While the oxidation of binders in hot mix asphalt (HMA) pavements and its subsequent detrimental effects on pavement life have been well recognized in the last few years, many important issues have not yet been investigated. Understanding how best to design mixtures taking this phenomenon into account and achieving maximum durability is an important and complex issue. This study was aimed at characterizing the effects of oxidative aging on durability in terms of mixture fatigue resistance of laboratory mixed-laboratory compacted (LMLC) samples. Direct tension tests were conducted on HMA samples to measure mixture stiffness and a Modified Calibrated Mechanistic with Surface Energy (CMSE*) analysis method was used to predict fatigue life. The effect of various mix design parameters was evaluated to understand their importance with respect to the aging phenomena and mixture fatigue resistance. Analysis of the results showed that aging has a significant negative effect on mixture fatigue resistance. Considerable increase in the stiffness modulus (Eve) of the mixtures was observed with age for all three mixtures analyzed. Air voids (AV) played a substantial role in affecting the fatigue resistance with aging, but a difference of 0.5% in binder content near the optimum level did not statistically change mixture durability in terms of fatigue resistance with aging. For the three mixtures in Texas included in this study, when comparing Eve, one month of artificial aging in the laboratory was equivalent to 10.5 months of natural aging in the field. A good correlation was also found between the Eve of the mixture and the Carbonyl Area (CA) and Dynamic Shear Rheometer (DSR) function of the extracted binder. Thus, a connection exists between the properties of the extracted binder, laboratory mixtures and field mixtures. This relationship will facilitate development of a more mechanistic aging component in pavement performance prediction models.

The initial objective of this research project was to determine the feasibility of manufacturing carbon fiber-reinforced (CFR) composites with a matrix consisting of a phenylethynyl-terminated version of a thermoplastic poly(etherimide) termed PETU. Successful composite manufacture with 3,000 g/mol (3k) PETU led to a survey of CFR 3kPETU mechanical properties for comparison with other high-performance composites. Encouraging results led to a study of moisture sorption effects on CFR 3kPETU properties. The success of these initial studies spawned the large scale production of 2,500 g/mol (2.5k) PETU. Thermal characterization of neat and CFR 2.5kPETU via differential scanning calorimetry, dynamic mechanical thermal analysis, and parallel plate rheometry resulted in an understanding of the influence of cure time and temperature on reaction progress via both reaction kinetics and monitoring of the glass transition temperature. From the rheological characterization, a two-stage, dual-Arrhenius model was developed to successfully model isothermal complex viscosity over the range of processing temperatures. Neat 2.5kPETU and CFR 2.5kPETU specimens were exposed separately to elevated temperature environments of different moisture and different oxygen concentrations to evaluate the effects of moisture absorption, moisture desorption, and thermal oxidation on material properties. Moisture absorption took place in a 90 °C / 85% relative humidity environment followed by moisture desorption in a 90 °C / 10% relative humidity environment. Thermal-oxidative aging for up to 5000 hours took place at 204 204 °C in environments of four different oxygen partial pressures: 0.0 kPa, 2.84 kPa, 20.2 kPa, and 40.4 kPa. Following exposure to the different aging environments, the specimens were tested for retention of mechanical properties. In addition, moisture sorption properties were measured. Results from the moisture sorption studies on CFR 3kPETU and CFR 2.5kPETU suggest that fully cured composites will withstand moisture absorption and desorption with negligible effects on mechanical properties, whereas, lack of full cure allows moisture sorption to permanently damage the composites. Despite a lack of mass loss or visual evidence of degradation following thermal-oxidative aging, a decline in mechanical properties was observed with the reduction becoming greater with longer aging times and higher oxygen partial pressures. / Ph. D.

La pile à combustible comme moyen de production d'énergie propre et durable participera à la protection de l'écosystème en permettant à la filière hydrogène d'offrir une alternative aux énergies fossiles avant leur total épuisement. Cependant une baisse des coûts et une plus grande durabilité sont indispensables pour ces systèmes et notamment le cœur de pile, constitué d'un assemblage membrane-électrodes (AME). Cette étude a été menée sur une membrane alternative poly-aromatique sulfonée : le PolyEtherEtherCétone sulfoné, ou sPEEK. Cette membrane, qui n'offre qu'une stabilité chimique médiocre, a l'avantage d'offrir une bien meilleure tenue thermomécanique que la membrane de référence Nafion®. Le but de cette étude fut donc d'évaluer l'influence des conditions de fonctionnement sur les performances de la pile utilisant une membrane sPEEK, dans le but de les améliorer, mais aussi de mieux comprendre l'impact du vieillissement chimique de cette membrane sur ses propriétés physicochimiques et sur ses performances en pile. Ce travail fut réalisé en deux temps. Tout d'abord l'étude du comportement de la membrane sPEEK en pile pour différentes conditions d'utilisation a montré que le transport de l'eau dans l'AME est un point déterminant des performances de la pile. En effet une très forte hétérogénéité de fonctionnement imputable à la mauvaise répartition de l'eau dans la membrane sPEEK a été observé, aboutissant à des performances fortement dégradées par rapport à celles du Nafion®. Le diagnostic in situ de la dégradation de la membrane étant difficile et le système particulièrement complexe, il fut ensuite décidé d'étudier « ex situ » le vieillissement chimique de la membrane (dans des conditions de laboratoire). Les membranes vieillies sous l'action de H2O2 (oxydant responsable du vieillissement chimique des membranes en pile) ont ensuite été caractérisées et enfin testées en pile. Il apparaît que le vieillissement chimique résulte en des coupures des chaînes polymère, qui induisent une augmentation du gonflement de la membrane. Pour de forts vieillissements, ces coupures de chaînes entraînent une perte de la tenue mécanique de la membrane, incompatible avec une utilisation en pile. Cependant, pour des vieillissements contrôlés (très faible degré d'avancement), les modifications chimiques induites permettent un meilleur gonflement de la membrane qui résulte en une augmentation de sa conductivité ainsi qu'un meilleur transport de l'eau en pile, permettant d'obtenir des performances comparables à celles du Nafion®. / Fuel cells as production system of clean and sustainable energy will help to protect our ecosystem by providing an alternative to fossil fuels before their total exhaustion. However, lower costs and a greater durability are needed for these systems and more particularly the center of the cell, naming the membrane-electrodes assembly (MEA). This study was performed on a sulfonated poly-aromatic membrane: sulfonated polyetheretherketone, or sPEEK. This alternative membrane, which possesses only poor chemical stability, offers a much better thermomechanical behavior than Nafion®, the reference membrane. Aim of this study was first to understand the impact of operating conditions on fuel cell performance, for a sPEEK membrane, in order to improve performance, but also to better understand the impact of the membrane chemical aging onto its physicochemical properties and the resulting fuel cell performance. First the behavior of sPEEK in fuel cell for different operating conditions showed that water transport in the MEA is critical for fuel cell performance. Indeed a very high heterogeneity of operation due to slow water transport in the sPEEK membrane was observed, resulting in a major drop of fuel cell performance compared with what observed using Nafion®. As in situ diagnosis of membrane degradation is difficult and the system particularly complex, it was then decided to study "ex situ" the chemical aging of the membrane (laboratory conditions). Aged membranes under the action of H2O2 (oxidative responsible for the in situ chemical aging of the membranes) were characterized and finally tested in fuel cell. It appears that the chemical aging results in chains scissions, which induce an increase of the membrane swelling. For too much aging, these chains scissions result in the membrane loss of mechanical strength, incompatible with their use in fuel cell. However, for controlled aging (very low degradation), the induced chemical changes allow better swelling of the membrane resulting in an increase of the conductivity and better water transport in the MEA, making it possible to reach, with sPEEK, as good performance as with the use of Nafion®.

The thesis deals with determination the type, composition and structure of rubber materials comming from gas masks produced withing sixteen years. Rubber materials were tested to determine if storage conditions could influence or caused the change in composition and/or the structure. To judge it rubber specimens were exposed to termo-oxidative aging at 75 and 105 °C for 50 ad 20 days, respectively, to obtain data for comparison. Termogravimetry Fourie-transform Infrared Spectroscopy with Attenuated Total Reflection and Differential Scanning Calorimetry were used to characterize composition/structure of tested speciments. Thermo-oxidative aging at 75 °C led to degradation of additives in both types of rubber, at 150 °C also to chemical degradation of rubber network especially in case of NR (glass transition temperature increases with aging time). Neither additives or rubber network was degraded in original rubber specimens. Deterioration of mechanical and, thus, utility properties of gass masks are not supposed any they are recommended to safe usage.