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Green barrier materials from cellulose nano fibersSharma, Sudhir 07 January 2016 (has links)
Renewable, recyclable, and high performing barrier materials were made from
cellulose nano fibers. Various strategies to enhance performance in dry, wet and humid
conditions were proposed. These methods included thermal treatment to induce
hornification, PAE resin based cross linking, and inclusion of high aspect ratio filler
materials to form composites. Results indicated that hornification alone, even though
effective in enhancing the barrier properties comes at the cost of severe degradation of
mechanical properties. In the second case, where a cross linker was used, lower heating
temperature limited the degradation of mechanical properties. Moreover, the new bonds
included due to cross linking also modified the mechanical properties of the material and
cause significant improvement. In the case of inclusion of filler materials, improvement
of mechanical properties due to reinforcing effect was observed, and additionally the
improvement in barrier properties was observed due to increased tortuosity of the
materials. Furthermore, when the composites were made with cross linker, there was a
significant improvement in barrier and mechanical properties as compared to the barrier
material made from the pure cellulose nano fibers. In all cases the barrier materials were
found to be resistant to degradation by water, as measured by water retention value, and
surface contact angle. The resistance to water in the first case was as a result of severe
hornification of the material. Whereas in the second and third case the cross linking and
concomitant limited hornification played a significant role in water resistance. In
addition to the three methods to improve barrier properties, the use of nano fibers made
from cellulose II was also studied. Different stages of fibrillation of the starting cellulose
pulps were studied and the fibers and films made from them were characterized in detail.
Results from this study indicated that fibers made from cellulose II pulp are much harder
to fibrillate as compared to cellulose I fibers. Moreover, due to fibril aggregation it is
harder to form nano fibers from cellulose II. Even though from the perspective of better
inter and intra fibril bonding cellulose II might be favorable over cellulose I, significant
work in the formation of nano fibers from cellulose II is required before they can be used
for making barrier materials.
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Effectiveness of a home cleaning method of selected pile floor coverings manufactured from man-made fibersPreston, Wilma Vivian Humbert January 2011 (has links)
Digitized by Kansas State University Libraries
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Photomicrographs of unstained and stained cross sections of selected cotton and nylon fabric before and after abrasionWahrenbrock, Mary Ann. January 1966 (has links)
LD2668 .T4 1966 W137 / Master of Science
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Eksperimentele ondersoek na die vervaardiging van enkele stelselkomponente vir 'n hidrofoon in optiese veseltegnologie25 February 2015 (has links)
M.Ing. / A study was done on optical fibre hydrophones. Integrated optic hydrophone components as well as optical fibre components were investigated. An optical fibre coupler was successfully manufactured with an etch process. The coupling ratio can be varied mechanically or by means of refraction index variation. Experimental procedures and results will be shown. Bending losses excited in an optical fibre coil were investigated as a function of different coil diameters. The results were extrapolated to determine the amount of losses arising in a hydrophone coil.
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Impact of different materials on cracking of corrugated fibrecement sheetsMtsweni, Ntombikayise Beauty 07 July 2014 (has links)
The replacement of asbestos fibres with cellulose fibres in producing
corrugated fibre reinforced cement sheets by the Hatschek process resulted
in edge cracking for stacked sheets. This was due to the hydrophilic nature of
cellulose, which increases its tendency for exchanging water with the
surroundings. The drying process of corrugated sheets, in a stack, resulted in
shrinkage hence edge cracking along the sheet. To reduce the magnitude of
drying shrinkage and edge cracking potential, several mitigation strategies
were proposed including the surface treatment of cellulose fibres,
incorporation of wollastonite microfibres, addition of admixtures and
superplasticizers, kaolin inclusion as partial replacement of cement and
different exposure conditions. A fundamental understanding in mechanisms
behind volume changes and how cracks form was crucial for optimization of
the mitigation strategies.
This thesis initially used a review approach to understand the mechanisms
involved in different types of shrinkage and the role of different mitigation
techniques. The ultimate goal was to achieve lower drying shrinkage and
cracking risks in corrugated sheets along with reducing its economic impact.
As a result, surface treatment of cellulose fibres, based on transforming the
hydrophilic nature of cellulose to hydrophobic state, was investigated.
Furthermore, inclusion of wollastonite/ kaolin as partial replacement of
cement, were evaluated. Also, the potential of adding admixtures/
superplasticizers was explored. Finally, investigation on development of edge
cracks in stacked corrugated fibrecement sheets was conducted under
different exposure conditions.
The results and findings of this research showed no significant improvement
in permeability with cellulose surface treatment. Wollastonite microfibres
promoted pore discontinuity hence significant reduction in permeability thus lower drying shrinkage. However, the resultant sheets were brittle. By
reducing water content with addition of superplasticizers, density was
enhanced thus reducing volume change from drying and wetting. Kaolin
acted as internal restraint for shrinkage, refining the microstructure at the
interfacial transition zone thus increasing density and its pozzolanic reaction
enhanced mechanical properties. The inclusion of kaolin in the fibrecement
mix in conjunction with controlling exposure conditions managed to eliminate
edge cracking.
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The quantitative analysis of components of fibre-reinforced cement boards.Kuming, Andrew Paul January 1993 (has links)
A Research Report submitted to the Faculty of Architecture, University of the
Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of
Master of Science in Building. / Environmental and health considerations have led to the substitution of cellulosic
fibres for asbestos fibres in many cement-based products. Inevitably, the
substitution has required modifications to the manufacturing process.
Certain production techniques associated with the switch to cellulosic fibres and
other additives needed elucidation. It is possible that to ensure the required
concentration of certalr additives in the final product, an excess is being used in
the process because of uncertainties about the quantitative balance of the process.
My intention was to examine the potential tole for Fourier Transform Infrared (FTtR)
Spectroscopy in the investigation of the materials constituting fibre-reinforced
cement boards.
I was able to show that qualitative and quantitative determination of certain of the
components in the final product are possible with adequate precision and
reproducibility to be of value to the manufacturer, I also showed that care taken
in the preparation of standard and analytical samples was essential for the success
of such analyses. / Andrew Chakane 2018
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The quantitative analysis of components of fibre-reinforced cement boards.Kuming, Andrew Paul January 1993 (has links)
A Research Report submitted to the Faculty of Architecture, University of the
Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of
Master of Science in Building. / Environmental and health considerations have led to the substitution of cellulosic
fibres for asbestos fibres in many cement-based products. Inevitably, the
substitution has required modifications to the manufacturing process.
Certain production techniques associated with the switch to cellulosic fibres and
other additives needed elucidation. It is possible that to ensure the required
concentration of certaln additives in the final product, an excess is being used in
the process because of uncertainties about the quantitative balance of the process. / Andrew Chakane 2019
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Optical branching and coupling devices.January 1988 (has links)
by Hung Wing-yiu. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves 98-103.
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Nano-grinding for fabrication of microlenses on optical fibers endfacesGharbia, Yousef Ahmed, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2003 (has links)
This work presents mechanical nano-grinding as an alternative technique for the fabrication of optical fibers endface microlenses. It also presents a novel surface-roughness improvement technique called Loose Abrasive Blasting (LAB). Traditionally, the majority of such microlenses are made using either chemical etching or heating and pulling methods. Despite the success of these methods, they suffer some common drawbacks such as the lack of controllability on the produced lens profile. Consequently the possible variations of the lens profiles that can be made by these methods are also limited. The difficulty to center the lens on the fiber core is another problem associated with heating and pulling method. The exposure to hazardous chemical such as hydrofluoric acid is yet another problem associated with chemical etching. Nano-grinding technique described in this thesis should provide a much better alternative to the traditional optical fabrication techniques. Nano-grinding experiments were conducted on a nano-grinding machine (NGM) specially built for this purpose. The machine incorporates state-of-the-art air-bearing spindles, piezo electric actuators, and capacitive displacement sensors with accuracy down to 2 nm. Such precise motion provided by this system is the key for the success of this technique. With such system, it was possible to produce a multitude variety of lens profiles with high profile accuracy and with surfaces of optical quality without the need for exposure to any kind of hazardous chemicals. In achieving this objective, the research was conducted on many frontiers. First, the possibility of grinding optical fibers without inducing surface and subsurface damages was investigated. Micro-indentation, nano-indentation, and nano-scratch tests were conducted to determine the critical depth of cut that can be achieved before the occurrence of surface and subsurface cracks. Nano-scratch test in particular provided a clear insight to the cracking and the chipping mechanisms that might unfold if the critical depth of cut was exceeded in an actual grinding situation. The knowledge gained from this exercise laid the ground base for the design of the NGM. Using the NGM, further experiments were carried out to determine the optimal grinding parameters for an efficient and successful grinding process. Parameters investigated include the grit size, the cutting speed, and the in-feed rates. The optimum parameters have to ensure the best endface surface quality and the same time maintain a high throughput. This study shows that based on these optimal parameters, it should be possible to produce endface microlenses of optical surface quality free surface and/or subsurface damages in less than 30 seconds with surface roughness (Ra) less than 3 nm. A novel post-grinding surface improvement techniques was also developed. The technique called loose abrasive blasting (LAB) can be used for polishing at and non-flat surfaces. Experiments were conducted on a loose abrasive blasting machine built specially for this purpose. The performance of this technique was compared with other techniques such as slurry polishing and chemical etching used for polishing of brittle materials. The results showed that while chemical etching was found unsuitable for polishing of at optical fiber endfaces, LAB outperformed slurry polishing by significant margin. After the optimal grinding conditions were established, the NGM was used for grinding of different kinds of optical fiber microlens profiles. Among the endface profiles produced were conical lenses, tapered lenses, D-shaped lenses and others. It has also been shown, in case of conical lenses for instance, that there is almost unlimited number of profiles that can be produced by simply changing the contact angle between the fiber endface and the grinding film. The effect of surface roughness on light coupling efficiency between a fiber endface and a laser diode was also investigated. Cleaved fiber endfaces as well as ground endfaces with variant degrees of surface roughness were used in this experiment. The results showed that surface roughness has significant effect on light coupling efficiency. The effect of lens eccentricity on light coupling was also investigated.
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Mechanics of Nb-Ti superconducting compositesGuo, Zhiqiang 23 June 1994 (has links)
Mechanical behavior of Nb-Ti superconducting composites with copper matrices have
been studied experimentally and theoretically.
Experimental work includes extensive measurements of Cu/Nb-Ti composite system.
Techniques for fine fiber testing and composite wire measurement have been developed.
Experimental parameters examined in this research include geometry, hardness, Young's
modulus, Poisson's ratio, yield strength and ultimate strength. Three theoretical models
have been developed to study the mechanics of the Cu/Nb-Ti composite system. The
influence of several design parameters on the mechanics of the Nb-Ti composites was
studied and provides some insight on superconducting composite design for improvements
in processing and performance.
The mechanical behavior of the Cu/Nb-Ti composite system are found to be functions
of geometry, composition and processing.
Geometry of Nb-Ti superconducting composites is different from most engineering
composites and there are two factors affecting sample geometry: the variability of fiber
geometry and the placement of fibers within the composite. The strength distribution of
Nb-Ti fibers is closely related to the distribution of fiber geometry and the composite
strength increases as the scatter of fiber strength decreases.
Heat treatment reduces the hardness of the bulk copper dramatically. The first heat
treatment increases the strength and hardness of the Nb-Ti fibers, further heat treatments
reduce the strength and hardness while increasing Young's modulus of the fibers. As the
extent of cold work increases, the strength of Nb-Ti fibers and that of the composite wires
increases. Cold work effects on the Young's modulus of the composites and the Nb-Ti
fibers are not significant.
For a constant global Cu/SC ratio, the lower the local Cu/SC ratio, the lower the micro-in-plane stresses. From this point of view, the fibers should be packed as close as possible
to one another. For a constant local Cu/SC ratio, when the inner radius of the Nb-Ti
assembly increases (the fibers are packed further from center), the macro-in-plane stresses
increase. From this point of view, the fibers should be packed as close to the center of the
wire as possible.
For a constant geometry, the higher the difference between E[subscript f] and E[subscript m], the lower the in-plane
stresses, and the higher the difference of the Poisson's ratio between the
components, the higher the in-plane stresses. / Graduation date: 1995
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