Accelerated Weathering Conditions Research Articles

Influence of Specimen Size on Accelerated Weathering of Laminated Veneer Lumber

Abstract Moisture intrusion can be significantly higher along specimen edges, particularly at edges where longitudinal grain is exposed, which is referred to as the edge effect. The influence of edge effects on moisture durability are assumed to decrease as the edge area to total-surface-area ratio decreases. Moisture durability assessment of laminated veneer lumber (LVL) is commonly evaluated using accelerated weathering (AW) and outdoor exposure methods, where small specimens are analyzed. The influence of specimen size (i.e., edge effect) on moisture durability evaluation of LVL was investigated in this study. To vary specimen size, three widths with constant length and thickness were evaluated. In addition, three AW methods were used to characterize how the method of inflicting degradation influenced edge effects. No consistent trends in mechanical property loss were found across AW methods, indicating that the influence of specimen size varied with AW method. The greatest influence of specimen size occurred when cyclic vacuum-soak-dry was included, where water absorption decreased significantly with increasing width, and three of four mechanical properties evaluated displayed an influence of specimen size. The smallest influence of specimen size occurred when a single soak-dry procedure was included, where only one of four mechanical properties evaluated displayed an influence of specimen size. Results from this study provide evidence that edge effects may occur during LVL moisture durability assessment but that the severity is dependent on AW conditions.

Weathering of aromatic engineering thermoplastics: Comparison of outdoor and xenon arc exposures

A series of 31 aromatic engineering thermoplastic formulations was exposed at outdoor sites in Florida, Arizona, and the Kingdom of Saudi Arabia (KSA) for 24 months as well as under modified ISO 4892-2 xenon arc accelerated weathering conditions. The series included black, white, and transparent formulations. Measured properties were color, gloss, haze, transmission, tensile strength and elongation, Charpy impact, and erosion. There was surprisingly little difference in weathering among the outdoor sites except for the effects of blowing sand and slower erosion at the KSA site. Xenon arc accelerated weathering run at high irradiance and using state of the art filters provided very good predictions of color shifts, transmission, Charpy impact mode (break/no break), and tensile elongation at break. Prediction of gloss loss was only fair, especially for black samples, and haze was poorly predicted on the transparent samples. This suggests the need for better simulating the effects of rain and wind in accelerated weathering cabinets. Tensile strength and Charpy impact strength generally exhibited little change and were not useful properties to differentiate material performance.

Loss of thermoplastic elastomer toughening in polylactide after weathering

ABSTRACTIt has been already pointed out that one of the best ways to increase toughness of the inherently brittle polylactide (PLA) without sacrificing strength and modulus is the use of thermoplastic elastomer toughening approach; but what happens under outdoor conditions was not explored. Therefore, the objective of this study was to explore the degree of losses especially in fracture toughness of PLA when blended with thermoplastic polyurethane (TPU) elastomer or thermoplastic polyester elastomer (TPE) after weathering. For this purpose, neat PLA, its 10 phr TPU and TPE blends were exposed to accelerated weathering conditions of both ultraviolet‐irradiation cycles and moisture cycles as described in the standard of ISO 4892‐3 for various periods. In general, due to the significant molecular weight reduction via chain scission reactions, drastic losses in the strength and toughness of the specimens were observed. On the other hand, in terms of %retention in the properties after weathering periods, it could be suggested that, rather than use of neat PLA, the use of its TPU or TPE blends would be still advantageous for both “indoor use” and also for “outdoor use.” © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47177.

Stability of acrylic polyurethane coatings under accelerated aging tests and natural outdoor exposure: The critical role of the used photo-stabilizers

The effect of photo-stabilizers on the crosslinking and weathering durability of acrylic polyurethane coatings based on the HSU 1168 acrylic polyol and the Desmodur N-75 polyisocyanate has been investigated. The aging of these coatings under accelerated weathering conditions and natural outdoor conditions upto a decade has been compared. Our findings showed that photo-stabilizers had a negligible effect on the conversion of isocyanate groups during the photocroslinking but enhanced the aging resistance. Coatings containing photo-absorbers exhibited an excellent weathering durability, upto 72 cycles upon accelerated aging and 10 years in natural outdoor exposure, while the unstabilized coatings appeared serious cracks, damages and chalking after 48 cycles of accelerated aging and after 5 years in outdoor weathering exposure. The degradation of coatings was also investigated by monitoring atomic force microscopy, weight loss and gloss loss, cracking, blistering and flacking of the coating. The degradation of coatings in the surface of natural and accelerated was compared by using Atomic force microscopy coupling with naonoscale infrared spectroscopy (AFM- IR) by following oxidized products on the coating surface.

Observation of the degradation of three types of plastic pellets exposed to UV irradiation in three different environments

Plastic debris represents one of the most prevalent and persistent pollution problems in the marine environment. In particular, microplastics that are mainly degraded from larger plastic debris have become a growing environmental concern. However, studies on the degradation of plastics in the aquatic environment that hydrobios reside in have been limited, while several studies regarding the degradation of plastics have been conducted under outdoor or accelerated weathering conditions. Thus, observation of the degradation of three types of virgin plastic pellets exposed to UV irradiation in three different environments (i.e., simulated seawater, ultrapure water, and a waterless (air) condition) was carried out. Data on the changes in physical and chemical properties were collected. The FTIR spectra showed that hydroxyl groups and carbonyl groups developed in three types of weathered plastic pellets under the air and ultrapure water environmental conditions after 3months of UV irradiation, while only carbonyl groups were found in plastic pellets in the simulated seawater environment. In contrast, the Raman spectra showed no significant changes in the weathered plastic pellets, but there were different intensities of characteristic peaks after exposure to UV irradiation. In addition, SEM images illustrated that granular oxidation, cracks and flakes were common patterns during degradation, and the plastic pellets in the three different environments experienced different levels of chemical weathering. We suggest that further studies on the degradation processes of plastic debris are needed to predict the fate of plastic debris in the environment.

Weathering degradation performance of PLA and its glass fiber reinforced composite

The objective of this study was to explore the degree of improvement in the resistance of biodegradable polylactide (PLA) structure against atmospheric weathering (outdoor) conditions when reinforced with only 15wt% E-glass fibers (GF). For this purpose, both neat PLA and PLA/GF composite specimens were exposed to accelerated weathering conditions of both UV-irradiation and moisture cycles in accordance with ISO 4892-3 standards for various periods until 400h. Many characterization techniques used revealed that the alterations in the structure and properties of the specimens were due to the drastic decrease in the molecular weight of the PLA matrices via chain scission reactions. It was observed that reductions in the mechanical properties (strength-modulus-toughness) of the neat PLA were much more critical compared to the reductions in the PLA/GF composite. For instance, the reduction in the tensile strength of the neat PLA specimen was as much as 92%; while that reduction for the PLA/GF specimen was only 34%. Because, inorganic strong glass structure of the GF reinforcements having almost no chemical degradation during weathering periods kept their actions in the composite strengthening-stiffening-toughening mechanisms.

Durability and mechanical performance of a photo-catalytic water-based nanocomposite coating

Abstract In this study, different combinations of nanoparticles including; TiO 2 , SiO 2 , silica grafted TiO 2 , titania grafted SiO 2 , physical blends of TiO 2 /SiO 2 nanoparticles and nanocomposite particles made of titanium tetra-isopropoxide/tetraethylorthosilicate (TTIP/TEOS) precursors, were loaded into an acrylic emulsion coating. Photo-activity of the coatings was evaluated through the photo-degradation of Rhodamine B dyestuff, as a pollutant model, on the surface of the coatings under UVA irradiation. The coating films were exposed to accelerated weathering conditions for different time intervals. As the criteria for durability of the coatings, morphology and topology of coatings surface were studied using scanning electron microscopy (SEM) and atomic force microscopic (AFM) techniques, respectively. Mechanical properties of the coatings were assessed before and after exposure to accelerated weathering conditions. The results exhibited a favorable balance of photocatalytic activity and mechanical properties in the coatings containing TTIP/TEOS nano-composite particles even after exposing to the accelerated weathering conditions.

Improvement, the Performance of Polyurethane (PUR), Y-290 Resin as Coating of Oil Pipeline by Using Multi-Walled Carbon Nanotubes (MWCNTs)

In this study, polyurethane epoxy-Y290 (PUR-Y290) as a matrix material was reinforced by 1%MWCNTs. Polyurethane is a thermoset polymer and using for several applications particularly as coatings of gas and oil pipeline. Polyurethane uses as a liquid coating against the corrosion, and that is caused by the direct exposure for long periods of UV irradiation and humidity. The nanocomposites were prepared by adding 1wt% MWCNTs to polyurethane and mixed by using an ultrasound mixer. Polyueethane-1%MWCNTs composite sample was exposed to accelerate weathering (UV irradiation coming from sunlight, moisture, and salt water spray) during the exposure to different durations 6 months, 12 months and 24 months. Exposed and unexposed samples were investigated and evaluated by thermal and mechanical tests.It was found that the incorporation 1.0%wt of MWCNTs filler, enhanced the thermal stability and improved the mechanical properties during the exposure for long-term life to accelerated weathering conditions, compared with polyurethane coating without MWCNTs filler. These results indicated that polyurethane (liquid coating) nanocomposites have a higher resistance to environmental condition and give more protective against corrosion of oil pipelines and applied as coatings by spray method to protect the oil pipeline surfaces from environmental conditions.

High Density Polyethylene/Pistachio Shell Flour/Nanoclay Composites - Effect of Accelerated Weathering Conditions on Mechanical Properties, Relative Brightness and Total Colour Change

This study investigates the effect of the addition of nanoclay (Cloisite 20A) on some mechanical properties, % relative brightness (ΔLrel) and total colour change (ΔEab) of high density polyethylene (HDPE)/pistachio shell flour (PSF) composites when exposed to accelerated weathering conditions. X-ray diffraction (XRD) patterns of samples containing 3 and 6 per hundred composite (phc) of nanoclay indicated partial exfoliation and intercalation. The tensile modulus and tensile strength of HDPE/PSF composites (without nanoclay) decreased when the exposure time increased to 1500 h, while the tensile modulus and tensile strength increased. For samples with nanoclay, ΔLrel and ΔEab increased upon accelerated weathering conditions up to 500 h, and thereafter remained constant. But results show that ΔLrel and ΔEab increased significantly upon accelerated weathering exposure in HDPE/PSF samples up to 1500 h. Scanning electron microscopy (SEM) results after 1500 h exposure to weathering condition showed signs of the presence of cracks in samples without nanoclay, unlike the samples with nanoclay.

Used engine oil as alternate binder for buildings – a comparative study

At present, global warming and climate change are the major challenges of foremost significance that substantially influence the earth's environment. The construction sector, especially buildings, is one of the largest sources of greenhouse gas emissions. Conventional building materials such as clay bricks and cement are considered as environmentally unfriendly due to enormous emissions during their production. This paper investigates the utilisation of used engine oil (UEO) as an alternative to the usual cementitious binders. Prototypes were produced from UEO to optimise the compositions and conditions of the process and tested for compressive and flexural strength, permeability and water absorption, respectively, following the ASTM standards. Furthermore, environmental and weathering aspects were also demonstrated to ensure the feasibility of the product. Samples constituting 5% by weight UEO have shown significant results for flexural stress, compressive strength and water absorption and also passed the permeability test. Moreover, 5% of UEO samples have negligible effect in strength for accelerated weathering conditions as demonstrated by the ultraviolet test. Conclusively, UEO can be used as a replacement to conventional binding materials such as a clay bricks and cement. Sustainable development and waste management are the hallmarks of this research.

Durability of anti-graffiti coatings on stone: natural vs accelerated weathering.

Extending the use of novel anti-graffiti coatings to built heritage could be of particular interest providing the treatments are efficient enough in facilitating graffiti removal and long-lasting to maintain their protective properties without interfering with the durability of the substrates. However, studies of the durability of these coatings are scarce and have been mainly carried out under accelerated weathering conditions, the most common practice for assessing the durability of materials but one that does not reproduce accurately natural working conditions. The present study aimed to assess the durability of the anti-graffiti protection afforded by two anti-graffiti treatments (a water dispersion of polyurethane with a perfluoropolyether backbone and a water based crystalline micro wax) on Portland limestone and Woodkirk sandstone after 1 year of outdoor exposure in the South of England with periodic painting and cleaning episodes taking place. A parallel study under artificial weathering conditions in a QUV chamber for 2000 hours was also carried out. Changes to the coatings were assessed by measuring colour, gloss, water-repellency, roughness and microstructure, the latter through micro-Raman and optical microscope observations, periodically during the experiments. The results show that both anti-graffiti treatments deteriorated under both artificial and natural weathering conditions. For the polyurethane based anti-graffiti treatment, artificial ageing produced more deterioration than 1 year of outdoor exposure in the south of England due to loss of adhesion from the stones, whereas for micro wax coating there were no substantial differences between the two types of weathering.

Improving Environmental Durability of Epoxy Resin Using Tetra-n-butylammonium (TBA) Salt Modified Montmorillonite Nanoplatelets

This study aimed to investigate the effect of organoclay concentration variation (1-5 wt%) on the weathering resistance of epoxy resin in terms of the strength, modulus and weight changes of the specimens after exposure to accelerated weathering conditions. Transmission electron microscopy (TEM) revealed an exfoliated and good dispersed nanofiller structure throughout the matrix up to 3 wt% loading. The tensile strength, modulus, and weight of the samples decreased after combined UV radiation and condensation, with much less extent for the nanocomposites than neat epoxy indicating that the presence of organoclay led to dominant enhancement in mechanical properties endurance of epoxy resin to environmental degradation. Nanocomposites also displayed much lower weight loss as compared to the unfilled epoxy after being subjected to the accelerated weathering by either temperature-humidity or by combined UV radiation and condensation.

Durability of a sunlight-curable organic–inorganic hybrid protective coating for porous stones in natural and artificial weathering conditions

Abstract Several weathering aging tests were performed for assessing the durability of an innovative sunlight photopolymerizable nanostructured organic-inorganic (O-I) hybrid coating, namely HYBRIDSUN. The latter was applied on a calcarenitic porous stone typical of Apulia Region, Italy (Lecce Stone, i.e. LS) and photo-cured by means solar radiations up to 55 h. The protective performances of the stone specimens treated with HYBRIDSUN, when exposed to both realistic and accelerated weathering conditions, were studied by performing natural and artificial aging tests, such as resistance to abrasion, salt crystallization, freeze-thaw and SO2 in moist environment. The effects of the natural and artificial weathering aging on hydrophobicity and color change of treated stones were, finally, monitored, upon to two exposure years to outdoor conditions, confirming the outstanding properties of the experimental product to protect the stone surface from all the environmental agents investigated.

Release of arsenic from cyanidation tailings

At a gold mine in northern Sweden, gold occurring as inclusions in pyrrhotite and arsenopyrite is leached by cyanidation of the ore. The main sulphide minerals in the ore are pyrrhotite and arsenopyrite. Effluents from the cyanidation process are treated with Fe2(SO4)3 to form Fe-precipitates suitable for the co-precipitation of As. The aim of this study was to perform static and kinetic leaching tests on the ore and tailings to define geochemical processes governing As mobility. Sequential leaching tests suggested that the majority of dissolved As deriving from the sulphide fraction in the ore was incorporated in newly formed Fe-precipitates in the tailings. The mobility of As in the tailings was therefore mainly dependent on the stability of these As-bearing Fe-precipitates. Weathering cell tests (WCT) involving 31 weekly cycles of wetting and air exposure were conducted to assess the stability of the As in the tailings under accelerated weathering conditions. The first stage of the WCT was characterized by a pH≈5 and low As leaching, probably driven by the dissolution of amorphous Fe-As species. In the second stage of the WCT, leaching of Fe, S and As increased and the pH decreased to <3.5. An increase of the leachate’s molar Fe/S-ratio suggested that pyrrhotite oxidation was occurring. The falling pH destabilized As-bearing Fe-precipitates, causing further As release. The total As release during the WCT corresponded to only a small proportion of the tailings’ total As content. The accelerated As-leaching observed towards the end of the WCT could thus indicate that its release could increase progressively over time.

Aging analysis of high voltage silicone rubber/silica nanocomposites under accelerated weathering conditions

Abstract Silicone rubber (SiR) is extensively used in outdoor insulation and other applications. However, like other polymers, SiR also degrades and lessens its performance in the exposition of environmental stresses. Nanofillers improve the aging behavior of polymeric insulating materials. To investigate the effect of nanosilica on the aging behavior of SiR, we fabricated nanocomposites of SiR with 2.5 wt.% nanosilica (SNC-2.5) and 5 wt.% nanosilica (SNC-5) by mechanical mixing and ultrasonication method. The prepared samples were subjected to uniform ultraviolet (UV) radiation, heat, humidity, salt fog, and acid rain along with neat SiR in cyclic manner at 2.5 kV for 5000 h in a specially fabricated weathering chamber. Neat SiR and both nanocomposites showed gradual decrease in transparency. Random loss and recovery in hydrophobicity and increase and decrease in leakage current (LC) were recorded for all samples, in which SNC-5 showed the best hydrophobic behavior and least LC. For SNC-5, Fourier transform infrared (FTIR) results showed negligible reduction in absorption peaks at important wave-numbers and increase and intactness were observed at absorption peaks related to the hydrophobic methyl group. Scanning electron microscopy (SEM) results also concurred with FTIR, LC measurements, and hydrophobicity analysis.

Screen-printed nanoparticles as anti-counterfeiting tags

Metallic nanoparticles with different physical properties have been screen printed as authentication tags on different types of paper. Gold and silver nanoparticles show unique optical signatures, including sharp emission bandwidths and long lifetimes of the printed label, even under accelerated weathering conditions. Magnetic nanoparticles show distinct physical signals that depend on the size of the nanoparticle itself. They were also screen printed on different substrates and their magnetic signals read out using a magnetic pattern recognition sensor and a vibrating sample magnetometer. The novelty of our work lies in the demonstration that the combination of nanomaterials with optical and magnetic properties on the same printed support is possible, and the resulting combined signals can be used to obtain a user-configurable label, providing a high degree of security in anti-counterfeiting applications using simple commercially-available sensors.

Layer-by-layer assembly of Nafion on Surlyn with ultrahigh water vapor barrier.

A layer-by-layer approach was used for the fabrication of multilayer films for ultra high gas barrier applications. The ultra high gas barrier material was designed by incorporating Nafion layer in between bilayers of poly(ethylene imine) and poly(acrylic acid) on a Surlyn substrate. When the barrier film with self-assembled Nafion is exposed to the moist environment, Nafion absorbs and desorbs water molecules simultaneously, thereby reducing the ingress of moisture in to the film. In order to study the effect of Nafion, the fabricated barrier materials with and without the presence of Nafion were tested for water vapor barrier properties. The barrier films were further used for encapsulating organic photovoltaic devices and were evaluated for their potential use in barrier applications. The devices encapsulated with the films containing Nafion exhibited better performance when subjected to accelerated aging conditions. Therefore, this study demonstrates the effectiveness of self-assembled Nafion in reducing the water vapor permeability by nearly five orders of magnitude and in increasing the lifetimes of organic devices by ∼22 times under accelerated weathering conditions.

Superhydrophobic durable coating based on UV‐photoreactive silica nanoparticles

ABSTRACTSuperhydrophobic surfaces can be obtained by tailoring both the chemistry and roughness topography, mimicking the Lotus leaf characteristics. Most of the synthetic superhydrophobic surfaces reported have been composed of micro and nanoparticles (NPs) embedded in polymer‐based coatings. The particles which tailor the topography are bonded to the base polymers by weak secondary forces. Consequently, the topography integrity is highly affected by handling and surface drag making them unsuitable for long term applications. This work is focused on promoting covalent bonding between the NPs and the base polymer to obtain durable superhydrophobic surfaces. The rough topography was achieved by ultraviolet (UV) curing of SiO2 NPs containing a photoreactive benzophenone moiety in addition to methylated fumed silica NPs which can bind covalently to the polymer base coating, on UV radiation. The hydrophobic chemistry was obtained by fluoroalkylsilane top coating. Coating durability was evaluated using surface air drag and accelerated weathering conditions (UV radiation, humidity and temperature). Results indicated that the proposed approach resulted in superhydrophobic surfaces having high contact angle (&gt;150°) and low sliding angle (&lt;10°) with improved long term durability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41122.

Polyolefin Nanocomposites with Enhanced Photostability Weathering Effect on Morphology and Mechanical Properties

This research aims to study the effect of accelerated weathering conditions on the photodegradation characteristics for fibrillar silicate clay-filled Polypropylene (PP) nanocomposites in the presence of metallocene linear low density polyethylene (m-LLDPE). Silane-treated attapulgite (ATP) clay along with ethylene octene elastomer-grafted maleic anhydride (POE-g-MAH) was used to compatibilize both blend and nanocomposite system. The result showed that developed PP/m-LLDPE nanocomposites displayed good UV resistance with little change in retained stress-at-break and elongation-at-break values. Balanced loss of toughness values noted maintaining higher fracture toughness values for nanocomposites containing 5 phr ATP clay. Infrared analysis was used to detect progress of degradation followed by change in carbonyl index revealed predominated chain scission in late irradiation, while crosslinking was dominant for initial irradiation period. An increase in crystallinity during UV exposure (chemi-crystallization) was detected with exposure time for all compositions and virtually independent of initial structure of the polymer. The highest value of crystallization observed for PP and the lowest one for nanocomposites containing 5 phr of ATP clay revealed good oxidation stability. Surface morphology revealed induced degradation throughout cross-section of PP, while severity of the surface degradation was significantly reduced for developed nanocomposites.

Effect of Methyltrimethoxy Silane Modification on Yellowing of Epoxy Coating on UV (B) Exposure

The exterior durability of epoxies is severely affected due to its poor weathering resistance. Epoxies exhibit chalking and discoloration under UV exposure caused as a result of photodegradation. The present work aims at studying the extent to which the color change and yellowing caused due to weathering under accelerated weathering conditions, of DGEBA epoxy, could be lowered by in situ modification of the epoxy polymer backbone with a silane, namely, MTMS. The epoxy resin and silane-modified epoxy resin were formulated into a TiO2-based white coating, applied on mild steel panels, and exposed in a UV (B) weatherometer. The color change (dE) and yellowness index (YI) values of weathered panels were evaluated using a spectrophotometer. The weathered samples were also characterized using FTIR-imaging technique to study the effect of weathering on the structural backbone of the formulated coatings. The silane-modified epoxy coatings showed lowered yellowing by 45% on UV exposure and the enhanced resistance to yellowing of the modified coatings was indicated by lowered dE and YI values. The enhanced resistance to yellowing by the silane-modified epoxy was attributed to the strengthening of the epoxy backbone by introduction of Si–O–C linkage onto the epoxy polymeric chain.