Effects Of Chemical Aging Research Articles

Composition and Stability of Plasma Polymer Films Exhibiting Vertical Chemical Gradients.

Controlling the balance between stability and functional group density in grown plasma polymer films is the key to diverse applications such as drug release, tissue-engineered implants, filtration, contact lenses, microfluidics, electrodes, sensors, etc. Highly functional plasma polymer films typically show a limited stability in air or aqueous environments due to mechanisms like molecular reorganization, oxidation, and hydrolysis. Stabilization is achieved by enhancing cross-linking at the cost of the terminal functional groups such as -OH and -COOH, but also -NH2, etc. To overcome such limitations, a structural and chemical gradient was introduced perpendicular to the surface plane; this vertical gradient structure is composed of a highly cross-linked base layer, gradually changing into a more functional nanoscaled surface termination layer. This was achieved using CO2/C2H4 discharges with decreasing power input and increasing gas ratio during plasma polymer deposition. The aging behavior and stability of such oxygen-functional vertical gradient nanostructures were studied in air and in different aqueous environments (acidic pH 4, neutral pH ≈ 6.2, and basic pH 10). Complementary characterization methods were used, including angle-resolved X-ray photoelectron spectroscopy (ARXPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) as well as water contact angle (WCA) measurements. It was found that in air, the vertical gradient films are stabilized over a period of months. The same gradients also appear to be stable in neutral water over a period of at least 1 week. Changes in the oxygen depth profiles have been observed at pH 4 and pH 10 showing structural and chemical aging effects on different time scales. The use of vertical gradient plasma polymer nanofilms thus represents a novel approach providing enhanced stability, thus opening the possibility for new applications.

Chemical aging of single and multicomponent biomass burning aerosol surrogate particles by OH: implications for cloud condensation nucleus activity

Abstract. Multiphase OH and O3 oxidation reactions with atmospheric organic aerosol (OA) can influence particle physicochemical properties including composition, morphology, and lifetime. Chemical aging of initially insoluble or low-soluble single-component OA by OH and O3 can increase their water solubility and hygroscopicity, making them more active as cloud condensation nuclei (CCN) and susceptible to wet deposition. However, an outstanding problem is whether the effects of chemical aging on their CCN activity are preserved when mixed with other organic or inorganic compounds exhibiting greater water solubility. In this work, the CCN activity of laboratory-generated biomass burning aerosol (BBA) surrogate particles exposed to OH and O3 is evaluated by determining the hygroscopicity parameter, κ, as a function of particle type, mixing state, and OH and O3 exposure applying a CCN counter (CCNc) coupled to an aerosol flow reactor (AFR). Levoglucosan (LEV), 4-methyl-5-nitrocatechol (MNC), and potassium sulfate (KS) serve as representative BBA compounds that exhibit different hygroscopicity, water solubility, chemical functionalities, and reactivity with OH radicals, and thus exemplify the complexity of mixed inorganic/organic aerosol in the atmosphere. The CCN activities of all of the particles were unaffected by O3 exposure. Following exposure to OH, κ of MNC was enhanced by an order of magnitude, from 0.009 to ~ 0.1, indicating that chemically aged MNC particles are better CCN and more prone to wet deposition than pure MNC particles. No significant enhancement in κ was observed for pure LEV particles following OH exposure. κ of the internally mixed particles was not affected by OH oxidation. Furthermore, the CCN activity of OH-exposed MNC-coated KS particles is similar to the OH unexposed atomized 1 : 1 by mass MNC : KS binary-component particles. Our results strongly suggest that when OA is dominated by water-soluble organic carbon (WSOC) or inorganic ions, chemical aging has no significant impact on OA hygroscopicity. The organic compounds exhibiting low solubility behave as if they are infinitely soluble when mixed with a sufficient number of water-soluble compounds. At and beyond this point, the particles' CCN activity is governed entirely by the water-soluble fraction and is not influenced by the oxidized organic fraction. Our results have important implications for heterogeneous oxidation and its impact on cloud formation given that atmospheric aerosol is a complex mixture of organic and inorganic compounds exhibiting a wide range of solubilities.

Correlation of the loss in photovoltaic module performance with the ageing behaviour of the backsheets used

AbstractThe influence of the type of backsheet on the electrical performance of test modules was evaluated before and after increasing time of accelerated ageing (damp heat [DH] exposure). Besides the measurement of the electrical power of the modules and the performance of the cells by electroluminescence, the ageing‐induced changes within the polymeric encapsulate and backsheets were investigated by means of vibrational spectroscopy and by thermo analytical methods. In addition, the permeability of the backsheets in the original and aged state was determined. This wide set of test parameters and methods allowed for the detection of correlations between (i) physical and chemical properties as well as their ageing‐induced changes of the materials and (ii) the module performance. A clear dependence of the relative loss in power output upon exposure under DH conditions for 2000 h could be observed for a set of identical test modules varied in composition only in the type of back cover used. While the modules containing gas‐tight backsheets and glass experienced only little loss in the relative power output, some modules with permeable backsheets showed a significant relative decrease in the power output and fill factor in dependence of the backsheet type used. Cell degradation could be visualised by recording electroluminescence images before and after the accelerated ageing test. The permeation properties of the backsheet used and their ageing‐induced changes seem to have an influence on the module performance. However, the absolute values neither of the water vapour transmission rate (WVTR) nor of the oxygen transmission rate (OTR) are directly linked to the loss in power output upon accelerated ageing under DH conditions. It could be shown that the ageing‐induced changes (relative transmission rates) between WVTR and OTR can be correlated with the module performance. These ageing‐induced changes in the permeation behaviour of the backsheets can be explained by (i) physical changes (e.g. post‐crystallisation, changes in the crystal structure or the crystalline microstructure) and (ii) chemical ageing effects such as a decrease in the molecular mass of the polyester (PET) polymer chains because of hydrolytic polymer degradation leading to a change in the crystallisation behaviour of PET. Hydrolytic degradation (= chemical ageing) of the PET core layer was observed (with varying extent) for all PET‐based backsheets and can, thus, not be directly correlated with the loss in performance of the corresponding test modules. The physical ageing effects, however, were detected only for those backsheets showing (i) strong deviating changes in the relative permeation rates for oxygen and water vapour upon accelerated ageing and (ii) a clear loss in electrical performance. Copyright © 2015 John Wiley & Sons, Ltd.

Aging of a polymer core composite conductor: Mechanical properties and residual stresses

Polymer core composite conductor specimens were aged in atmospheric conditions at 140 and 180°C and then tested under four point bending. When aged up to a year at a temperature of 140°C no detrimental effect on flexural performance of the composite was observed, as opposed to aging at 180°C, which had a very negative effect on the properties. A finite element model was developed to characterize the residual stress in the composite on a micro scale using representative volume elements (RVE). The residual stresses developed after aging at 140°C for a year were minimal. However, at temperatures higher than 160°C significant increases in the stresses were observed. The effect of chemical aging on the failure process of the rods was not considered but could result in the rapid reduction in the loads at failure for the rods tested at 180°C for up to a year.

Effects of chemical aging on the ice nucleation activity of soot and polycyclic aromatic hydrocarbon aerosols.

The role of soot particles as ice nuclei (IN) in heterogeneous freezing processes in the atmosphere remains uncertain. Determination of the freezing efficiency of soot is complicated by the changing properties of soot particles undergoing atmospheric aging processes. In this study, the heterogeneous freezing temperatures of droplets in contact with fresh and oxidized soot particles were determined using an optical microscope apparatus equipped with a sealed cooling stage and a CCD video camera. Experiments were also conducted using fresh and oxidized polycyclic aromatic hydrocarbons (PAHs), including anthracene, pyrene, and phenanthrene, as potential ice nuclei. Chemical changes at the surface of the aerosols caused by exposure to ozone were characterized using Fourier transform infrared spectroscopy with horizontal attenuated total reflectance (FTIR-HATR). In addition, Brunauer-Emmett-Teller (BET) measurements were used to determine the specific surface areas of the soot particles. Mean freezing temperatures on fresh particles ranged from -19 to -24 °C, depending on the IN composition and size. In all cases, exposure to ozone facilitated ice nucleation at warmer temperatures, by 2-3 °C, on average. In addition, nucleation rate coefficients for a single temperature and IN type increased by as much as 4 orders of magnitude because of oxidation. Furthermore, a fraction of the oxidized soot particles froze at temperatures above -10 °C. A modified version of classical nucleation theory that accounts for a range of contact angles on nucleation sites within an IN population was used to derive the probability of freezing as a function of temperature for each type of IN. In summary, our results suggest that atmospheric oxidation processes may both extend the range over which particles can act as ice nuclei to warmer temperatures and increase heterogeneous nucleation rates on soot and pollutant aerosols.

Effects of chemical aging on global secondary organic aerosol using the volatility basis set approach

A global 3-D chemical transport model (GEOS-Chem) is used with the volatility basis set (VBS) approach to examine the effects of chemical aging on global secondary organic aerosol (SOA) concentrations and budgets. We present full-year simulations and their comparisons with the global aerosol mass spectrometer (AMS) dataset, the Interagency Monitoring of Protected Visual Environments (IMPROVE) dataset from the United States, the European Monitoring and Evaluation Programme (EMEP) dataset from Europe, and water-soluble organic carbon observation data collected over East Asia. Using different chemical aging constants, we find that the model results with 4 × 10−11 cm3 molecule−1 s−1 are in better agreement with all observations relative to the model results with other aging constants, without aging, and with the two-product approach. The model simulations are improved when chemical aging is considered, especially for rural regions. However, the simulations still underestimate observed oxygenated organic aerosol (OOA) in urban areas. Two sensitivity simulations including semi-volatile primary organic aerosol (POA) were conducted. We find that including semi-volatile POA improves the model in terms of the hydrogen-like organic aerosol (HOA) to OOA ratio. However, the total OA concentrations are not improved. The total SOA production is considerably increased by 53%, from 26.0 to 39.9 Tg yr−1, after considering chemical aging, remaining lower than top-down estimates of SOA production. Direct radiative forcing (DRF) increases by −0.07 W m−2 due to the chemical aging of SOA, which is comparable to the mean DRF (−0.13 W m−2) of OA from the AeroCom multi-model study. This result indicates considerable global and, more importantly, regional climate implications. For example, the regional DRF change due to chemical aging of SOA in the eastern US is −0.29 W m−2, which is 4 times greater in magnitude than the global mean value.

Impact of aging mechanism on model simulated carbonaceous aerosols

Abstract. Carbonaceous aerosols including organic carbon and black carbon have significant implications for both climate and air quality. In the current global climate or chemical transport models, a fixed hydrophobic-to-hydrophilic conversion lifetime for carbonaceous aerosol (τ) is generally assumed, which is usually around one day. We have implemented a new detailed aging scheme for carbonaceous aerosols in a chemical transport model (GEOS-Chem) to account for both the chemical oxidation and the physical condensation-coagulation effects, where τ is affected by local atmospheric environment including atmospheric concentrations of water vapor, ozone, hydroxyl radical and sulfuric acid. The updated τ exhibits large spatial and temporal variations with the global average (up to 11 km altitude) calculated to be 2.6 days. The chemical aging effects are found to be strongest over the tropical regions driven by the low ozone concentrations and high humidity there. The τ resulted from chemical aging generally decreases with altitude due to increases in ozone concentration and decreases in humidity. The condensation-coagulation effects are found to be most important for the high-latitude areas, in particular the polar regions, where the τ values are calculated to be up to 15 days. When both the chemical aging and condensation-coagulation effects are considered, the total atmospheric burdens and global average lifetimes of BC, black carbon, (OC, organic carbon) are calculated to increase by 9% (3%) compared to the control simulation, with considerable enhancements of BC and OC concentrations in the Southern Hemisphere. Model evaluations against data from multiple datasets show that the updated aging scheme improves model simulations of carbonaceous aerosols for some regions, especially for the remote areas in the Northern Hemisphere. The improvement helps explain the persistent low model bias for carbonaceous aerosols in the Northern Hemisphere reported in literature. Further model sensitivity simulations focusing on the continental outflow of carbonaceous aerosols demonstrate that previous studies using the old aging scheme could have significantly underestimated the intercontinental transport of carbonaceous aerosols.

A study of chemical aging effects on HDD Fe–zeolite SCR catalyst

The effect of phosphorus (P) on iron (Fe)–zeolite based selective catalytic reduction (SCR) monolith catalysts was studied in the absence and the presence of sulfur, and at two different exposure temperatures (220 and 450 °C). It was found that exposure of Fe–zeolite SCR catalyst to P resulted in a loss of NOx conversion and an increase of NH 3 slip relative to a degreened baseline sample. Some of the increased slip was attributed to a loss of NH 3 storage capacity due to P blockage of adsorption sites. Additional increased slip resulted from a rise in the slip to storage ratio, likely due to a shorter effective channel length for NH 3 adsorption since most of the P blocked sites at the sample inlet. DeNOx activity was then reduced due to the decreased amount of adsorbed NH 3. P exposure using zero sulfur fuel resulted in the same amount of deactivation as aging done using low sulfur (350 ppm S) fuel, suggesting that this amount of S did not affect this formulation. An initial loss of activity proved to be due to hydrocarbon exposure, and was reversible simply by ramping the sample up in temperature during the evaluation test. Increasing the exposure temperatures also increased the loss of DeNOx performance. It is proposed that P impacts these catalysts by physically blocking adsorption sites for NH 3, primarily at the monolith channel inlet.

Molecular relaxation phenomena during accelerated weathering of a polyurethane coating

Results from a polyester-urethane (PU) coating system under accelerated weathering showed that crosslink density, obtained from high-temperature modulus data, diminished due to chain scission. However, T g and room-temperature tensile modulus both increased with weathering. Molecular relaxation phenomena in polymers have long been investigated to explore changes occurring in a polymer at temperatures below its glass transition and were explored for an explanation to supplement chemical degradation for these observations. Relaxation was quantified using “enthalpy recovery” which first increased with exposure, then diminished. The concurrent physical and chemical aging effects were characterized by tracking nonexponentiality in the spectrum of relaxation times, and the size of “co-operatively relaxing regions” deduced from relaxation around the glass transition. Mechanical relaxation in this coating extended longer than cycle periods typical of accelerated weathering, suggesting that frequency effects might be important when comparing accelerated to natural weathering.

Studies on Poly(Methyl Methacrylate) (PMMA) and Thermoplastic Polyurethane (TPU) Blends

Blends of poly(methyl methacrylate) (PMMA) and thermoplastic polyurethane (TPU) in different compositions viz., 95/5, 90/10, 85/15 and 80/20 (by wt/wt, % of PMMA/TPU) were blended by melt mixing using a twin‐screw extruder. All the PMMA/TPU blends have been characterized for physico‐mechanical properties such as density, melt flow index, tensile behavior and izod impact strength. The impact strength of the PMMA/TPU blends were found to increase significantly with an increase in the percentage of TPU up to 20%, by retaining the tensile strength of PMMA. The effect of chemical aging on the performance of blends has been studied.

A colloidal interpretation of chemical aging of the C-S-H gel and its effects on the properties of cement paste

The properties, structure, and behavior of cement paste, including surface area, drying shrinkage, creep, and permeability are discussed with the assumption that the C-S-H gel is an aggregation of precipitated, colloidal-sized particles that undergoes chemical aging. A basic thesis of this paper is that C-S-H particles bond together over time, increasing the average degree of polymerization of the silicate chains and causing the C-S-H to become stiffer, stronger, and denser. This process occurs slowly at ambient temperatures, but can be greatly accelerated by elevated temperature curing and is also encouraged by drying, which introduces large local strains that may provide a microstructural basis for creep sites. This chemical aging process of C-S-H can thus affect many of the physical properties of cement paste, and there is particular relevance for the complex shrinkage and creep behavior of this material. The effects of a short heat treatment, which causes rapid aging, depend strongly on the moisture of the paste when it is heated. Many of the observations and insights presented here are not new. The primary objective of this paper is to demonstrate, by reporting a variety of published findings in one place, the significant amount of evidence that has been generated over the past 50 years favoring this interpretation. Another objective is to show that the properties and behavior of the C-S-H gel, and of cement paste, do not require a layered microstructure. Separating chemical aging effects from other changes, such as continued hydration, may well lead to a better understanding of the microstructural causes of creep and shrinkage.

Load and depth sensing indentation as a tool to monitor a gradient in the mechanical properties across a polymer coating: A study of physical and chemical aging effects

AbstractLoad and depth sensing indentation has been used to characterize the elastic modulus and hardness of various polycarbonate films. This analytical technique is shown to be extremely suitable for the determination of gradients in these mechanical properties. Furthermore, it is demonstrated that such a gradient exists over a length of micrometers in chemically aged polycarbonate, but it is virtually absent in physically aged polycarbonate. From these results, it is concluded that, although the first 100 nm cannot be probed, physical aging occurs homogeneously throughout the bulk of the sample. However, chemical aging starts at the surface and moves progressively into the bulk of the material. From the study of these films, it appears that for the interpretation of these measurements, knowledge about the amount of creep occurring during the measurements and about the mechanical properties of the substrate on which these films are applied is needed. Creep can be measured with the same indenter through the application of a constant load for a period of time. Load and depth sensing indentation appears to be a powerful method for studying the physical and chemical aging of polymers. It is especially valuable for coatings and films for which conventional tensile testing is problematic. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1628–1639, 2004

QUANTIFICATION OF 14C-LABELED HYDROPHOBIC ORGANIC COMPOUNDS IN SOIL SAMPLES BY A SCINTILLATION FLUID EXTRACTION METHOD

Hydrophobic organic chemicals labeled with 14C are often used as tracers to study chemical fate and transport in soil. Wet oxidation is the recognized but labor-demanding method used most often to measure the concentration of radioactive organic tracers in the soil. In this study, we test an alternative, simpler method for quantification of 14C-labeled hydrophobic organic chemicals in soil samples. The soil samples were extracted directly with scintillation fluid in glass scintillation vials (Scintillation Fluid Extraction, SFE method) and were subsequently analyzed by liquid scintillation counting. Application of internal standards showed no significant quenching or reduced counts of the 14C-labeled chemical caused by the presence of settled soil particles in the scintillation vials. Hence, the scintillation fluid could be used simultaneously as both scintillation and extraction media. Decreasing the amount of soil containing 14C-labeled chemicals added to the scintillation vial was shown to increase the extraction efficiency of the SFE method. Aging (contact time) and concentration were shown to affect the results of the SFE method. However, in a naphthalene diffusion experiment, where aging varied between almost no contact time and 20 days and concentration of naphthalene varied between ∼0 to 40 μg g−1, the estimated naphthalene diffusion coefficient was shown to be influenced only minimally when using the SFE method compared with the wet oxidation method. We emphasize that the SFE method is applicable only to sterile systems with no degradation or assimilation of 14C-labeled compounds. If this condition is met and there is appropriate consideration of the effects of chemical aging and concentration, the SFE method seems to be a useful and labor-saving alternative to the traditional wet oxidation method for determination of the concentration of 14C-labeled organic chemicals in soil samples.

Bioavailability of the genotoxic components in coal tar contaminated soils in Fischer 344 rats.

The effect of chemical aging on the bioavailability and subsequent genotoxicity of coal tar (CT)-contaminated soils was evaluated in a 17-day feeding study using Fischer 344 male rats. Rats consumed a control diet or diets amended with soil, 0.35% CT, or soil freshly prepared or aged for 9 months with 0.35% CT. Mild treatment-related microscopic lesions in liver tissue and elevated enzyme levels in serum were detected in all CT treatment groups. The (32)P-postlabeling assay was employed to determine DNA adduct formation in treated animals. All CT treatment groups induced DNA adducts in both the liver and lung. Adduct levels were 3-fold higher in lung DNA compared to hepatic DNA. After correcting adduct levels for total ingested polycyclic aromatic hydrocarbons (PAHs), a significant decrease (p < 0.05) in adduct levels was observed in both CT/soil treatment groups compared to CT control in liver and lung DNA. Adduct profiles of (32)P-postlabeled hepatic and lung DNA displayed several nonpolar DNA adducts that comigrated with PAH-adducted calf thymus DNA standards as determined through both thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC). These results suggest that soil, but not aging of contaminants in soil, decreases the bioavailability of genotoxic components in CT, as evidenced by DNA adduct analysis.

A Fundamental Overview of Accelerated Testing Analytical Models

This paper describes analytical models that are commonly used for product life estimation and accelerated life testing. Model descriptions include: Miner's "Rule" for describing accumulated fatigue damage; Coffin-Manson nonlinear power law, often applied to mechanical fatigue damage; Rudra model for CFF failures; Arrhenius steady-state temperature acceleration model for estimating chemical aging effects; Peck's model for accelerated combined temperature-humidity effects; and Kemeny model for combined temperature and voltage acceleration effects. The general form of these models will be presented along with specific guidance regarding: relative strengths and appropriate applications for each model; limitations and sources of uncertainty for each model; and example values for exponents and material coefficients.

Measurement of O3 and related compounds over southern Nova Scotia: 2. Photochemical age and vertical transport

Chemical measurements of O3 and other trace substances in the atmosphere over southern Nova Scotia, obtained during 48 flights of the National Research Council of Canada Twin Otter aircraft, provide evidence for a variable degree of processing associated with transport times ranging from less than 1 day to 5 days or more. Effects of chemical aging and dilution are determined using photochemical age estimates derived from the ratios, In (n‐butane/propane) and ln (i‐butane/propane). Age estimates are used in a qualitative sense to divide the data set into four age groups. Vertical profiles and relations between O3 and other trace substances are examined as a function of age group. We find that high‐O3 events occurring in dry air are in the oldest age category. Moist high‐O3 events have photochemical ages that span all four age categories, but the most polluted episodes are only observed in relatively “new air.” A geographically wide range of emission regions is suggested by the hydrocarbon measurements, which is consistent with back trajectory results. The relative depletion of soluble substance (i.e., aerosol particles and NOy) in dry, relative to moist, high‐O3 air masses is discussed with respect to the dilution or precipitation scavenging that must accompany the transport of pollutants from the boundary layer to the dryer middle or upper troposphere. Four case studies are presented that span a wide range of conditions associated with high O3 concentrations. In a pair of these cases, samples were obtained in air masses having about the same photochemical age, altitude, and C2H2 and O3 concentration. One of the pair was from dry air and the other from moist air. The dry air mass had much lower concentrations of NOy and aerosol particles, which was interpreted as evidence for the selective removal of soluble constituents during vertical lifting. The other case studies illustrate a biomass burning plume and the effects of a stable layer over the ocean on transport.

An Evaluation of Chemical Aging/Oxidation in High Performance Composites Using the Vickers Micro-Indentation Technique

Vickers micro-indentation was utilized to follow the changes in micro-hardness and thereby evaluate the chemical aging/oaidation phenomena in two different high performance polymeric composite systems. The two systems under study were1M8/954-2, a carbon fiber-reinforced thermoplastic-toughened thermoset composite, and IM8/ITX, a semicrystalline thermoplastic composite. Oxidation profiles with aging, were obtained on [0°]8 s (unidirectional) composite specimens by indenn across the thickness of the samples in the fiber direction. Samples were aged up to 6 months in environmental chambers at 150°C in three different environments: an inert nitrogen environment, a reduced air pressure of 13.8 kPa (2 psi air), and ambient air pressure. The experimental results show a considerable drop in overall hardness of both IM8/954-2 and 1M8/ITX composites after a week of aging in all of the three environments, possibly attributable to a thermal stress-reieving effect. Very little additional change was observed after 6 weeks aging. Thereafter, the hardness profiles show drops in hardness starting at the specimen edges initially, and then gradually spread to the specimen interior with time. The above observations were indicative of diffusion controlled oxidation in the samples. Also, the hardness drops in the composites appeared to be sensitive to oxygen partial pressure in the aging environment. Samples aged in ambient air were most affected, those in nitrogen least affected, and specimens aged at the reduced pressure were intermediate. A similar diffusion controlled oxidative process was also seen from Vickers indentation results on aged 1M7/5260 thermoset (bismaleimide) composites. This study is a preliminary effort and one of the first of its kind to study the effect of chemical aging in composites using the micro-indentation technique. This work has left some questions unanswered, nevertheless it has shown potential for utilizing micro-indentation as a tool for studying composite behavior in the future. Some suitable modifications to this test technique could enhance its usefulness, thereby gaining greater insights in the area of composite durability.

Chemical aging effects on the physico-mechanical properties of polyester and polypropylene geotextiles: A. Mathur, A. N. Netravali & T. D. O'Rourke, Geotextiles & Geomembranes, 13(9), 1994, pp 591–626

Chemical aging effects on the physico-mechanical properties of polyester and polypropylene geotextiles: A. Mathur, A. N. Netravali & T. D. O'Rourke, Geotextiles & Geomembranes, 13(9), 1994, pp 591–626

Chemical aging effects on the physio-mechanical properties of polyester and polypropylene geotextiles

The influence of groundwater chemistry on the durability of geotextiles is important for the design of municipal and hazardous waste landfills, geotextile reinforcement of slopes and subgrades, and earth retention systems. A series of tests are described in this paper, which explore the effects of various pH and saline environments on geotextiles, thus contributing to an improved understanding of durability as a basis for design. Accelerated aging was performed on polyester and polypropylane geotextiles at room temperature and temperatures elevated to 95°C for six months in saline ( ph∼8 ), strong alkaline (pH 10) and acidic (pH 3) media. Property changes as a result of aging were studied using tensile testing, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and intrinsic-viscosity (I.V.) measurements. Scanning electron microscopy (SEM) was employed to study changes in the surface topography of the fibers upon aging. An Arrhenius model was used to extrapolate results of this short term study to the actual lifetime of the geotextiles. Results indicate that polyester undergoes hydrolytic degradation under both acidic and alkaline conditions at and above the glass transition temperature, with the degradation being more severe under alkaline conditions. The polypropylene geotextile, on the other hand, was relatively inert to the pH conditions and showed no changes in strength. An increase in crystallinity in the initial period of aging was observed for both polyester and polypropylene. In polyester, this was due to preferential attack on the amorphous regions whereas in polypropylene this may be due to nucleation growth and lamellar thickening.

The modelling of aging processes in aerospace materials

The development of a Finite Element (FE) based analytical method to treat the aging of polymers is motivated by the need to assess the effects of chemical aging on the mechanical and failure properties and the subsequent mechanical performance of polymers and polymeric composites under applied loads. There is an additional need to assess the effectiveness of corrective action options when aging problems do occur. An example of a multilayered polymeric - metal component aging problem treated by FE analysis featuring simultaneous diffusion and chemical reaction is presented.