endo-cellulase in refining process wouldincrease the effect of the fiber cut、swelling、fibrillation and so on, andit would play a role in reduce the energy consumption of refining. Butin the lower PFI revolutions, cellulase pretreatment contribute little toreduce the energy consumption of refining. Cellulase enzymaticrefining had different effect on fiber morphology compared withmechanical refining. In the same pulp freeness, enzymatic refining would make the fiber thinner、more incision and there would have muchmore fragments in the pulp.In the case of without mechanical refining, the paper properties ofthickness, tensile index, softness and air permeability all increased atfirst and then decreased with the increasing of the enzyme dosage ofCellulast1.5L. In the enzyme dosage of0.1FPU/g, the tensile index ofpaper reached the maximum of21.77N·m/g and increased by26.36%compared with the control sample. While in the enzyme dosage of10.0FPU/g, the tensile index of paper declined to10.97N.m/g anddecreased by39.89%compared with the control sample. The internalbond strength of paper increased gradually with the increasing of theenzyme dosage.In the process of enzymatic refining used Celluclast1.5L orNovozym476, while in the case of less enzyme dosage, the tensileindex, internal bond strength and bulk of paper all increased with lowerPFI revolutions; In the case of higher enzyme dosage, for the reasonthat the surface or internal molecular chain of cellulose was broken, thesurface of the fiber would have a gap or loose, so the fibers would bethinner, shorten with the mechanical force, which led to the decreasingof the fiber strength, so the tensile index of paper decreased. The higherof the enzyme dosage, much more declined of the tensile index.Enzymatic refining with cellulase was not conducive to improve paper’sair permeability.Hydrolyzing by xylanase Pulpzyme HC had no beneficial to reducethe energy consumption of refining, but the enzymatic refining withPulpzyme HC would help to improve the tensile index and internalbonding strength of paper.The different effect on structure and performance of fiber withdepth enzymatic hydrolysis and acid hydrolysis was investigated. Theresults showed that hydrolyzed by hydrochloric acid, the DP of bleachedsoftwood fiber reduced to limit DP of about200rapidly, and fiber yieldwere more than90%. Hydrolyzed by the cellulase Celluclast1.5Ldeeply, the DP of cellulose maintained at about700, while the fiber yield sharply declined. It shows that although both of the hydrolysiswith dilute acid hydrolysis and cellulase would break the beta-1,4-glycosidic bond on the cellulose macromolecules, but there had quitedifference in the location of the breaking occurs. Depth enzymatichydrolyzed fiber and acid hydrolyzed fiber have a similar morphology,the average length of fibers dropped to only0.1to0.2mm. however,after crushing, there had a big difference between particles in the formof microscopic: the acid hydrolyzed cellulose were oval particles withsmall size, and it lost the original structure of the fiber cell wallcompletely, so it met with the particle characteristics ofmicrocrystalline cellulose. The enzymatic hydrolyzed cellulose had abigger size, and it had a quilt complete cell wall structure of fiber anddid not meet with the characteristics of microcrystalline cellulose.Depth enzymatic hydrolyzed cellulose and acid hydrolyzed cellulosehad similar crystal structure; the crystallinity of them was similar andincreased compared with the control sample. Acid hydrolyzed cellulosehas a slightly higher thermal stability than the enzymatic hydrolyzedcellulose.