UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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Subject: search.filters.subject.polyethylene

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    An Assessment of the Use of Flame Retardant Plastics for Museum Applications
    (2007-12-18) Leikach, Danielle Caryn; Mowrer, Frederick; Brostoff, Lynn; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Halogenated flame retardant plastic sheeting may help to reduce flame spread in museums; however, the plastics contain chemicals that may be harmful to museum objects in situ, particularly metals. This study assesses historical and contemporary problems and benefits associated with flame retardant plastics with respect to museum applications. This issue was addressed by pairing statistical data on museum fires with standard and novel methods for assessing corrosivity, while also creating a format for future assessments of fire-safety related practices as they are applied in museum settings. Flame retardant plastics were found to cause small rates of corrosion in copper, approximately 1.2 milli-inches per year (mpy), compared to pure polyethylene which corrodes at approximately 0.83 mpy. Conventional testing methods show that flame retardant plastics can be considered safe for limited museum use and that they delay ignition from small heat sources, but they must be assessed for each individual scenario.
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    PHYSICS BASED MODELING AND CONTROL OF REACTIVE EXTRUSION
    (2004-04-30) Elkouss, Paul; Bigio, David I; Mechanical Engineering
    Kinematic modeling has been shown to be important for the understanding and control of co-rotating twin screw extruders. The residence time distribution (RTD) is often used to characterize the steady-state behavior of an extrusion process. Due to the complex rheological behavior of polymer flow in the extruder, few have felt that the RTD would be independent of changes in operating conditions for the same screw configuration. To investigate, we are asserting that resident distributions could be independent of operating conditions for certain types of polymers. Four different polymers, two polyethylenes and two polypropylenes, were processed on the same 30mm Werner and Pfleiderer co-rotating twin-screw extruder (CoTSE) equipped with reflectance optical probes to compare their RTD's. Additionally, each material was tested to determine its complex viscosity, to better understand the phenomena involved. Using physically motivated models to control reactive extrusion processes is attractive because of the flexibility and robustness it could provide. This thesis uses residence distribution analyses to characterize the material flow through a co-rotating twin-screw extruder. Furthermore, we examine the applicability of residence distributions as the basis for kinematic modeling of the extrusion process. This demonstration of using a steady-state model - the residence distribution - as a basis for kinematic behavior is unique. The signals have been deconvoluted to kinematically characterize the flow in the different regions of the extruder, such as the melting, mixing and metering zones. Studies of step changes have shown that the steady state value of extrudate viscosity is dependent on the peroxide concentration, volume mixing, and on the residence time from the specific throughput. This data has also provided plant models of the peroxide initiated degradation reaction using system identification techniques. Although a specific example of vis-breaking of polypropylene is studied, the techniques are general. A proportional and integral controller (PI) with a Smith predictor was used to track set point changes and regulate the viscosity.
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    Ethylene Polymerization Using a Zirconium Amidinate Supported Catalyst
    (2004-05-07) Young, Andrea Elise; Sita, Lawrence; Chemistry
    A series of W. R. Grace Davison IOLA(TM), methylaluminoxane-silica (MAO/Silica) and MAO/IOLA support materials were used to activate and immobilize a zirconium amidinate single site catalyst of the formula Cp*ZrMe2[tBuNC(Me)NCEt]. Ethylene homo-polymerizations and co-polymerizations with 1-hexene were conducted in heptane and compared. The catalysts activity was investigated under varying condition such as pre-catalyst loading, pressure, temperature, co-monomer incorporation and additives. The catalyst supported on the MAO/IOLA B support material proved to be more active than the IOLA and m-IOLA support activators, and the MAO/Silica and MAO/IOLA A support materials. A difference in activity of as much as 1015 gPE/gcat.h-1 was noted. The catalyst sensitivity to varying ethylene polymerization conditions such as temperature and pressure were investigated for the MAO/IOLA B supported catalyst. Catalyst activities of more than 2100 gPE/gcat.h-1 were achieved. Homo-polymer and co-polymer samples were characterized and compared with respect to their melting temperature, molecular weights and polydispersities.