Doctoral Degrees (Forest and Wood Science)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/545

Browse

Browsing Doctoral Degrees (Forest and Wood Science) by Author "Du Plessis, Marius"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    A fibre optimisation index developed from a material investigation of Eucalyptus grandis for the Kraft pulping process.
    (Stellenbosch : Stellenbosch University, 2012-03) Du Plessis, Marius; Rypstra, T.; Zbonak, A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    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.