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1
Gornall, Tina. "Catalytic degradation of waste polymers." Thesis, University of Central Lancashire, 2011. http://clok.uclan.ac.uk/4886/.
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Plastics have become an integral part of our lives. However, the disposal of plastic waste poses an enormous problem to society. An ideal solution would be to break down a polymer into its monomer, which could then be used as the building-blocks to recreate the polymer. Unfortunately, the majority of plastics do not degrade readily into their monomer units. Thermal degradation of polymers usually follows a radical mechanism (which is of high energy and requires high temperatures) and produces a large proportion of straight chain alkanes, which have low relative octane number (RON) and so cannot be used in internal combustion engines. However, a suitable catalyst can help to branch straight alkane chains and so give high RON fuels that can be blended into commercial fuels. An extensive thermogravimetric study of polymer-catalyst mixtures was undertaken and produced dramatic reductions in the onset temperature of degradation and significant changes in the activation energy, suggesting a change to a desirable Brønsted- or Lewis-acid catalysed degradation mechanism in many cases. For example, GC-MS analysis of low-density polyethylene (LDPE) degraded with Fulcat 435 clay showed the polymer forming a large number of C6-C7 single-branched alkanes of intermediate RON value. In comparison, degradation of LDPE in the presence of a ZSM-5 zeolite (280z) resulted in the production of a large aromatic content (41% of Total Mass at 450ºC) together with branched C6-C8 hydrocarbons (40%). This formation of a large proportion of high RON components from polyethylene and other polymers could move us one step closer to tackling the enormous problem of plastic waste disposal that the world faces today.
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Holland, Barry John. "The thermal degradation of commercial polymers." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369177.
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Agarwal, Reena. "Degradation of polymers in chemical mechanical polishing." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/11828.
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Argyropoulos, Dimitris S. "Synthesis and degradation of model network polymers." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72032.
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Theoretical expressions essentially based on the Flory-Stockmayer statistics of gelation were experimentally examined for their applicability beyond the gel point. By studying the crosslinking process of a polyester network formed from 1,3,5-benzenetriacetic acid and 1,10-decamethylene glycol beyond the gel point, the validity of the expressions was quantitatively confirmed, and their limitations were delineated.On stepwise degradation of a similar network, increasingly large soluble fractions were obtained at each step, and their weight-average molecular weights increased as the degelation point was approached. The molecular weights and distributions of these fractions were in close quantitative agreement with theory, i.e., they represented a near-mirror image of the molecular weights of sol fractions obtained on crosslinking beyond the gel point. Similar results were obtained by degrading a network prepared by the random crosslinking of monodisperse primary chains of polystyrene.
Experimental support was thus obtained for treating random network degradation by reversing the statistics of the Flory-Stockmayer theory of gelation.
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Diamond, R. J. "Labelled polymers : Synthesis, analysis and degradation studies." Thesis, University of Surrey, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383958.
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Miller, Charles Andrew. "MODELING OF THERMAL DEGRADATION OF PHYSICALLY HETEROGENEOUS POLYMERIC SOLIDS." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291219.
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Jenkins, Andrew Tobias Aveling. "Electrochemical studies of coating degradation." Thesis, University of Newcastle Upon Tyne, 1995. http://hdl.handle.net/10443/967.
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The polymer coatings considered in this thesis work principally by creating a barrier, in order to prevent a corroding medium such as water and / or oxygen from contacting the surface of the underlying metal. Such coatings are subject to attack from the environment in which they are placed. This attack can lead to failure of the coating and corrosion of the underlying metal. In this thesis, three principle means of coating degradation, leading to subsequent corrosion of the substrate have been considered: Mechanical damage of the coating, the effect of ultra-violet light weathering and filiform corrosion. Electrochemical measurements have been made in order to attempt to quantify both the degree of coating breakdown and the extent of corrosion of the substrate. The principle method for measuring coating breakdown and substrate corrosion utilised in the work for this thesis was Electrochemical Impedance Spectroscopy (EIS). EIS, in principle, allows both changes in coating porosity resulting from coating breakdown, and the extent of corrosion of the substrate to be measured. The extent of delamination under polymer coatings on defects of different sizes and on different substrates has been measured. The effect of ultra-violet light weathering of polymer coatings was measured using EIS and correlated with measurements of light reflection of the coating. Filiform corrosion was induced on two different substrates, coated with various coatings. The effect of substrate and coating on filiform corrosion growth rate and mechanism has been considered.
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Li, Tong. "Influence of stress on photo-degradation of polymers." Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283648.
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Lambert, Scott. "Environmental risk of polymers and their degradation products." Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/4194/.
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Polymer-based materials are found everywhere in the environment, but their impacts are yet to be fully understood. The degradation of different polymer types has been extensively investigated under specific laboratory conditions. However, only limited data are available on their degradation under environmentally relevant conditions, where a number of processes are assessed at once. This thesis therefore describes a series of outdoor aquatic microcosm studies and laboratory experiments to investigate the degradation of a case study polymer (natural rubber latex), to characterise the formation of degradation products, and to assess the effects these may have on aquatic organisms. The outdoor microcosm studies showed that the exclusion of light and material thickness had a greater influence on degradation rate than media pH and sample movement. Analysis of the degradation solutions demonstrated that when the latex polymer degraded, there was an increase in the formation of microscopic latex particles; zinc (used to speed up the rate of curing processes) migrated from the latex polymer into the test solutions; and a mixture of dissolved substances that are potentially oxidised latex oligomers with additives residues were formed. Further analyses also showed that the atmosphere is a receiving environmental compartment for polymer degradates though the identification of a range of volatile substances produced during the degradation process. Laboratory experiments were then conducted to investigate the direct toxicity of the formed degradate mixtures, using two freshwater organisms with different life cycle traits, the water column crustacean Daphnia magna and the sediment-dwelling larvae of Chironomus riparius. The results suggest that, to the organisms tested, there is limited environmental risk associated with latex degradation products. Overall, environments receiving polymer debris are potentially exposed to a mixture of compounds that include the parent polymer, fragmented particles, leached additives, and subsequent degradation products; however at environmentally relevant concentrations this latex degradates pose little risk.
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Cui, Futong. "Biomimetic studies related to lignin degradation." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30993.
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Lignin is the second most abundant biopolymer on Earth. It is an amorphous, cross-linked, aromatic polymer composed of phenylpropanoid units. There has been an ever growing interest in the biodegradation of this complex polymer for the last 30 years. White-rot fungi have been found to be an important lignin degraders in the natural environment. With the discovery of two groups of hemoprotein enzymes, lignin peroxidases and manganese(II)-dependent peroxidases, from the lignin degrading culture of a white-rot fungus, Phanerochaete chrysosporium, rapid progress has been made in understanding the mechanism of lignin biodegradation.
Synthetic metaUoporphyrins, the iron(III) and manganese(III) complexes of meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrin (TDCSPPFeCl and TDCSPPMnCl) and meso-tetra(2,6-dichloro-3-sulfonatophenyl)-B-octachloroporphyrin (Cl₁₆TSPPFeCl and Cl₁₆TSPPMnCl), were used in this study to mimic the functions of the "lignin degrading" enzymes. Factors affecting the catalytic activities of these biomimetic catalysts were studied. TDCSPPFeCl could closely mimic lignin peroxidase in the degradation of a number of lignin model compounds, including veratryl alcohol, B-l, B-O-4, B-5, 5-5' biphenyl, phenylpropane, and phenylpropene model compounds. The reactions catalyzed by TDCSPPFeCl include benzyl alcohol oxidation, C[formula omitted],-C[formula omitted] side chain cleavage, demethoxylation, aromatic ring cleavage, benzylic methylene hydroxylation, and C[formula omitted]-C[formula omitted] double bond hydroxylation (glycol formation). Novel solvent incorporated compounds isolated from the oxidation of veratryl alcohol give insights about the site of attack of substrate cation radical by solvent molecules. The isolation of a solvent incorporated product from the oxidation of a phenylpropene model compound suggests a cation radical mechanism for the oxidation of this lignin substructure. The formation of
a number of direct aromatic ring cleavage products during the oxidation of some model compounds supports the previously proposed mechanism of aromatic ring cleavage. TDCSPPFeCl was also able to catalyze the oxidation of environmental pollutants such as pyrene and 2,4,6-trichlorophenol.
Veratryl alcohol and manganese(II)-complexes have been suggested to function as redox mediators for lignin biodegradation. Evidence has been provided to demonstrate their mediating power during electrochemical and biomimetic degradation of lignin model compounds.
In addition to the mechanistic information obtained, the successful oxidation of the model compounds suggests that metalloporphyrins can be important catalysts for the pulp and paper industry and for pollution control.Science, Faculty of
Chemistry, Department of
Graduate
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Formosa, Joseph S. "Thermal degradation of polymer blends containing the poly (hydroxy, ether of bisphenol-A) /." Online version of thesis, 1987. http://hdl.handle.net/1850/10289.
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Pelillo, Enrico. "Scratch deformations of polymers." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286438.
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Gleadall, Andrew Colin. "Modelling degradation of biodegradable polymers and their mechanical properties." Thesis, University of Leicester, 2015. http://hdl.handle.net/2381/32212.
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Bioresorbable polymers are used for a wide range of medical applications inside the human body including fixation screws and plates for broken bones, sutures and scaffolds for tissue regeneration. Over a period of months or years, these devices degrade by hydrolysis of the ester bonds; they become fully absorbed into the body, thus removing the need for repeat surgery. The degradation pathway of these devices, including the loss of mechanical properties, is of great importance. However, the complexity of the degradation process, and the number of factors involved, means that degradation trends are not fully understood. Also, for many of the commonly used biodegradable polymers, no theoretical understanding exists for changes to mechanical properties during degradation. The devices are therefore currently designed to be over-supportive, which may inhibit the healing process due to the stress shielding effect. A general mathematical framework has been developed through several PhD projects at Leicester to model the degradation of bioresorbable polymers. This PhD thesis consists of three parts. The first part reviews the existing understanding of bioresorbable polymer degradation. In the second part, the previous models are simplified and improved. These new models are then used to reveal an in-depth understanding of the underlying mechanisms of the degradation process. The third part of this thesis focuses on understanding the change in Young’s modulus of degrading polymers. In order to do so, a novel atomistic finite element method is developed, which can simulate the mechanical response of a representative unit of a biodegradable polymer. The method is used to study the mechanical behaviour of polymer chains once chain scissions are introduced. The study leads to a concept for effective cavities for polymer chain scission, called the Effective Cavity Theory, which can be used to predict the change in Young’s modulus of a degrading polymer.
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Chen, Xinpu. "Modelling degradation of medical implants made of biodegradable polymers." Thesis, University of Leicester, 2017. http://hdl.handle.net/2381/40023.
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Bioresorbable polymer is widely used inside the human body as resorbable medical devices such as fixation screws, plates, sutures, and tissue engineering scaffolds. The most important feature for such devices is that they ‘disappear’ after serving the temporary function that is surgically required. The current design for these devices is still based on trial and error. The degrading process is complex and many factors were involved. This makes the design optimisation very hard. The degradation rate for such devices varies from months to years, making the experimental work expensive and time-consuming. Mathematical modelling could be used in the early stages of designing, and would give an indication of certain degradation behaviours without doing experiments first. The existing mathematical models developed by the Leicester group were used to successfully capture the trend of average molecular weight, degree of crystallisation, and Young’s modulus. However, the previous models still have many gaps to fully capture the underlying chemistry and physics of polymer degradation. Some of the models are also over-complicated to be used in practical designs. This thesis presents several new developments and simplifications to the previous models. These include the separation of long and short polymer chains in the rate equation for polymer chain scission, adding the effect of water diffusion and providing a list of analytical solutions for simple but commonly used situations. A complete set of governing equations are provided by integrating the new rate equation with previously developed equations for crystallization, oligomer diffusion and short chain diffusion. A major issue in the development of biodegradable devices is that it is extremely time consuming and expensive to obtain experimental data for degradation rate because the degradation can take up to several years. The thesis presents a demonstration on how the mathematical model, together with the finite element method, can be used to project degradation rate from one device, for which experimental data are available, to another which is under design. Finally the effective cavity theory for change in Young's modulus and degradation detection using mode analysis, previously developed by the Leicester group, are simplified to make them much more straightforward to use by end users.
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Thomya, Panthida. "STRUCTURAL CHARACTERIZATION OF COMPLEX POLYMER SYSTEMS BY DEGRADATION / MASS SPECTROMETRY." Akron, OH : University of Akron, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1163969934.
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Thesis (Ph. D.)--University of Akron, Dept. of Chemistry, 2006."December, 2006." Title from electronic dissertation title page (viewed 04/24/2008). Advisor, Chrys Wesdemiotis; Committee members, Matthew P. Espe, Jun Hu, Wiley J. Youngs, Frank W. Harris; Department Chair, Kim C. Calvo; Dean of the College, Ronald F. Levant; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
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Straub, Craig A. "Microbial degradation of synthetic polymers as influenced by disposal environment." Virtual Press, 1990. http://liblink.bsu.edu/uhtbin/catkey/722439.
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Biodegradable plastics are currently being developed as a short-term solution to the problem of conventional plastics which persist in the soil. Little is known regarding the decomposition of the new plastics including products formed and microbial populations responsible.Polyethylene-based plastic films interspersed with 0, 5, 10 or 15% (w/w) starch were incubated for up to 112 days in laboratory and filed soils, a forced-air compost pile, and a simulated sanitary landfill. Biologically-mediated polymer decomposition was monitored via measurement of microbial respiration, release of soluble organic carbon ()C) and anions, total microbial counts, and scanning electron microscopic (SEM) observations. Microbial respiration was greatest in all treatments within the first 14 days coincided with greatest soluble OC and acid production.The 15% starch samples decomposed most rapidly in the field soils (2.57. decrease in mass over 11 days) due to the influence of sunlight and temperature extremes. Decomposition was lowest (0.1%) in the anaerobic landfill.Actinomycetes and bacteria predominated in most environments while fungi growth was inhibited in the landfill and compost. The SEM observations revealed a preferential attack of starch granules by microbes followed by a more gradual weathering of polyethylene sheets.Department of Natural Resources
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Ozdemir, Tonguc. "Effect Of Ionizing Radiation On Different Polymers And Possible Use Of Polymers In Radioactive (nuclear) Waste Management." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607296/index.pdf.
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In this study three polymers, namely poly(carbonate urethane), poly(bisphenol-a-epichlorohydrin) and poly(methyl methacrylate), were selected and change of properties with gamma treatment were studied. Two different dose rates were used for irradiations and the properties of the
irradiated polymers exposed to same total absorbed dose were compared. In addition, long irradiations of up to about six months with high dose rate were done in order to understand the radiation stability of the polymers,
which may be possible candidates for embedding media for low and intermediate level radioactive (nuclear) waste before their final disposal.
Tensile, DSC, DMA, TGA, FTIR-ATR, FTIR tests were completed to understand the degradation of the polymers as a function of dose rate and total absorbed dose.
The DSC and FTIR results showed that there was not much structural chemical changes in polymer chains with irradiation. However, the changes in mechanical properties were recorded.
It was concluded that poly(carbonate urethane) and poly(bisphenol-aepichlorohydrin) can possibly be used in conditioning of radioactive waste, as they are radiation stable polymers. However, due to the moderate resistance of poly(methyl methacrylate) to ionizing radiation, it can be used
for low level radioactive waste conditioning.
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Lee, David W. "Thermal degradation of polymer blends containing poly(vinyl chloride) /." Online version of thesis, 1987. http://hdl.handle.net/1850/10287.
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Ramacieri, Patricia. "Microstructure and kinetics of thermal degradation of alkene copolymers of vinyl chloride." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72819.
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Oborná, Jana. "Studium degradace biokompatibilních kopolymerů." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2011. http://www.nusl.cz/ntk/nusl-216802.
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This diploma thesis is focused on biocompatible polymers degradation study. Copolymers were studied based on poly(lactic-co-glycolic) acid and poly(ethylene glycol) PLGA-PEG-PLGA and further these copolymers modified with itaconic acid ITA-PLGA-PEG-PLGA-ITA. This paper investigated the influence of pH phosphate solution on the degradation of polymers. Degradation of polymers occurred at 37 °C in phosphate solution with pH 4.2, 7.4 and 9.2. High performance liquid chromatography with UV-VIS detection of diode-array type was used for quantitative determination of lactic acid and glycolic acid as the final degradation products. For qualitative identification of additional degradation products were used tandem connection liquid chromatography and mass spectrometry. Gel permeation chromatography with refractive index detector was used to determine the molecular weight decrease polymer chain after the degradation.
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Cameron, R. M. "Oxidation and degradation of polymers in near and supercritical water." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597242.
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Polymer disposal and recycling is an important issue in society today, particularly in Europe and the USA where pressures to recycle waste materials are intense. Existing recycling technologies are often expensive and result in low-grade applications, which are less likely to be recycled again. Most waste polymers end up at landfill sites and some, at worst, get incinerated and create 'green house gases'. The ideal solution to polymer waste treatment is to consider it as a resource, where the objective is to recover useful chemicals, which have a commercial value. The unique properties of near and supercritical water (374 oC, 218 atm) mimic polar organic solvents thus acting as a medium for organic synthesis. It also has the ability to be miscible with gases, at the critical temperature, which makes it ideal for oxidation reactions. The ion dissociation constant (Kw) changes by an order of magnitude from the ambient temperature to the cortical, thus facilitating acid and base catalysed reactions, making it ideal for hydrolysis chemistry. A full discussion of the latest developments in near and supercritical water are discussed in Chapter One. Chapter Two demonstrates the successful use of near and supercritical water to oxidise polyethylene and polypropylene at a variety of temperatures and pressures. The mechanism of oxidation is also discussed. The oxidations of polystyrene and block co-polymer elastomer are covered in Chapter Three. Chapter Four details an extensive investigation into potential oxidation catalyst for polymers in superheated water, which have demonstrated selectivity and yields of oxidation products. The hydrolysis of polymers is discussed in Chapter Five, with particular attention to polyvinyl acetate (PVAC). PVAC was converted to polyvinyl alcohol (PVA) at varying degrees of hydrolysis.
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Noorsal, Kartini. "Degradation and drug release studies of slowly degrading semicrystalline polymers." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619805.
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Conrad, Jason David. "The rheology, degradation, processing, and characterization of renewable resource polymers." Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1263396529/.
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Zhuge, Jinfeng. "Fire Retardant Polymer Nanocomposites: Materials Design and Thermal Degradation Modeling." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5591.
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Compared to conventional materials, polymer matrix composites (PMCs) have a number of attractive properties, including light weight, easiness of installation, potential to lower system-level cost, high overall durability, and less susceptibility to environmental deterioration. However, PMCs are vulnerable to fire such that they degrade, decompose, and sometimes yield toxic gases at high temperature. The degradation and decomposition of composites lead to loss in mass, resulting in loss in mechanical strength. This research aims to improve the structural integrity of the PMCs under fire conditions by designing and optimizing a fire retardant nanopaper coating, and to fundamentally understand the thermal response and post-fire mechanical behavior the PMCs through numerical modeling. Specifically, a novel paper-making process that combined carbon nanofiber, nanoclay, exfoliated graphite nanoplatelet, and ammonium polyphosphate into a self-standing nanopaper was developed. The nanopaper was then coated onto the surface of the PMCs to improve the fire retardant performance of the material. The morphology, thermal stability, flammability, and post-fire flexural modulus of the nanopaper coated-PMCs were characterized. The fire retardant mechanism of the nanopaper coating was studied. Upon successfully improving the structure integrity of the PMCs by the nanopaper coatings, a thermal degradation model that captured the decomposition reaction of the polymer matrix with a second kind boundary condition (constant heat flux) was solved using Finite Element (FE) method. The weak form of the model was constructed by the weighted residual method. The model quantified the thermal and post-fire flexural responses of the composites subject to continuously applied heat fluxes. A temperature dependent post-fire residual modulus was assigned to each element in the FE domain. The bulk residual modulus was computed by assembling the modulus of each element. Based on the FE model, a refined Finite Difference (FD) model was developed to predict the fire response of the PMCs coated with the nanopapers. The FD model adopted the same post-fire mechanical evaluation method. However, unlike the FE model, the flow of the decomposed gas, and permeability and porosity of the composites were taken into account in the refined FD model. The numerical analysis indicated that the thickness and porosity of the composites had a profound impact on the thermal response of the composites. The research funding from the Office of Naval Research (ONR) and Federal Aviation Administration Center of Excellence for Commercial Space Transportation (FAA COE AST) is acknowledged.ID: 031001281; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Jihua Gou.; Title from PDF title page (viewed February 26, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 179-198).
Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
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Liau, Leo Chau-Kuang. "Kinetic investigations of thermal degradation of poly(vinyl butyral) using TG/FT-IR /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9841167.
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Saunders, John Mark. "Some aspects of the chemistry and thermal degradation of poly(ethylene terephthalate)." Thesis, University of Salford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240000.
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Reeves, Jennifer Anne. "Photochemistry: Its Application to Reversible Deactivation Radical Polymerization, Degradation, and Post-polymerization Modification." Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami154297403540796.
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Luo, Shyh-Chyang. "Behavior of light-emitting polymers film formation, optical properties, and degradation /." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011397.
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Richards, Vicki Lewana. "The degradation and conservation of natural organic polymers from historic shipwrecks." Thesis, Richards, Vicki Lewana (1996) The degradation and conservation of natural organic polymers from historic shipwrecks. Masters by Research thesis, Murdoch University, 1996. https://researchrepository.murdoch.edu.au/id/eprint/51656/.
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The aggressiveness of a shipwreck site towards submerged materials can be assessed by obtaining the physical, chemical and biological characteristics of that particular wreck site. To this end, environmental parameters and chemical characteristics of selected metal and organic artefacts were measured, in-situ, on a number of different shipwreck sites. Interpretation of these measurements allowed the predominant modes of degradation occurring on these marine archaeological sites to be determined. In addition, metal impregnated, waterlogged wood samples were analysed by spectroscopic techniques. The effects of the incorporated corrosion products on the extent of degradation of the waterlogged wood samples were assessed.
One of the major problems associated with the conservation of metal/organic composite materials is the detrimental effect of iron corrosion products on the post-treatment stability of organic materials. Therefore, a series of trials were carried out to determine the impact of different impregnants on the rate of iron removal from iron impregnated, waterlogged concretion, wood and rope. The rates of iron extraction were monitored and the effectiveness of treatments determined via physical, chemical and spectroscopic techniques. For concretion and wood, the optimal rate of iron removal was achieved by using aqueous solutions of 5% polyethylene glycol (PEG) 1500 and 20% PEG 800, respectively. The addition of citrate and dithionite to these solutions significantly increased the extraction rate of iron. For rope, a consolidation solution of 5% PEG 400, 2% glycerol and 1% ethulose combined with 2% citrate and 5% dithionite was found to give the best results.
A further series of experiments were conducted to determine the most appropriate consolidant for the conservation of friable, acid affected timbers from which the iron corrosion products had not been previously extracted. Interpretation of quantitative physical measurements allowed selection of the most effective consolidant system for the timbers. Of the consolidants tested, polyvinylpyrrolidone (10%) in n-butanol was found to be the most effective.
Degradation of aqueous PEG solutions was successfully monitored by measuring changes in solution pH and viscosity, Higher molecular weight PEG solutions of lower concentrations were more susceptible to oxidative degradation at ambient temperatures than more concentrated, lower molecular weight PEG solutions.
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Kaali, Peter. "Antimicrobial Polymer Composites for Medical Applications." Doctoral thesis, KTH, Polymera material, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33393.
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The current study and discuss the long-term properties of biomedical polymers in vitro and invivo and presents means to design and manufacture antimicrobial composites. Antimicrobialcomposites with reduced tendency for biofilm formation should lead to lower risk for medicaldevice associated infection.The first part analyse in vivo degradation of invasive silicone rubber tracheostomy tubes andpresents degradation mechanism, degradation products and the estimated lifetime of thematerials.. It was found that silicone tubes undergo hydrolysis during the long-term exposurein vivo, which in turn results in decreased stability of the polymer due to surface alterationsand the formation of low molecular weight compounds.The second part of the study presents the manufacturing of composites with single, binary andternary ion-exchanged zeolites as an antimicrobial agent. The ion distribution and release ofthe zeolites and the antimicrobial efficiency of the different systems showed that single silverion-exchanged zeolite was superior to the other samples. Antimicrobial composites wereprepared by mixing the above-mentioned zeolites and pure zeolite (without any ion) withdifferent fractions into polyether (TPU), polyether (PEU) polyurethane and silicone rubber.The antimicrobial efficiency of binary and ternary ion-exchanged samples was similar whichis thought to be due to the ion distribution in the crystal structure.The changes in the mechanical and surface properties of the composites due to the zeolitecontent demonstrated that the increasing zeolite content reduced the mechanical propertieswhile the surface properties did not change significantly. The antimicrobial tests showed thatthe silver-containing composite was the most efficient among all the other samples. Thebinary and ternary ion-exchanged composites expressed similar antimicrobial efficiency as itwas seen previously for the different zeolite systems. Biocompatibility was studied byexposure to artificial body fluids to simulate the degradation of the composites in the humanbody. Significant changes were observed in the morphology, the surface properties and the chemical structure.QC 20110511
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Wang, Yu. "BRIDGING THE GAP BETWEEN ACCELERATED AND FIELD AGING OF PHOTOVOLTAIC BACKSHEETS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case155445993551404.
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Ballany, Jane M. "An investigation of the factors affecting the degradation of cellulose acetate artefacts in museum collections." Thesis, University of Strathclyde, 2000. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27542.
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Plastics have had an increasing influence on human activity since the early years of the 20th century and as such are becoming an increasingly important part of museum collections. These plastics are already exhibiting signs of degradation, which raises the question of how they should be stored and treated. However, little is known about the specific degradation processes which occur. Further research is required because the lack of information is hindering the correct approach to plastic conservation. Current interest concerns the degradation of cellulose acetate artefacts; the work carried out and reported here examines this problem by studying artefacts of various ages and degrees of degradation using accelerated ageing and comparing these results to those for naturally aged samples. Initial work has been carried out to investigate the plastic each artefact is made from and also its chemical composition. Various analytical techniques have been used to investigate the additives, impurities and degradation products that may be present. The results from these techniques and further work are discussed. Micro-Fourier Transform Infrared (FTIR) Spectroscopy has been found to be an excellent technique for the identification of the base polymer in a plastic artefact, as minute samples are used. It has also been used to monitor changes in the base polymer of the plastic artefacts. Ion chromatography has been used to study levels of water-extractable acetate and oxalate as well as other significant anions. The presence of oxalate in degraded samples indicates chain scission occurring and high levels of acetate indicate deacetylation is occurring. Non-destructive and destructive sampling for ion chromatography have been used to explore if this is a viable screening process to identify artefacts in the early stages of degradation. Chain scission has been investigated further using gel permeation chromatography. X-ray fluorescence spectroscopy results indicate that trace levels of Se may be important in preventing the initiation of degradation, as so far it has only been detected in undegraded artefacts. Results indicate that deacetylation is the predominant process; while chain scission is secondary or a possible surface reaction. Another factor is plasticiser loss.
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Karmore, Vishal K. "Kinetics Of Polymerization And Degradation By Non-Conventional Techniques." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/269.
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Non-conventional techniques for polymerization and depolymerization were investigated. The rates of polymerization were enhanced higher in ultrasonic, supercritical fluids and microwaves. However in these system under certain conditions, simultaneous degradation also occurred. Depolymerization was studied by various methods like thermal degradation in supercritical fluids and in presence of oxidizers, Lewis acid and other organic acids. Degradation by ultrasound and thermal degradation of polymer mixtures were also investigated. The scission of the polymer backbone is random for thermal degradation while the scission occurs at the midpoint for ultrasonic degradation. The degradation rates in all the investigated techniques were higher than the degradation rates observed for pyrolysis. Degradation was possible at low temperature (< 50°C) for oxidative and ultrasound degradation while the degradation rates were two orders of magnitude higher in supercritical conditions. The molecular weight distribution was obtained by GPC analysis and the continuous distribution models were used to obtain the rate coefficients. The activation energies were calculated from the temperature dependence of the rate coefficients.
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Wang, Menghong. "Degradation of Photovoltaic Packaging Materials and Power Output of Photovoltaic Systems: Scaling up Materials Science with Data Science." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1595416965256375.
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Pattenden, Caroline Sarah. "The effect of radiation on the thermal stability of polyisobutylene." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366649.
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Azhari, Zein. "The degradation and drug release mechanisms of poly(ethylene glycol)-functionalised poly(L-lactide) polymers." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275968.
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Poly(L-lactide) (PLLA) is a well-recognised bioresorbable polymer known to degrade after 1.5 to 5 years by hydrolysis. For certain medical device or drug delivery applications, it would be desirable to reduce this degradation time as strategies for tailoring degradation and drug release rates remain limited. This work aimed to examine a consistent series of polymers based on a large block of PLLA and small quantities of hydrophilic poly(ethylene glycol) (PEG) initiator. The polymers had PLLA number average molecular weight (Mn) values ranging between about 60 kDa and 200 kDa and PEG Mns ranging between 550 Da and 5000 Da giving very low PEG wt% values ranging between 0.1 and 1.5 wt%. There are currently no studies which consider high molecular weight PLLA polymers with small quantities of PEG for potential use in structural implants. Furthermore, reports in the literature do not consider the individual effects of PEG addition and PEG and PLLA lengths. The focus of this project was on the impact of processing, hydrolytic degradation and drug release on the morphological aspects of the materials. The materials were thoroughly characterised in their as-synthesised and processed forms. The assynthesised polymers were semi-crystalline and retained the unit cell of PLLA. The glass transition temperature (Tg) was significantly reduced by PEG functionalisation. After injection moulding, nuclear magnetic resonance (NMR) indicated that the PEG component was still present. The Mn of the PEG functionalised samples decreased by approximately two-fold compared with the as-synthesised materials while the PLLA control polymers, processed beyond 200 °C, were more affected as the processing temperature was increased. The degradation properties of the materials were considered. The processed materials were submerged in phosphate buffered saline (PBS) (pH = 7.4) at 37 °C over an 8-month degradation study. During hydrolytic degradation, PEG functionalisation resulted in an increased water uptake. Mass loss began in all polymers when the Mn fell below a threshold of about 20 kDa. In the PEG functionalised samples, the degree of crystallinity increased with time, facilitated by plasticisation from PEG and the increased water content. The molecular degradation rate, k for the PEG-functionalised polymers was dependent on the presence of PEG functionalisation but was little affected by PEG length or PLLA length in the ranges studied. The time taken to reach the critical Mn, and hence the time for mass loss to begin, therefore depended on both the initial Mn and the presence or absence of PEG functionalisation. In the presence of PEG, k, was dramatically enhanced: k for PEG-functionalised polymers fell in the range of 6 x $10^{-4}$ $h^{-1}$ to 1 x $10^{-3}$ $h^{-1}$, as compared with that of the PLLA control of 2.9 x $10^{-5}$ $h^{-1}$. The mechanism of drug release from an analogous series of polymers was investigated. Propranolol. HCl was selected as a model drug for the drug release studies due to its thermal stability and solubility in PBS. Drug loading of propranolol.HCl was achieved by mixing the polymer and drug then injection moulding. A second method of drug incorporation using supercritical CO2 to load propranolol into as-synthesised polymer granules before injection moulding was examined for comparison. The materials processed through injection moulding showed that while drug crystals were present at the surface and in the polymer matrix, a level of drug solubility was also achieved in the PEG-functionalised polymers whereas the PLLA control showed no signs of polymer-drug interaction and only a distribution of drug crystals confined to the surface. The presence of drug crystals on the surface of the PLLA control resulted in the instant dissolution of propranolol.HCl and gave a burst release compared with an initial burst release in the PEG-functionalised polymers followed by a gradual release of the drug. This initial burst release was eliminated from the profile of the samples processed via supercritical CO2. The amorphous dispersion of the drug in the matrix gave a slow, sustained release throughout the duration of the drug release study. The results in this thesis have elucidated the intricate mechanisms of degradation and drug release from PEG-functionalised PLLA polymers. The overall outcome shows new ways of controlling the degradation and drug release rates of already medically established poly(-hydroxy acid) polymers extending their potential for use within temporary structural implants.
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Matti, Y. Y. "The thermal degradation of vinyl chloride polymers and its relation to structure." Thesis, Cardiff University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372345.
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Cumpston, Brian Hylton. "Bulk and interfacial degradation of polymers used for electronic and photonic applications." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10634.
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Sauron, Alain. "Computer modelling of crack growth in rubber-toughened polymers." Thesis, Sheffield Hallam University, 1997. http://shura.shu.ac.uk/20328/.
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We present results from a computer modelling study of fracture propagation in a rubber-toughened polymer subject to external uniaxial tension. Using a simple lattice model comprising two bond types (one for rubber and one for polymer), simulations have been performed on both 2- and 3-dimensional systems. Each bond is characterised by two parameters : an elastic constant and a mechanical strength. All bonds behave in a purely elastic manner up to fracture; this limits the model's applicability to impact failure of brittle glassy polymers. We employ a stochastic breaking process based on Eyring's reaction rate theory, and allow the system to equilibrate fully after each bond breakage. It is found that the Conjugate Gradient method is the most efficient technique for calculating these equilibria. The model allows straightforward measurement of the total damage at failure, which is a crude approximation of the material toughness, and the stress distribution during the damage evolution. We show that, for a wide range of bond parameters, as the rubber loading is increased the damage goes through a sequence of behaviour : embrittlement; toughening; saturation; and weakening. This sequence is consistent with experimental data for rubber-toughened Poly (methyl methacrylate) (RT-PMMA). Our results show that the embrittlement and saturation stages are sensitive to the ratio of the two elastic constants but that they disappear as this ratio approaches unity. The toughening achieved is sensitive to both the concentration and the mechanical strength of the rubber bonds, the most damaged systems being those with large rubber mechanical strength at approximately 50% concentration. We also find that the damage is dependent on the spatial distribution of the rubber bonds, the greatest toughness being achieved using a homogeneous rubber distribution. We also find that the evolution of the system's failure goes through four regimes. In the first of these, the damage is evenly distributed throughout the system but showsa propensity for occuring adjacent to rubber bonds. Subsequently, short cracks develop between some of these weakly damaged sites. As more of these develop, a number of long rubber-bridged cracks appear. In the third regime, the stabilising effect of the bridging rubber bonds forces the damage to extend throughout the system, leading to branching and interconnecting of rubber-bridged cracks. Finally, the stress experienced by the crack-bridging rubber bonds becomes unsustainable and catastrophic failure occurs. Zones of material consistent with each of these four regimes can be observed in experimentally fractured RT-PMMA. The main toughening mechanisms in operation in our model are, therefore, crazing (which occurs mainly in the second regime) and rubber-bridging (which occurs in the third). The former is enhanced by using a lower rubber elastic constant, whereas the latter is prolonged by a large rubber mechanical strength. We also apply the model to simulations of 2D and 3D systems containing rubber macro-particles, i.e. large volumes of connected rubber bonds, and we present visual results of the damage and the stress field evolution in such systems. In these, the damage appears to develop in accordance with the four regimes described above. The stress maps of multi-particle 2D systems show the gradual stress transfer which takes place as cracks develop, from initially high-stressed inter-particle polymer regions to the crack tips and, then, to the rubber particles along the crack lines. These visual results also highlight three possible modes of particle-crack interaction : particle debonding, particle splitting and crack reflection.
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Pan, Lin. "In-situ Infrared Study of Amine-Functionalized Polymer Sorbents for CO2 Capture." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1427207675.
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Deshpande, Girish Nilkanth. "Effect of polysiloxane side groups on chemistry and kinetics of degradation and evolution of pores in the resultant polymer." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/11845.
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Swart, Morne. "The effect of controlled degradation with an organic peroxide on the molecular characteristics and properties of heterophasic propylene-ethylene copolymers (HECO)." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80194.
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Thesis (PhD)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Heterophasic copolymers (also known as HECO polymers) or often referred to only as impact copolymers or block copolymers comprise a polymer matrix with a dispersed rubbery copolymer phase. The polymer under investigation in this study consists of a polypropylene homopolymer matrix and ethylene-propylene copolymers (EPCs). Due to its diverse range of applications and unique properties, polypropylene is the choice of polymer for a vast array of applications. This has led to the development of an entire class of polypropylene materials known as visbroken or controlled rheology polypropylene. By adding a suitable peroxide to the polymer in the presence of heat, radicals are formed which will attack the polymer chains in a random fashion. The resultant polymers generally have a higher melt flow rate (MFR), a narrower molecular weight distribution than the parent polymer, and good impact-stiffness balance. The main focus of this investigation was to determine if there exist any differences in the molecular structure and physical properties of controlled rheology HECO polymers and if differences do exist, how they influence the physical characteristics of the polymer. Eight HECO polymers with equal ethylene contents were visbroken to varying degrees by making use of two different types of organic peroxide. The effects of the amount of visbreaking on the molecular characteristics and physical properties were subsequently studied by making use various types of fractionation techniques, including preparative temperature rising elution fractionation (PTREF) and crystallisation analysis fractionation (CRYSTAF). Subsequent offline analysis was then done on the fractionated samples that included nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), high temperature size exclusion chromatography (HT-SEC), Fourier transform infrared spectroscopy (FTIR) and deposition of the SEC fractions via the LC Transform Interface (SEC-FTIR) as well as high temperature high performance liquid chromatography (HT-HPLC), a novel technique for the characterization of olefins according to their chemical composition.
AFRIKAANSE OPSOMMING: Heterofase kopolimere, ook bekend as HECO polimere, of dikwels na verwys net as impak kopolimere of blok kopolimere bestaan uit 'n polimeer matriks met 'n verspreide rubberagtige kopolimeer fase. Die polimeer wat in hierdie studie ondersoek was het bestaan uit 'n polipropileen homopolimeer matriks en etileen-propileen kopolimere (EPCs). As gevolg van sy veelseidigheid van toepassings en unieke eienskappe is polipropileen die keuse van polimeer vir 'n wye verskeidenheid van toepassings. Hierdie veelseidigheid het gelei tot die ontwikkeling van 'n hele klas van polipropileen materiaal bekend as gevisbreekte of beheerde reologie polipropileen. Deur die byvoeging van 'n geskikte peroksied tot die polimeer in die teenwoordigheid van hitte, word radikale gevorm wat die polimeerkettings in 'n ewekansige wyse sal aanval. Die gevolglike polimere in die algemeen het 'n hoë smelt vloeitempo (MFR), 'n smaller molekulêre gewig verspreiding as die moeder polimeer, en 'n goeie impak/styfheid balans. Agt HEKO polimere met gelyke etileen inhoude was gevisbreek in wisselende hoeveelhede deur gebruik te maak van twee verskillende tipes organiese peroksiedes. Die gevolge van die hoeveelheid van visbreeking op die molekulêre eienskappe en fisiese eienskappe was vervolgens gebestudeer deur gebruik te maak van verskillende fraksionasie tegnieke, insluitend preparatiewe TREF (P-TREF) en CRYSTAF. Daaropvolgende analiese is gedoen op die gefraktioneerde monsters en sluit in kernmagnetiese resonansie spektroskopie (KMR), differensiële skandeer kalorimetrie (DSC), 'n hoë temperatuur grootte uitsluitings chromatografie (HT-SEC), Fourier transform infrarooi spektroskopie (FTIR) met deponeering van die SEC fraksies via die LC transform koppelvlak (SEC-FTIR) sowel as 'n hoë temperatuur hoë werkverrigting vloeistof chromatografie (HT-HPLC), 'n nuwe tegniek vir die karakterisering van olefiene volgens hul chemiese samestelling.
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Heffner, Kenneth Henry. "Radiation Induced Degradation Pathways for Poly (Methyl Methacrylate) and Polystyrene Polymers as Models for Polymer Behavior in Space Environments." [Tampa, Fla.] : University of South Florida, 2003. http://purl.fcla.edu/fcla/etd/SFE0000175.
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Brunacci, Antonio. "Physical aging in polymers, copolymers and blends of polystyrene derivatives." Thesis, Heriot-Watt University, 1995. http://hdl.handle.net/10399/1332.
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Keim, Terra Ann. "Synthesis, Characterization, and Cyclic Stress Influenced Degradation of a Poly(Ethylene) Glycol Based Poly(Beta-Amino Ester)." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19872.
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Poly(beta-amino esters) are photopolymerizable and biodegradable polymers prepared by the combination of amines with diacrylates. This study aims to fundamentally understand the polymer network formed by poly(ethylene)glycol diacrylate (PEGDA) MW 700 and 3-methoxypropylamine (3MOPA) as well as to characterize the degradation response of this material with and without cyclic loading. The networks were formed by a two-step process; (1) the synthesis of amine-co-peg diacrylate macromers through a step growth reaction, followed by (2) UV initiated chain growth network formation of the diacrylated macromers. Macromer reaction chemistry was confirmed by 1H NMR measurements. UV calorimetric analysis revealed that network formation was dependent on molecular weight of the PEGDA monomer and light intensity, but not temperature in the range of 20 °C to 40 °C. The glass transition temperature of all networks was measured to be in the range of -40 °C to -30°C with a rubbery moduli ranging from 4 to 10 MPa, depending on the molecular weight of the PEGDA monomer. Partial crystallization was discovered to occur in the networks containing higher molecular weight PEGDA only in the presence of humidity and high frequency cyclic loading. Degradation studies were performed with and without applied cyclical stress, and in both cases elastic modulus decrease and mass loss occurred steadily over a 24-hour period. Increasing frequency of applied compressive stress during degradation served to slightly lower degradation rates, especially in samples cycled at high frequency, which crystallized. In all materials, applied cyclic load resulted in catastrophic fracture of the material prior to an appreciable decrease in modulus. The experiments reveal that degradation rate and failure mode can be influenced by the addition of cyclic loading and this should be considered when screening biodegradable polymers for applications that include mechanical loading.
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LU, ZIBIN. "Etude des mecanismes de degradation de polymers par decharges electriques de type filamentaire." Paris 6, 1991. http://www.theses.fr/1991PA066689.
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Le travail a ete consacre a l'etude des differents mecanismes de degradation de polymeres utilises comme isolants. En utilisant un systeme constitue des electrodes pointe-plan, nous avons etudie les processus de vieillissement de polymeres par exposition aux produits des decharges electriques en regime de streamers dans l'air, de maniere a simuler des decharges partielles dans les installations electriques. Parmi les parametres de degradation que nous avons etudies (l'effet joule, le champ d'autopolarisation, le potentiel de surface, l'evolution de la conductivite des materiaux, ainsi que la perte dielectrique), nous avons demontre que la perforation provient essentiellement de la propagation des streamers successifs, qui transportent a leur tete un potentiel important au point d'impact. Ce potentiel pourrait conduire a la disruption du materiau, soit a court terme, soit apres un certain temps de vieillissement
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Guzel, Aylin. "Photo-oxidative Degradation Of Abs Copolymer." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610895/index.pdf.
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ABSTRACT
PHOTO-OXIDATIVE DEGRADATION OF ABS COPOLYMER
Güzel, Aylin M.S., Department of Polymer Science and Technology Supervisor: Prof. Dr. Teoman Tinç
er Co-Supervisor: Prof. Dr. Cevdet Kaynak September 2009, 55 pages Acrylonitrile-butadiene-styrene (ABS) polymer is one of the most popular copolymer having an elastomeric butadiene phase dispersed in rigid amorphous styrene and semi-crystalline acrylonitrile. Due to double bonds in the polybutadiene phase, ABS copolymers are very sensitive to photo-oxidative degradation. Photo-oxidation of butadiene rubber phase results in the formation of chromorphores and these chromorphores act as initiators in photo-oxidative degradation and after a while ABS starts yellowing. In this work, the relationship between the UV light and the yellowing of ABS samples was also investigated with respect to time. In this study, pure, light stabilized and commercial ABS samples were aged under UV light. As the UV light intensity increased from 800 to 2800 &
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W/cm2, yellowing of the samples were increased for pure ABS. This increase in yellowing of the samples was about 27 times higher compared to lower energy. In this study, UV stabilizers IRGANOX 1076 (sterically hindered phenolic antioxidant), IRGAFOS 168 (hydrolycally stable phosphite stabilizer) and TINUVIN P (hydroxyphenol benzotriazole) were used alone or in combination with each other. Pure ABS samples, commercial ABS samples and UV stabilized ABS samples were aged under the same UV light. UV aging degradation was followed by measuring the yellowness of the samples at certain time intervals. Yellowness of the samples was followed by using Coloreye XTH Spectrometer. Degradation in ABS, however, was followed by using FTIR with an increase in the peak area of carbonyl groups in the ABS matrix. Both color analysis and the FTIR analysis showed that combination of the IRGANOX 1076 and IRGAFOS 168 stabilizers gave the best stabilization. This revealed that combination of phenol and phosphate containing stabilizer is the most useful combination to prevent photo-oxidative degradation of ABS copolymer. Additionally, vegetable oil was applied to the surface of a new set of ABS samples and these samples were aged for 700 h. Yellowing tendency of these samples was compared with the yellowing tendency of ABS samples that are directly aged for 500 h. It was clearly observed that samples with oil smeared had more resistance to UV radiation with respect to others. This shows that oil acts protective layer to the UV light and oxygen and slow down the photo-oxidative degradation. Lastly some commercial ABS samples were compared to each other with respect to their yellowing tendency. Commercial ABS samples coded as K, L, A, B, C and D were aged under UV light at about 500 h. Sample A showed the best resistance against the yellowing among the other commercial ABS samples.
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Rollinson, Mark. "Pyrolysis g.c. m.s. used to measure rates and deduce mechanisms of the degradation of some polymers of industrial importance." Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268962.
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Mannell, Shaun M. "Orientation of polymers in die-drawing with superimposed transverse shear deformations." Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/27997.
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For polymer materials to compete with metals in engineering applications, they must possess adequate mechanical properties. Some crystalline plastics are able to offer enhanced properties but these tend to be very expensive. Often a viable alternative is to modify commodity polymers through further processing techniques which introduce molecular orientation, thereby producing high modulus polymers.
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O'Neil, Joseph M. "Factors contributing to the degradation of poly(p-phenylene benzobisoxazole) (PBO) fibers under elevated temperature and humidity conditions." Thesis, Texas A&M University, 2006. http://hdl.handle.net/1969.1/4439.
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The moisture absorption behavior of Zylon fibers was characterized in various high temperature and high humidity conditions in a controlled environment. The results of these thermal cycling tests show that PBO fibers not only absorb, but also retain moisture (approximately 0.5-3%) when exposed to elevated temperature and humidity cycles. Also, the impurities of Zylon fibers were characterized through the use of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and solid state Nuclear Magnetic Resonance (NMR). These tests demonstrated that, in addition to other impurities, PBO fibers may contain up to 0.55 weight percent phosphorus, and that this phosphorus is present in the form of phosphoric acid. It was also shown through accelerated hydrolytic degradation tests that production procedures used to neutralize the acid present in the fibers have a beneficial effect on the hydrolytic performance of the fiber. The data collected in this study was then compared and contrasted to known Kevlar studies, identifying similarities, differences, and potential trends. The results of these tests seem to indicate that there is accelerated acid catalyzed hydrolysis occurring in the fiber which is causing these fibers to degrade at an increased rate. This condition is further accelerated by heat and humidity induced permanent fiber swelling.