Thermodynamics of Thermoplastic Polymers and their Solutions

Glassy organic polymers are technologically important across the gamut of materials applications from structural (hyperbaric windows) to electronic (ionic conductors, surface coatings for printed circuit boards) to environmental (membranes for industrial gas separation). A formal description and understanding of the glass transition temperature is necessary in order to determine the configurational state and hence physical properties of the glass. Moreover, the non-equilibrium glassy state appears to be unstable: volume-relaxation studies of glassy materials have revealed that they undergo slow processes, which attempt to establish equilibrium. These types of retardation/ relaxation phenomena are called physical ageing. As well as pressure and temperature, sorption of a plasticizer may affect in several ways the membrane physical properties. Generally speaking structural rearrangement of the chains is enhanced and, consequently, the glass transition temperature decreases, physical ageing is usually speed up, the membrane is affected by swelling and/or plasticization and even crystallization can be activated. The research work focuses on the investigation of industrial polymers’ glassy – rubbery behaviour due to thermodynamic state variables change (e.g. temperature T, mechanical pressure P and solvent content ) within the polymer matrix. The goal is to obtain a fundamental insight of the sorption process on both macroscopic and microscopic levels. As a result several polymer—penetrant systems have been studied. Different techniques have been implemented to achieve this goal: dilatometry, MTDSC, gravimetry, manometry and in situ FTIR. The instruments used are: a PVT apparatus from GNOMIX®; a MDSC from TA Instruments®; four different handmade systems consisting of a CAHN microbalance from Thermo Fisher Scientific®, a QSM from RUSKA Co.®, a pressure decay system from MKS® and finally a FTIR from Perkin-Elmer®. All data have been modelled with statistical thermodynamic theories and empirical approaches . The study is divided as follows: the first chapter introduces the research goal and fields of application along with the theoretical background for membrane science; the second chapter reports the study conducted on the system PEI—CO2; the third chapter describes the results obtained on the PS—Toluene system; finally in the fourth chapter the results for the PPO—benzene system are given. The order in which these systems are presented is related to the increase of structural modifications as a result of polymer— penetrant interactions

The Crystallization and Nucleation of Stearic Acid Containing Molecules Under Non-Isothermal Cooling Conditions

Crystallization is commonly used in the production of many products such as ice cream, butter and chocolates. Due to the practical limits of the equipment, crystallization in the industry occurs non-isothermally. Currently, there are a limited number of models which can characterize the crystallization behaviour under such conditions. Crystallization under non-isothermal cooling conditions was studied by using molecules with a stearic acid moiety. These stearic acid containing molecules were selected for their different dimensional crystal growths. 12-hydroxystearic acid (12HSA) was selected to represent one-dimensional crystal growth, stearic acid for two-dimensional crystal growth and trihydroxystearin for three-dimensional crystal growth. In study 1, the modified Avrami model was experimentally validated to model crystallization using non-isothermal cooling conditions. Four techniques were tested which included: small deformation rheology, differential scanning calorimetry, polarized light microscopy and Fourier transform infrared spectroscopy (FT-IR). The experimental validation of the model was done by accurately fitting the parameters of the modified Avrami model; such as induction time, maximal phase change and the Avrami exponent; to the data. FT-IR was the most accurate method because the data collected fitted well to the modified Avrami model. The Avrami exponent obtained from FT-IR was the only technique to be sensitive to both the mode of nucleation as well as the dimensionality of crystal growth. By using the modified Avrami model to characterize crystallization under non-isothermal cooling conditions, the apparent rate constant obtained from the model gave further insights to the kinetics of crystallization under these conditions. Study 2 investigated the nature of crystallographic mismatches in 12HSA fibres which causes branching due to the imperfect incorporation of 12HSA molecules into the crystal lattice. FT-IR was used to monitor the changes during crystallization in the 1700 cm-1 and 3200 cm-1 peaks which corresponded to the dimerization of carboxylic acid monomers and the formation of non-specific hydrogen bonding, respectively. When FT-IR data was fitted to the modified Avrami model, the rate constants obtained increased linearly with the cooling rate for hydrogen bonding while the dimerization of carboxylic acid monomers plateaued at cooling rates above 5 °C/min. Therefore at cooling rates above 5 °C/min, 12HSA does not effectively dimerize when incorporating into the crystal lattice which causes crystal imperfections leading to branching in 12HSA fibres. In study 3, the activation energy for nucleation under non-isothermal cooling conditions was determined using a statistical method. The activation energies for stearic acid, 12HSA, trihydroxystearin and triglycerides were 1.52 kJ/mol, 5.40 kJ/mol (Rogers & Marangoni, 2009), 7.87 kJ/mol and 24.8 kJ/mol (Marangoni, Tang, & Singh, 2006); respectively. The activation energy for nucleation for a molecule is partially affected by its polarity relative to the solvent such that an increase in polarity would result in a decrease in activation energy. However, this was not always observed as the activation energy for stearic acid was less than that for 12HSA. Since the polarity of the molecule does not fully explain the activation energy, a specific interaction was used to account for the larger activation energy observed in 12HSA. The specific interaction describes how molecules are arranged in a nucleus and its ability to hide the polar groups away from the crystal-solvent interface. When the polar groups were not effectively hidden, an increase in the activation energy for nucleation was observed

Mechanochemical Investigation of a Glassy Epoxy-Amine Thermoset Subjected to Fatigue

Covalent bonds in organic molecules can be produced, altered, and broken through various sources of energy and processes. These include photochemical, thermochemical, chemical, and mechanochemical processes. Polymeric materials derive their physical properties from the time scale of motion, summation of intermolecular forces, and number of chain entanglements and crosslinks. Glassy thermoset polymers experience mechanical fatigue during dynamic stress loading and properties diminish with inevitable material failure at stress levels below the ultimate tensile strength (UTS). Damage modeling has been successful in predicting the number of cycles required to induce failure in a specimen due to stress. However, it does not directly provide an explanation of the origin of fatigue in polymers. It is hypothesized herein that mechanical failure at stress levels below the ultimate strength property is due to the accumulation of mechanically induced homolytic chain scission events throughout the glassy thermoset network. The goal of this research will be to quantify homolytic chain scission events with fatigue cycles with the ultimate goal of correlating mechanical property loss with degradation of covalent network structure. To accomplish this goal, stable free nitroxyl radicals were incorporated into an epoxy-amine matrix to detect homolytic chain scission resulting from fatigue. Chapter II discusses a successful synthesis and characterization of the nitroxyl radical molecule, a product of 4-hydroxy-2,2,5,5-tetramethylpiperdin-1-yl-oxyl (TEMPO) and isophorone diisocyanate designated as BT-IPDI. In Chapter III, the epoxy-amine reaction was determined to be unaffected by incorporation of up to 5 wt% of BT-IPDI. Although 50% UTS fatigue studies produced property degradation and fatigue failure as shown in Chapter IV, analysis of BT-IPDI through EPR did not detect homolytic chain scission. Chapter V reveals that mechano-radicals were produced from cryo-grinding the glassy epoxy-amine thermoset, and although the mechano-radicals reacted through recombination at elevated temperatures, the reaction between mechano-radicals and the BT-IPDI was not detected to occur within the glassy state. During mechanical testing, observations of unusual tensile yield behavior were coupled with production of atypical fracture surfaces. In Chapter VI, physical aging was used as an investigative tool to verify that viscous deformation (plastic flow) was required to produce the atypical fracture surfaces. Atomic force microscopy and scanning electron microscopy of the fracture surface both revealed a tendril nodule morphology. It is our hypothesis that this morphology produces the unusual mechanical behavior. In Chapter VII, NIR, AFM, and SEM were used to measure the conversion and morphology of the epoxy-amine thermoset correlated with mechanical properties. The thermal cure profile of the epoxy-amine thermoset affects the size and formation of the nodular nanostructure. Eliminating vitrification during thermoset polymerization forms a more continuous phase, reduction in size of the nodules, and eliminates the capacity of the material to yield in plastic flow. Specific findings of this research reveal that morphology control through thermal cure design may indicate a route in which thermoplastic type failure mechanisms can be incorporated into glassy epoxy thermosets

The production of pure hydrogen with simultaneous capture of carbon dioxide

The need to stabilise or even reduce the production of anthropogenic CO2 makes the capture of CO2 during energy generation from carbonaceous fuels, e.g. coal or biomass, necessary for the future. For hydrogen, an environmentally-benign energy vector whose sole combustion product is water, to become a major energy source, it must be produced in an efficient, CO2-neutral manner. A process, which uses a packed bed of iron and its oxides, viz. Fe, Fe0:947O, Fe3O4 and Fe2O3, has been formulated to produce separate, pure streams of H2 and CO2. The process is exothermic and has the following stages: 1. Reduction of Fe2O3 to Fe0:947O or Fe in syngas (CO + H2) from gasifying coal or biomass. This stage generates pure CO2 for sequestration, once the water has been condensed. 2. Subsequent oxidation of Fe or Fe0:947O to Fe3O4 using steam. This stage generates H2 of sufficient purity for use in polymeric membrane fuel cells. 3. Further oxidation of Fe3O4 to Fe2O3 using air to return the oxide to step (1). It was shown that reduction to Fe0:947O in step (1) gave stable yields of H2 in step (2) after 40 cycles, near those predicted from reaction stoichiometry. By contrast, reduction to Fe, rather than Fe0:947O, in step (1) gave low levels of H2 in step (2) after just 10 cycles. This demonstrates that modifying the iron oxide is unnecessary unless reduction to Fe is performed. Wet-impregnation of Fe2O3 was performed with salts of Al, Cr and Mg or with tetraethyl orthosilicate for Si to give loadings of 1-30 mol % of the additive element. The addition of Al stabilised the quantity of H2 produced when the sample was reduced to Fe. Using a sol-gel method, composite particles with diff erent mass ratios of Fe2O3 and Al2O3 were prepared. For reduction to Fe over 40 cycles, 40 wt. % Al2O3 was required to give stable conversions near 75 % of that expected from reaction stoichiometry. Prior to this research, it had been assumed that the alumina acted as an inert support. However, this was shown to be incorrect since the formation of FeO.Al2O3 was quantitatively confirmed using X-ray diffraction. The presence of the compound, FeO.Al2O3, is significant since it reduces the loss in internal surface area but binds reactive iron, two contradictory e ects for the production of H2. The production of separate streams of pure H2 and CO2 from solid fuels, lignite and subbituminous coal, was demonstrated. Pure H2 with [CO] ~< 50 ppmv and [SO2] ~~ 0 ppmv was produced from a low-rank coal, showing that the process is e cacious with an impure fuel. Contaminants found in syngas which are gaseous above 273 K apparently do not adversely affect the iron oxide material or purity of the hydrogen. Subsequent oxidation of the Fe3O4 with air, step (3), removed sulphurous and carbonaceous contaminants deposited during reduction, generated useful heat and did not lead to a decrease in the H2 yield in step (2). It is therefore recommended that step (3) be included in the process. Rates of reaction are reported for the reduction of iron oxide particles by a mixture of CO, CO2 and N2. Importantly, rates were investigated over multiple cycles. Reduction of either Fe2O3 to Fe3O4 or of Fe3O4 to Fe0:947O was found to be first-order in CO. With the particle sizes used, the rates of reduction were controlled by intrinsic chemical kinetics. Activation energies and pre-exponential factors are reported. The rates were used to simulate, satisfactorily, the reduction of a packed bed of iron oxide. The rate of reduction was doubled by the addition of 1 mol. % Ce to the granulated iron oxide. The overall rate was shown to be dependent on the active surface area of the iron oxide. A lattice Boltzmann model, which incorporates hydrodynamics, mass transport and reaction, was developed. The composition of the solid changed with time. Quantitative agreement between the model and experiments for the reduction of a single particle of Fe2O3 to Fe3O4 in CO was achieved. Additionally, the model correctly predicted a sharp front in the CO concentration for reduction of a packed bed of Fe2O3 to Fe3O4

SREF - a Simple Removable Epoxy Foam decomposition chemistry model.

A Simple Removable Epoxy Foam (SREF) decomposition chemistry model has been developed to predict the decomposition behavior of an epoxy foam encapsulant exposed to high temperatures. The foam is composed of an epoxy polymer, blowing agent, and surfactant. The model is based on a simple four-step mass loss model using distributed Arrhenius reaction rates. A single reaction was used to describe desorption of the blowing agent and surfactant (BAS). Three of the reactions were used to describe degradation of the polymer. The coordination number of the polymeric lattice was determined from the chemical structure of the polymer; and a lattice statistics model was used to describe the evolution of polymer fragments. The model lattice was composed of sites connected by octamethylcylotetrasiloxane (OS) bridges, mixed product (MP) bridges, and bisphenol-A (BPA) bridges. The mixed products were treated as a single species, but are likely composed of phenols, cresols, and furan-type products. Eleven species are considered in the SREF model - (1) BAS, (2) OS, (3) MP, (4) BPA, (5) 2-mers, (6) 3-mers, (7) 4-mers, (8) nonvolatile carbon residue, (9) nonvolatile OS residue, (10) L-mers, and (11) XL-mers. The first seven of these species (VLE species) can either be in the condensed-phase or gas-phase as determined by a vapor-liquid equilibrium model based on the Rachford-Rice equation. The last four species always remain in the condensed-phase. The 2-mers, 3-mers, and 4-mers are polymer fragments that contain two, three, or four sites, respectively. The residue can contain C, H, N, O, and/or Si. The L-mer fraction consists of polymer fragments that contain at least five sites (5-mer) up to a user defined maximum mer size. The XL-mer fraction consists of polymer fragments greater than the user specified maximum mer size and can contain the infinite lattice if the bridge population is less than the critical bridge population. Model predictions are compared to 133-thermogravimetric analysis (TGA) experiments performed at 24 different conditions. The average RMS error between the model and the 133 experiments was 4.25%. The model was also used to predict the response of two other removable epoxy foams with different compositions as well as the pressure rise in a constant volume hot cell

Numerical simulation of ion transport membrane reactors: Oxygen permeation and transport and fuel conversion

Ion transport membrane (ITM) based reactors have been suggested as a novel technology for several applications including fuel reforming and oxy-fuel combustion, which integrates air separation and fuel conversion while reducing complexity and the associated energy penalty. To utilize this technology more effectively, it is necessary to develop a better understanding of the fundamental processes of oxygen transport and fuel conversion in the immediate vicinity of the membrane. In this paper, a numerical model that spatially resolves the gas flow, transport and reactions is presented. The model incorporates detailed gas phase chemistry and transport. The model is used to express the oxygen permeation flux in terms of the oxygen concentrations at the membrane surface given data on the bulk concentration, which is necessary for cases when mass transfer limitations on the permeate side are important and for reactive flow modeling. The simulation results show the dependence of oxygen transport and fuel conversion on the geometry and flow parameters including the membrane temperature, feed and sweep gas flow, oxygen concentration in the feed and fuel concentration in the sweep gas.King Fahd University of Petroleum and MineralsKing Abdullah University of Science and Technology (KAUST) (grant number KSU-I1-010-01

Applications of Calorimetry

Calorimetry is used to measure the transfer and exchange of heat. It is a technique that has applications in different research and industrial sectors. It can be applied in kinetic studies as well as to measure physical changes of first- and second-order transitions such as glass transition, melting, and crystallization. It can also be used to evaluate thermodynamic parameters. This book reports on calorimetry in three sections: “Applications in General”, “Calorimetry in Materials”, and “Calorimetry in Biotechnology”

The polymorphs and solvates of phenylbutazone and their phase transition behaviour

In this study, which was conducted between March 2007 and December 2008, the crystal structure of the alpha polymorph of phenylbutazone has been determined by single crystal X-ray diffractometry. The present findings support those of Singh & Vijayan (1977) and Paradies (1987). Efforts to grow single crystals of the beta and delta polymorphs of phenylbutazone did not locate specimens of adequate quality for structure determination. Nonetheless it was possible to isolate high purity powder samples of these two forms. The powder diffraction pattern of the delta polymorph was measured with improved accuracy at the Diamond synchrotron, and reveals a number of peak overlaps in previously published diffraction patterns of this crystal form. The improved diffraction data have enabled the crystal system of the delta form to be identified as orthorhombic, and space-group selection has been narrowed down to Pnn2 or Pnnm. Four new solvated forms of phenylbutazone have been identified. The crystal structures of two of these new solvates have been determined by single crystal diffractometry. Both have space-group C2/c, and may be considered isostructural with five formerly identified solvates, whose structures were published by Hosokawa et al. in 2004. Previously phenylbutazone has been found to change polymorphic forms at above-ambient temperatures. This behaviour has been examined both in a differential scanning calorimeter and on a powder X-ray diffractometer equipped with isothermal sample heating, where the transition of the alpha and beta polymorphs to the delta polymorph was observed. Thermodynamic methods of predicting the transition temperatures of polymorphs are discussed, particularly those derived from dissolution data. In the case of phenylbutazone, a substantial amount of dissolution data has been collected elsewhere, and these data are used to generate computational predictions of the polymorphic transition temperatures for comparative purposes

ONE-DIMENSIONAL PSEUDO-HOMOGENEOUS PACKED BED REACTOR MODELING INCLUDING NO-CO KINETICS

The air pollution generated from mobile sources creates a large impact on the environment and on people's health. In order to meet the stringent emission regulations worldwide, aftertreatment devices are employed to reduce the toxic emissions emanating from the Internal Combustion engines in these mobile sources. In order to continually reduce emissions levels, it is essential to understand and develop more predictive aftertreatment models. Traditional devices are of the monolithic geometry consisting of small channels employing laminar flow. However, often the reaction rate expressions utilized in these models are derived from more conventional packed bed reactor experimental setups. The aim of this thesis is to develop a one-dimensional pseudo-homogeneous packed bed reactor model for this type of reactor setup built in collaboration with the Chemical and Petroleum Engineering Department at the University of Kansas. A brief summary of the pseudo-homogeneous model is presented in order to properly develop the chemical species and energy equations for dynamically incompressible flow in one-dimension. Furthermore, the chemical kinetics on the reduction reaction of nitric oxide by carbon monoxide over rhodium-alumina and platinum-alumina catalysts is investigated in detail. This is accomplished in order to validate the model using fundamentally correct reaction kinetics via a precise global reaction mechanism. Finally, parametric studies including the different model components are presented and the specific choice of model does not largely influence the conversion profiles because of the similar effective transport values. Also, it is found that a careful consideration of source terms are required to model reactions accurately