Outdoor Weathering Conditions Research Articles

FE-Simulation and Experimental Characterisation of Environmental Effects on the Diffusion and Mechanical Performance of Hyperelastic Adhesive Joints

In operational applications, hyperelastic adhesive joints are exposed to environmental conditions (moisture and temperature) that affect their mechanical performance. The understanding of how the environment can influence the joint durability through both static and cyclic loading is a key aspect to ensure safety and avoid over-dimensioning. The current work presents an investigation of the effect of environment conditions on the diffusion and mechanical performance of two different hyperelastic adhesive joints (a polyurethane and a silicon-modified polymer). To assess the process of moisture mass diffusion, pure adhesive samples were weighted for 387 days when subjected to outdoor weathering conditions. An FEA-diffusion procedure method was demonstrated by (i) predicting the saturation concentration at steady conditions of 40 °C/15% r.h. (40/15) and 40 °C/60% r.h. (40/60), and (ii) predicting the experienced mass change due to outdoor weathering. The reversibility of the effect of conditioning at 40 °C/60% r.h. on the mechanical properties of the adhesives was assessed via quasi-static and fatigue tensile shear testing. The results support the conclusion that conditioning with the surrogate climate of 40 °C/60% r.h. does not cause irreversible damage, as any potential decrease in shear modulus, tensile shear strength and fatigue life due to 40/60 conditioning can be reversed by re-drying at 40/15.

Cellulose Fibre Degradation in Cellulose/Steel Hybrid Geotextiles under Outdoor Weathering Conditions.

Risks from rockfall and land sliding can be controlled by high-tensile steel nets and meshes which stabilise critical areas. In many cases, a recultivation of the land is also desired. However, high-tensile steel meshes alone are not always sufficient, depending on the location and the inclination of the stabilised slope, to achieve rapid greening. Cellulose fibres exhibit high water binding capacity which supports plant growth. In this work, a hybrid structure consisting of a nonwoven cellulose fibre web and a steel mesh was produced and tested under outdoor conditions over a period of 61 weeks. The cellulose fibres are intended to support plant growth and soil fixation, and thus the biodegradation of the structure is highly relevant, as these fibres will become part of the soil and must be biodegradable. The biodegradation of the cellulose fibres over the period of outdoor testing was monitored by microscopy and analytical methods. The enzymatic degradation of the cellulose fibres led to a reduction in the average degree of polymerisation and also a reduction in the moisture content, as polymer chain hydrolysis occurs more rapidly in the amorphous regions of the fibres. FTIR analysis and determination of carboxylic group content did not indicate substantial changes in the remaining parts of the cellulose fibre. Plant growth covered geotextiles almost completely during the period of testing, which demonstrated their good compatibility with the greening process. Over the total period of 61 weeks, the residual parts of the biodegradable cellulose web merged with the soil beneath and growing plants. This indicates the potential of such hybrid concepts to contribute a positive effect in greening barren and stony land, in addition to the stabilising function of the steel net.

Characterizing photovoltaic backsheet adhesion degradation using the wedge and single cantilever beam tests, Part I: Field Modules

Photovoltaic backsheets are exposed to harsh outdoor weathering conditions throughout their service lives that can compromise their protective function, through adhesive debonding between their constituent layers and between the backsheet and the module. A large-scale study on adhesive degradation was conducted on 37 field-exposed modules, that spanned 19 different module manufacturers, that were deployed among six Köppen–Geiger climatic zones, and that were fielded between 0 and 28 years. Six outer layer polymer classes were identified among the backsheets: polyamide (PA), polyethylene terephthalate (PET), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), fluoroethylene vinyl ether copolymer (FEVE), and tetrafluoroethylene hexafluoropropylene vinylidene fluoride copolymer (THV). Two adhesion tests were used to measure the adhesive strength: the wedge test and the width-tapered single-cantilever beam (SCB) test. Adhesion energies were compared across exposure time and Köppen–Geiger climatic zone. Many of the PET-, PVF-, and PVDF-based backsheets experienced degradation of the adhesive layer between the backsheet outer and core layers. A consistent trend of decreasing adhesion energy with exposure time was observed in five out of the six backsheet types. Trends among adhesion energy and climatic zone, while expected, were not observed, possibly due to broad ranges in temperature, humidity, and precipitation defining Köppen–Geiger climatic zones. The cantilever beam measurements produced an upper cutoff of approximately 100 J/m2, above which no modules exhibited field delamination. The results are part of a two-part study quantifying adhesion in both field-weathered and indoor-exposed PV backsheets.

Uncovering the illegible: multi-analytical approach to reveal paint stratigraphy of corroded signposts from the Auschwitz-Birkenau State Museum

Object discoveries from the Auschwitz-Birkenau State Museum (PMA-B) in Poland challenge the efforts to preserve paint on corroded steel supports. The objects have been exposed to outdoor weathering conditions and then buried for about 65 years. This caused severe damage, such as corrosion and paint delamination. The fragile condition of such cultural heritage objects makes their preservation difficult and comprehensive studies for paint conservation are lacking. Additionally, a thorough investigation of used materials is needed to put objects produced by forced labour in historical context. In this study, we analysed signposts from the Auschwitz-Birkenau State Museum (Poland) collection to gain information about used materials, the object’s genesis as well as damage phenomenology. Literature research suggests that the signposts may be produced within the former German NAZI concentration and extermination camp. Inorganic constituents were identified using elemental analysis, such as X-ray fluorescence (XRF) and scanning electron microscopy coupled to an energy dispersive X-ray spectrometer (SEM–EDS). Organic matter was analysed utilizing vibrational spectroscopic instrumentation Fourier transform infrared spectroscopy (FTIR). Our results include the use of synthetic organic pigments (SOPs) and binders, which were newly emerged paint materials at that time. The study highlights the need for conservators to have detailed understanding of composite materials and demonstrates the need for further investigation concerning painted steel objects.

Classification of pre-dyed textile fibers exposed to weathering and photodegradation by non-destructive excitation-emission fluorescence spectroscopy paired with discriminant unfolded-partial least squares

Undyed textile fabrics such as Acrylic 864, Nylon 361 and Cotton 400 were pre-dyed with Basic Green 4 (BG4), Acid Yellow 17 (AY17) and Direct Blue 1 (DB1) dyes, respectively; and then exposed to two extremely diverse weather conditions in the United States: desert and humid environmental settings in Arizona (AZ) and Florida (FL) respectively, for different time intervals of exposure, which included 0, 3, 6, 9 and 12 months. After every interval of a 3 months period, ten fibers were uniformly sampled from each cloth piece, and fluorescence microscopy was employed to collect two-dimensional excitation and fluorescence spectra (2-D spectra) and three-dimensional (3D) excitation-emission matrices (EEMs). A significant loss of fluorescence intensity was observed upon fiber exposure to outdoor weathering conditions. For a comprehensive statistical data analysis and to be able to discriminate between any two single fibers weathered under different conditions, a multiway calibration algorithm known as discriminant unfolded partial least-squares (DU-PLS) method was applied to the exposed fibers. Results indicate that fluorescence spectroscopy combined with DU-PLS has the ability to appropriately classify and differentiate between any two pairs of dyed cotton or nylon fibers (acrylic in some cases) exposed to dry versus humid weather environments under different time intervals of exposure. These results provide the foundation for future studies towards a non-destructive approach capable to provide information on the weathering history of the fiber.

In vitro bioaccessibility of copper azole following simulated dermal transfer from pressure-treated wood

Micronized copper azole (MCA) and micronized copper quaternary (MCQ) are the latest wood preservatives to replace the liquid alkaline copper and chromated copper arsenate preservatives due to concerns over the toxicity or lack of effectiveness of the earlier formulations. Today, the use of MCA has become abundant in the wood preservative industry with approximately 38millionlbs of copper carbonate being used to treat lumber each year. Despite this widespread usage, little information is available on the bioaccessibility of this preservative upon gastrointestinal exposure. Using a simulated hand-to-mouth/gastric system exposure study we investigated several types of commercially available copper-treated lumber products as-purchased and after exposure to outdoor weathering conditions. Soluble and particulate fractions of copper were measured after transfer to and release from surface wipes passed along copper-treated lumber and exposed to synthetic stomach fluid (SSF, pH1.5) or deionized (DI) water. Wipes passed along new boards contained greater amounts of copper than wipes from weathered boards. The total copper recovered from the wipes after microwave extraction varied among the different wood types. For all wood types the copper released into SSF was more soluble than what was soluble in DI water. The data suggest that copper from treated wood is highly bioaccessible in SSF regardless of wood type and weathering condition.

Methodology for quantifying engineered nanomaterial release from diverse product matrices under outdoor weathering conditions and implications for life cycle assessment

Accurate measurement of engineered nanomaterial (ENM) release from diverse product lines and matrices during use is critical to evaluating environmental impacts across the life cycle of a nano-enabled product.

Relationship between physical and mechanical properties of accelerated weathering and outdoor weathering of PVC-coated membrane material under tensile stress

To estimate the photo-oxidation aging performance of PVC-coated membrane material in atmospheric conditions under tensile stresses, the relationship between physical and mechanical properties under accelerated weathering test and outdoor weathering test is studied with the same cumulative UV radiation energy. And then, both tensile strength and whiteness index were measured and compared to characterize the property change of membrane material after aging under four different tensile stresses (0%, 5%, 10% and 20% of the breaking strength), respectively. In addition, FTIR spectrometry was applied to characterize the chemical components of the samples under different weathering conditions, and the carbonyl index was extracted. The results show that there were significant differences of tensile strength and carbonyl index between two kinds of aging conditions, whereas with the increasing tensile stresses, the whiteness index represented a consistent increasing deviation of accelerated weathering from the outdoor weathering. However, the relationship have been built between both whiteness index and tensile strength retention of accelerated weathering and those of outdoor weathering conditions after a Schwarzschild’s modification. Therefore, the service lifespan of PVC-coated membrane materials can be evaluated by accelerated weathering tests under tensile stresses.

Moisture behavior and structural changes of plywood during outdoor exposure

Plywood is an important wood-based construction material yet prone to water uptake, as such potentially decreasing mechanical properties and increasing decay risk. It is therefore, essential to understand the moisture behavior and structural changes of plywood in service. In this research, several plywood specimens were exposed to outdoor weathering conditions for approximately 1 year. During this period, the average moisture variation of and moisture distribution in different veneer layers of a set of plywood specimens and detailed field weather information were recorded continuously. The internal structure of the specimens was also monitored by periodically scanning using X-ray CT. Measurements indicate that moisture distribution in plywood is not homogeneous in outdoor conditions. The second layer can, in some plywood types, accumulate a significant amount of rain, and long rainy periods and cloudy weather can keep the moisture content of the inner layers of plywood significantly high. Moisture accumulation and moisture dynamics, in combination with wood species, are the main factors causing structural changes, mainly occurring as cracks, of the plywood veneers in service. The glue line between the veneers, however, is not ruptured after 1 year of outdoor exposure. Plywood with layers having a slow water sorption and fast water desorption could effectively avoid internal moisture accumulation and cracks in service. Based on the knowledge of the interrelationship of weather data, internal moisture behavior and structural changes in service, fit-for-purpose design of plywood could be improved and service life prediction is at hand.

Mechanical behavior and color change of facial prosthetic elastomers after outdoor weathering in a hot and humid climate

Statement of problemA common reason for replacing a maxillofacial prosthesis is the deterioration of its properties. PurposeThe purpose of this study was to compare the effect of weathering in a hot and humid climate on the tear strength, tensile strength, modulus of elasticity, elongation percentage, and color of 3 maxillofacial materials. Material and methodsThree silicone materials were tested. Specimens were exposed to outdoor weathering for 6 months in a hot and humid environment. Tear and tensile strengths were measured with a universal testing machine before and after outdoor weathering. Color change was evaluated by recording L*, a*, and b* values at base line and after outdoor weathering with a spectrophotometer. The ΔE, ΔL*, Δa*, and Δb* of the specimens were calculated. Data were analyzed with 2-way ANOVA and the post hoc Scheffé test (α=.05). ResultsFor all tested elastomers, outdoor weathering decreased the tear strength and modulus of elasticity values significantly (P<.001). Also, weathering reduced percentage elongation values significantly (P<.05). Tensile strength values were significantly reduced for TechSil S25 and MED-4210 specimens only (P<.05). The effect of weathering on the color of pigmented specimens was greater than the acceptable value (ΔE>3.0). The color change (ΔE) of pigmented specimens ranged from 4.31 to 6.68. A-2186 silicone elastomer experienced the greatest color changes (P<.05). Within nonpigmented specimens, none of the tested silicone elastomers showed significant color changes (P>.05). ConclusionsOutdoor weathering in a hot and humid climate adversely affected the properties of silicone elastomers. The heat-polymerized TechSil S25 elastomer showed better mechanical durability and color stability compared with the room-temperature polymerized A-2186 and MED-4210 materials. TechSil S25 showed the greater values of tear and tensile strengths and elongation of specimens exposed to outdoor weathering conditions. It also showed the least amount of color change among the pigmented specimens exposed to outdoor weathering.

An amino-alkyl siloxane oligomer as hydrophobation agent for particleboards used under high humidity conditions

In this study, an amino-alkyl siloxane oligomer was used as a hydrophobation agent in order to improve the behaviour of particleboards under moist and outdoor weathering conditions and to be compared to conventionally used paraffin waxes. Melamine-urea-phenol-formaldehyde (MUPF, 15.0 %) was used as adhesive and mixed with the hydrophobation agents at concentrations of 1, 3, and 5 % related to the dry particle mass. The siloxane oligomer improved the water-related properties (thickness swelling, water uptake, internal bond strength (IBS) and IBS after boil test) in comparison to a control without hydrophobation agent. It also tended to enhance bending strength, modulus of elasticity, and IBS compared to specimens containing wax. IBS after boil test was significantly higher at addition of 3 and 5 % siloxane than that of wax-added reference boards. Specimens with siloxane oligomer, however, displayed higher thickness swelling and water uptake than those with wax added. It is assumed that the siloxane oligomer is able to contribute to bonding via hydrogen and covalent bonds and particularly enhance wet strength, while waxes exclusively act by their non-polar nature and, thus, water repellent behaviour.

The use of waterborne paints in contemporary murals: Comparing the stability of vinyl, acrylic and styrene-acrylic formulations to outdoor weathering conditions

Abstract This paper reports on the photochemical degradation of waterborne paints, products which have been widely used in the creation of outdoor contemporary murals. For this purpose, 15 artist-grade formulations, including three binders (poly( n -butyl acrylate- co -methyl methacrylate), poly(vinyl acetate- co -vinyl versatate), poly( n -butyl methacrylate- co -styrene- co -2-ethylexyl acrylate)) and five pigments (titanium white, artificial ultramarine blue, mars yellow, quinacridone red, phthalocyanine green) were selected and brushed on cement lime mortar supports, simulating the stratified structure typically used by artists. Samples were exposed to UVA-340 lamps (295 λ

Photostability of HDPE Filaments Stabilized with UV Absorbers (UVA) and Light Stabilizers (HALS)

HDPE monofilaments were photostabilized with hindered amine light stabilizers (HALS) and UV absorbers at varying stabilizer concentrations. The filaments were assessed for UV resistance by exposure to simulated outdoor weathering conditions in artificial weathering apparatus and testing the exposed samples at regular intervals for retained tensile properties. Films of HDPE of varying thickness and containing different concentrations of photostbilizers were also prepared. The UV protective ability of the films was assessed by measuring Ultra Violet Protection Factor (UPF). The results indicate that UV absorbers improve the stability of the filaments significantly. However, the best performance was displayed by filaments containing HALS.

Photodegradation of bisphenol A polycarbonate with different types of stabilizers

When unstabilized bisphenol A polycarbonate is exposed to outdoor weathering conditions, it degrades due to irradiation, humidity and other parameters. To overcome this undesired degradation process BPA-PC can be stabilized. In this study the influence of different types of stabilizers (i.e. UV-absorbers and hindered amine stabilizers) on the photodegradation of BPA-PC were compared. It is shown that the best way to stabilize BPA-PC is to keep the harmful UV light out. Almost all stabilizers caused a decreased degradation rate. The UVAs showed the best results, although radical scavengers cause a decrease in degradation too. By applying a layer of UVA-stabilized BPA-PC on top of unstabilized BPA-PC led to a decreased degradation rate of the unstabilized BPA-PC, which can quantitatively be explained by a reduction of the irradiation intensity.

Effect of photooxidative ageing at natural conditions on dynamic mechanical properties of PE-LD/PE-LLD blends

The blends of low density polyethylene with linear low density polyethylene and pure polyolefins were blown for their use in agriculture. These films were stabilized with a commercial Hindered Amine Light Stabilized (HALS). Blends with this stabilizer were photodegraded under natural outdoor weathering conditions during two years. Photodegradation involves oxidation of the polymer chain and causes modifications of the mechanical properties of the exposed films that were monitored by dynamic mechanical spectroscopy. The mechanical relaxation spectra show the alfa, beta and gamma relaxation zones, in decreasing order of temperature. Their characterization was carried out using the deconvolution method proposed by Charlesworth, together with the Fuoss-Kirkwood equation. The results obtained for pure PE-LLD and PE-LD and their blends show that the storage modulus increases as a function of the exposure time. The maximum storage modulus is reached at different exposure times depending on the blend composition. The beta relaxation zone is the most affected by weathering. A new relaxation was detected between -85° and -75°, which was modified as a function of the exposure time, and finally even disappeared. All the samples exhibit the same evolution, but at different time scales. It has been found that after two years of exposure, the degradation of the interfacial region is already initiated. The blends with 50% of PE-LD are the most resistant to weathering.

Modelling and optimizing imperfect maintenance of coatings on steel structures

Steel structures such as bridges, tanks and pylons are exposed to outdoor weathering conditions. In order to prevent them from corrosion they are protected by an organic coating system. Unfortunately, the coating system itself is also subject to deterioration. Imperfect maintenance actions such as spot repair and repainting can be done to extend the lifetime of the coating. This paper considers the problem of finding the set of actions that minimizes the expected (discounted) maintenance costs over both a finite horizon and an infinite horizon. To this end the size of the area affected by corrosion is modelled by a non-stationary gamma process. An imperfect maintenance action is to be done as soon as a fixed threshold is exceeded. The direct effect of such an action on the condition of the coating is assumed to be random. On the other hand, due to maintenance the parameters of the gamma deterioration process may also change. It is shown that the optimal maintenance decisions related to this problem are a solution of a continuous-time renewal-type dynamic programming equation. To solve this equation time is discretized and it is verified theoretically that this discretization induces only a small error. Finally, the model is illustrated with numerical examples.

A comparison of models for measurable deterioration: An application to coatings on steel structures

Steel structures like bridges, tanks and pylons are exposed to outdoor weathering conditions. In order to prevent them from corrosion they are protected by organic coating systems. This paper focuses on modelling the deterioration of the organic coating layer that protects steel structures from corrosion. Only if there is sufficient knowledge of the condition of the coating on these structures, maintenance actions can be done in the most efficient way. Therefore the course of the deterioration of the coating system and its lifetime, which is also of importance for doing maintenance, have to be assessed accurately. In this paper, three different stochastic processes, viz. Brownian motion with non-linear drift, the non-stationary gamma process and a two-stage hit-and-grow physical process, are fitted to two real data sets. In this way we are the first who compare the three stochastic processes empirically on criteria such as goodness-of-fit, computational convenience and ease of implementation. The first data set is based on expert judgement; the second consists of inspection results. In the first case the model parameters are obtained by a least-squares approach, in the second case by the method of maximum likelihood. A meta-analysis is performed on the two-stage hit-and-grow model by means of fitting Brownian motion and gamma process to the outcomes of this model.