A fibre optimisation index developed from a material investigation of Eucalyptus grandis for the Kraft pulping process.

Du Plessis, Marius (Stellenbosch : Stellenbosch University, 2012-03)

Thesis (PhD (For))--Stellenbosch University, 2012.

Thesis

ENGLISH ABSTRACT: A primary reason for the existence of the forest industry is to provide a renewable and natural resource for much needed timber and fibre products. Substantial improvements in management practices are required to increase forest volume and pulp yields for increased demand. Eucalyptus grandis clonal trees of age 6.75 years, grown in a Nelder 1a spacing experiment, were sampled and analysed to describe the effect of planting density on i) growth and yield, ii) wood properties and iii) pulp and paper quality. The main objective was to populate a fibre productivity index (FPI) which would be suitable from technical and economical perspectives. A material study was conducted on the wood and in addition, two methods were developed to further describe the variability of the forest resource to i) separate growth rings by means of wood density peaks from gamma-ray densitometry and ii) calibrate near infrared (NIR) prediction models. The results indicated that planting density did not influence the variability of wood density but mechanisms affecting available soil water are important. NIR prediction models were developed to rapidly and reliably assess wood properties on a non-destructive basis. The validation models for wood density, total pulp yield, kappa number and insoluble lignin returned high predictive ability. When applied to predict chemical properties from an independent data set, the outcomes were accurate in comparison with measured data. Growth and yield functions were developed for tree survival, dominant height and basal area. They accurately predicted outcomes as demonstrated by the goodness of fit and their logical behaviour tested over the range of planting densities. When the most extreme stand density treatments, 6809 and 275 trees per hectare (TPH) were evaluated for wood and fibre properties, the larger trees grown at 275 TPH, produced wood of better quality for pulp processing; basic wood density at 0.520 g cm–3 (21 % higher), fibre cell wall thickness at 2.10 μm (18.6 % thicker) and fibre lumen diameter at 8.16 μm (9.9 % lower) than for 6809 TPH. Intra-specific tree variability of wood and product properties increased from diameter at breast height (DBH) to 35 % and then decreased to 65 % of tree height. The effect of planting density was carried throughout the product value chain up to the paper manufacturing phase. Paper with higher bulk mass and thickness and more porous sheets is most likely to be made from lower planting densities (801 and 275 TPH), and stronger, smoother and denser paper is most likely to be made with trees at high planting densities (6809 or 2336 TPH). From the growth and yield and materials investigation, technical indicators identified to populate a fibre productivity index were: i) mean annual increment (MAI) as a forestry growth indicator, ii) wood density, summarising the composition of wood and, iii) pulp yield, the indicator of the amount of fibre processed through a chemical cooking process. Delivered cost of timber to the mill, was identified as the most suitable economic indicator which included fixed costs elements, variable costs and aspects of mill efficiency. The product of the technical and economic indicators concluded in a profit/loss scenario of producing 1 ton of pulp was deemed the best index to describe the entire and integrated value chain. This index, termed the Fibre Productivity Index (FPI) at the Mill, denoted as FPMill, is an integrated index that is easy to interpret in the realms of a forestry - pulp manufacturing, and can be used for differential pricing of timber for wood quality.

AFRIKAANSE OPSOMMING: 'n Primêre rede vir die bestaan van die bosbouindustrie is om ‘n hernubare, natuurlike hulpbron vir hout en vesel te voorsien. Aansienlike verbeterings in bestuurspraktyke is nodig om die houtvolume en pulpopbrengste vir die toename in aanvraag te verhoog. Eucalyptus grandis klonale bome met ‘n ouderdom van 6.75 jaar en wat in 'n Nelder 1a spasiëring eksperiment gegroei is, is versamel en ontleed om die effek van opstandsdigtheid te beskryf op a) groei en opbrengs, b) houteienskappe en c) pulp- en papiergehalte. Die hoofdoel was om 'n veselproduktiwiteitsindeks (FPI), wat geskik sou wees in terme van tegniese en ekonomiese perspektiewe, te ontwikkel. 'n Materiaalkundigestudie is op hout uitgevoer. Twee metodes is ontwikkel om die variasie in hout as natuurlike hulpbron te beskryf deur a) vroeëhout- en laathoutdigtheidspieke deur gammastraal-densitometrie van mekaar te skei en variasie in groeiringe te beskryf en b) daarstelling van naby-infrarooispektroskopiese (NIR) voorspellingsmodelle. Die resultate het aangedui dat aanplantingsdigtheid nie ‘n invloed het op die variasie van houtdigtheid nie, maar dat meganismes wat beskikbare grondwater bepaal, belangrik is. NIR-voorspellingsmodelle is ontwikkel om houteienskappe op 'n nie-destruktiewe manier betroubaar te kan evalueer. Die validasiemodelle vir houtdigtheid, pulpopbrengs, kappanommer en onoplosbare lignien, openbaar akkurate voorspellingsvermoë. Wanneer dit toegepas word om chemiese eienskappe van 'n onafhanklike datastel te voorspel, was die resultate akkuraat in vergelyking met gemete data. Groei- en opbrengsfunksies is ontwikkel vir mortaliteit, dominante boomhoogte en basale area. Akkurate voorspellingsuitkomste is verkry soos gedemonstreer deur die logiese gedrag wat getoets is vir alle plantdigthede. Toe die mees ekstreme opstansdigtheidbehandelings vir hul hout- en veseleienskappe geëvalueer is, was die hout van die groter bome, teen 275 stamme per hektaar (SPH), van beter gehalte. Dit was veral prominent vir houtdigtheid van 0.520 g cm-3 (21 % hoër), veselselwanddikte van 2.10 μm (18.6 % dikker) en vesellumendeursnit van 8.16 μm (9.9 % laer) as by die hoër (6809) SPH. Intra-spesifieke boomvariasie van hout- en produkeienskappe het toegeneem van deursnee op borshoogte (DBH) tot 35 % en dan weer afgeneem tot 65 % van die boomhoogte. Die effek van plantdigtheid is regdeur die produkwaardeketting tot by die papiervervaardigingstadium sigbaar. Papier met hoër basismassa en dikte, en meer poreuse papiervelle kan meer waarskynlik van laer aanplantdigtheid (801 en 275 TPH) bome gemaak kan word. Papier wat sterker, gladder en digter is, kan waarskynlik gemaak word van hout van bome teen hoë aanplantdigthede (6809 of 2336 SPH). Die veselproduktiwiteitindeks wat ontwikkel is uit die materiaalondersoek en tegniese aanwysers wat geïdentifiseer is sluit in i) gemiddelde jaarlikse aanwas, as 'n bosbou groei-indikator, ii) houtdigtheid, wat ‘n opsomming van die samestelling van hout is, en iii) pulpopbrengs; die aanduiding van die hoeveelheid vesel verwerk deur 'n chemiese verpulpingsproses. Gelewerde koste van hout by die pulpmeul is geïdentifiseer as die mees geskikte ekonomiese aanwyser wat vaste kosteelemente, veranderlike koste en aspekte van die meul se doeltreffendheid insluit. Die produk van die tegniese en ekonomiese aanwysers is saamgevat in 'n wins / verlies opsie vir die vervaardiging van 1 ton pulp, en is beskou as die mees geskikte indeks om die geïntegreerde waardeketting te beskryf. Dié indeks, die sogenaamde Vesel Produktiwiteitsindeks (VPI) by die Pulpmeul, aangedui as VPMeul, is 'n geïntegreerde indeks wat maklik is om te interpreteer in 'n bosbou - pulpvervaardigingsopset, en kan gebruik word in die differensiële prysbepaling van hout waarby die kwaliteit in ag geneem word.

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