Weathering Protocol Research Articles

Impact of weathering on a cement-treated sand

This study’s main goal was to examine how the wetting/drying solicitations affect the mechanical behavior of a cementtreated sand. A quantitative method based on the stress-dilatancy approach was used to assess the effects of two types of wetting and drying cycles of different intensities. The results showed that bonding is primarily altered by the wetting/drying cycles, leading to lower mechanical performances. It has been demonstrated that the weathering effect not only depends on the cement dosage, but also on the cycles’ intensity. The early cycles appeared to have the greatest impact on changes in mechanical performance on the samples treated with 4% cement. However, the accumulation of numerous cycles caused a more progressive degradation on the samples treated with 1% cement. The quantitative assessment of the treatment effect and the weathering progress with cycles was made possible through the evaluation of the bonding ratio. The importance of the imposed wetting/drying cycle protocol for a proper evaluation of the long-term performance of treated soils is highlighted. Further research is needed to define an appropriate weathering protocol that makes sense in light of the real solicitation faced by engineered structures.

Nanoplastics Weathering and Polycyclic Aromatic Hydrocarbon Mobilization.

Despite increasing efforts to recycle plastic materials, large quantities of plastics waste continue to accumulate in the oceans. Persistent mechanical and photochemical degradation of plastics in the oceans yields micro- and nanoscale plastic particles, which represent potential vectors for mobilizing hydrophobic carcinogens in an aqueous milieu. Yet, the fate and potential threats associated with plastics remain largely unexplored. Herein, we apply an accelerated weathering protocol to consumer plastics to characterize the effect of photochemical weathering on the size, morphology, and chemical composition of nanoplastics under defined conditions and validate that the photochemical degradation is consistent with plastics harvested from the Pacific Ocean. Machine learning algorithms trained with accelerated weathering data successfully classify weathered plastics from nature. We demonstrate that photodegradation of poly(ethylene terephthalate) (PET)-containing plastics produces enough CO2 to induce a mineralization process that results in the deposition of CaCO3 on nanoplastics. Finally, we determine that despite UV-radiation induced photochemical degradation and mineral deposition, nanoplastics retain their ability to sorb, mobilize, and increase bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in water and under simulated physiological gastric and intestinal conditions.

Impact of wetting and drying cycles on the mechanical behaviour of a cement-treated soil

The core objective of this study is to analyse the impact of the wetting/drying protocol on the mechanical behaviour of a cement-treated sand. The impact of two types of wetting and drying cycles of different magnitudes was evaluated with a quantitative approach based on the stress-dilatancy approach. The main effect of the wetting/drying cycles is to alter the bonds and consequently diminish the mechanical performance. The weathering effect is shown to be dependent on the cement dosage but also on the intensity of the cycles. For the samples treated with 4% cement, the very first cycles seem to bring the most alteration of the mechanical performance. For those treated with 1% cement, however, the accumulation of multiple cycles leads to more progressive degradation. The evaluation of the bonding ratio permitted the quantitative assessment of the treatment effect and the weathering progress with cycles. The results highlight the role of the imposed wetting/drying cycle technique for a better assessment of the long-term performance of treated soils, even if the definition of an adequate weathering protocol that makes sense with regard to the real solicitation endured by engineered structures deserves additional investigation.

Adhesion between SRP and masonry: Laboratory simulations of the field moisture and salt conditions

Steel-reinforced polymer (SRP) composites are a new addition to the fiber-reinforced polymer (FRP) composite toolbox for structural strengthening. While several authors investigated the bond behavior of SRP composites applied to a masonry substrate, little is known about the role played by the presence of moisture and salt in the wall. This study aims at investigating the bond behavior of SRP-masonry joints under two conditions: i) SRP strips are applied to masonry blocks that have been previously subjected to an artificial weathering protocol consisting in salt crystallization cycles; ii) SRP strips are applied to masonry blocks, and then the SRP/masonry joints are saturated with water. Single-lap shear tests are conducted on the SRP-masonry joints that underwent those two conditions. Digital image correlation (DIC) is used to obtain the strain on the surface of the SRP strips. The distribution of salts in the masonry blocks and at the SRP-masonry interface after failure are investigated as well. Finally, the tensile strength of brick tested in both dry and saturated conditions is determined and compared.

Fragmentation of polymer nanocomposites: modulation by dry and wet weathering, fractionation, and nanomaterial filler.

In recent years, an increasing number of polymeric composites incorporating engineered nanomaterials (ENMs) have reached the market. Such nano-enabled products (NEPs) present enhanced performance through improved mechanical, thermal, UV protection, electrical, and gas barrier properties. However, little is known about how environmental weathering impacts ENM release, especially for high-tonnage NEPs like kaolin products, which have not been extensively examined by the scientific community. Here we study the simulated environmental weathering of different polymeric nanocomposites (epoxy, polyamide, polypropylene) filled with organic (multiwalled carbon nanotube, graphene, carbon black) and inorganic (WS2, SiO2, kaolin, Fe2O3, Cu-phthalocyanines) ENMs. Multiple techniques were employed by researchers at three laboratories to extensively evaluate the effect of weathering: ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), optical microscopy, contact angle measurements, gravimetric analysis, analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectroscopy. This work aimed to elucidate the extent to which weathering protocol (i.e. wet vs. dry) and diverse filler characteristics modulate fragment release and polymer matrix degradation. In doing so, it expanded the established NanoRelease protocol, previously used for analyzing fragment emission, by evaluating two significant additions: (1) simulated weathering with rain events and (2) fractionation of sample leachate prior to analysis. Comparing different composite materials and protocols demonstrated that the polymer matrix is the most significant factor in NEP aging. Wet weathering is more realistic than dry weathering, but dry weathering seems to provide a more controlled release of material over wet. Wet weathering studies could be complicated by leaching, and the addition of a fractionation step can improve the quality of UV-vis measurements.

Adhesion between SRP and Masonry: Influence of Moist Condition of Specimens and Presence of Salts in the Substrate

In recent years, steel reinforced polymer (SRP) composites have emerged as a new technology for structural strengthening, and several researches have validated the effectiveness of SRP for masonry strengthening. Research has been carried out to study the bond behavior of SRP composites applied to a masonry substrate. However, how the moist and salt on masonry surface will affect bond, which is the weak link in real strengthening applications, is little known yet. This study aims at investigating the bond behavior of SRP composites applied to moist and salt-laden masonry blocks that were subjected to an artificial weathering protocol. Single-lap shear tests were conducted to determine the bond behavior, while ion chromatography provided the salts distribution of weathered specimens to interpret some results of the shear tests.

Non-linear release dynamics for a CeO2 nanomaterial embedded in a protective wood stain, due to matrix photo-degradation

The release of CeO2-bearing residues during the weathering of an acrylic stain enriched with CeO2 nanomaterial designed for wood protection (Nanobyk brand additive) was studied under two different scenarios: (i) a standard 12-weeks weathering protocol in climate chamber, that combined condensation, water spraying and UV–visible irradiation and (ii) an alternative accelerated 2-weeks leaching batch assay relying on the same weathering factors (water and UV), but with a higher intensity of radiation and immersion phases. Similar Ce released amounts were evidenced for both scenarios following two phases: one related to the removal of loosely bound material with a relatively limited release, and the other resulting from the degradation of the stain, where major release occurred. A non-linear evolution of the release with the UV dose was evidenced for the second phase. No stabilization of Ce emissions was reached at the end of the experiments. The two weathering tests led to different estimates of long-term Ce releases, and different degradations of the stain. Finally, the photo-degradations of the nanocomposite, the pure acrylic stains and the Nanobyk additive were compared. The incorporation of Nanobyk into the acrylic matrix significantly modified the response of the acrylic stain to weathering.

NanoRelease: Pilot interlaboratory comparison of a weathering protocol applied to resilient and labile polymers with and without embedded carbon nanotubes

A major use of multi-walled carbon nanotubes (MWCNTs) is as functional fillers embedded in a solid matrix, such as plastics or coatings. Weathering and abrasion of the solid matrix during use can lead to environmental releases of the MWCNTs. Here we focus on a protocol to identify and quantify the primary release induced by weathering, and assess reproducibility, transferability, and sensitivity towards different materials and uses. We prepared 132 specimens of two polymer-MWCNT composites containing the same grade of MWCNTs used in earlier OECD hazard assessments but without UV stabilizer. We report on a pilot inter-laboratory comparison (ILC) with four labs (two US and two EU) aging by UV and rain, then shipping for analysis. Two labs (one US and one EU) conducted the release sampling and analysis by Transmission Electron Microscopy (TEM), Inductively Coupled Plasma- Mass Spectrometry (ICP-MS), Ultraviolet–Visible Spectroscopy (UV–Vis), Analytical Ultracentrifugation (AUC), and Asymmetric Flow Field Flow Fractionation (AF4). We compare results between aging labs, between analysis labs and between materials. Surprisingly, we found quantitative agreement between analysis labs for TEM, ICP-MS, UV–Vis; low variation between aging labs by all methods; and consistent rankings of release between TEM, ICP-MS, UV–Vis, AUC. Significant disagreement was related primarily to differences in aging, but even these cases remained within a factor of two.

Water concentration distribution in coatings during accelerated weathering protocols

The long outdoor service life of painted metal and wood objects, often measured in decades, requires the use of accelerated weathering protocols to predict the long-term efficacy and performance of new barrier protective coating candidates. The mechanism of damage imposed on a coating system in accelerated weathering tests must have parity with the damage mechanisms occurring within the system as it undergoes natural, in-service weathering. Similarly, the physical conditions involved in the accelerated exposure regime, including water distribution as it is defined both temporally and spatially, must show equivalency to the natural exposure regime. An added complication in accurately accelerating coating damage is that the wet and dry cycles of accelerated weathering and corrosion test protocols are often performed at different and elevated temperatures from in-service exposure, which results in altered bulk transport and diffusion rates of water during each phase of the weathering or corrosion protocol, when compared to those rates experienced in field or in-service conditions. In this study, Fick’s law of diffusion is applied to coating surfaces exposed to surface water concentrations at cyclical intervals for a set of two-stage accelerated weathering protocols. The governing equations are solved using Laplace transforms followed by time rescaling to account for the variation in temperature, which impacts the diffusion coefficient between the wet and dry portions of several accelerated weathering protocols. This serves to predict the asymptotic average water concentration within the coating as well as at the coating–metal interface, based on the diffusion and temperature parameters of the coating and the parameters of the accelerated weathering protocol, including the duration of each imposed wet or dry stage. The analytic solution to Fick’s second law also allows the water concentration at the substrate–coating interface to be predicted based on Arrhenius parameters of the diffusion process. This resultant average time of wetness and water concentration variance at the coating–substrate interface can be used to more directly compare corrosion and adhesion loss between various accelerated weathering protocols and natural weathering conditions. The numerical average and range of water concentration as a function of coating depth can then be used to interpret coating damage distribution with depth, and enable more insightful comparison of the results of various accelerated weathering protocols. The simulations indicate that good barrier systems may actually exhibit increased barrier properties in accelerated protocols as compared to systems with mediocre or poor barrier performance as determined by global diffusion coefficients. The good barrier coating imparts substantially less exposure challenge to the interface than the mediocre or poor barrier coatings in accelerated weathering protocols. Therefore, in industry-standard tests, the observed performance gain of good barrier coating systems over poor systems may be unduly exaggerated. However, the overall exposure challenge to the interface of a good barrier coating is likely to be larger in service or field conditions due to the much extended time of wet exposure. Thus, laboratory-accelerated weathering cycles that do not consider the impact of temporal and spatial diffusion could potentially misrepresent the quality of a coating, in most cases overestimating the performance of coatings with good baseline barrier protection for adhesion or corrosion protection. In other words, the accelerated weathering protocols do not equally challenge the interface of different coatings operating in the same in-service conditions.

An improved accelerated weathering protocol to anticipate Florida exposure behavior of coatings

A new accelerated weathering protocol has been developed which closely replicates the performance of automotive and aerospace coating systems exposed in South Florida. IR spectroscopy was used to verify that the chemical composition changes that occurred during accelerated weathering in devices with a glass filter that produced a high fidelity reproduction of sunlight’s UV spectrum matched those that occurred during natural weathering. Gravimetric water absorption measurements were used to tune the volume of water absorption during accelerated weathering to match that which occurred during natural weathering in South Florida. The frequency of water exposure was then scaled to the appropriate UV dose. A variety of coating systems were used to verify the correlation between the physical failures observed in the accelerated weathering protocol and natural weathering in South Florida. The new accelerated weathering protocol correctly reproduced gloss loss, delamination, cracking, blistering, and good performance in a variety of diverse coating systems. For automotive basecoat/clearcoat paint systems, the new weathering protocol shows significant acceleration over both Florida and previous accelerated weathering tests. For monocoat aerospace systems, the new weathering protocol showed less acceleration than for automotive coatings, but was still an improvement over previous accelerated tests and was faster than Florida exposure.

Two-Electrode Electrochemical Impedance Sensor: Part 1—Response to Coating Degradation on Conductive Substrates

Abstract Electrochemical impedance spectroscopy (EIS) is widely used for understanding and quantifying the corrosion protective quality of coatings. However, the traditional single-cell EIS (SCEIS) configuration has largely been limited to laboratory testing on small panels partly due to the requirement of an electrical connection to the substrate, which implies damage to the protective coating. We have studied a two-cell EIS (TCEIS) configuration that increases the flexibility of EIS, enabling its use in the field testing of coatings without the need to damage the coating to achieve an electrical connection to the substrate. Comparison measurements between the SCEIS and the TCEIS were carried out with coated panels under three different accelerated weathering protocols (ultraviolet [UV], salt spray, and alternating UV/salt spray). Measurements from the TCEIS and the SCEIS showed similar impedance spectral changes with exposure time under the first two exposure protocols but had significant measurement de...

Natural and artificial weathering characteristics of stabilized acrylic–urethane paints

Depth-profiling by Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA), microhardness and scanning electron microscopy (SEM) observations have been used to monitor degradation chemistries in two-package acrylic–urethane coatings when exposed to different exposure conditions. Three artificial and three natural weathering protocols (QUV, ASTM D5894, ISO20340, Pipady (south of France), Bandol (south of France) and Kure Beach (USA)) were selected for this study. The same chemical events were found to occur under all conditions, particularly under natural and artificial exposures. Both loss of the amide II band at 1520 cm −1 and carbonyl growth occurred but at relatively low rate owing to the presence of hindered-amine light stabilizers in the film. A less typical loss of urea biuret linkages also occurs during all exposures and results in a change in the balance between urethane and urea links across the depth of the film during weathering. The chemical degradation of the polymer matrix involves the formation of species that are readily ablated from the surface and results in loss of gloss, increase in hardness and a rougher topology. The dramatic loss of gloss observed after Pipady and Bandol exposures show that loss of gloss should not be systematically correlated to the advance in chemical degradation.

Failure of navy coating systems 1: chemical depth profiling of artificially and naturally weathered high-solids aliphatic poly(ester-urethane) military coating systems

A variety of weathering protocols are in use in industry and research laboratories to both replicate and accelerate the effects of weathering on coating systems. This work focuses on the use of two artificial and one natural weathering protocol (QUV, GM9540P, Florida beach exposure) in combination with spatially resolved transmission-mode Fourier transform infrared (FT-IR) spectroscopy for the purpose of chemically depth-profiling highly opaque high solids multi-layer poly(ester-urethane) coatings employed by the U.S. Department of Defense. Samples were prepared via subjection to 6/12-week GM9540P exposure, 7/13/25-week Florida beach exposure, or 6-/18-week QUV protocol. Thin (3 μm) cross-section samples were prepared via microtomy and depth-dependant trends in chemical evolutions were analyzed using transmission-mode micro-FT-IR. Scanning electron/energy-dispersive microscopy (SEM/EDS) was conducted on 10 μm cross-sections and spatial distribution/chemical makeup of inorganic constituents were analyzed. An apparent synergistic relationship between weathering protocols was found. It was theorized that a combination of chemistry and morphology of the inorganic fillers was primarily responsible for greater-than-expected photooxidative modification of the polymeric binder.

Failure of navy coating systems 2: failure pathways of artificially weathered navy coating systems applied to chromate conversion coated AA2024-T3 substrates

Dual layer coating systems consisting of volatile organic compound (VOC)-based aliphatic polyurethane topcoats and epoxy primers applied to AA2024-T3 substrates pretreated with chromate conversion coating (CCC) are the current mainstay of the U.S. Navy. Government mandates preclude their future use, however, and they are being phased out of service in favor of new VOC-free topcoat and primer high-solids reformulations. The durability of this new formulation to artificial weathering protocol GM9540P was evaluated using transmission-mode and diffuse reflectance Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) imaging, optical and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) and laser-confocal topography. Extensive blistering of the coating system was observed. Depth-resolved FTIR spectra show a lack of chemical modification of the topcoat layer. Data collected show localized corrosion of the substrate material in the form of pitting, as well as chemical inhomogeneities within the primer layer manifest as regional undercuring of the epoxy matrix. It is hypothesized that barrier failure of the coating/pretreatment system is the result of a cascading series of component-specific failures, notably an apparent shift in the target polydispersity of the prepolymer components of the epoxy primer.

Predicting in-service weatherability of automotive coatings: A new approach

The prediction of long-term weatherability of coatings has always been a difficult task. This task has been made significantly more difficult by the recent, rapid changes in coatings technology. Conventional weathering protocols which rely on observation of appearance changes after outdoor or laboratory exposures have not always been successful in anticipating in-service failures. This paper discusses the reason for this and describes a new approach for estimating inservice weatherability in coatings. The formalism begins by identifying specific failure modes and developing time-to-failure models which are based on fundamental studies of the chemistry and physics of failure. The statistical variation of the key material, process, and exposure parameters in the failure model are described in terms of distribution functions. Since photooxidation plays a critical role in most weathering issues, a specific distribution function for exposure harshness is estimated that can be used to describe the variation in photooxidation rate under actual in-service conditions. By combining a specific failure model with in-service variations in the key parameters, it is possible to estimate in-service failure rates as a function of material and processing variables, thus, allowing for improved risk assessment of any proposed material or processing change. The formalism also provides clearer direction in the design and use of specific laboratory and out-door exposures in predicting performance. The method is illustrated by deriving distributions of time-to-failure based on two different hypothetical mechanisms of photo-induced coating delamination.