Tesi sul tema "Chemical upcycling of polyethylene"
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1
Idris, Adamu Aminu. "Upcycling of polyethylenes by catalysis". Electronic Thesis or Diss., Lyon 1, 2023. https://n2t.net/ark:/47881/m6fx79jm.
Abstract (sommario):
La synthèse d’oligomères/molécules téléchéliques fonctionnels directement à partir de déchets de polyéthylène (PE), bien que très intéressante d'un point de vue environnemental et économique, reste encore aujourd'hui un problème majeur à résoudre. En effet, la forte inertie chimique du polyéthylène (liaisons covalentes C(Sp3) – C(Sp3) & C(Sp3) – H(Sp3) très robustes et difficiles à activer) est un frein important à un recyclage chimique efficace et durable de ce type de matériau. Parmi les différentes méthodes chimiques actuellement disponibles pour le traitement des déchets de polyoléfines, on peut citer la pyrolyse, le craquage thermique et/ou l'hydrocraquage catalytique. Cependant, de telles approches conduisent le plus souvent à des mélanges d'hydrocarbures de manière non sélective, difficilement valorisables. Dans cette thèse, nous cherchons à développer une voie plus intéressante vers la circularité des polyoléfines avec comme objectif le recyclage chimique de polyéthylènes en oligomères α,ω – divinyle ou diacétate. Notre stratégie repose sur un processus en deux étapes via d'abord la création d'alcènes internes réactifs sur le squelette principal du polymère par déshydrogénation catalysée par l'iridium, suivie de la dépolymérisation des polymères insaturés résultants par métathèse catalysée par le ruthénium. Cette approche nous a semblé particulièrement bien adaptée à nos objectifs de développer un procédé économe en énergie pour la dépolymérisation du polyéthylène en oligomères fonctionnalisés de faible poids moléculaire à fort potentiel circulaire de réintégration dans la chaîne de valeur du polyéthylène. Une étude approfondie de l’influence des paramètres réactionnels, nature du catalyseur et grades de différents polyéthylènes a d'abord été entreprise pour les deux réactions. Dans un premier temps, nous avons montré que différents niveaux d'insaturations internes pouvaient être générés sur le squelette du PE en faisant varier le ligand du catalyseur et sa concentration ou les conditions de déshydrogénation sans compromettre ses propriétés structurelles et thermiques. Dans un deuxième temps, la métathèse croisée appliquée à ces polyéthylènes insaturés avec l'éthylène et le cis–1,4–diacétoxy–2–butène comme agents de transfert de chaîne a permis d’obtenir des produits téléchéliques divinyle et diester avec des conversions élevées de 86 % et 91 % respectivement. Les produits finaux à haute valeur ajoutée de ce procédé en deux étapes pourraient être utilisés comme matière première pour la conception de nouveaux polymères recyclés, réduisant ainsi à la fois l'exploitation des ressources fossiles pour la production de polymères et son impact environnemental associéThe synthesis of functional telechelic oligomer/molecule platforms directly from polyethylene (PE) wastes, although very appealing from an environmental and economic point of view, remains today a major problem to tackle. Indeed, the strong C(Sp3) – C(Sp3) & C(Sp3) – H(Sp3) σ-covalent bonds of polyethylenes are undoubtedly not only at the origin of the robustness and chemical inertness of PEs relative to many reagents but also dramatically hamper their chemical recycling. Among the different chemical methods currently available for the treatment of polyolefin wastes, one can cite pyrolysis, thermal cracking, and/or catalytic hydrocracking. However, such approaches most often lead to mixtures of hydrocarbons in a non-selective manner, which are difficult to valorize. In this dissertation thesis, we seek to develop a more valuable route toward polyolefins circularity through polyethylenes upcycling into α,ω–divinyl, or diacetate oligomers. Our strategy involves a two-step process via first the creation of reactive internal alkenes on the main polymer backbone by iridium-catalyzed dehydrogenation followed by depolymerization of the resulting unsaturated polymers using Ru–catalyzed metathesis. A thorough screening of the reaction parameters, nature of the catalyst, and substrate scope was first undertaken for both reactions. We have shown that different levels of internal unsaturation can be generated on the PEs backbone by playing with the catalyst ligand, loading, or conditions of dehydrogenation without compromising its structural and thermal properties Subsequent cross-metathesis of these internally unsaturated polyethylenes with ethylene and cis–1,4–diacetoxy–2–butene as chain transfer agents afforded divinyl and diester telechelic products with 86 % and 91 % conversions (of internal double bonds into functional chain ends) respectively. The high-value-added end-products of this two-step process could be used as feed for the synthesis of recycle-by-design polymers, thereby reducing the exploitation of fossils for polymer production and its associated environmental impact
2
Chohan, Sukhvinder K. "Environmental degradation of polyethylene-based plastics". Thesis, Aston University, 1996. http://publications.aston.ac.uk/9675/.
Abstract (sommario):
The criteria involved in the degradation of polyethylene-based degradable polymer samples have been investigated, with a view to obtaining a clearer mechanism of photo-biodegradation. The compatibility of degradable polymer samples during materials recycling was also studied. Commercial and laboratory prepared degradable polymer samples were oxidised in different environments and the oxidation products formed were studied using various analytical chromatographic and spectroscopic techniques such as HPLC, FT-IR and NMR. It was found that commercial degradable polymer samples which are based on the ECO systems, degrade predominantly via the Norrish II process, whereas the other degradable systems studied (starch-filled polyethylene systems, transition metal systems, including metal carboxylate based polyethylene systems and the photoantioxidant-activator systems) photodegrade essentially via the Norrish I process. In all cases, the major photoxidation products extracted from the degradable polymer samples were found to be carboxylic acids, although, in the polymer itself a mixture of carbonyl containing products such as esters, lactones, ketones and aldehydes was observed. The study also found that the formation of these hydrophilic carbonyl products causes surface swelling of the polymer, thus making bioerosion possible. It was thus concluded that environmental degradation of LDPE is a two step process, the initiation stage being oxidation of the polymer which gives rise to bioassimilable products, which are consequently bioeroded in the second stage, (the biodegradation step). Recycling of the degradable polymer samples as 10% homogeneous and heterogeneous blends was carried out using a single screw extruder (180°C and 210°C) and an internal mixer (190°C). The study showed that commercial degradable polymer samples may be recycled with a minimal loss in their properties.
3
Müller, Stefan 1971. "Biodegradation of polyethylene thermolysis residue". Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20509.
Abstract (sommario):
The ability of several microorganisms to degrade polyethylene thermolysis residue was investigated. This residue is mainly comprised of n-alkanes and n-1-alkenes ranging in chain length of 15 to 45 carbon units and therefore resembles crude oil. The microorganisms investigated were: Y. lipolytica ATCC 8662, Y. lipolytica ATCC 20460, A. paraffineus ATCC 19558, P. aeruginosa PAO1, P. putida ATCC 12633, R. rhodochrous ATCC 21766 and Rhodococcus sp. ATCC 29671. It was found that all seven microorganisms tested were able to degrade the polyethylene thermolysis residue. Results suggest that R. rhodochrous produced a biosurfactant when growing on the polyethylene thermolysis residue.It was also found that the acclimation of the microorganism to the substrate was an important factor in the degradation of the residue. Using two different acclimation times, two different strains of R. rhodochrous were selected for in the acclimation step. The two different strains showed very different degradation patterns of the polyethylene thermolysis residue. Strain A showed almost no effect of chain length on the degradation rate of the hydrocarbons while the degradation rate of the hydrocarbons for strain B decreased with increasing chain length. This difference in the degradation pattern was attributed to the varying amounts of enzymes present in each strain. Another factor found to affect the degradation pattern was the liquidity of the polyethylene thermolysis residue.
4
Tang, Zuojian 1967. "Surface morphology of polyethylene blown films". Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31072.
Abstract (sommario):
The properties of blown polyethylene (PE) films depend on various factors, including crystallinity, morphology, and orientation, in addition to chemical composition. It has been shown that the optical properties are strongly influenced by surface morphology. In this project, we use non-contact atomic force microscopy (AFM) and polarized light microscopy (PLM) to visualize surface and bulk morphology. Various techniques, such as surface and line roughness, surface and line fractal dimension, pair-correlation function and nearest neighbor distance distribution function, are employed to quantify the description of morphology and to compare the morphological characteristics of a number of polyolefin films of commercial interest. A comprehensive quantitative analysis of surface topography has been performed. The co-monomer of the PE resins was found to play a significant role in the formation and the orientation of spherulite-like domains. The film cross-section microstructure has been evaluated qualitatively by using both AFM and PLM. However, quantitative analysis of bulk morphology cannot be obtained due to knife effects.
5
McCaffrey, William Chessleigh. "Thermolysis of polyethylene and polyethylenepolystyrene mixtures". Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40397.
Abstract (sommario):
Thermolysis was investigated as a process to convert waste olefin-based polymers into value-added products at a moderate temperature. Virgin, linear low density polyethylene was used for the majority of the experiments. The thermolysis of virgin polystyrene, recycled polyethylene and 3:2 mixtures of polyethylene and polystyrene were also investigated. The final process that was developed employed the reactive distillation of polyolefins under an inert atmosphere and at moderate reaction temperatures, ranging from 375 to 450$ sp circ$C. The major products from thermolysis of polyethylene were a distribution of low-molecular-weight straight chain alkanes and $ alpha$-olefins ranging from C$ sb6$ to C$ sb{25}.$ Overall volatile product yields up to 90% were obtained from the starting polymer. The initial molecular structure of the polyethylene was found to have a large effect on the rate of molecular weight reduction. A significantly enhanced rate of thermolysis was also observed when polyethylene was processed as a mixture with polystyrene. The mechanisms of thermolysis of polyethylene, polystyrene and mixtures of the two polymers were elucidated. Furthermore, the mechanism of dimer production from polystyrene was found to be different than what has been reported previously.
6
Brues, Michael J. (Michael Jason). "Thermolysis of mixtures of polyethylene and polystyrene". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22642.
Abstract (sommario):
The thermolysis of mixtures of polyethylene and polystyrene was investigated. Overall liquid production for the mixture was above the values predicted from individual polymer reactions. No detrimental effects on the styrene production were evident, as over 50% of the initial polystyrene charge was converted to styrene for polystyrene and for mixtures. There were, however, some differences in the secondary products. No incorporation of one polymer onto another was observed, either in the liquid or the residue.Different reaction conditions were examined. It was determined that using a single reaction temperature (445$ sp circ$C) was as effective at separating the aromatic and aliphatic products as using two different reaction temperatures.
Polystyrene was found to catalyze the thermolysis of polyethylene. Conventional catalysts (Mordenite and FCC zeolite) affected the overall production and product distributions for mixtures and polyethylene, while only changing the product distribution for polystyrene. Hydrogen in the purge gas only slightly decreased the ratio of 1-alkenes to n-alkanes.
Recycled plastics yielded results similar to virgin polymers, although overall liquid production was decreased (probably due to the additives present in the plastics).
7
Lageraaen, Paul R. (Paul Robert). "Thermolysis of mixtures of polyethylene and polystyrene". Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56791.
Abstract (sommario):
Thermolysis of mixtures of linear low density polyethylene, LLDPE, and polystyrene, PS, was investigated. Mixtures having various polyethylene/polystyrene ratios were reacted in a stirred, batch reactor under a nitrogen atmosphere at moderate temperatures, ranging between 350 and 420$ sp circ$C. The major products collected included a volatile product, which was liquid at room temperature, and a wax-like residue. The liquid products were consistently found to contain over 90 percent styrene and toluene with the yield of styrene decreasing as the percentage of polyethylene in the mixture increased. Two fractions were identified in the residue: a high molecular weight polyethylene fraction and a lower molecular weight polystyrene fraction. A significant increase in the solubility of the residue in organic solvents at room temperature was observed as the polystyrene content was raised. The residue became completely soluble in chloroform at a 60/40 ratio of polyethylene/polystyrene. The effect of temperature on the degradation of a selected mixture was also investigated. At temperatures below 390$ sp circ$C, the volatile/residue ratio was independent of the reaction temperature. Above 390$ sp circ$C, the styrene and total liquid product yields increased with increasing temperature, while the yield of residue decreased.
8
Feng, Lijun 1966. "Melting and crystallization behavior of linear low-density polyethylene". Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86069.
Abstract (sommario):
The melting and crystallization behavior of linear low-density polyethylene (LLDPE) is of great scientific and industrial importance. It depends strongly on polymer molecular structural characteristics and processing conditions, and determines polymer application properties. In this work, we study three different types of LLDPE polymers: metallocene-based LLDPEs (m-LLDPEs), Ziegler-Natta-based LLDPEs (ZN-LLDPEs), and m-LLDPE blends.A generalized equation is introduced to clarify conceptual definitions of polymer melting temperatures. It incorporates the effects of comonomer volume, crystal length, folding surface free energy and enthalpy of fusion. It is successful in describing the characteristic melting temperatures of various alpha-alkene-ethylene copolymers. The proposed equation is used, along with melting traces obtained by differential scanning calorimetry (DSC), to estimate the crystal size number distributions. Furthermore, the melting temperature characteristics are identified, using crystal size number distributions.
The crystallization behavior of LLDPEs is studied by polarized light microscopy (PLM) and DSC. A modified Hoffman-Lauritzen (MHL) expression is proposed for the linear crystallization kinetics by replacing the equilibrium melting temperature, Tm0, with the melting temperature of the crystal stem with the maximum possible length, TmC,n*. The concept of the effective nucleation induction time is introduced, in order to employ the Avrami equation to analyze the overall crystallization kinetics during the initial crystallization stage.
The MHL analysis suggests the presence of three crystallization regimes: regimes III and II, and a special regime IM. The Avrami exponents are respectively 2, 1.5, and 1 in these regimes. The typical optical morphology of LLDPEs is spherulitic. As the crystallization temperature increases, the morphology changes from spherulites without ring bands, to ring-banded spherulites and sometimes to irregular structure with rough ring bands. These structural characteristics seem to correspond to MHL regimes.
Non-linear spherulitic growth behavior is observed in regimes II and IM. This behavior is explained by the reduction of the concentration of crystallizable ethylene sequences in the melt phase. The MHL expression may be still used to analyze non-linear growth crystallization kinetics by employing a variable TmC,n*.
9
Williams, Gregory R. (Gregory Richard). "Catalyzed thermal oxidation to recover value from waste polyethylene". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60482.
Abstract (sommario):
Polyethylene was thermally oxidized in the presence of air with cobalt(III) tris-(2,4-pentanedionate) as a catalyst and dicumyl peroxide as an initiator. The optimum temperature for oxygen addition was found to be 150$ sp circ$C. At this temperature, after reaction with 4 wt% catalyst and.4 wt% initiator for three hours, the solid residue was 11.5 mol% oxygen, with a number average molecular weight of 2,500, and there was no overall weight loss. Higher temperatures led to lower oxygen content, equal or higher molecular weight and significant weight loss. Infrared analysis indicated that the ratio of carbonyl to hydroxyl oxygen was a constant.It was concluded that volatilization became a dominant factor and oxygen containing molecules were lost from the solid. Some of the samples were used as the sole carbon source in fermentations with Yarrowia lipolytica and Arthrobacter paraffineus, but no growth was achieved.
10
Abdallah, Mohammad Raji AlGhazi. "Role of polymer entanglements in polyethylene oxide induced fines flocculation". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38140.
Abstract (sommario):
On a papermaking machine, fines and colloids are retained in a paper sheet. The most important particle interactions are among particles having a high weight fraction and a short characteristic interaction time. Most of these interactions follow Langmuir kinetics, in which the flocculation efficiency is one of the important parameters. To enhance retention, many retention aids are available, one of which is neutral polyethylene oxide (PEO) used in combination of a phenolic cofactor (CF).In this work, a new model was derived in which all possible interactions were considered and assumed to follow Langmuir kinetics. Since fines are the main component in the headbox of mechanical grade furnishes, fines homo- and heteroflocculation with a PEO/CF retention aid were investigated in a circulating flow loop, and found to follow Langmuir kinetics. The small amount of fines deposited on the fibers was attributed to the large detachment rate in turbulent shear. The apparent difference in the deposition time and the half time of flocculation was attributed to difference in efficiency. Fines homoflocculation showed that fines are flocculated (without a retention aid) to various extents depending on shear, and that aggregates of flocs will form when a retention aid is added.
The PEO/CF flocculation efficiency was found to be a function of various parameters, i.e., aging of PEO solution, stirring intensity and time of stirring during dissolution, concentration at storage, shearing and dilution prior to injection. Optimum conditions were found for most parameters, and a critical shear intensity was determined. This PEO behavior was attributed to the extent of entanglements of PEO coils, which can be characterized prior to its addition to the flocculation vessel by a newly developed method. In this method, the pressure drop of a PEO solution passing through a capillary constriction was measured and correlated with its flocculation efficiency. Using the derived correlation, the flocculation efficiency can be estimated, and the relevant parameters can be controlled. Moreover, the salt effect on a PEO/CF system in a pulp was investigated. Salt was found to react with a CF causing a decrease in the flocculation efficiency. The effect of this reaction can be eliminated if PEO is added directly after CF addition.
11
Mijangos-Santiago, Faustino. "Effect of particulate filler on molecular orientation in molten polyethylene". Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74236.
Abstract (sommario):
This research involves the study of the effects of the presence of a calcium carbonate filler, with particle sizes smaller than 1 $ mu$m, in the matrix of a medium density polyethylene on: (a) extrudate swell, (b) the relaxation expectrum, and (c) mechanical properties such as the Young's modulus and the yield strength.It was found that: (a) the Young's modulus and the yield strength are improved most when untreated filler particles are used, (b) the relaxation spectrum is shifted the most to longer times when untreated filler particles are used, and (c) extrudate swell is reduced by the presence of filler particles, due to some sort of interaction between them and the polymer molecules, and not by a simple substitution of polymer molecules by filler particles.
Filled polymers were used to produce tubular extrudates in an attempt to use the long relaxation times to delay swell and thus maintain the anisotropy generated by flow through a die having an expanding channel. It was found that the storage modulus of samples taken along the hoop direction was not different from that of samples taken along the axial direction. This lack of anisotropy was attributed to the low shear rate in the die and to competition between extensional flow that tends to orient polymer molecules in the hoop direction and shear flow that tends to orient polymer molecules in the axial direction. It is concluded that it is not possible to obtain significant differences in the loss modulus between the axial and hoop directions, i.e., measurable anisotropy, unless one of these processes becomes predominant.
The last part of the research involved a study of the role of uniaxial extension in promoting orientation. Molten strips were stretched at different strain rates, and it was found that molecular orientation in the stretching direction levels off at a particular strain rate. The maximum orientation depends on the treatment of the filler particles and on the additives used. This finding points to the possibility of using the total energy used to deform the molten strips as a criterion for obtaining the maximum molecular orientation in the direction of stretching.
12
Tiang, Jen Shueng 1977. "Evaluation of two techniques for testing of polyethylene film resins". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83936.
Abstract (sommario):
The processability of a resin in film blowing is strongly influenced by its flow behavior in extension. In this study, the suitability of the Sentmanat Extensional Rheometer (SER) and of a novel tester for polyethylene film resins was evaluated. The SER, which subjects the resin to simple extension, is simple and fast to use, requires a small quantity of sample and gives reliable data that can be used to detect differences in molecular weight, molecular weight distribution and levels of long-chain branching. The data are also related to the stability of the bubble in film blowing. The tester, on the other hand, is a simple device that generates biaxial extension by inflating a sheet into a bubble. The resulting pressure traces from this empirical test were found capable of differentiating resins on the basis of their flow in biaxial extension.
13
Waheed, Numan. "Molecular simulation of crystal growth in alkane and polyethylene melts". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32324.
Abstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005.Includes bibliographical references (p. 195-207).
Molecular simulation has become a very powerful tool for understanding the process of polymer crystallization. By using carefully constructed simulations, one can independently observe the two phenomena responsible for melt crystallization: nucleation and growth. This research focuses on modeling the growth process using potentials that are well-parameterized for alkanes and polyethylene. In experiment and modeling of the kinetics of alkane crystallization, focus has been concentrated on growth rates very near the melting temperature, where the growth of these systems is optically observable. In this temperature range near .., diffusion is not a limiting factor, which has led to theory that models the thermodynamic driving force and its effect on kinetics. Phenomenologically, one observes a maximum growth rate at a temperature intermediate between the glass transition temperature ... and the melt temperature ... This arises as a competition between a thermodynamic driving force towards crystal growth, associated with locking chains into crystallographic registry and the ability of chains to diffuse to the new layer and rearrange themselves conformationally to satisfy the restrictions of crystal symmetry. The thermodynamic driving force is rate limiting at high temperatures, while melt mobility is rate limiting at low temperatures. Growth rates are of interest to the polymer processing community, who require accurate crystallization kinetic data over the entire temperature range, in order to predict solidification under process conditions and thus final fiber properties.
(cont.) A model which retains its connection to molecular structure would certainly be of benefit for purposes of product design; such connection is possible using molecular simulations. Nonequilibrium molecular dynamics enables us to observe growth for a range of temperatures around the temperature at which the maximum growth rate occurs. We present a molecular dynamics (MD) framework for measuring crystal growth rates for n-eicosane (C₂₀H₄₂, denoted C20), by simulating growth on a pre-existing crystal surface. We show that growth rates for short alkanes such as C20 are directly observable over a range of quench temperatures, for the case where the crystallization front is preceded by a supercooled amorphous region, and heat transfer occurs faster than the characteristic time for crystallization. We present data that we have acquired from these simulations through analysis of the propagation of orientational order, using the bond order parameter, and density changes, using Voronoi volumes. To determine molecular weight effects, we use the same technique to look at systems of C₅₀H₁₀₂ and C₁₀₀H₂₀₂ (denoted C50 and C100). With these higher molecular weight n-alkanes, we can also measure the occurrence of folds during crystal growth. From these MD simulations, we obtain data for the growth rate of n-alkane crystals over a range of temperatures and molecular weights. Qualitatively, we see frequent adsorption and desorption of chain segments on the surface in both C50 and C100 systems. We find evidence for a surface nucleus involving 4-5 chain segments, from multiple chains, that are approximately 20 beads long, shorter than the ultimate thickness of the chain stem in the crystal.
(cont.) We construct a general crystal growth model that can be parameterized entirely in terms of universal properties of polymer chains, described by polymer physics and chemically specific quantities that can be estimated polymer by polymer using molecular dynamics simulations. The model is an extension to polymer crystallization models to incorporate molecular weight effects, using a small number of chemically specific quantities that can be estimated from molecular dynamics simulations. It accounts for the thermodynamic driving force, using classical nucleation theory, and melt relaxation time, using WLF theory. Our model can predict rates as a function of temperature and molecular weight, up to the entanglement molecular weight. Past the entanglement molecular weight, the analysis reveals that the growth rate of alkanes and polyethylene can both be described by the same relationship. The appropriate relaxation time is used to describe the kinetic barrier to crystallization. For chains shorter than the entanglement length, this is the Rouse time. For chains longer than the entanglement molecular weight, kinetic limitations are modeled by the local relaxation of an entangled segment at the interface. Use of the model is illustrated for polyethylene crystallizing in a fiber spin line under conditions of slow cooling and fast cooling. Finally, we present a simplified framework for the study of polymer crystallization using Kinetic Monte Carlo (KMC). We have developed a general KMC algorithm for measuring growth of a polymer crystal phase during melt crystallization, based on the algorithm of Bortz et al.
(cont.) We have incorporated new moves into a general framework to allow multi-chain, three-dimensional growth and the escape of chains from the crystal to the melt, through the fold surface. We performed parametric studies on the melt-crystallization of C20 to study the effects of each energy barrier. In addition, the KMC algorithm allows us to consider the importance of individual moves in contributing to growth. We have shown, as a proof-of-concept, that this algorithm is capable of generating morphologies characteristic of several theories of secondary nucleation in polymer melts.
by Numan Waheed.
Ph.D.
14
Burnett, Connah Andrew. "Radical block copolymers of linear low density polyethylene macromonomers". Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/106401/.
Abstract (sommario):
Chapter 1 introduces the concept of wax crystal modification in middle distillate fuels and reviews the more common chemical additives used commercially, and by examination of the advantages and drawbacks of these additives discusses the possible benefits of polyolefin block copolymers. From this end functionalisation of polyethylene (PE) as a route to block copolymers is reviewed from different literature methods for their synthesis. Chapter 2 introduces the catalytic hydride insertion polymerisation mechanism as a route to end functional polyolefins and goes on to focus on the production of end functional ethylene/hexene copolymers. Using a range of comonomer concentrations and a number of catalysts, end-functional copolymers with a range of comonomer incorporation are produced. The thermal properties of these polymers are investigated and matrix assisted laser desorption/ionisation (MALDI) mass spectra were acquired. Finally, the chapter discusses the synthesis of short chain analogues of end functional PE. Chapter 3 describes the production of polyolefin-polar block copolymers via the free radical polymerisation of the functional polyolefins with a range of polar monomers. A reversible termination mechanism similar to nitroxide mediated polymerisation is proposed. The products are analysed by gel permeation chromatography (GPC) and by an in detail 2D NMR study to confirm block copolymer structure. Chapter 4 examines the physical properties of the synthesised block copolymers. The tendency of the copolymers to aggregate in solution into particles of varying size is investigated by VT NMR and dynamic light scattering (DLS), these findings were supported by transmission electron microscopy (TEM). The thermal properties of these copolymers were studied by differential scanning calorimetry (DSC). Following this the efficacy of these polymers as wax crystal modifiers (WCM) for fuels was investigated by cold flow plugging point (CFPP), optical microscopy and DSC of the treated fuels. Finally, the behaviour of the polymers in solid polyethylene wax was investigated by drop shape analysis (DSA) and x-ray photoelectron spectroscopy (XPS). Chapter 5 details the various experimental procedures used to carry out the work in this thesis. Appendix A gives an overview of polymerisations between ethylene and α- methylstyrene comonomers catalysed by hafnocene catalysts and goes on to detail the investigation of the materials acquired. Analysis was conducted using 2-D NMR, MALDI and diffusion-ordered spectroscopy (DOSY). Appendix B contains the DLS correlograms for samples analysed in chapter 4. Appendix C contains the schematic diagram for the gas burettes system used for metallocene polymerisations.
15
Ehteshami, Gholam Reza 1951. "Synthesis and characterization of bioaffinity interactive heterobifunctional polyethylene glycols". Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/282210.
Abstract (sommario):
Novel methods for synthesis of monoprotected homobifunctional polyethylene glycols and subsequent synthesis and application of heterobifunctional derivatives in protein immobilization and separation is described. In addition, modification of proteins with PEG and properties of the conjugates are presented. Heterobifunctional PEG derivatives having a chelate at one end and at the other one specific ligands for proteins have been synthesized. Metal binding constants and kinetic parameters of these bifunctional chelate polymers were found in excellent correlation with the binding affinities shown by corresponding unconjugated groups. These heterobifunctional PEG derivatives were used to characterize the partitioning behavior of several proteins in Affinity Two-Phase Partitioning, ATPP, at different conditions. Both sides of these bioaffinity chelating polymers were found to be effective in the partitioning of these model proteins. These modified heterobifunctional affinity chelating polymers were also adsorbed in aqueous media to different chelating adsorbents used in IMAC separation. In this scheme an IMA-adsorbent could be transformed to a more selective affinity separation mode, by adding an affinity-chelating ligand. The attached ligand could be removed by weakening the metal interactions between the two chelates in the system which allow the column to operate again in the original IMAC mode, if desired. The amount of these bioligands bound to the columns were a function of the type of the IMA-adsorbents, pH, salts and the metal immobilized on the gels. Trypsin and avidin were bound on columns loaded with a PAB-PEG-chelate and a biotin-PEG-chelate respectively. As a typical example, bound trypsin was eluted from the columns with the trypsin inhibitor, benzamidine, acting as a competitive ligand. The bioligands were eluted reversibly from the IMA-adsorbents, using free IDA as a competitive ligand, using low pH buffers or EDTA. PEG derivatives of 5000 daltons, were chemically fixed to non essential groups on trypsin through amidation with amino groups using two different methods. Kinetic studies were performed upon modification to determine the activity and stability of the modified biomolecule under these conditions. In both cases the modified enzyme adduct, retained their original biological activities and showed substantial changes in properties.
16
Wilhelmi, John L. (John Lawrence). "Simulation of the structure and properties of the polyethylene crystal surface". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11259.
17
Ye, Yufeng 1971. "The study of long time relaxation behavior of metallocene polyethylene /". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31081.
Abstract (sommario):
The long time relaxation behavior of linear and long chain branched (LCB) metallocene polyethylene (mPE) is very important for understanding their flow properties. One linear and four LCB mPEs were studied in shear creep and recovery measurements. All the mPEs have similar molecular weight and molecular weight distribution but different levels of long chain branching. A technique was developed to eliminate the effect of non-ideal start-up at the beginning of creep experiment and the small residual stress that exists during the creep recovery period. It is found that the existence of long chain branching is responsible for the increasing of the zero shear viscosity, the steady state compliance and the longest relaxation time. The retardation and relaxation spectrums were calculated from the creep compliance. The dynamic compliance calculated using retardation spectrum is compared with that measured directly. Both are in very good agreement. These observations are compared with the molecular dynamics theory.
18
Tavichai, Orasa. "Effect of shear on growth rates during polyethylene melt crystallization". Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33996.
Abstract (sommario):
During processing, polymers are exposed to complex thermal and deformation fields. Under these conditions, partially crystalline polymers undergo crystallization, which contributes significantly to their ultimate properties. While the thermal effects on polymer crystallization have been studied extensively, there is much less research carried out with regard to the effects of deformation and stress on crystallization kinetics. This is in part due to experimental difficulties in making appropriate measurements. In the present work, the Linkam Shearing Cell, in conjunction with a polarized light microscope, was used to study the effect of shear on the growth kinetics of various linear low-density polyethylene (LLDPE) resins. Simultaneously, an effort was made to evaluate the effect of shear on morphology. The experimental and analytical aspects of the work will be described, and preliminary results will be reported.The spherulitic growth rate increased under shear compared to that under quiescent conditions. The circular shape morphology of spherulites was obtained under the shear rate range of consideration (0--1 s-1). The effect of molecular structure in terms of co-monomer and branching content on spherulitic growth rate under quiescent and shear condition was observed. Moreover, the effect of temperature on growth rate under quiescent and shear (0.5 s-1) was studied. The modified Lauritzen-Hoffman equation was used to fit experimental data. The diffusion energy barrier under shear condition (0.5 s-1) was estimated and was found to be lower than the diffusion energy barrier under quiescent conditions.
19
Yang, Yan. "Characterization of polyethylene terephthalate, cellulose acetate and their blends". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-03302010-020651/.
20
Kinsley, Chris. "Soybean peroxidase-catalysed treatment of phenol in the presence of polyethylene glycol". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0001/MQ44018.pdf.
21
Lo, Wendy. "Thermo-chemical recovery of low molecular weight oligomers from polyethylene waste". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61313.
Abstract (sommario):
This study focused on the chemical recycling of polyethylene using controlled thermo-chemical degradation. Polyethylene was degraded in a stirred, batch reactor under a nitrogen atmosphere. The reaction temperatures that were investigated ranged between 375$ sp circ$C and 421$ sp circ$C. The reaction time ranged between 20 and 50 minutes. Three major products were collected, an insoluble solid residue, a condensable wax that was volatile during the reaction, and a residual wax that was not volatile during the reaction. It was determined that above 409$ sp circ$C, 90% of the original resin weight was converted to both the volatile and residual wax. Both waxes had a final Mn of 400 to 500. Analysis revealed that the volatile wax was a mixture of straight chain hydrocarbons, with 4% of the carbon bonds unsaturated. The residual wax was a mixture of hydrocarbons, both straight and branched components. No liquid product was collected, and gaseous components did not exceed 10% of the original resin weight. It was also determined that silica alumina did not enhance degradation.
22
Sentmanat, Martin Lamar. "The effect of pressure on the wall slip of linear polyethylene". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39998.
Abstract (sommario):
Experiments were performed on a slit die rheometer to determine the effect of pressure on the wall slip of linear polyethylene. A novel shear stress transducer was developed to measure local wall shear stress at several locations along the die. It was found that above the critical shear stress for the onset of slip, the shear stress distribution along the die was nonuniform. Furthermore, it was discovered that the local wall shear stress near the exit of the die was greater than the nominal, or length-averaged, shear stress within the die as calculated from the pressure drop. Teflon$ sp circler$ wall coatings were used to promote slip by lowering the critical shear stress for the onset of slip. Relative local slip velocities were calculated and found to be a function of pressure and wall shear stress.A new semi-empirical model for the pressure dependence of slip was developed based on the effect of pressure on the work of adhesion and the work needed for flow. The new model indicates that pressure can both suppress and promote slip depending on the level of stress involved. At low pressures, and for a given shear stress, slip is markedly suppressed due to the increase in the work of adhesion. As pressure increases, however, the work needed for flow overcomes the work of adhesion, and slip dramatically increases. However, at higher pressure, the effect of pressure on slip becomes weaker. Numerical simulation results with the new model predict the existence of a local maximum in the shear stress distribution along the die for flow with slip.
23
Kim, Soo Yeon. "Poly(ethylene terephthalate) filamentary materials for molding applications : processing and morphological considerations". Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/11265.
24
Carignan, Alain. "The influence of cofactors on the flocculation properties of polyethylene oxide". Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=24053.
Abstract (sommario):
Adding polyethylene oxide (PEO) at the wet end of a paper machine, can result in an increase in retention of the fine particles. The results obtained with PEO and the cofactors (SNS, MPR, and CAR), are discussed in terms of the association-induced polymer bridging mechanism.Dynamic Light Scattering (DLS) of polymer solutions revealed that each of the three cofactors are forming complexes with PEO. CAR radically increased the apparent diameter of the PEO chains, and MPR seems to decrease it. In latex suspensions, the SNS was found very efficient in the sequence latex-polymer-cofactor (LPC), increasing the PEO hydrodynamic layer thickness (HLT).
Flocculation experiments with the help of a Photometric Dispersion Analyser (PDA), with PEO only (no cofactor) suggested that the fines are composed of more than one component. SNS was found to make all the fines alike by adsorbing on them. Adding the PEO after SNS gave homoflocculation. As a result, the specific surface of fines, calculated by PEO adsorption was found to be 0.223 m$ sp2$/g.
The association-induced polymer bridging mechanism can happen in three different manners depending if the cofactor and the polymer are adsorbing onto fines. When neither of PEO nor cofactor adsorb onto the collector, the PEO/cofactor association-complexes bridge the particles (van de Ven and Alince (1996)). When the cofactor (e.g. SNS) and the polymer adsorb onto the fines, in the sequence fines-cofactor-polymer (FCP), with a chemical ratio cofactor/PEO of 3/1, adsorption of the PEO chains onto cofactor-coated fines is likely to occur at the beginning followed by the flocculation of the fines. In the sequences fines-polymer-cofactor (FPC), when the polymer adsorbs onto the fines and the cofactor adsorbs (e.g. SNS) or not (e.g. MPR), a reenforcement of the bondstrength was noticed. (Abstract shortened by UMI.)
25
Wang, Bing. "Copper-oxides catalyzed polyethylene depolymerization in a pilot-scale reactor". Ohio : Ohio University, 2000. http://www.ohiolink.edu/etd/view.cgi?ohiou1173210030.
26
Coulton, Jerome Philip Jack. "Effect of elevated strain rates on the mechanical performance of polyethylene structures". Thesis, University of Warwick, 1996. http://wrap.warwick.ac.uk/50492/.
Abstract (sommario):
The theme of this research was the development of an integrated approach to establish how the stiffness of a thermoplastic material could be measured and modelled for use in impact simulations. By undertaking this an understanding was obtained of how thermoplastic materials behave and the structures that are made from them perform when subjected to mechanical impact loads. A series of tensile tests was undertaken using three control methods to establish a tensile test control method suitable for a wide range of strain rates. The effect of applied strain rate on the mechanical performance of High Density Polyethylene (HDPE), as illustrated by the tensile stress-strain curve, was investigated. Tests were performed at various elongation rates and temperatures to simulate different practical operating conditions. Extensive use of the finite element method was made in simulating the mechanical impact performance of various beam, disc and automotive fuel tank structures with the predictions of these analyses being correlated with experimental test data. The research is novel and of direct practical relevance as indicated by the prediction and correlation with experimental data, of the impact performance of a HDPE fuel tank, which to the author's knowledge has not been previously done. The demonstrated methodology thus provides a significant advance in the prediction of the impact performance of components made from polymers, whose mechanical performance is strain rate sensitive.
27
Calmeyn, Timothy J. "Optimization of the melt-phase polyethylene terephthalate manufacturing process". Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1179336415.
28
Venugopalan, Premnath. "Radiation induced structure/property changes in ultrahigh molecular weight polyethylene : implications for total hip replacements". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10288.
29
Ralph, J. "Chemical treatment of backsawn Tasmanian Oak with Polyethylene Glycol (PEG) prior to drying". Thesis, University of Tasmania Library, Special & Rare Materials Collections, 2006. https://eprints.utas.edu.au/1222/1/JRalphthesis_front.pdf.
Abstract (sommario):
A series of experiments was conducted with the view of obtaining baseline information
on the use of polyethylene glycol (PEG) on Tasmanian Oak for the purpose of improving
the quality of the seasoned structural timber product. Tasmanian Oak is the marketing
name for a triad of Tasmanian-grown eucalypt species (E. delegatensis, E. obliqua, and E.
regnans). Incubation of freshly-milled timber in aqueous PEG solutions prior to
seasoning follows on from investigations in northern hemispheric timber species such as
hoop pine and spruce in the middle of the 20th Century.
PEG penetrates freshly sawn Tasmanian Oak in a manner which is considerate of
incubation time, temperature, PEG molecular weight/size and timber density.
Histological examination indicated that PEG penetrated completely throughout the
structure of the wood substance in three orientations (transverse, radial and tangential).
During air-drying of PEG soaked timber, further migration of PEG into Tasmanian Oak is
negligible. The rate of moisture content loss in Tasmanian Oak was shown to be retarded
by PEG pre-treatment although the ability to prevent moisture loss was not concomitant
with dimensional stability. An investigation to explain the change in rate of moisture loss
examined effects on the thermodynamic property, water activity. Results indicated that a
change in solution water activity could partly expain changes in the rate of moisture
content loss, but more research is required to better divine this relationship.
Shrinkage in Tasmanian Oak was reduced after treatment with aqueous PEG 400
solutions at or above 30% (v/v), with a greater percentage reduction in tangential
shrinkage compared to reduction in radial shrinkage. This is significant as backsawn (a.k.a. flatsawn) timber, with its broader tangential face, was in particular focus. The
reduction in shrinkage was consistent with PEG concentration in the incubating medium.
A decrease in the formation of drying defect, such as surface and internal checking
accompanied the improvement in keeping sawn dimensions.
Backsawn Tasmanian Oak obtained from young trees (less than 20 years) from plantation
resource presents a challenging profile for commercial timber drying and will become
more prevalent as the logging of old-growth forests is phased out. Timber seasoners may
be faced with options of longer drying times or lower yields due to drying defect unless a
method can be developed to provide added protection to the sawn timber product during
drying. At this stage, pre-treatment of Tasmanian Oak with PEG shows the hallmarks of
providing a solution to this emerging dilemma.
30
Li, Pi Shan Colin. "Approaches to Tailoring the Structure and Properties of Polyethylene". Thesis, University of Waterloo, 2002. http://hdl.handle.net/10012/798.
Abstract (sommario):
Alternative methods to control the molecular weight and short chain branching distribution of polyethylene were investigated. The ability to produce polyolefins with multimodal microstructural distributions using single catalyst/single reactor set-up is very attractive and could, in principle, be used to produce polyolefin resins with advanced molecular architecture. In this thesis, resins with controlled microstructures were produced, characterized and properties tested in order to develop a better understanding of polymerization structure-property relationships. Copolymerizations of ethylene and 1-hexene were carried out with an in-situ supported metallocene catalyst. Copolymers were produced with different alkylaluminum activators and the effect on molecular weight and short chain branching distributions was examined. It was found that different activator types produce polymer with unimodal and narrow molecular weight distributions but with very different short chain branching distributions. Each activator exhibits unique comonomer incorporation characteristics to produce bimodal short chain branching distributions with the use of a single activator. By using individual and mixed activator systems, it is possible to control the short chain branching distributions of the resulting copolymers while maintaining narrow molecular weight distributions. To further investigate the capabilities of this in-situ supported catalyst system, an experimental design was carried out to study the effect of polymerization conditions on the catalyst activity and microstructure of poly(ethylene-co-1-octene). The parameters investigated were: polymerization temperature, monomer pressure, chain transfer to hydrogen, comonomer/ethylene feed ratio and concentration of alkylaluminum. The effect of each parameter on the catalyst activity, comonomer incorporation and molecular weight distribution was investigated. The results obtained were not typical of a conventional single-site catalyst. The copolymerization system was sensitive to all of the parameters and many interactions were evident. The most prominent effect was the catalyst response to temperature. As the temperature was decreased, the short chain branching distributions of the copolymers became broad and bimodal. Overall, it was found that a wide range of microstructures could be produced, ranging from copolymers with low and high 1-octene content with unimodal to broad short chain branching distributions, and from low to high molecular weight with narrow to broad molecular weight distributions. To examine the effect of these broad short chain branching distributions on the polymer properties, a series of poly(ethylene-co-1-hexene) resins with very distinct, and in some cases bimodal crystalline distributions, were synthesized. The attractive feature of the resins in this study is that their molecular weight distributions are similar but each possesses a different short chain branching distribution, thus effectively minimizing the effect of molecular weight on the properties investigated. It was found that the tensile properties of a copolymer could be controlled by the ratio of the crystalline species present in the sample. In this study, a balance of stiffness and toughness was exhibited by a copolymer containing a large proportion of crystalline material and a small fraction of material of lower crystallinity. A series of poly(ethylene-co-1-octene) resins with tailored molecular weight and short chain branching distributions were synthesized with a heterogeneous metallocene catalyst in a two-stage polymerization process. Blends of high molecular weight copolymer and low molecular weight homopolymer and reverse blends of low molecular weight copolymer and high molecular weight homopolymer were produced. The physical properties of these resins were tested for their dynamic mechanical (tensile) and rheological properties. Increasing the copolymer content in the blend resulted in a decrease in stiffness. However, the energy dampening properties of these blends benefit from the presence of the copolymer. It was also confirmed that the melt flow properties of polymers mostly depend on their molecular weight distribution. Regardless of the comonomer content, the melt viscosities decreased with the addition of low molecular weight polymer.
31
Pan, Junjie Pan. "Carbon Particulate Assisted Extrusion Foaming of Polyethylene Terephthalate (PET) by Controlled-Hydrolysis for Thermal Insulation Applications". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1542054222984301.
32
Itim, Bachir. "Influence of polyolefin contamination on the thermal characteristics of bottle grade recycled polyethylene terephthalate". Thesis, London Metropolitan University, 2015. http://repository.londonmet.ac.uk/922/.
Abstract (sommario):
During the mechanical recycling, especially during the sorting and separation process of bottle grade PET, cross contamination with polyolefin is inevitable. Very small number of polyolefin bottles, caps and closures pass through the separation process and get recycled with PET bottles and affect the final characteristics of the recyclate. The effect of this cross contamination and the influence of polyolefin contamination on the overall characteristics of bottle grade recycled PET, especially the thermal characteristics with emphasis on crystallinity, were thoroughly investigated. The investigation showed that the inclusion of polyolefin contamination influenced the overall characteristics of the bottle grade rPET matrix and indicated incompatibility of polyolefin contaminants and rPET-bg. This influence had an impact on the viscosity, elasticity and strength of the rPET-bg matrix. Furthermore, the crystallinity of the rPET-bg matrix showed the impact of polyolefin contamination as a result of variation of cooling rates and that cross-linking and chain branching predominated over chain scissions as a result of repetitive extrusions. The crystallisation process of the non contaminated rPET-bg and rPET-bg contaminated with polyolefin depended on many influencing factors, such as impurities, cross-linking, chain branching, chain scissions, cooling rates and repetitive extrusion cycles. Also, the crystallisation mechanism fully depended on the nucleation and growth rates and that competition between nucleation and molecular mobility was influenced by the variation of cooling rates and repetitive extrusion cycles. As a result, the thermal characteristics were greatly influenced by the inclusion of polyolefin contamination, especially crystallinity, as shown and validated by the Avrami and Ozawa models and that the findings are a step forward and an original insight on the influence of polyolefin contamination at industrial scale.
33
Pattalachinti, Ravi Kumar. "Modeling and optimization of continuous melt-phase polyethylene terephthalate process". Ohio : Ohio University, 1994. http://www.ohiolink.edu/etd/view.cgi?ohiou1178728743.
34
Goring, Paul Derek. "Amphiphilic polyethylene block copolymers and their application as wax crystal modifiers in middle-distillate fuels". Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/99180/.
Abstract (sommario):
Chapter 1 Reviews the synthesis of polyolefin block copolymers, focussing on strategies involving catalytic coordination polymerisation to produce end-functionalised polyolefins followed by the growth of a second block from the reactive end group using living/controlled techniques. The advantages and disadvantages of the various literature methods are discussed. Chapter 2 Discusses the utilisation of the Catalytic Hydride Insertion Polymerisation (CHIP) mechanism for the synthesis of low molecular weight polyethylene macromonomers by manipulating the relative concentrations of dihydrogen and ethylene in the reactions. The application of the mechanism is investigated further with the introduction of two non-styrenic comonomers 5-vinyl-2-norbornene and 5-ethylidene-2-norbornene. Observations made when we studied the effects of comonomer concentration and dihydrogen partial pressure on the products are discussed and some mechanistic insights for the copolymerisation between ethylene and norbornene derivatives in the presence of dihydrogen are proposed. Chapter 3 Focusses on the investigation of the mechanism for the copolymerisation between the PE-i-DIB macromonomer and n-butyl acrylate using a small-scale batch process and a larger scale starved feed semi-batch process. Observations are found to be consistent with a reversible cross-propagation mechanism between PE-i-DIB and the propagating P(n-BA) chain in which the continued availability of monomer is key to the lifetime of the process, as demonstrated by the difference in the evolution of molecular weight in the batch and semi-batch processes. The semi-batch process also provides superior control over the copolymerisation compared to the batch process. Chapter 4 Investigates the versatility of the PE-i-DIB macromonomer in copolymerisations with several other types of polar monomer. Copolymer products with vinyl esters, methacrylates and styrenes are synthesised and the challenges provided by the new monomer types are discussed. The products discussed here and in Chapter 3 are characterised by NMR, GPC, DLS and DSC and the evidence is found to be consistent with the presence of block copolymers. Chapter 5 Describes the testing of some of the block copolymers synthesised in Chapters 3 and 4 for their wax crystal modification properties in one type of diesel fuel. The block copolymers were tested as neat additives and in formulation with commercial nucleators and growth arrestors in the Cold Filter Plugging Point (CFPP) test to assess performance and to indicate mode of action. The mode of action was then investigated further by observing the effect of the additives on the crystallisation events using DSC. The performance in CFPP and the observations in DSC are consistent with the block copolymers generally acting as nucleating agents, though some also display single-shot activity. There is an observable trend in performance with the varying size of the polar block as well as varying the polar block itself. Chapter 6 Details the experimental procedures used to carry out the work in this thesis.
35
Onggar, Toty, Shayed Mohammad Abu, Rolf-Dieter Hund e Chokri Cherif. "Silvering of three-dimensional polyethylene terephthalate textile material by means of wet-chemical processes". Sage, 2015. https://tud.qucosa.de/id/qucosa%3A35399.
Abstract (sommario):
The aim of this research is to develop a wet-chemical silvering method for a three-dimensional (3D) textile material made of polyethylene terephthalate (PET) to prevent and eliminate biological contaminants in drinking water and other liquid-containing systems. Three-dimensional textile fabrics are particularly well-suited as silvered disinfection materials in water systems, because they have 3D structures, pressure-elastic textile design, and provide large contact areas. Furthermore, water can easily be passed through the structure. The developed wet-chemical procedures are based on aminosilane, which consists of at least two amine groups and is well-suited to form a silver diamine complex. The silvered textile material was coated with cationic silver. After the chemical reduction, the cationic silver turns into metallic silver on the surface of PET spacer fabrics.
The surface morphology of silver-coated spacer fabrics was analyzed and the uniform silver layer on the PET fiber surface was found. X-ray diffraction and energy-dispersive X-ray spectroscopy analysis spectrums showed that the silver was immobilized on the PET fiber surface. The layer thickness and the silver amount were also determined. The silvered spacer fabrics can be used in sealing and/or cooling water systems; therefore, the silver ion release in water was analyzed. Furthermore, textile physical tests for the measurement of breaking force and elongation were carried out. No significant change in breaking force and elongation was observed after silvering of PET spacer fabric.
36
Zhao, Junwei. "Dynamics of space charge and electroluminescence modelling in polyethylene". Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/337550/.
Abstract (sommario):
Space charge has been recognized as an important factor contributing to the electrical failure of the cable insulation. Extensive efforts have been made to investigate space charge dynamics within polymeric insulations under electric stresses. Basic information about space charge has been recognized resorting to modern charge mapping techniques but the underlying mechanisms for charge transport, charge trapping characteristics are not yet well understood. Hence theoretical modelling and numerical simulation are employed to simulate the space charge and provide an insight into the charge distribution in dielectrics. This thesis comprises the quantitative analysis of space charge through numerical modelling and experimental investigations of charge trapping in polymeric insulation materials. A bipolar charge transport model which involves bipolar charge injection from the electrodes, charge transport with trapping and recombination in the bulk has been developed to simulate the dynamics of space charge in polyethylene. The build-up of space charge in polyethylene under dc electric fields has been modelled. The influence of parameters related to the properties of polyethylene on the formation of space charge has been recognized. Furthermore, this model is introduced to simulate the dynamics of corona charge decay in polyethylene. The formation of charge packets in polyethylene is also investigated using a numerical modelling approach. A fast pulsed electro-acoustic system along with a data processing program has been developed to investigate the behaviour of space charge in polyethylene under ac voltages. The understanding of space charge under ac stresses has also been simulated using the further developed bipolar charge transport model. Experiments and simulation have also been expanded into understanding electroluminescence, which is an indication of pre-aging of polymers under ac stress.
37
McCoy, John Themba. "Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene". Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20347.
Abstract (sommario):
High density polyethylene is commonly produced by the slurry phase co-polymerisation of ethylene and other alkenes, using heterogeneous titanium-based Ziegler-Natta catalysts. During grade transitions, when reactor conditions are manipulated to change polymer properties, significant quantities of off-specification product result. Implementing a model-predictive controller based on a dynamic reactor model may allow for minimising losses during unsteady-state operation. Such a model must be developed from a fundamental understanding of polymerisation reaction kinetics and the interaction of effects at various scales, including those of catalyst sites, catalyst/polymer particles and reactor hydrodynamics. The model must also be computationally efficient enough for application to real-time control. The recently-developed pseudo-sites model was used as a fundamental kinetic explanation of polymer property distributions and catalyst activity profiles, in contrast to empirical multi-site models. Laboratory polymerisation experiments were performed at industrially-relevant conditions. Kinetic parameters were fitted to the data, using a novel proposed regression procedure to extract meaningful kinetic parameters. A dynamic reactor model was developed, based on the Segregation Approach. Whereas the more common Population Balance Model must consider multivariate distributions of population members within a chosen volume and requires partial differential equation solution, the Segregation Approach can generate the moments of a distribution by evaluating the evolution of properties without requiring solution over the whole volume. The Segregation Approach and PBM were rigorously compared in the context of Particle Size Distributions, and the Segregation Approach shown to be an order of magnitude more computationally efficient. Steady-state industrial data was used to reconcile model predictions for laboratory and industrial polymerisation. This was the first application of the pseudo-sites model to laboratory data, and first extension to industrial scale. Unsteady-state data from three industrial grade transitions was used to validate the reactor model, which closely matched industrial reactor performance. The model simulated 30-40 hours of real time in 15-25 seconds of calculation time. The reactor model was used to propose improved grade transition strategies; transition duration and waste production were improved by 20-40%. The reactor model has been shown to accurately reproduce real-world results, and is computationally efficient enough to be applied to model-based control applications.
38
Lang, Mason J. "CATALYTIC WASTE GASIFICATION: WATER-GAS SHIFT & SELECTIVITY OFOXIDATION FOR POLYETHYLENE". Cleveland State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=csu1560982761165342.
39
Matsunaga, Masashi. "Development of physico-chemical pretreatments to enhance the biodegradability of synthetic low-density polyethylene film". Thesis, University of Surrey, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343487.
40
Tuesca, Anthony D. Lowman Anthony M. "Synthesis, characterization, and application of polyethylene glycol modified insulin for oral delivery using complexation hydrogels /". Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2715.
41
Tang, Jia. "Modeling contaminant transport in polyethylene and metal speciation in saliva". Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/33734.
Abstract (sommario):
Properties of both chemical contaminants and polymers can impact contaminant diffusivity and solubility in new and aged polyethylene materials for pipes and geomembranes. Diffusivity, solubility, polymer and chemical properties were measured for thirteen contaminants and six polyethylene materials that were new and/or aged in chlorinated water. Tree regression was used to select variables, and linear regression was used to develop predictive equations for contaminant diffusivity and solubility in polyethylene. Organic contaminant properties had greater predictive capability than polyethylene properties. Model coefficients significantly changed between new materials to chlorine-aged materials, indicating changes of polyethylene properties impact the interaction between contaminants and polymers.
The metallic flavor of copper in drinking water influences the taste of water and can cause the taste problems for water utilities. The mechanism of metallic flavor caused by these metals is related to free or soluble ions. Free copper concentrations were measured at different pH in diluted artificial saliva using a cupric ion selective electrode. Three major proteins in human saliva: α-amylase, mucin and lactoferrin, were added in the artificial saliva and the impacts on the chemical speciation of copper were analyzed. Inorganic saliva components, typically phosphate, carbonate and hydroxide combined with copper and greatly influenced the levels of free copper in the oral cavity. Proteins such as α-amylase, mucin and lactoferrin also impacted the chemical speciation of copper, with different affinity to copper. Mucin had the greatest affinity with copper than α-amylase.
Master of Science
42
Ghasem, Nayef Mohamed. "Static and dynamic bifurcation behaviour of the industrial unipol process for polyethylene production in bubbling fluidized bed reactors (S.D.B.B.I.U.P.P.P.F.B.R.)". Thesis, University of Salford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244866.
43
Aydemir, Bugce. "Synthesis Of Mesoporous Catalysts And Their Performance In Pyrolysis Of Polyethylene". Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612830/index.pdf.
Abstract (sommario):
Plastic materials are widely used throughout the world due to their low prices and easy processing methods. A serious problem of environmental pollution is brought with the widespread use of these materials due to their non-biodegradabilty. For this reason, plastic materials are degraded into lower molecular weight liquid and gaseous products which are potential raw materials and fuels for petrochemical industry. The use of catalysts enhances the formation of more valuable hydrocarbons at lower reaction temperatures and residence times.
In this study, aluminum containing MCM-41 and tungstophosphoric acid (TPA) loaded SBA-15 materials were synthesized by impregnation of Al and TPA into hydrothermally synthesized MCM-41 and SBA-15, respectively to be used in catalytic degradation of polyethylene. Al was incorporated into MCM-41 framework with different Al/Si ratios using aluminum triisopropylate as the aluminum source and TPA was incorporated to the porous framework of SBA-15 with different W/Si ratios, using tungstophosphoric acid hydrate as the acid source.
From XRD analysis, it was observed that introducing acidic compounds did not cause deformations in the regularity and by EDS analysis, it was found out that at lower loadings, acidic compounds were introduced more effectively for MCM-41 materials. Nitrogen adsorption-desorption isotherms showed that the synthesized materials exhibited type IV isotherms. SEM and TEM pictures showed the hexagonal regularly ordered structure of SBA-15 and MCM-41 materials. FTIR analysis of the pyridine adsorbed synthesized materials revealed the existence of Lewis and Brønsted acid sites in the synthesized materials. From TGA analysis it was observed that aluminum impregnated MCM-41 samples reduced the temperature of the degradation reaction significantly and TPA loaded SBA-15 samples reduced activation energy of the reaction effectively. In the degradation reaction system, non-catalytic and catalytic degradation experiments of polyethylene were performed. In non-catalytic degradation and catalytic degradation reactions carried out using aluminum containing MCM-41 materials, selectivity of C3 and C4 hydrocarbon gases was high and in catalytic degradation reactions carried out using TPA impregnated SBA-15 materials, selectivity of ethylene was high. In the liquid analysis of non-catalytic degradation reactions, it was observed that the product distribution was mainly composed of hydrocarbons greater than C18. The use of aluminum loaded MCM-41 and TPA loaded SBA-15 materials resulted in a liquid product distribution in the range of C5-C14, which is the hydrocarbon range of gasoline fuel.
44
Fernandez, Loretta A. (Loretta Ana). "A method for using polyethylene passive samplers to measure polycyclic aromatic hydrocarbon chemical activity in sediments". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33699.
Abstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.Includes bibliographical references.
In order to aid in the determination of the hazards posed by hydrophobic organic compounds (HOCs) in sediment beds, a method for the use of polyethylene (PE) sheets as passive sampling devices for measuring chemical activities was explored. A model which depends on a concentration gradient and two mass transfer limiting zones in series was used. Internal tracer chemicals within the polyethylene devices (PEDs) were used to calibrate the mass transfer model which can have different mass transfer coefficients depending on the site and target chemicals being investigated. The model allowed for the measurement of HOC chemical activities by measuring the change of mass of tracer and target chemical within the PED, and knowing the PE-water partitioning coefficient, ..., and the liquid solubility, ..., of the target chemical. The method was tested using PEDs impregnated with dlO-phenanthrene and dlO-pyrene. First, PEDs were used to measure known concentrations of phenanthrene and fluoranthene in stirred seawaters. Seeing that the PEDs performed well, returning results which were within 25% of the known chemical activities, PEDs were then tested for measuring phenanthrene, fluoranthene, and pyrene in Boston Harbor sediments.
(cont.) Porewaters of Boston Harbor sediments were extracted as a benchmark against which to assess the performance of three methods for measuring sediment chemical activities: (1) PEDs using impregnated tracers exposed for 52 and 92 days to simulated sediment beds, (2) sediment extractions and an equilibrium partitioning model as recommended by EPA for determining sediment benchmarks, and (3) PE samplers brought to equilibrium with sediment slurries. The results of this study showed that the two methods using PE passive samplers produced measurements which were within a factor of 2 of the porewater extraction results. The equilibrium partitioning model, however, produced results which were at least an order of magnitude different from the measurements of the other methods. Future work on PEDs is needed to develop faster response times and internal standards which will allow for the measurement of a more diverse set of HOCs.
by Loretta A. Fernandez.
S.M.
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Ahart, Megan Leanne. "Sorption and desorption of the industrial chemical MCHM into polymer pipes, liners and activated carbon". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/73425.
Abstract (sommario):
Polyethylene pipes and epoxy or polyurethane linings are increasingly used in drinking water infrastructure. As a recent introduction to the water industry, there are still many unknowns about how polymers will behave in the distribution system specifically relating to sorption and desorption of chemical contaminants. This study is in response to a spill of 4-methylcyclohexane methanol (MCHM) that occurred in January 2014 contaminating the drinking water of nine counties in West Virginia. This study investigated sorption and desorption of the odorous chemical MCHM into polymer drinking water infrastructure and granular activated carbon (GAC). Experiments for sorption of non-polar toluene and polar 1-butanol were conducted as a comparison for MCHM sorption. Additionally, a brief odor analysis was done on the ability of activated carbon to remove odor from contaminated water and on leaching of MCHM from pipe material into clean water. The results show that MCHM diffusion and solubility in polyethylene pipe materials is low. Solubility in polyethylene ranged from 0.003-0.008 g/cm3 and was more similar to the polar contaminant n-butanol than the non-polar contaminant toluene. Desorption experiments indicated that MCHM sorbed to polyethylene diffused back into water at levels that produced odor. MCHM diffused very quickly into epoxy; its solubility was similar to polyethylene pipe. MCHM caused the polyurethane lining to swell and deform. Granular activated carbon effectively sorbed MCHM to below its odor threshold. The sorption properties of MCHM indicate the potential for contamination of infrastructure and the desorption indicates subsequent recontamination of drinking water.Master of Science
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Labde, Rohan Khushal. "Preparation and Characterization of Polyethylene Terephthalate/Montmorillonite Nanocomposites by In-situ Polymerization Method". University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1271126238.
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Ng, Robin. "Novel tissue scaffolds comprising nano- and micro-structures". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196260817.
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Fernandes, Wren Austin. "Synthesis of an erodible biomimetic hydrogel for drug delivery using native chemical ligation". Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/59502/1/Wren_Fernandes_Thesis.pdf.
Abstract (sommario):
Hydrogels are hydrophilic, three dimensional polymers that imbibe large quantities of water while remaining insoluble in aqueous solutions due to chemical or physical cross-linking. The polymers swell in water or biological fluids, immobilizing the bioactive agent, leading to drug release in a well-defined specific manner. Thus the hydrogels’ elastic properties, swellability and biocompatibility make them excellent formulations for drug delivery. Currently, many drug potencies and therapeutic effects are limited or otherwise reduced because of the partial degradation that occurs before the administered drug reaches the desired site of action. On the other hand, sustained release medications release drugs continually, rather than providing relief of symptoms and protection solely when necessary. In fact, it would be much better if drugs could be administered in a manner that precisely matches physiological needs at desired times and at the desired site (site specific targeting). There is therefore an unmet need to develop controlled drug delivery systems especially for delivery of peptide and protein bound drugs. The purpose of this project is to produce hydrogels for structural drug delivery and time-dependent sustained release of drugs (bioactive agents). We use an innovative polymerisation strategy based on native chemical ligation (NCL) to covalently cross-link polymers to form hydrogels. When mixed in aqueous solution, four armed (polyethylene glycol) amine (PEG-4A) end functionalised with thioester and four branched Nterminal cysteine peptide dendrimers spontaneously conjugated to produce biomimetic hydrogels. These hydrogels showed superior resistance to shear stress compared to an equivalent PEG macromonomer system and were shown to be proteolytically degradable with concomitant release of a model payload molecule. This is the first report of a peptide dendrimers/PEG macromonomer approach to hydrogel production and opens up the prospect of facile hydrogel synthesis together with tailored payload release.
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NOVOA, DANNY MESIAS CHAVEZ. "PHYSICAL -CHEMICAL EVALUATION OF HIGH DENSITY POLYETHYLENE PROCESSED BY THE 3D PRINTING METHOD OF FUSED DEPOSITION MODELING FDM". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=24466@1.
Abstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
O objetivo deste trabalho foi estudar a influencia das condições da impressão 3D nas propriedades finais do polietileno de alta densidade usando a modelagem por fusão e deposição, FDM. Foram impressos protótipos com formato de corpos de prova para teste de tração tipo V segundo norma ASTM D638, a três temperaturas de processamento: 220, 240 e 260 Graus Celsius. Para a impressão das amostras foram mantidos constantes os parâmetros de controle, entre eles a espessura da camada de impressão. As amostras impressas foram caracterizadas por difração de raios X, espectroscopia infravermelha, calorimetria diferencial de varredura, análise termogravimétrica, ensaio de tração, índice de fluidez e teste de contração. Os resultados das caracterizações das amostras impressas foram comparados com os resultados do material sem processar, cujas propriedades foram obtidas usando os mesmo métodos de caracterização. Estes resultados demostraram que as condições de impressão por FDM empregadas neste trabalho causaram apenas uma leve mudança nas características estruturais das amostras processadas do PEAD em relação ao material original sem processamento. Houve um leve aumento da cristalinidade no PEAD impresso (em torno de 1,3 a 3 porcento). Além disso, foi comprovado que por causa do resfriamento desigual na superfície e no interior da amostra impressa, o grau de cristalinidade foi levemente maior no interior que na superfície do corpo de prova impresso. A leve mudança no grau de cristalinidade não foi suficiente para causar mudança no módulo de elasticidade e no limite de escoamento em relação ao PEAD original. Outros resultados demostraram que não houve mudança significativa envolvendo formação de ligações duplas, quebra de cadeias e degradação térmica por efeito da condição do processamento utilizada durante a impressão.
The aim of this work was to study the influence of process conditions for 3D printing on the final properties of prototypes of high density polyethylene (HDPE) using the method of the fused deposition modeling. Prototypes for type-V tensile testing according to ASTM D 638 were printed; They were made to three processing temperatures: 220, 240 and 260 Celsius degree. Control parameters for printing were kept constant in all the samples. The printed samples were characterized by X – ray diffraction, infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, tensile test, melt flow index test, and, shrinkage test. The results of the characterization of the printed samples and of the original material were compared. These results demonstrated that the printing conditions employed in this study caused a slight change in the structural characteristics of the printed samples compared to the unprocessed original material, there being a slight increase in crystallinity (about 1,3 to 3 percent) for HDPE which was printed. In addition, it has been proven that the degree of crystallinity was slightly greater on the inside that on the surface of the printed samples, because of uneven cooling on the surface and inside of these samples. The slight change in the degree of crystallinity was not enough to cause change in the elastic modulus and yield strength compared to the original HDPE. Other results showed that there was not significant change involving bond formation, break chains, and, thermal degradation by the effect of the processing conditions used during printing.
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Chen, Jia. "Modified Yttrium Hydroxide/MC Nylon Nanocomposites and Scaling Effects in Multilayer Polyethylene Films". Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6073.
Abstract (sommario):
In this thesis, monomer casting (MC) nylon was synthesized. MC nylon could replace nonferrous metals in certain applications, including gears, wheels, and other moving parts. However, compared with metals, MC nylon products have poor strength and stiffness, and crack easily, especially at low temperatures. In addition, the dimensional stability of MC nylon is poor, especially in the large casting nylon products, causing significant internal stresses due to shrinkage. Thus, MC nylon cracks easily when cast and molded. The yttrium hydroxide particles were modified by stearic acid and dispersed in the caprolactam. The polymerization time was short due to fast anionic polymerization. Copolymerization with different ratios of yttrium hydroxide particles can be used to prepare the copolymer. The effects of different amounts of yttrium hydroxide on the performance of the monomer casting nylon were studied. The products were characterized using X-ray diffraction, impact, and tensile testing. When the percentage of modified yttrium hydroxide is 0.3 wt %, the composite exhibits the maximum impact strength, thus the 0.3 wt % of modified yttrium hydroxide is the suitable percentage to enhance the impact strength of MC nylon.
Transparency and color of polyethylene film layered packages change with the number of layers. When polyethylene layer thickness is between 50 µm and 200 µm, each additional subsequent layer in the package leads to an abrupt change of color and transparency. Polarized light optical effects can be used to manufacture packaging films and labels with forgery protection. A significant influence of the scaling factor on the latent effect and optical properties of the film package is demonstrated for 1 to 6 layers with the total thickness of 200±50 µm. Prior thermal treatment of individual layers before they are assembled into a package or assembled package heat treatment change the laminate color. This allows hidden marking and recording text or graphics on the multi-layer films, not visible under normal lighting conditions, but appearing when viewed in polarized light, or through the polarizer.