No description available.

No description available.

No description available.

Polymer composites are fast becoming a material in the manufacturing of automotive interior and exterior parts such as facias and dashboard components. Production of rigid structural foams are ideal because they reduce the overall weight as well as reduce the amount of material used to manufacture the part. Polymer-clay nanocomposites are a classification of materials containing a blend of polymer and a small weight percentage of nanoclay. These materials are currently of interest to automotive part manufacturers because they are known to deliver improved mechanical properties and increase foamability of a polymer. The current study investigates the changes in material properties and the foamability of a thermoplastic polyolefin (TPO)-clay nanocomposite as the degree of intercalation was varied. The TPO-clay nanocomposite was produced by melt blending TPO, nanoclay and maleic anhydride grafted polypropylene (MAHgPP) in a co-rotating twin screw extruder. The material was subjected to a multi-pass process to vary the degree of intercalation. Degree of intercalation was tracked by rheology, XRD and TEM micrographs. Part density, cell density and flexural modulus measurements were performed on foamed and non-foamed injection molded bars to observe changes in the foamability of the material. Material was also processed without clay and analyzed in the same manner. Through TEM and XRD analysis it was found that the degree of intercalation and delamination was varied with increasing number of passes. Rheological measurements showed that the TPO-clay nanocomposite underwent (beta)-scission and intercalation simultaneously. The changes in intercalation had a positive effect on the foamability of the TPO-clay nanocomposite. As well, the TPO-clay nanocomposite experienced an increase in flexural properties for both unfoamed and foamed parts compared to the TPO-PPgMAH blend; TPO-clay nanocomposite experienced a 44% and 23% increase in the flexural modulus for unfoamed and foamed parts respectively. Data also showed that there was a limit to the number of times the TPO-clay nanocomposite can be recycled before the foamability of the material begins to decrease, which was attributed to material degradation. / Thesis / Master of Applied Science (MASc)

No description available.

Thesis (Ph.D.)-- University of Wisconsin--Madison, 2007. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.)-- University of Wisconsin--Madison, 2007. / Includes bibliographical references.

Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Cavitation is the formation of vapor bubbles in a liquid that is a consequence of tensions acting on the liquid. It is of great interest to lots of different scientific fields such as fluid mechanics, acoustics, hydraulic engineering and biology. Although widely studied in macroscale and microscale confined liquids, heterogeneous cavitation at the nanoscale has only been experimentally observed recently in 2-D nanofluidic channels during an evaporation process, where vapor bubbles form and expand inside the nanochannels instead of menisci receding along the channels. Such evaporation-induced cavitation shows a strong correlation with the nanochannel cross-section non-uniformity and exhibited lots of interesting phenomena, including fast evaporation rate and self-controlled bubble dynamics. In this work, we further investigated this new cavitation phenomenon using a series of specially designed 2-D multi-section nanochannels. Each of these channels includes two or three sections of nanochannel with heights of 25 and/or 35 nm and the same width of 3 μm. A modified sacrificial layer etching method was developed to fabricate these nanochannel devices. Water evaporation processes in these channels were recorded using a high-speed camera mounted on an inverted microscope. We observed that cavitation only occurred in multi-section nanochannels with a “Low to High” channel design. In such nanochannels, when menisci receded to the “Low to High” step, bubbles occurred in the higher channel section and started expansion until they occupied the whole section. We explored the origin of these cavitation phenomena and discovered that that initial bubbles were formed during a snap-off process, where meniscus curvature difference induced reverse liquid flows cause air trapping right at the step. The following bubble expansion is a result of evaporation-induced negative pressure (up to -58 bars) as water inside the nanochannels is in a metastable state. We also analyzed water evaporation rates (bubble growth rates) in these nanochannels in the presence of cavitation. While most evaporation rates can be explained by classic vapor diffusion theories or the kinetic limit of evaporation, water evaporation rates in nanochannels with a Low-High-Low design in the presence of cavitation were as high as 630 μm/s, which is even much higher than the kinetic limit of evaporation and cannot be explained by any current theories. This study further expands our understanding of cavitation and provides new insights and explanations for phase-change phenomena at the nanoscale, including cavitation in plants and quick drying process in nanoporous media. The discovered ultra-high evaporation rates in the Low-High-Low nanochannels also offer a new solution to address thermal management needs for next generation electronic devices. / 2031-01-01

Promoter effects on SBA-15 supported iron Fischer-Tropsch catalysts were investigated for their potential to improve high temperature catalyst performance. FTS catalysts promoted by manganese (0.15%-1.4%), copper (0.15%-1%), and potassium (0.5%-3%), with all percentages stated on the basis of mass percentage of final catalysts, were prepared and tested at 430°C and ambient pressure in a fixed bed reactor. Manganese showed the ability to promote the FT reaction, increasing both the CO conversion and the average chain length of hydrocarbon products. Compared to the unpromoted catalyst composed only of iron supported on SBA-15, 1.4%Mn (mass) promotion of 15% (mass) iron on SBA-15 improved CO conversion from 29% to 32%, increased alpha from 0.21 to 0.34, decreased carbon dioxide selectivity from 76% to 50%, increased C2-C4 selectivity from 9.6% to 30% and increased C5+ selectivity from 0.21% to 2.2%. Copper promotion gave increased conversion, but did not significantly affect alpha or carbon dioxide selectivity. Potassium promotion in the range of 0.5% to 3% by mass, on the other hand, had a negative effect on CO conversion at all concentrations tested.

Understanding the evolution of water demand is of paramount importance for countries that want to implement the correct water demand management strategies that aim at increasing water use efficiency. This paper analyses household water demand in the capital city of the Mpumalanga Province of South Africa, in order to develop a better understanding of residential water demand in developing country contexts. Using survey data from 526 households in the Mbombela Municipality of Mpumalanga, South Africa, we estimate the price and income elasticities of household water demand, and investigate the factors that drive water demand of households that are located in heterogenous income groups. Households in the study areas have the unique characteristic seen in developing countries of having access to several sources of water, such as tap, ground and rainwater, implying the possibility of substitution. We run different estimation strategies that range from OLS, 2SLS and instrumental variable approaches to identify the factors that influence urban water demand. The findings reflect that price and income elasticities vary across different household groups, with price elasticities ranging from -0.140 to -0.879 and income elasticities ranging from 0.172 to 0.628. Other statistically significant variables which drive household water consumption are household size, education level, use of water saving technologies, and the use of rainwater tanks and systems. A crucial finding in this study was that water saving technologies were revealed to reduce water consumption levels by between 28.3% to 43.4%, and we hence provide specific policy recommendations based upon this finding. Overall, the results from this study can contribute substantially towards the development of appropriate and sustainable water policy making in South Africa.