Show simple item record

dc.contributor.advisorDu Preez, J. C.
dc.contributor.advisorWolfaardt, J. F.
dc.contributor.authorSteel, Crystal Leone
dc.date.accessioned2017-02-08T08:31:38Z
dc.date.available2017-02-08T08:31:38Z
dc.date.issued2010-11
dc.identifier.urihttp://hdl.handle.net/11660/5576
dc.description.abstractEnglish: Refining of pulps requires a large amount of energy, capital input and maintenance costs. Wood fibres can be treated enzymatically prior to refining to reduce the refining energy requirement of the pulps and/or to improve drainage and strength properties. Cell-wall modifying enzymes such as the cellulases and hemicellulases can assist refining by opening up the crystalline and amorphous cellulose and hemicellulose in the fibre walls. This application requires cell-wall modifying enzymes to be matched to the specific pulp. Characterisation of commercially-available cellulases showed that the activities of the enzymes were suitable for paper mills. The protein content of the enzyme formulations were determined to establish levels for comparative dosing. Using this information the effects of over-dosing and the extended incubation with the enzymes were also determined. The pulp yield and fibre strength appeared to be at risk of being decreased with elevated enzyme dosages, since Ecopulp® Energy, Novozyme 613 and Celluclast 1.5L increased the release of reducing sugars. The critical period for fibre modification by enzyme treatment was the first 30 min of incubation. The most suitable enzyme for application to a paper mill appeared to be Novozyme 476 due to its ability to improve bonding strength with minimal loss in fibre strength. According to published reports, dried and never-dried Eucalyptus globulus pulps responded differently to enzyme treatments and it was, therefore, likely that dried and never-dried E. grandis pulps would also respond differently. Ecopulp® Energy, Novozyme 476 and Celluclast 1.5L were applied to E. grandis pulps and refined on pilot scale. Overall, the dried E. grandis fibres responded differently to the enzyme treatments than never-dried fibres and enzymes should, therefore, be matched to the specific fibre used. It was proved that the enzymes can be used to save on refining energy usage as well as to improve strength properties of paper made from dried or never-dried E. grandis pulps. Ecopulp® Energy and Novozyme 476 were subsequently applied to the E. nitens pulps and refined on pilot scale. All of the enzyme applications had a similar effect on the never-dried pulp, where the properties were not changed as much as on the dried pulp. Novozyme 476 was the most suitable enzyme for application on the dried E. nitens pulps, because it saved on refining and drying energy due to the decreased freeness and water retention values. The Novozyme 476 also improved the physical properties of the pulps where tear and tensile indices and porosity were increased and bulk was reduced. This work demonstrated that enzymes must be selected to match the pulps being used and to suit product requirements. Novozyme 476 was selected for application on a fine-paper machine in order to improve the refining efficiency of E. nitens pulp. At the high dosage (100 ml/t) the refining current of the mixed stock refiner was reduced and the porosity and tear strength was decreased and tensile strength was increased. The reduction in tear strength was probably due to too much refining energy applied to enzyme treated pulp, thereby damaging the fibres. The damage to the fibres was confirmed by electron microscopy, showing excessive fibrillation of the fibres treated with the endoglucanase. The endoglucanase successfully improved the refining efficiency of the paper machine and should be considered for application on a permanent basis.en_ZA
dc.description.abstractAfrikaans: Die verfyning van pulp verbruik groot hoeveelhede energie asook besteding aan kapitaal en onderhoudskoste. Houtvesels kan ensimaties behandel word voor verfyning om die behoefte aan verfyningsenergie te verminder en/of die dreinerings- en sterkte-eienskappe te verbeter. Ensieme soos sellulase en hemisellulase kan verfyning aanhelp deur die kristallyne en amorfe sellulose en hemisellulose in die veselwande los te maak. Hierdie toepassing vereis dat selwand-modifiserende ensieme vir spesifieke pulptipes geselekteer word. Die karakterisering van ensieme wat kommersieel beskikbaar is, het getoon dat die aktiwiteit van die ensieme geskik is vir toestande in papiermeulens. Die proteïeninhoud van die formulasies is bepaal om te beslis oor vergelykbare vlakke van ensiemtoediening. Deur hierdie inligting te gebruik, kon die effek van oordosering en verlengde inkubasie met die ensieme ook bepaal word. Dit kom voor of die pulpopbrengs en veselsterkte verlaag word deur hoër ensiemdosisse omdat Ecopulp® Energy, Novozyme 613 en Celluclast 1.5L die vrystelling van reduserende suikers verhoog het. Die kritiese tydperk vir veselmodifikasie met ensiembehandeling was die eerste 30 min van inkubasie. Die mees geskikte ensiem vir toepassing in ’n papiermeule blyk Novozyme 476 te wees as gevolg van sy vermoë on bindingsterkte te verbeter met ʼn minimale verlies aan veselsterkte. Volgens gepubliseerde resultate, reageer gedroogde en ongedroogde Eucalyptus globulus pulp verskillend op ensiembehandeling en dit is daarom moontlik dat E. grandis pulp ook verskillend kan reageer. Eucalyptus grandis pulp is met Ecopulp® Energy, Novozyme 476 en Celluclast 1.5L behandel en op loodsskaal verfyn. Oor die algemeen het die gedroogde E. grandis vesels anders op ensiembehandeling gereageer as ongedroogde pulp en ensieme behoort dus vir ‘n spesifieke veseltipe geselekteer te word. Dit is ook bewys dat die ensieme gebruik kan word om verfyningsenergie te bespaar en sterkte-eienskappe van papier wat van gedroogde en ongedroogde E. grandis pulp vervaardig is, te verbeter. Ecopulp® Energy en Novozyme 476 is vervolgens op E. nitens pulp aangewend en op loodsskaal verfyn. Al die ensiembehandelings het ’n soortgelyke effek op ongedroogde pulp gehad, waar die invloed minder was as op gedroogde pulp. Novozyme 476 was die mees geskikte ensiem vir toediening op gedroogde E. nitens pulp omdat dit verfynings- en drogingsenergie kan bespaar a.g.v. laer vrydreinering en waterretensie waardes. Die Novozyme 476 het ook die fisiese eienskappe van die pulp verbeter deur skeur- en trekindekse en porositeit te verhoog en digtheid te verlaag. Hierdie werk het gedemonstreer dat ensieme vir die pulp wat gebruik word, geselekteer moet word en ook om te pas by produkvereistes. Novozyme 476 is gekies vir aanwending by ’n fynpapiermasjien om die doeltreffendheid van die verfyning van E. nitens pulp te verbeter. Teen die hoër dosis (100 ml/t) is die elektriese stroom na die gemengde-pulpverfyner verminder terwyl die porositeit en skeursterkte verminder en treksterkte verhoog het. Die verlaging in skeursterkte kan moontlik aan die aanwending van te veel verfyningsenergie aan die ensiembehandelde pulp toegeskryf word wat daardeur die beskadiging van vesels veroorsaak het. Die beskadiging van die vesels is deur elektronmikroskopie bevestig, wat oormatige fibrillering van die vesels wat met endoglukanase behandel is, getoon het. Die endoglukanase het die doeltreffendheid van die verfyning vir die papiermasjien verbeter en die toediening van die ensiem op ’n permanente basis moet oorweeg word.af
dc.description.sponsorshipSappi Manufacturingen_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectDissertation (M.Sc. (Microbial, Biochemical and Food Biotechnology))--University of the Free State, 2010en_ZA
dc.subjectEucalyptus grandisen_ZA
dc.subjectWood-pulp -- Biotechnologyen_ZA
dc.subjectWood-pulp -- Microbiologyen_ZA
dc.subjectWood-pulp -- Refiningen_ZA
dc.subjectEndoglucanaseen_ZA
dc.subjectEnergyen_ZA
dc.subjectEnzymesen_ZA
dc.subjectEucalyptus nitensen_ZA
dc.subjectFibrillationen_ZA
dc.subjectFreenessen_ZA
dc.subjectFibre modificationen_ZA
dc.subjectPulp fibresen_ZA
dc.subjectTensile strengthen_ZA
dc.titleEvaluation of cell-wall modifying enzymes for improved refining of pulp from two Eucalyptus speciesen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record