No description available.

No description available.

No description available.

A laboratory sheet former using the twin-wire concept has been designed and constructed. It is capable of simulating a wide range of industrial papermaking conditions and can generate a pressure profile very close to that of an industrial machine. The machine has three components: the headbox section, the drainage section and the sheet pick-up section. All three sections are activated and brought up to operating speeds independently, with the headbox flow being diverted back into a reservoir. Once all systems are running at their operating conditions, the headbox flow is diverted to form a jet and steady-state sheet forming occurs for a certain period. The sheet and seven white water streams are collected during operation. / The system is currently able to simulate the papermaking process up to the beginning of the vacuum drainage section; the sheet which it creates has a consistency in the vicinity of 11%. Mass balances of better than 95% have been achieved for both water and fibre. The magnitude of the pressure profiles generated has been measured or calculated. Continuing work will bring the sheet consistency into the 15% to 20% range; once this is attained, an efficient tool to optimize wet-end chemistry will be available.

Paper in a calender nip is subjected to a pressure pulse which reduces its thickness and roughness, thus improving the product quality. Strain recovery after the nip is time-dependent, and some permanent strain remains. The material behaviour is viscoelastic; recovery depends on the pulse magnitude and duration, and does not occur immediately on exiting the nip. An improved description of the viscoelastic response to a calender pulse would allow design of adaptive control systems using feedforward techniques. / Measurements of paper thickness in the nip, immediately after the nip and 24 hours after calendering were made with newsprint sheets running through an experimental calender operating at industrial conditions. The calculated strains were first related to the operating conditions using empirical curve-fitting methods, then using linear viscoelastic models. Empirical results describe the data well, and can be used to design improved control systems. Linear viscoelastic modeling was less successful since the material behaviour is not linear. Photomicrographs of sheet cross-sections were taken, and the observed non-linearities were discussed qualitatively in terms of paper and fibre properties.

The surfaces of well characterised microfibrils from Ventricaria and Micrasterias denticulata (M.d.), wood sections, kraft pulp fibres and paper have been examined with both atomic force microscopy (AFM) and Tapping Mode atomic force microscopy (TM-AFM), under ambient conditions in both air and water. Artifacts and limitations inherent to these techniques in the study of microfibrils, pulp fibres and paper are discussed. AFM images of the surface of the highly crystalline cellulose microfibrils, Ventricaria and M.d., were obtained at molecular resolution under ambient conditions; the molecular images showed periodicities along the microfibril axis that correspond to those of the fibre and glucose unit repeat distances of cellulose, respectively. Images of the section surface of Black Spruce (Picea mariana) wood clearly show features of the underlying cell wall structure. The apparent lamellation, with periodicities from tens or nanometers down to 15 nm, were observed in radial sections of the middle secondary wall (S2). However, transverse sections of the same S2 layer did not show a lamellation independent of the knife direction. AFM images of unbeaten and beaten unbleached kraft pulp fibre surfaces indicate the orientation of the component microfibrils; fibrillar material attached to the surface of the beaten fibres was readily observed. Images from the scale of the fibre web down to the microfibril level in air and water show the dimensional changes of the paper surface and fibres. However, little or no change was seen at the microfibril level. The dimensions of the lamella in wood sections and the size of the microfibrils at both the surface of pulp fibres and the fibrillated material indicate that microfibrils as small as 1.5 nm across are present.

No description available.

The role of surfactants in the neutral sulfite pulping process was studied. The mass transfer of the pulping liquor into the wood as well as the interfacial properties between the liquor and wood, and the changes in the properties due to the surfactants present in the liquor were investigated. / A mixture of anionic and nonionic surfactants, effective in neutral sulfite pulping, was selected during the pulping experiments. Due to the surfactants present in the pulping liquor, the reaction rate of carbohydrate degradation was found to be considerably lower when compared with those of control without surfactants. / The surfactant mixture was observed to accelerate the deresination process during the pulping heat-up period. However, the dissolved extractives diffused out of the wood chips at slower rate when the surfactants were present. This was a result of more micelles being formed by surfactants and dissolved extractives which also are surfactants. / The sodium sulfite concentration profiles in wood after cooking indicated that the surfactant mixture could increase the diffusion process by improving the swelling of the lignin fraction. It was concluded that surfactants could modify the mass transfer mechanism. However, the experiments also indicated that the diffusion of surfactants was rather slow. Compared to the cooks with the surfactants, the reaction rates of the control cooks were found to be higher. As more of the wood components got dissolved, the more porous wood structure was developed during pulping, which explains, why after certain period of time, the sodium sulfite content of the control cook was higher. / In order to obtain quantitative information on the diffusion process, the chemical profiles in wood were simulated using the diffusion model with simultaneous reactions. The simulated chemical distribution curve was adjusted to fit the measured ones by changing the effective diffusivity. / Measurements of a dynamic contact angle, as well as a diameter and volume of a droplet of pulping liquor were carried out to obtain an in-depth understanding of the surfactants behavior in pulping process. The results show that the surfactants did not improve the spreading wetting but improved the absorption. This phenomenon could not be simply explained as a function of capillary pressure, in fact, the liquor containing surfactants must have been able to disperse the air inside the wood structure and therefore to reduce the resistance of air to penetration and diffusion. / Finally, it was found that surfactants improved the pulp yield as a result of a slower reaction rate and faster diffusion rate, as less lignin condensation and carbohydrate degradation was observed.

Adding polyethylene oxide (PEO) at the wet end of a paper machine, can result in an increase in retention of the fine particles. The results obtained with PEO and the cofactors (SNS, MPR, and CAR), are discussed in terms of the association-induced polymer bridging mechanism. / Dynamic Light Scattering (DLS) of polymer solutions revealed that each of the three cofactors are forming complexes with PEO. CAR radically increased the apparent diameter of the PEO chains, and MPR seems to decrease it. In latex suspensions, the SNS was found very efficient in the sequence latex-polymer-cofactor (LPC), increasing the PEO hydrodynamic layer thickness (HLT). / Flocculation experiments with the help of a Photometric Dispersion Analyser (PDA), with PEO only (no cofactor) suggested that the fines are composed of more than one component. SNS was found to make all the fines alike by adsorbing on them. Adding the PEO after SNS gave homoflocculation. As a result, the specific surface of fines, calculated by PEO adsorption was found to be 0.223 m$ sp2$/g. / The association-induced polymer bridging mechanism can happen in three different manners depending if the cofactor and the polymer are adsorbing onto fines. When neither of PEO nor cofactor adsorb onto the collector, the PEO/cofactor association-complexes bridge the particles (van de Ven and Alince (1996)). When the cofactor (e.g. SNS) and the polymer adsorb onto the fines, in the sequence fines-cofactor-polymer (FCP), with a chemical ratio cofactor/PEO of 3/1, adsorption of the PEO chains onto cofactor-coated fines is likely to occur at the beginning followed by the flocculation of the fines. In the sequences fines-polymer-cofactor (FPC), when the polymer adsorbs onto the fines and the cofactor adsorbs (e.g. SNS) or not (e.g. MPR), a reenforcement of the bondstrength was noticed. (Abstract shortened by UMI.)

The objectives of this work were to investigate and improve impregnation of regular (2-8mm thickness range) black spruce wood chips in CMP-AQ pulping. Impregnation and pulping experiments were performed while varying several pulping parameters. Experiments were analyzed in terms of yield, lignin content, percent screen rejects, and strength properties. The goal was to determine optimum pulping conditions that would improve chemical impregnation. Impregnation is a function of percent screen rejects: well impregnated chips have fewer rejects. / Cooking temperature and cooking time were held constant in all experiments at 170$ sp circ$C and 30 minutes, respectively. The liquor pH was adjusted to 7.9 and a liquor-to-wood ratio of 6:1 was used. Presteaming pressure was held constant at 138 kPa and soaking temperature was maintained isothermal at 90$ sp circ$C. / Process variables which can influence the chemical penetration were investigated. These are: wood chip thickness, pre-treatment agents, compression ratio, partial crushing of wood chips, and also pre-steaming and evacuation prior to chemical treatment as a possible method of entrapped air removal. Additional process parameters investigated were the concentration of pulping chemicals and dosage of AQ catalyst. / The advantages provided by the use of thinner wood chips, caustic pretreatment and high compression prex-impregnation were confirmed for improving chemical impregnation. The addition of SAQ catalyst to the CMP pulping process produced pulps of unusually high screened yield for given lignin content. Improvements were also observed in strength properties compared to the control cook where no SAQ was used.