M.Dip.Tech. / Please refer to full text to view abstract

M.Tech. (Fine Art) / Papermaking as an activity area at the Technikon Witwatersrand (TWR) was initially introduced to equip fine art students with the basic knowledge and skills required to produce their own handmade papers, primarily for printmaking techniques. This need was identified through the fact that quality art papers were only available on campus at an expense that aspiring students could not afford. As the Papermaking Research and Development Unit (PRDU) at TWR expanded, students were able to specialise in paper-based research that targets certain issues that impact on and in our immediate environment. One issue that took priority was to investigate the properties, use and production of archival handmade papers to service local artists and students. South Africa does not have an extensive indigenous history or tradition in hand papermaking. It is a relatively new medium with little literature available on the subject. Research has become necessary to understand the properties of this medium in order to explore its various possibilities. This investigation would be viable to the local marketand manufacturers of paper, as well as to those who utilise paper in their creative activities. The bulk of archival papers available on the South African market are currently manufactured overseas and are imported to our country. With importing costs and current exchange rates, this increases their price in the South African market. The research specifically aims at producing a local handmade equivalent to the imported product that will meet, or lower, the cost and increase the availability of the product to the local market. Handmade papers have many advantages to the artists that exceed mould-made papers, all of which are investigated in this research. The specific market had to be identified in order to streamline the research possibilities and improve product potential. This market was identified as papers for selected traditional printmaking techniques, such as silkscreening; intaglio and relief processes. The research thesis, once published, will provide a resource on the subject, with specific application to a local situation. It will enable papermakers to further understand the composition of their product, as well as expand on its use and application.

The main purpose of this study was to determine the effect of contour height on the passage ratio of pulp through screen apertures, and determine which operating variable has the greatest affect on screen performance. In addition, a freeness model was to be developed, in hopes of helping to predict the freeness drop between feed and accepts. The study was conducted at The University of British Columbia (UBC) using a laboratory scale pressure screen. Slot velocity, feed consistency and contour height were the changing variables. Samples were collected from which passage ratio, freeness, fibre length and coarseness were determined. From the studies conducted it was found that slot velocity had the greatest influence on the screen operation. As the slot velocity increased a greater force was applied to the fibre to help push it through the screen aperture. However, this increase in slot velocity decreases the fractionation ability (separation of fibres into different lengths) of the screen. The second most important variable was the contour height. The main function of the contour height is to disrupt the flow of thick stock at the wall of the screen and allow for unhindered movement of fibre to the screen wall. The greater the contour height is, the greater the passage ratio (pulp fibre passing through screen). However, there is a decrease in fractionation. The third most important factor was the feed consistency. At low feed consistencies there is less crowding in the screen. Less crowding leads to more loosely-formed flocs, which are easier for the contour height and the rotor to dissipate and thus leads to unhindered movement. Thicker feed stock has a negative effect on passage A Freeness model was developed that showed that freeness had a power law relationship to passage ratio. The passage ratio was raised to a constant B, which is a function of the contour height and the feed consistency. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

[No abstract available] / Science, Faculty of / Chemistry, Department of / Graduate

Fractional stress relaxation ( S(t)/S(0.04 ) ) was used to compare time-dependent properties of papers, plastics and paper plastic composites ( PPC ). No similar observations appear in the literature. Laboratory handsheets were prepared from commercial western hemlock ( Tsuga heterophylla (Raf.) Sarg. ) unbrightened and brightened groundwoods, as well as unbleached and bleached kraft pulps. Adjustments were made to provide equivalent basis weights ( 150 ± 30 g/m² ) for materials of the study. Handsheets were impregnated with methyl methacrylate ( MMA ) and tetraethylene glycol dimethacrylate ( TEGDMA ) (co)monomer systems. Saturated handsheets and plastic films were cured by ⁶⁰Co gamma irradiation ( 1.4 ± 0.9 Mrad ). It was found that the standard log-time equation, S(t)/S(0.04) = a + b ln t, applied to data collected between 0.04 and 35 min following completion of simulated step-loading ( r ² mostly 0.97 or higher ). A second quantity, energy dissipation ( ΔS), ΔS = 1 - S(35)/S(0.04), was used to compare between treatments. Some plastics gave the highest ΔS values, while groundwoods gave lowest values and kraft papers were intermediate. Pulp delignification level appeared to relate directly to ΔS. Within limits of the study it seems that PPC stress relaxation curves were influenced by both polymer ( matrix ) and fibre ( substrate ) employed. The former contributed in minor ways, while the latter operated in major ways. / Forestry, Faculty of / Graduate

Many countries in the world today have reached the point of full utilization of their forest resources, to satisfy their need for lumber and pulp and paper products. Others have reached the point where their consumption is far in excess of the capacity their domestic forest stands can sustain and they are net importers of these products. Still fewer have developed the practice of recycling these products to any appreciable extent. Canada and United States are approaching full utilization and have only accomplished a recycling rate of approximately 20% of paper and paperboard products. On the other hand conservationists are calling for more efficient utilization of resources, ecologists are calling for less waste and less pollution, while the burden on city garbage collection facilities, 50% of which is paper products, is increasing exponentially. In this thesis the technical processes required to make first quality newsprint from recycled newspaper are shown to be available. The economics of such a plant is examined in detail leading to the judgment that it is economically sound. The conclusion is reached that a 300 ton/ day newsprint mill can be entirely supported by locally generated waste newspaper in a city of three million population or over. Furthermore, it is concluded that if the collection and transportation of waste newspapers is not impeded by governmental regulations or unanticipated competition in the feeder cities, such a plant is still economically feasible after allowing for water barge transportation of the raw materials as far as 200 miles. / Business, Sauder School of / Graduate

The nature of ballistic-type internal paper tear test methods has been reviewed. The kinetic energy of the tester sector is considered to be the prime contributor to paper rupture. In agreement with energy dissipation concepts and the principle of energy conservation, a mathematical model expressing tearing energy was derived based on kinetic energy variations in paper during tearing. It is shown that this mathematical model can be used to calculate the net energy of the tester sector, which is available for tearing paper, and the residual energy. Consequently, the difference between net and residual energy, or tearing energy, is that portion expended in the rupture process. Furthermore, the mathematical model relates tearing energy to velocity, hence can be used to examine the effect of tear rate and time-dependent properties of paper subjected to tearing stress. A method was devised for measuring the time required to tear standard samples. From an oscilloscope trace, the tear distance and time relationship was measured and represented by a quadratic equation. From this equation, sector swing and tearing velocities were calculated for computing various energy factors and their variation at any instant of the tearing process. Results have shown that ballistic-type tear test methods are time-dependent, in that time required to tear paper varies with the sample condition. The higher the number of plies torn simultaneously, the longer was the time required to tear a paper sheet. The energy required to tear paper was also time-dependent, increasing with decreasing tear rate. It was found that the direct relationship between tearing strength and number of plies torn simultaneously does not always hold, but that a constant direct relationship exists between tearing strength and tearing energy. Although the ballistic-type tear test is time-dependent, inherent specimen properties may have a profound effect on results. Test results with an Elmendorf tear tester on five paper grades varying in tearing strength from 14 to 156 g/sheet have confirmed that the energy dissipation concept is adequate. / Forestry, Faculty of / Graduate

A pilot scale machine was designed and constructed to allow study of the continuous microwave drying at 2.45 GHz of paper impregnated with water or with phenol formaldehyde resin. This equipment could deliver microwave power at levels up 2.90 KW. Resin impregnated paper dried by microwaves showed better resin distribution, abrasion resistance, and internal bond strength when compared to similar papers dried in a hot air natural convection oven. No significant differences in tensile strength, stretch, Young's modulus, or bending strength were observed. A quantitative method for the determination of resin distribution was devised. Overall efficiencies for the microwave drying based on power input to the microwave power supply were of the order of 50 to 70%. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

This paper will examine and evaluate via computer simulations different methods, both adaptive and non-adaptive, for the feedback control of the color of dyed paper. The objectives are to maintain the paper color at a desired setpoint despite disturbances such as addition of recycled dyed paper (i.e. broke), and to perform color changes as smoothly as possible. The dynamics of a three dye system are multivariable and nonlinear with a significant transport time delay: thus the incentive for adaptive control. Several predictor-based and Dahlin controllers with gain scheduling are designed, tested in simulation, and compared. Adaptive versions using parameters identified with Recursive Least Squares (RLS) are also tested. For practical applications, the non-adaptive Dahlin algorithm with gain scheduling is shown to offer the best performance, together with relative ease of use. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

No description available.