The bonding of fibres in paper is influenced by environmental changes (e.g. moisture) that may cause unstable fibres to move. These movements include cell-wall swelling, fibre lifting and/or puffing that break inter-fibre bonds and lead to reduced strength and surface roughness. Fibre puffing is defined as the expansion of the lumen area as result of changes in the environment. Puffing was investigated through image analysis of scanning electron micrographs. Detailed images were obtained with samples that were embedded in resin and then etched. Puffing of fibres was then quantified by calculating the ratio of lumen area to fibre area. Stability of softwood and hardwood fibres was studied in this way, and to simulate printing, handsheets were calendered and rewetted. This method was later validated against commercial sheets. Compared to softwood, hardwood fibres were more stable and most of the handsheet properties were retained after rewetting. Mannanase and/or endoglucanase treatments resulted in improved fibre stability by increasing fibre bonding, fibrillation or fibre collapse. Mannanase improved handsheet smoothness and strength as well as fibre stability, but endoglucanase was less effective. The effect of the enzymes was more difficult to observe on hardwood fibres, because even untreated fibres were more stable under moist conditions. Thin-walled fibres such as earlywood were less stable than latewood fibres, but it responded better to mannanase treatment. Thick-walled fibres (latewood), on the other hand, were more difficult to improve with enzymes. The potential of enzymes to improve fibre stability of commercial pulp was tested on chemi-thermo-mechanical pulp (CTMP) and bleached CTMP. Enzyme treatment improved fibrillation and reduced beating energy of bleached CTMP. Mannanase again resulted in the most improved fibre stability. On rejects, a lack of response to enzymes was overcome by pre-treating the pulp with alkaline peroxide. This study provided new insights into the stability of fibres with different morphology. It was also demonstrated that fibre stability can be improved with enzyme treatment and it is expected that this knowledge could have significant commercial value. / Dissertation (PhD)--University of Pretoria, 2010. / Microbiology and Plant Pathology / unrestricted

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The distribution of different free chemical functional groups on wood and pulp fibres was determined by means of atomic force microscopy (AFM) with chemically modified tips. Because these functional groups show a higher affinity to similar groups on the substrate surface during scanning, AFM images were recorded using an additional digital pulsed-force mode (DPFM) controller. This allowed the distribution of the chemical components to be imaged and to a degree, also to be quantified. The investigated tip coatings showed different sensitivities towards the major chemical components present in wood fibres. These components were determined on spin-coated films as well as wood fibres. It was possible to make a clear distinction between cellulose and lignin in both cases. This technique could therefore be used to differentiate between cellulose and lignin present on pulp fibre surfaces and to confirm the successful removal of lignin by pulping. The chemical composition of wood fibres and fibre surfaces of several acacia and eucalyptus species, and hybrids originating from various growth sites in South Africa, are compared. The objective was to determine the differences in chemical surface composition due to genetics or site. The motivation for this was to eventually facilitate a tailor-made supply of wood for pulping which results in an optimal blend of fibres that can be pulped together with similar yields. This, however, first requires a sound knowledge of the fibre properties. The surface functionality on the single fibre level is a key property because it determines how good inter-fibre bonding will be when paper is formed, which in turn depends to a large degree on the amount of free hydroxyl groups that are available and therefore on the cellulose content on the fibre surface. The cellulose and lignin contents on the fibre surface were determined with chemical force microscopy (CFM), a variation of AFM. CFM involves the use of chemically modified tip using selected functional groups. Since, the general bulk composition of the fibre and the surface composition differ, both parameters were determined. Significant differences in the cellulose and lignin content on fibre surfaces were found, with regard to genotype and site, respectively. In some, but not all, cases the surface composition of wood fibres followed the bulk composition and differences were generally more pronounced. Differences due to genotype were significant, especially with regards to the surface lignin content - but variation due to site was also distinctly recognisable. This variation in surface functionality could be the reason why some pulpwood blends result in a lower pulp yield and different quality. / AFRIKAANSE OPSOMMING: Die verspreiding van verskillende vrye chemiese funksionele groepe op hout en pulpvesels is bepaal deur middel van atoomkragmikroskopie (AFM), met chemies-gemodifiseerde punte (tips). Omdat hierdie funksionele groepe 'n hoër verwantskap tot soortgelyke groepe op die substraat se oppervlak gedurende skandering toon, kan AFM-beelde wat met 'n addisionele digitalepulskragmodusbeheerstel bepaal word dit moontlik maak om die verspreiding van die chemiese komponente uit te beeld en tot op ‘n sekere vlak te kwantifiseer. Die ondersoekte punt-oppervlakmiddels het verskillende sensitiwiteite teenoor die hoof chemiese komponente in die houtvesels en spin-bestrykte films getoon. 'n Duidelike onderskeid kon in beide gevalle tussen sellulose en lignien gemaak word. Hierdie tegniek kon dus gebruik word om te onderskei tussen sellulose en lignien wat op die pulpveseloppervlak teenwoordig was en om die suksesvolle verwydering van lignien gedurende die pulpproses (pulping) te bevestig. In hierdie studie is die chemiese samestelling van houtvesels en die veseloppervlaktes van verskeie akasia en eucalyptus spesies, asook dié van gekruisde spesies wat van verskeie werfliggings in Suid-Afrika afkomstig is, vergelyk. Die doel was om te toets vir verskille in chemiese oppervlaksamestellings, wat veroorsaak kan word deur genetika of werf verskille, met die uiteindelike mikpunt om ‘n spesiaal-gemaakte voorraad van hout vir pulping te fasiliteer, wat kan lei tot 'n optimale mengsel van vesels wat saam gepulp kan word met soortgelyke opbrengs. Dit vereis natuurlik 'n goeie kennis van die veseleienskappe. Die oppervlakfunksionering van enkel vesels is ‘n kritiese eienskap omdat dit bepaal hoe goed interveselverbindings sal wees wanneer papier gevorm word. Dit hang tot ‘n groot mate af van die hoeveelheid vry hydroksielgroepe wat beskikbaar is en dus ook van die sellulose inhoud op die veseloppervlak. Die sellulose- en lignieninhoud op die veseloppervlak is bepaal met chemiese kragmikroskopie – 'n variasie van atoomkragmikroskopie. Omdat die algemene grootmaat samestelling van die vesel en die oppervlaksamestelling mag verskil, is altwee parameters bepaal. Beduidende verskille in die sellulose- en lignieninhoud, met betrekking tot genotipe en werfligging, op veseloppervlaktes is gevind. In sommige, maar nie alle, gevalle het die oppervlaksamestelling van houtvesels ooreengestem met die grootmaatsamestelling, en verskille was oor die algemeen meer beduidend. Verskille as gevolg van genotipe was beduidend, veral met betrekking tot die oppervlak lignieninhoud, maar variasie as gevolg van werfligging was ook duidelik herkenbaar. Hierdie variasie in oppervlakfunksionering kan die rede wees hoekom sommige pulp–hout mengsels lei tot 'n laer pulpopbrengs en verskille in kwaliteit.

The regular transmittance of light or similar radiation through a flowing suspension of particles fluctuates because of the random occurrence of particles in the beam.In the work presented here, a theory for this fluctuating behaviour with the emphasison dispersions of mm-length slender cylindrical particles having circular crosssections is given. The particles in question are wood pulp fibres, which as a first approximation are considered to have a cylinder shape. Four possible measurementprinciples are described theoretically and experimentally. The four principles are for the measurement of concentration, length distribution characterized as lengthclasses, mean length, and mean width. The usefulness in industrial process monitoring of two of these principles is exemplified with pulp measurements. In order to estimate model errors, numerical simulations were used. Although other techniques such as image analysis may compete, the technique presented here is attractive because of the simplicity of the measurement device used. / QC 20100806