This research effort investigated the influence of confinement on the physical aging behavior of thin and ultrathin glassy polymer membranes. Membrane permeability changes with time due to physical aging, and for reasons not completely understood, the rate of permeability change can become orders of magnitude faster in films thinner than one micron. Special experimental techniques were developed to enable the study of free standing, ultrathin glassy polymer films using gas permeability measurements. The gas transport properties and physical aging behavior of free-standing glassy polysulfone (PSF) and Matrimid® films from 18-550 nm thick are presented. Physical aging persists in glassy films approaching the length scale of individual polymer coils. The membranes exhibited significant reductions in gas permeability and increases in selectivity with aging time. Additionally, the influence of physical aging on the free volume profile in thin PSF films was investigated using variable energy positron annihilation lifetimespectroscopy (PALS). The films exhibited decreasing o-Ps lifetime during physical aging, while o-Ps intensity remained constant. The o-Ps lifetime was reduced at lower implantation energies, indicating smaller free volume elements near the film surface. Thin films aged dramatically faster than bulk PSF and the PALS results agree favorably to behavior tracked by gas permeability measurements. The physical aging behavior of ultrathin films with different previous histories was also studied. The state of these materials was modulated by various conditioning treatments. Regardless of the previous history, the nature of the aging response was consistent with the aging behavior of an untreated film that was freshly quenched from above Tg, i.e., permeability decreased and pure gas selectivity increased with aging time. However, the extent of aging-induced changes in transport properties of these materials depended strongly on previous history. The properties of these ultrathin films deviate dramatically from bulk behavior, and the nature of these deviations is consistent with enhanced mobility and reduced Tg in ultrathin films, which allows them to reach a lower free volume state more quickly than bulk material. The Struik physical aging model was extended to account for the influence of film thickness on aging, and was shown to accurately describe the experimental data. / text

Long time annealing of semicrystalline PEEK above the glass transition results in the observation of several time dependent phenomena - "physical aging", "secondary crystallization", "multiple melting" of lamellae with different thermal stability etc. Their interrelation - common origin and kinetics of development, is characterized extensively for the first time in this study. The evolution of the crystallinity during the secondary crystallization process was monitored by DSC and density measurements. Crystallinity was characterized according to the standard two-phase model of semicrystalline polymers and analyzed with respect to the failure of the model to adequately describe the physical state of the polymer. A discrepancy was observed between DSC and density crystallinity values and their respective rates of development during the secondary crystallization stage. WAXS reveals that the crystal density is not a physical constant, but depends on the crystallization and/or annealing temperature. Furthermore, the crystalline lamellae densify with time during crystallization and/or annealing. This observation leads to the conclusion that there is no one-to-one correspondence between density and crystallinity and necessitates the application of a revised equation for density crystallinity which accounts for the dynamics of crystal densification. The characteristics of the low temperature endothermic peak in the DSC scan of PEEK (peak maximum, transition enthalpy etc.) were found to evolve with annealing time and temperature during the secondary crystallization process in a way similar to the kinetics of development of the enthalpy relaxation process in amorphous polymeric glasses. This study reports for the first time in the literature the observation of "physical aging" above the glass transition in the case of PEEK (according to the definition of this term given by Struik). An extensive investigation of the "double melting"/"multiple melting" phenomenon, which is observed as a result of isothermal treatment of the polymer above Tg, was performed and several new observations reported. After the end of the primary crystallization process, the semicrystalline polymer is a nonequilibrium system due to the fact that crystallinity is less than unity. The system's continuing approach to equilibrium and its response to mechanical perturbations follow kinetics similar to that of segmental relaxation below the glass transition. / Ph. D.

No description available.

Cyanate ester thermosetting resins are a novel family of materials for high technology and aerospace applications. The high glass transition temperatures available from cured cyanate ester networks and subsequently, their resistances to corrosive materials make these resins attractive for harsh environmental applications. These features of cyanate ester resins presented a threefold opportunity for investigation, namely: 1) establish a characterization technique for the long term mechanical properties of the cured resins, 2) develop a method for determining the effect of physical and chemical aging on these mechanical properties, and 3) evaluate the AroCy® B-10 cyanate ester resin from Ciba-Geigy for use in applications where temperatures could easily reach 177°C (300°F). Dynamic mechanical analysis used in a step isothermal mode was developed to characterize the mechanical properties of the cured resin and a family of isothermal modulus curves was established. These data were then shifted, following WLF theory, to create a master curve of storage modulus with respect to measurement frequency. The resultant master curves allowed the prediction of long term mechanical behavior of the resin networks via short duration, accelerated experimental tests. The test methodology and experimental procedures were especially useful in determining the effects of physical and chemical aging on the mechanical properties of the resin. Cured resins were aged in oxidative and inert atmospheres (air and nitrogen, respectively) for varying time and temperature to study the suitability of cyanate ester resins for harsh environmental applications. After aging, the samples were tested by DMA, DSC and TGA and master curves of their mechanical behavior were generated. The results were then grouped to form a family of master curves as a function of atmosphere, time and temperature. This approach allowed for the separation of the competing chemical and physical degradation processes and established the practical application conditions for this class of cross-linked polymers. Using the techniques established above, a model cyanate ester resin was selected based upon its chemical simplicity and availability. AroCy® B-10 cyanate ester resin manufactured commercially by Ciba-Geigy was evaluated for its application where temperatures could easily reach 177C. While this material was clearly unacceptable for the stated application conditions (especially in an oxygen rich atmosphere), its investigation provided experimental confirmation of the techniques developed. The test procedures and performance evaluation techniques described allow for the systematic assessment of not only the cyanate ester class of networking polymers, but any glass forming material, and a separation methodology for their concomitant chemical and physical degradation pathways. / Ph. D.

Polycarbonate (PC) is a glassy engineering thermoplastic that has been used for decades because of its superior mechanical properties such as high toughness and stiffness, and for its general thermal stability. However, the industrial demand for higher performance polymers with faster processing times has caused PC to be gradually replaced by different engineered polymer blends, such as polycarbonate/acyrlonitrile-butadiene-styrene (PC/ABS). Blends combine the advantages of the individual components but because they are a relatively new class of materials, their time-dependent behaviour is less well understood. The goal of the present work is to characterize two primary time-dependent processes in a commercial 75:25 PC:ABS blend that are known to affect the long-term mechanical properties of the individual components. The first is physical aging which is a result of non-equilibrium fast cooling of glassy or amorphous polymers. Physical aging is associated with structural relaxation due to enthalpic and volumetric recovery. The second process is hygrothermal conditioning which is the combined application of thermal aging and moisture absorption. Three sets of characterization tests were conducted using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared spectroscopy (FTIR). The enthalpic relaxation results determined from DSC data for aging at nine different combinations of time and temperature showed that aging experiments are best conducted at temperatures between 80 and 90°C. This range is below the glass temperature of the ABS component. The activation energy for enthalpic relaxation for the unaged blend was found to fall between energies for PC and ABS relaxations, but not according to the rule-of-mixtures. The present study attempted to adopt the Tool–Narayanaswamy-Moynihan (TNM) phenomenological model to predict relaxation kinetics but was found to be complicated by multiple endothermic peaks. It was then concluded that the TNM model, although very useful for single polymer systems, is unsuitable for blends. A semi-empirical model was applied instead to fit the experimental data which provided a reasonable estimate of the relaxation behaviour. Aging at 80°C for the period investigated did not reach equilibrium and it is expected that aging times of upwards of 2 years will be necessary to minimize the errors associated with the data fitting to provide a better fit of the model. The FTIR studies revealed that thermal aging at 80°C in dry atmosphere results in oxidation of the butadiene component. However, the addition of moisture to the aging process appears to prevent, or at least impede, oxidation from occurring. The presence of moisture seems to trigger hydrogen bonding, which saturates regardless of the moisture content after approximately 80 days. The initial rate of moisture diffusion in PC/ABS appeared to depend predominantly on temperature while the ambient moisture concentration tends to only affect the final equilibrium content in the blend.

Polycarbonate (PC) is a glassy engineering thermoplastic that has been used for decades because of its superior mechanical properties such as high toughness and stiffness, and for its general thermal stability. However, the industrial demand for higher performance polymers with faster processing times has caused PC to be gradually replaced by different engineered polymer blends, such as polycarbonate/acyrlonitrile-butadiene-styrene (PC/ABS). Blends combine the advantages of the individual components but because they are a relatively new class of materials, their time-dependent behaviour is less well understood. The goal of the present work is to characterize two primary time-dependent processes in a commercial 75:25 PC:ABS blend that are known to affect the long-term mechanical properties of the individual components. The first is physical aging which is a result of non-equilibrium fast cooling of glassy or amorphous polymers. Physical aging is associated with structural relaxation due to enthalpic and volumetric recovery. The second process is hygrothermal conditioning which is the combined application of thermal aging and moisture absorption. Three sets of characterization tests were conducted using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared spectroscopy (FTIR). The enthalpic relaxation results determined from DSC data for aging at nine different combinations of time and temperature showed that aging experiments are best conducted at temperatures between 80 and 90°C. This range is below the glass temperature of the ABS component. The activation energy for enthalpic relaxation for the unaged blend was found to fall between energies for PC and ABS relaxations, but not according to the rule-of-mixtures. The present study attempted to adopt the Tool–Narayanaswamy-Moynihan (TNM) phenomenological model to predict relaxation kinetics but was found to be complicated by multiple endothermic peaks. It was then concluded that the TNM model, although very useful for single polymer systems, is unsuitable for blends. A semi-empirical model was applied instead to fit the experimental data which provided a reasonable estimate of the relaxation behaviour. Aging at 80°C for the period investigated did not reach equilibrium and it is expected that aging times of upwards of 2 years will be necessary to minimize the errors associated with the data fitting to provide a better fit of the model. The FTIR studies revealed that thermal aging at 80°C in dry atmosphere results in oxidation of the butadiene component. However, the addition of moisture to the aging process appears to prevent, or at least impede, oxidation from occurring. The presence of moisture seems to trigger hydrogen bonding, which saturates regardless of the moisture content after approximately 80 days. The initial rate of moisture diffusion in PC/ABS appeared to depend predominantly on temperature while the ambient moisture concentration tends to only affect the final equilibrium content in the blend.

This research project investigated physical aging and carbon dioxide plasticization behavior of glassy polymer films. Recent studies have shown that thin glassy polymer films undergo physical aging more rapidly than thick films. This suggests that thickness may also play a role in the plasticization and conditioning responses of thin glassy films in the presence of highly-sorbing penetrants such as CO₂. The effect of film thickness on CO₂ permeation and sorption was studied extensively through carefully defined and controlled methods that provide a basis for future study of plasticization behavior. Thin films are found to be more sensitive than thick films to CO₂ exposure, undergoing more extensive and rapid plasticization at any pressure. The response of glassy polymers films to CO₂ is not only dependent on thickness, but also on aging time, CO₂ pressure, exposure time, and prior history. Thin films experiencing constant CO₂ exposure for longer periods of time exhibit an initial large increase in CO₂ permeability, which eventually reaches a maximum, followed by a significant decrease in permeability for the duration of the experiment. Thick films, in contrast, do not seem to exhibit this trend for the range of conditions explored. For a series of different polymers, the extent of plasticization response tracks with CO₂ solubility. There is little data available for gas sorption in thin glassy polymer films. In this work, a novel method involving spectroscopic ellipsometry is used to obtain simultaneously the film thickness and CO₂ sorption capacity for thin glassy polymer films. This allows a more comprehensive look at CO₂ permeability, sorption, and diffusivity as a function of both CO₂ pressure and exposure time. Like the gas permeation data, these experiments suggest that thin film sorption behavior is substantially different than that of thick film counterparts. Dynamic ellipsometry experiments show that refractive index minima, fractional free volume maxima, and CO₂ diffusivity maxima correlate well with observed CO₂ permeability maxima observed for thin Matrimid® films. These experiments demonstrate that plasticization and physical aging are competing processes. Aging, however, dominates over long time scales. Over time, CO₂ diffusivity is most affected by these competing effects, and the evolution of CO₂ diffusivity is shown to be the main contributing factor to changes in CO₂ permeability at constant pressure. / text

This research project investigated the physical aging of glassy polymers in confined environments. Many recent studies of aging in glassy polymers have observed that aging behavior is often strongly affected by confinement. Understanding aging in confined environments (e.g., thin polymer films and nanocomposites) is vital for predicting long-term performance in applications that use confined glassy polymers, such as gas separation membranes and advanced nanocomposite materials. Aging in bulk and layered films produced via layer-multiplying co-extrusion was studied using gas permeability measurement and differential scanning calorimetry (DSC). The layered films consisted of polysulfone (PSF) and a rubbery co-layering material, with PSF layers ranging in thickness from ~185 nm to ~400 nm. Gas permeation aging studies at 35 °C revealed that the PSF layers in layered films aged in a manner that was similar to bulk PSF and independent of layer thickness. This finding differs from what was observed previously in freestanding PSF films, in which aging depended strongly on thickness and was accelerated relative to bulk. Isothermal aging studies at 170 °C and cooling rate studies were performed on both bulk and layered samples using DSC. The aging of the PSF layers was similar to aging in bulk PSF for films having PSF layer thicknesses of ~640 nm and ~260 nm, while the film with 185 nm PSF layers showed a slightly higher aging rate than that of bulk PSF. The results of the DSC studies generally support the conclusions of our gas permeation aging studies. The absence of strong thickness dependence in aging studies of layered films tends to support the idea that the effect of film thickness on physical aging stems from interfacial characteristics and not merely thickness per se. The physical aging of thin polystyrene (PS) films at 35 °C was also investigated using gas permeation techniques. PS films of 400 nm and 800 nm did not exhibit aging behavior that was highly accelerated relative to bulk or strongly dependent on film thickness. At the thicknesses and aging temperature considered, the aging of PS shows much weaker thickness dependence than that seen in polymers like PSF and Matrimid. / text

This thesis documents and discusses the analysis of material properties and pavement performance for Highway 17 and Highway 655 pavement trial sections located in northern Ontario. The object of this work was to compare laboratory-aged material with recovered asphalt cement and to develop an improved chemical aging method that provides asphalt cement that more closely reflects properties after 8-10 years of service. Physical testing of the asphalt cements was done using a bending beam rheometer (BBR) and double-edge-notched tension (DENT) test for laboratory aged material as well as recovered material from the road. The comparison of the regular BBR, extended BBR and elastic recovery test in BBR is also done for the laboratory-aged and recovered material. Two simple modifications to the regular pressure aging vessel (PAV) aging protocol were investigated as possible ways to improve the correlation between field and laboratory material properties. The length of the PAV aging was doubled to 40 hours and the weight for each pan was halved to 25 grams. It was observed that the presently used RTFO/PAV aging protocol does not produce sufficient aging. Hence, the conditions chosen were more severe and therefore are likely to bring the laboratory aging closer to the field aged condition. It was found that both the increase in time and the reduction in weight were able to accomplish the stated objective for most but not all asphalt cements. A separate investigation involved the infrared (IR) analysis of asphalt cements recovered from a large number of contracts in eastern and northeastern Ontario. This study indicated that those asphalts with a largely paraffinic structure (low aromatics index) showed excessive and premature cracking even at lower levels of oxidation (carbonyl index). In contrast, those pavements that were largely spared of thermal distress were constructed with asphalt cements that contained more aromatics (high IR aromatics indices). Aromatics allow the largely aromatic asphaltenes that are formed upon oxidation to remain well peptized rather than flocculated. Peptized asphaltenes allow for good stress relaxation during winter and spring thaw and thus such materials show a reduced tendency for cracking. / Thesis (Master, Chemistry) -- Queen's University, 2010-12-13 11:25:17.522

In this work the relationship between physical properties, such as physical aging and relaxation time distributions, and chemical structure for a variety of polymeric systems were investigated. Although there is a vast amount of physical aging data for polymers, most of these studies do not attempt to correlate structure with physical aging. Therefore, a set of engineering thermoplastics was examined with the goal of relating certain of their characteristic molecular dimensions to their mechanical and volumetric physical aging attributes.Another series of polymeric materials, based on a poly(ether sulfone) backbone, and having various endgroups differing in size, was also studied to determine physical aging rates and relaxation time distributions. Furthermore, it was concluded that the density of the poly(ether sulfones) increased while the glass transition temperature decreased as the endgroup became smaller.Thermoplastic toughened epoxies were also examined to clarify the importance of covalent bonds between toughener and epoxy on physical aging, relaxation time distributions and fracture toughness. In these studies the covalently bonded tougheners differed from their non-reactive counterparts in the rates of volumetric physical aging at high temperatures for the difunctional epoxy. The solvent resistance of the reactive thermoplastic toughened tetrafunctional epoxy was higher than the non-reactive thermoplastic toughened system. The tetrafunctional epoxies with the reactive toughener also had higher toughener glass transition temperatures. / Ph. D.