New accelerated weathering tests including acid rain

Aprocedure for the design of reliable accelerated weathering tests for service life prediction of automotive coatings was developed and used in designing an accelerated test based on SAE method J 1960. The influence of exposure conditions was investigated in several accelerated tests. Results from these tests and from Florida exposures were used to optimize test conditions. A test cycle that includes acid rain spraying was developed and evaluated by exposing 16 different coating systems using various methods. The results indicate that the new cycle is more reliable than a cycle commonly used today. P.O. Box 857, SE-50115 Bor?s. Sweden.     

Rapid,reliable tests of clearcoat weatherability: a proposed protocol

In this paper, a protocol is proposed for the rapid prediction of durability of automotive enamel clearcoats. The protocol is designed to minimize test time while maximizing test reliability. The protocol is based primarily on chemical measurements of degradation rates rather than observation of physical failure.There are two key aspects to the protocol. The first is the use of electron spin resonance spectroscopy (ESR) to measure the rate of formation of free radicals in the coating under near-ambient exposure conditions (photo-initiation rate). This measure is used to rapidly screen coatings under development and to monitor the weatherability of previously qualified materials. Extensive, conventional accelerated exposure tests are performed only on new materials with low photo-initiation rates.The second key aspect is the use of spectroscopic measurements of chemical degradation both to select an appropriate accelerated exposure and to determine the ratio of the rate of chemical change during accelerated exposure to that during natural exposure (i.e. the acceleration factor). Knowing the acceleration factor and the time to failure in a valid accelerated exposure, it is possible to estimate the service life. The service life is then related to the photo-initiation rate and photo-initiation rate measurements are used in coating quality control.This report describes in detail the steps in the protocol, the kind of chemical measurements which may be required, and provides examples of its application.     

Evaluation of the ASTM D7869-13 test method to predict the gloss and color retention of premium architectural finishes-I

A recently developed xenon arc-based accelerated weathering cycle, ASTM D7869-13, has been validated for automotive and aerospace coatings, but its ability to predict the gloss and color retention of premium architectural finishes has not yet been evaluated. We review new weathering data comparing the performance of poly(vinylidene fluoride) (PVDF) architectural finishes in south Florida exposure as well as several accelerated exposure methods including ASTM D7869-13. ASTM D7869 accurately reproduced Florida rank order gloss and color retention trends for coatings made with PVDF-acrylic blends and inorganic pigments, as well as the gloss and color changes seen in Florida for 70% PVDF masstone coatings made with a number of single organic pigments. However, the D7869 cycle has difficulty predicting the rank order of rutile TiO₂ grades for the gloss retention of PVDF coatings in Florida, as well as the magnitude and direction of color fade from organic pigment degradation in organic pigment/inorganic pigment blends. One open question that remains is whether the ASTM D7869 cycle might have some utility for industry standard or specification purposes, if the test is limited to specific reference colors or more ideally to specific reference pigments.     

Dual layer structural thermoplastic polyester powder coating film and its weathering resistance

Micro FTIR analysis was performed to the point with a 50–80 μm spatial resolution to verify the exact structure of a new blend thermoplastic powder coating film. Resistance to certain artificially accelerated conditions and actual outdoor exposure were examined to confirm the performance of the film as a protective coating for use in the telecommunication field. The new blend powder coating film consists of primary polyethylene terephthalate (PET) and secondary polyvinyl butyral (PVB) resins, and has a distinct dual phase structure. Specifically, it forms a continuous PVB phase in a surface layer with a thickness of approximately 100–150 μm. Good corrosion resistance was confirmed in artificially accelerated testing using salt water spray, heat cycle, and accelerated UV tests. Actual outdoor exposure in a metropolitan area (Shinkiba in Tokyo) and a coastal area (Miyake Island) revealed good weathering performance throughout the study period. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The interplay of physical aging and degradation during weathering for two crosslinked coatings

Polymer molecular relaxation, or ‘physical aging’, is a very important influence on permeability and mechanical properties of any polymer below its glass transition. ‘Physical aging’ occurs as even an unstressed polymer gradually relaxes towards its equilibrium conformation. This and the shorter term response to stress happen over periods much longer than the typical cycle of an accelerated weathering test, thus important properties of a polymeric coating may be affected by the difference in frequency between natural and artificial exposures, in addition to other factors. Further, ‘physical aging’ is affected by chemical changes to the polymer network caused by the degradation during a weathering exposure. In this investigation, purely physical aging was compared with the effect of concurrent chemical degradation by measuring ‘enthalpy recovery’ and mechanical stress relaxation at a variety of temperatures and at various stages during accelerated weathering exposure. The effect of physical aging was quite apparent in both an epoxy-polyamide coating and a polyester-urethane coating. Changes in physical aging behaviour during degradation were different for the two coatings, which points to further reasons for discrepancy between accelerated weathering and natural exposure.     

Considerations for characterizing moisture effects in coatings weathering studies

This article investigates the effects of weathering factors on moisture absorption of coatings and presents results from several projects including real-time and accelerated weathering studies of coatings moisture absorption. Moisture variable characteristics, observed in outdoor exposure environments, are reviewed. Data are presented from the experiments performed in end-use and accelerated weathering environments to characterize moisture characteristics on coatings. The information from natural outdoor environment characterizations and design of experiments (DOEs) indicates the new approaches for characterizing coatings weathering with regard to moisture effects. Considerations and new approaches for performing coating weathering studies are discussed. Presented at the 2007 FutureCoat! Conference, sponsored by Federation of Societies for Coatings Technology, October 3–5, 2007, in Toronto, Ont., Canada.     

Effect of titania and zinc oxide particles on acrylic polyurethane coating performance

The outer environment, especially UV portion of solar radiation and water (in the form of moisture or rain) has an adverse effect on the surface appearance of heat-treated wood. Exposure to UV triggers the chain scission reactions which change the intrinsic properties of heat-treated wood and discoloration of wood surface. Repeated temperature and humidity variations cause swelling and shrinking of wood surface, which consequently create cracks and fissures exposing wood's sub superficial layers to atmospheric agents. Therefore, wood industries move towards the development of coatings in order to protect the heat-treated wood while retaining wood's natural look. Water based acrylic polyurethane coatings are highly efficient, non toxic and durable coatings with upgraded film properties. In this study, an attempt is made to improve the performance of these coatings by incorporating natural antioxidant (bark extract) and inorganic UV absorbers (nano and micro titania and nano zinc oxide) into the coatings. The main objectives of this study are to investigate the wetting and penetration characteristic of these new coatings on the wood surface and to study coating thickness variation with weathering time. The Sessile-drop method and fluorescence microscope are used for this investigation. The wettability of different coatings applied to heat-treated jack pine early wood and late wood is compared. The results show that there is a significant difference between the contact angle of early wood and late wood for acrylic polyurethane coating containing titania micro particles. The contact angle between water and coated wood surface reveals that the degree of orientation of the coating materials increases as the weathering time increases. The penetration characteristics of all the four coatings are found to be very poor. In addition, the relationship between the coating thickness and the UV exposure time is studied for four water based acrylic polyurethane coatings with different additives. It is found that the coating thickness decreases with increasing weathering time and a tissue deformation beneath the coating surface takes place during weathering.     

Accelerated weathering properties of compatibilized composites made from recycled HDPE and nonmetallic printed circuit board waste

The main aim of this work is to examine the influence of the contents of nonmetallic printed circuit board (PCB) waste component on the photodegradation of recycled high‐density polyethylene (rHDPE) composites. The properties tested were chemical changes, flexural properties, color stability, water absorption, leaching properties, and crystallinity changes of the composites after exposure to 2,000 h of accelerated weathering. Surface degradation for composites with nonmetallic PCB was less compared to unfilled rHDPE mainly because glass fibers covered almost the whole surface of specimens, acting as a protective layer, thus, slowing down the photodegradation reaction. Incorporation of compatibilizer in rHDPE/PCB composites had played an important role in resisting degradation due to UV exposure. All the composite samples became lighter in the early stages of weathering exposure; however, compatibilized composites showed less lightening and reduction on strength and modulus. Carbonyl index increases with exposure time indicating that the oxidation reaction continuously occurred during the aging process. Incorporation of compatibilizer had successfully reduced the water absorption uptake by the composites and effectively delayed some degradation properties of weathering. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43110.     

Surface degradation and nanoparticle release of a commercial nanosilica/polyurethane coating under UV exposure

Many coating properties such as mechanical, electrical, and ultraviolet (UV) resistance are greatly enhanced by the addition of nanoparticles, which can potentially increase the use of nanocoatings for many outdoor applications. However, because polymers used in all coatings are susceptible to degradation by weathering, nanoparticles in a coating may be brought to the surface and released into the environment during the life cycle of a nanocoating. Therefore, the goal of this study is to investigate the process and mechanism of surface degradation and potential particle release from a commercial nanosilica/polyurethane coating under accelerated UV exposure. Recent research at the National Institute of Standards and Technology (NIST) has shown that the matrix in an epoxy nanocomposite undergoes photodegradation during exposure to UV radiation, resulting in surface accumulation of nanoparticles and subsequent release from the composite. In this study, specimens of a commercial polyurethane (PU) coating, to which a 5 mass% surface-treated silica nanoparticle solution was added, were exposed to well-controlled, accelerated UV environments. The nanocoating surface morphological changes and surface accumulation of nanoparticles as a function of UV exposure were measured, along with chemical change and mass loss using a variety of techniques. Particles from the surface of the coating were collected using a simulated rain process developed at NIST, and the collected runoff specimens were measured using inductively coupled plasma optical emission spectroscopy to determine the amount of silicon released from the nanocoatings. The results demonstrated that the added silica nanoparticle solution decreased the photodegradation rate (i.e., stabilization) of the commercial PU nanocoating. Although the degradation was slower than the previous nanosilica epoxy model system, the degradation of the PU matrix resulted in accumulation of silica nanoparticles on the nanocoating surface and release to the environment by simulated rain. These experimental data are valuable for developing models to predict the long-term release of nanosilica from commercial PU nanocoatings used outdoors and, therefore, are essential for assessing the health and environmental risks during the service life of exterior PU nanocoatings.     

Investigation of factors impacting the in-service degradation of aerospace coatings

The impact of in-service environmental stressors on the durability of exterior decorative aerospace coating systems was investigated using accelerated weathering for a high-gloss polyurethane-based monocoat with and without clearcoat. Color, gloss, surface roughness, hardness, and chemical composition changes were studied by varying UV irradiance, temperature, thermal extremes, particulate matter, and acid environment while using constant moisture condensation conditions. The use of a clearcoat was found to enhance the resistance to gloss loss regardless of the stressors applied; however, the clearcoat system also produced a larger increase in hardness under all experimental conditions and a larger color shift for all stressors except for the particulate matter and particulate matter combined with acid. A correlation between color shift and chemical degradation was established by monitoring changes in amide and carbonyl functional groups as a function of UV irradiance, temperature, and thermal extremes. The particulate matter, with or without acid was found not to affect chemical degradation, but produced large color shifts for both coating systems and some loss of gloss at high radiant exposures for the clearcoat system. For the accelerated tests studied here, only the highest UV irradiance and temperature level, with or without additional stressors, produced changes in the clearcoat relative to the monocoat system without clearcoat that correlate with in-service performance observations.     

Photocurable epoxy/cubic silsesquioxane hybrid materials for polythiourethane: Failure mechanism of adhesion under weathering

A new inorganic–organic hybrid coating containing epoxy‐functionalized cubic silsesquioxane (CSSQ) has been developed, which can be polymerized cationically by UV radiation. This solvent‐free solution can be used as hybrid coating for polythiourethane (PTU) substrate. The surface properties of the coating film were determined by adhesion and scratch resistance. The excellent adhesion of coating films on the substrate was observed at the initial stage before weathering, but deteriorated after exposure to the sunshine. The low viscosity of hybrid coating solution (～ 15 mPa s) leads to fast curing and the formation of hybrid coating film during the photopolymerization reaction. The adhesion failure was evaluated by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and X‐ray photoelectron spectroscopy (XPS) analyses. AFM images showed that the surface is smooth at the initial stage, but a texture surface was developed after weathering. The shrinkage of the hybrid film due to the increase in crosslinking density by postpolymerization would affect the surface roughness after weathering. XPS analysis indicated that the adhesion failure occurred by photodegradation of the PTU substrate during weathering. The weathering resistance was significantly improved by adding UV absorbers, which protected the polymer substrate from the photodegradation. The advantages of the hybrid coating include fast cure speed, solvent‐free formulation, and improved surface properties of the coating film. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Durability assessment of automotive coatings—Design and evaluation of accelerated tests

In this work the influence of different climatic parameters on the rate of gloss reduction was studied for a number of different automotive coatings. The purpose was to improve the reliability of accelerated test procedures by selecting test conditions that improve the simulation of the degradation processes that occur during outdoor exposure. Results from Florida exposure and accelerated exposure tests were evaluated using an acceleration factor based on the light dose needed to cause a certain reduction in gloss. The results indicate that agreement between accelerated tests and Florida exposure is improved when a test sequence simulating acid rain is included in the accelerated test cycle. Division of Surface Protection and Corrosion, Box 857, 501 15 Bor?s, Sweden. KARIN WERNST?HL received the M.Sc. and Lic. Eng. Degrees in Chemical Engineering from Chalmers University of Technology. Since 1987, she has been employed at the Swedish National Testing and Research Institute, Division of Surface Protection and Corrosion in Bor?s, Sweden. BO CARLSSON earned his M. Sc. in Chemical Engineering, Techn. Dr. and Assoc. Prof. in Physical Chemistry at the Royal Institute of Technology, Stockholm. Since 1984, he has been acting head of the Division of Surface Protection and Corrosion at the Swedish National Testing and Research Institute.     

汽车用高分子材料的老化测试技术进展

介绍影响汽车材料老化的主要因素，概述了国内外关于汽车材料、零部件、整车等的老化测试技术最新进展，包括自然老化和人工加速老化。另外，针对汽车内饰件和外饰件使用环境不同，给出了相关的试验标准。     

Analysis of test methods for UV durability predictions of polymer coatings

The purpose of this paper is to review procedures which are used for the evaluation of the durability of polymer coatings. In particular, methods of environmental acceleration and techniques of assessment of coating degradation have been examined, with an emphasis upon those which may produce reliable fast answer durability predictions. The advantages and disadvantages of the various exposure regimes currently used (such as Florida exposure, EMMAQUA or artificial light sources) have been discussed in terms of correlation with actual durability data and of degree of acceleration. A general rule of thumb is that the correlation of accelerated methods with natural exposure is inversely proportional to the degree of acceleration used. The common physical methods used to assess the extent of coating durability have been presented, with the general drawbacks to these techniques being highlighted. Finally, the benefits and drawbacks of a number of chemical techniques (in particular electron spin resonance (ESR), Fourier transform infrared spectroscopy (FTIR), hydroperoxide determination and chemiluminescence), which in principal could provide durability information in a fraction of the time of the physical techniques mentioned earlier, have been discussed. Of these, both ESR and FTIR spectroscopy show particular potential because of the short exposure times necessary to obtain significant results under UVA exposure.     

Behavior of UV‐cured print inks on LDPE and PBAT/TPS blend substrates during curing,postcuring, and accelerated degradation

During radiation curing, a reactive formulation is converted into a highly crosslinked coating film by means of polymerization reactions. This three‐dimensional (3D) network is resistant to external degrading factors as it cannot be undone by any physical–chemical means. In this study, various ultraviolet (UV)‐curable ink formulations with different pigments were developed. The behavior of the UV‐curable inks was evaluated during UV curing in a photocalorimeter or in a UV tunnel. Inks were exposed to accelerated aging in an accelerated weathering chamber and their physical–chemical properties were investigated. The presence of residual fractions of unreacted species trapped in the 3D network formed during UV curing interferes with the degradation of the main structure during exposure in the weathering chamber. The ink formulations that did not easily absorb UV light increased in gloss and hardness, indicating that residual crosslinking is taking place at the same time that degradation is occurring. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41116.     

Efficacy of hindered amines in woodflour‐polypropylene composites compatibilized with vinyltrimethoxysilane after accelerated weathering and moisture absorption

In this work, the aim was to analyze the efficacy of hindered amine light stabilizers (HALS) in woodflour‐polypropylene composites compatibilized with vinyltrimethoxysilane after moisture absorption and accelerated weathering. Moisture uptake of materials decreased with incorporation of silane due to diminished accessibility of water molecules to reactive regions. In dynamic mechanical experiments performed on wet samples, a marked reduction in the storage modulus in the glassy and rubbery zone was observed, since water has a plasticizing effect. After sample weathering, in a xenon‐arc apparatus, the changes in chemical structure and physical properties after exposure were analyzed by attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, color measurement, flexural properties, and morphological analysis by scanning electron microscopy (SEM). The data showed that HALS maintain the brightness of the materials after aging and prevent sample whitening. They also reduced color loss after aging and the SEM micrographs revealed that they inhibit surface cracking during weathering. Although a slight decline in the mechanical properties was not completely avoided, the combination of the additives studied (UV absorbers and HALS) successfully prevented the deterioration of surface materials by UV radiation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Curing and Photostabilization of Thermoset and Photoset Acrylate Polymers

The light‐stability of thermosetting acrylate and UV‐cured acrylate polymers has been tested in an accelerated QUV weatherometer. Infrared spectroscopy was used to monitor in situ the chemical changes occurring upon both curing and photoageing of 35 μm thick clearcoats. The curing was shown to proceed more extensively in photoset than in thermoset acrylate polymers which contain 6 and 20% unreacted functional groups, respectively. During photoageing, the loss of the binder structural groups is accompanied by the production of oxidation products (carbonyl and hydroxyl groups). The UV‐cured polyurethane‐acrylate coating was shown to be more resistant to accelerated weathering than the melamine/acrylate thermoset currently used as automotive finishes. The addition of a hydroxyphenyltriazine UV‐absorber and a hindered amine light stabilizer (HALS) radical scavenger was found to increase substantially the light stability of acrylate clearcoats.     

The settling of critical levels of soluble salts for painting

The presence of hydrosoluble species, mainly chlorides and sulphates, at the metal/paint interface promotes osmotic blistering of the coating and underfilm metallic corrosion when the concentration of the soluble salts exceeds a critical level. Both processes can lead to the deterioration of the paint system in a very short period of time. The International Standards Organization (ISO) has for some time been trying to develop a standard about guidance safe levels for water-soluble salt contamination before the application of paints and related products. However, it is difficult to set acceptable unique levels since each type of coating and thickness varies in susceptibility to soluble salt degradation and also the exposure conditions vary. In this study, by a variety of accelerated and natural weathering trials, realistic series of limits of soluble salt have been provided depending on the coating systems and exposure conditions. The results show that the generalised levels suggested in the draft version of the ISO standard are far too low compared with the critical levels obtained here. It is suggested that higher levels could be defined, which would save costs and time.     

Thermogravimetric and weathering study of novolac resin composites reinforced with mercerized bamboo fiber

The effect of alkali treatment of bamboo strips on the thermal and weathering properties of unidirectional bamboo strips‐novolac resin composites were investigated in this work. Both alkali treated and untreated bamboo fiber‐reinforced composites were fabricated. All types of composite specimens were subjected to accelerated weathering and the % water absorption and dimensional changes were recorded after 120 h immersion in water at room temperature and atmospheric pressure and further characterized by flexural property measurements. The composites were also subjected to exposure at 100% humidity and UV exposure (sun light) for 75 h. The results showed that the composites with treated bamboo strips showed a better weathering characteristics compared with the untreated ones. Thermogravimatric analysis of all the samples indicated better thermal properties of alkali treated samples. These findings confirmed the improved interfacial interactions arising from covalent bonds between the alkali treated bamboo fibers and novolac resin. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers