Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. Includes bibliographical references (leaves 337-340).

Thesis (Ph. D.)--Institute of Paper Science and Technology, Georgia Institute of Technology, 2005. / Alan Rudie, Committee Member ; Derek Page, Committee Member ; Douglas Coffin, Committee Member ; Kari Ebeling, Committee Member ; Timothy Patterson, Committee Member. Includes bibliographical references (p. 222-231).

Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 177-181).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 202-205).

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 196-199).

The catalysed organosolv process is a novel method of pulping that has many advantages over other chemical pulping processes. One of the most important advantages is its 6-12 percentage point higher yield of pulp in comparison to other chemical pulping processes. Short cooking time, low disintegration and refining energy requirements, ease of pulp washing and simplified method of by-product recovery are some of the other advantages. However, due to differences in the chemical nature of the cooking liquor, the basic properties of the fibers differ considerably. In this thesis a detailed study has been carried out on some of the unique phenomena i.e., fiber liberation at a high yield, topochemical preference of delignification and their manifestation on morphology and strength properties of fibers. Pulping results show that softwoods can be pulped easily to a high pulp yield (60%) with a high viscosity of cellulose of 50 mPas. The observed delignification pattern indicates two distinct stages both having first order kinetics. By this process, fast delignification occurs in the bulk delignification stage within which about 70% of the lignin is removed. Loss of residual lignin occurs at a slower rate in the residual delignification stage. The ease of penetration of the cooking liquor and preferential removal of lignin from the middle lamella result in complete fiber liberation at a pulp yield of 57.3% and a Kappa number of 72 (7% residual lignin). The loss of lignin to carbohydrate ratio at 57.3%pulp yield is 1.21:1. The topochemistry of delignification in organosolv pulping is limited to a preferential removal of lignin from the cell corner and middle lamella regions rather than from the secondary wall. In the initial stages of pulping, lignin removal is mostly from the cell corner and middle lamella region. Secondary wall lignin was removed quite slowly and a substantial amount of lignin remained in the secondary wall even after extended delignification. This can be accounted for by the slow hemicellulose removal (loss) from the secondary wall. The relatively high residual lignin retained in the cell corner in comparison to the complete delignification in the middle lamella raises questions about chemical differences and solubility characteristics of the cell corner lignin. The fibers of high-yield pulps are found to be stiffer and form a low density paper with high tear, and average burst and tensile strength. These factors can be correlated with the higher amount of residual lignin material in the fiber secondary wall and the low bonding properties of the fibers. High residual lignin content decreases the internal fibrillation and ability of the fibers to conform with each other during sheet formation. On the other hand, the low-yield fibers (49.8%) were found to be quite flexible and showed higher strength than obtainable with high yield pulps. Organosolv handsheets contain 20 to 30% fewer fibers than kraft papers of the same basis weight. However, the apparent difference in strength properties between organosolv and kraft papers is not disproportionately large. Organosolv lignins isolated from the spent liquor have low molecular weight (1400-2400) and low polydispersity (1.95) when recovered from extended pulping liquors. This indicates that most of the lignin is degraded to a fairly uniform low molecular weight polymer without substantially affecting the reactivity of the natural lignin as it occurs in the native fibers. The simplicity of the pulping process together with the comparable strength properties of the fibers even at higher yields, reveals large potentials of this method as a new pulping process. With some refinements and closer optimization, pulp fully acceptable commercially could be produced by this process. / Forestry, Faculty of / Graduate

No description available.

In order to gain insights into ultrastructural changes taking place during the conversion of hardwoods into mechanical pulps, refiner pulp fibres were studied in detail using several microscopical techniques. Aspen (Populus tremuloides Michx.) and white birch (Betula papyrifera Marsh.) wood chips were used to produce thermomechanical (TMP), chemithermomechanical (CTMP) and chemimechanical (CMP) pulps. Following the hypothesis that there are fundamental differences in the surface and state of the fibres due to species and processing conditions, four pulps for each species and process were analyzed. Trends in fibre characteristic development were obtained within each group, based on the detailed optical analysis of 300 fibre cross-sections for each pulp. Fibre surface quality was the most important aspect of this study. Retention of middle lamella and of the layer, as well as the extent of exposure of the S₂ layer were evaluated. It was found that TMP processing of wood chips produced fibres with more exposure of the S₂ layer. Chemical pretreatment did not improve the extent of S₂ layer exposure nor the extent of fibrillation. However, the TMP fibres remained stiff, producing pulp sheets of low density and strength. Birch fibres showed a marked tendency to produce separation at or near the S₁/S₂ boundary. This resulted in high exposure of S₂ layers in TMP fibres, but produced a sheath of S₁ and ML around fibres from chemically-treated chips. This sheath was sometimes rolled back, exposing the fibre S₂ layer. Aspen TMP pulps showed high proportions of fibres with partially exposed S₂ layer. The application of chemical pretreatments to aspen chips resulted in fibres of similar levels of S₂ exposure than those achieved by TMP processing of this species, but only after reaching freeness levels of about 100 mL CSF. Fibres that showed radial failure were frequent in TMP but not in CTMP nor CMP pulps. The breakdown pattern of tension wood fibres (G-fibres) was also studied. TMP processing showed preferential breakdown of G-fibres, from which the G-layers were freed. This was not the case in the G-fibres from chemically-treated chips, in which the G-layer generally remained inside the fibres. Other categories discussed in the analysis of fibre cross sections included fibres with delamination of the S₂ layer and proportion of fibres distorted due to chemical impregnation. The breakdown of vessel elements (VE) was studied by comparing VE size frequency distributions and the proportion of whole VE that survived refining. TMP reduced VE into small fragments showing virtually no whole VE, while wood softening due to chemical pretreatment was responsible for a high proportion of whole VE in CTMP and CMP pulps. The VE from birch tend to be destroyed more easily than those from aspen, due to the intervessel pitting arrangement of the former. It is concluded that despite superior bonding potential of TMP fibres due to: - large S₂ exposure in fibres on account of separation at or near the S₁/S₂ boundary, - increased fibrillation, - longer fibrils in fines, and - release and exposure of highly cellulosic G-layers from tension wood in the case of aspen, the lack of conformability of TMP fibres, which translates into low sheet density, negates the promising benefits that otherwise would be obtained. / Forestry, Faculty of / Graduate

No description available.

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 95-96).