Article

Effects of acid rain on the appearance of automotive paint systems studied outdoors and in a new artificial weathering test

Authors:
  • Bundesanstalt für Materialforschung und -prüfung, now retired
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Abstract

A study was performed exposing seven automotive OEM coatings (base coat/clear coat paint systems) outdoors in Jacksonville and to different variants of the acid dew and fog (ADF) test, a new approach to simulating the worst case of the weather conditions in harsh urban and industrial environments. Varying the climatic conditions and the severity of the simulated acid precipitation, a certain variant of the ADF test was found to show a satisfying practice correlation. Profilometric and chemical analysis revealed that the coatings differ in the rate of photodegradation after an acid attack due to the penetration of acid solution.

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... The acid catalyzed hydrolysis has been investigated in several works. [18][19][20] The degradations caused by acid rain, which are very common in urban and industrial areas, are included in this type of hydrolysis. It has been found that the acid rain and the acid catalyzed hydrolysis are most likely to occur at moderate to strong acidic environments. ...
... It has been found that the acid rain and the acid catalyzed hydrolysis are most likely to occur at moderate to strong acidic environments. For example, the results reported by Schulz et al. 19 showed that the pHs of a real acid rain even at the aggressive environments (Jacksonville, FL) existed in the range of 3.5-4.5. Also, they employed a method by which the harsher condition (even pH = 1.5) was applied to different clearcoats to evaluate their resistance to acid rain. ...
Article
This study aims at investigating the degradation mechanism of an automotive clearcoat caused by bird droppings. Natural bird droppings and their synthetic equivalent (pancreatin) were utilized for this purpose. The presence of highly-etched areas on the surface of coatings and structural variations of clearcoat after being attacked by these materials corresponded to a catalyzed hydrolytic degradation. This finding was obtained using different analytical techniques. Based on these studies, three possible hypotheses were presented, including acid catalysis, metal ion catalysis, and enzymatic catalysis. The conditions required for the occurrence of each hypothesis were discussed. It was found that acid and metal ions have a weak contribution to catalyze the hydrolysis reaction of clearcoat, whereas enzymes existing in bird droppings were mainly responsible for this hydrolytic degradation. KeywordsEnzymatic degradation–Bird droppings–Automotive coating–Hydrolysis–Pancreatin
... Materials are often tested using standardized methods, like the salt fog, the climatic chamber, the Q-UV chamber, thermal cycling, etc. and in some cases, a combination of these methods is proposed. Many accelerated ageing cycles are used in practice to try to find a balance between various tests and get the most natural possible exposition [3]. The evaluation of coating degradation after ageing is often made by visual inspection (in the case of salt fog), but sometimes, in order to get more accuracy, electrochemical techniques such as electrochemical impedance spectroscopy (EIS) [4] are used. ...
... A complete cure was obtained after 20 days at room temperature. The density of the coating is 1.83 g/cm 3 . ...
Article
In order to study the effect of a visco-elastic stress (tension and compression mode) onto the performances of a thick marine organic coating, free films and coated panels were immersed in natural seawater and in NaCl 3wt.% solution at room temperature (20°C), fixed temperature (45°C) or under cyclic temperatures. Free films were analysed using uniaxial elongation and Dynamic Mechanical Analysis (DMA) and the degradation of coated samples was investigated using Electrochemical Impedance Spectroscopy (EIS).In natural and artificial ageing, the glass transition temperature Tg and the Young modulus were found to increase with immersion time but different kinetics were observed depending on the ageing solution. For coated panels, the effect of tension was found to be harmful for the coating whereas the compression seemed to have a slight effect onto the coating degradation independently to the ageing environment.By comparing the degradation of coatings in natural and artificial sea water, it was shown that the kinetic of degradation was faster in artificial medium while the water absorption was larger in natural seawater. The results highlight the harmful impact of seasonal temperature variation in natural medium which could be explained by the development of internal stresses into the coating.
... Performance testing establishes the degree to which a component or assembly conforms to an acceptable level. To examine the impact of moisturing-drying the cycle was composed on the basis of earlier scientific research [1,3,6] and the statistic data of the Lithuanian climate [13], with respect to the average rain duration, number of sunny days, the maximal outdoor temperatures in warm seasons, the temperature at the surface of the building wall, and relative air humidity. With the knowledge of an average chemical composition of acidic rain, the moisturing-drying cycle (further on referred to as M-D) has been worked out. ...
... .ig 13 demonstrates that the maximal water absorption of the T sample in distilled water during the M-D cycles decreases slightly (.igs 8,13); meanwhile, the speed of water absorption of the samples immersed in water solutions whose pH = 4,5 and pH = 2,5 increases; however, at the same time their maximal value of water absorption decreases (.igs 6,7,13). It can be explained in the following way: free lime and the composed soluble calcium nitrate are washed off from capillaries, therefore their diameter in the uncarbonised plaster increases. ...
Article
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The essential function of exterior walls is to provide a continuous barrier to the exterior environmental conditions. The decay of the building facades is accelerated by atmospheric pollution and acidic precipitation. For determining of the impact of atmospheric pollution on the building facade face materials, the tests examining the impact of the cyclic moisturing‐drying have been carried out with the use of acidic water solution to imitate acidic rain. The results of the experiments demonstrated that water solutions have greater destructive effects on the paint film by penetrating through it into the plaster base, thus forming new derivatives in it, which increase water absorption in the plaster base. In order to improve the standard testing on weather resistance of facing building materials, which does not ignore the impact of the atmospheric pollution, for localities where acidic precipitations are frequent, the climatic tests should also include the deteriorating effect of acidic water solutions on facing materials. The results of the experiments will be used for a creation of the prognostic method which will lead to the establishment of a new accelerated climatic ageing test cycle meant for determining a more reliable prognosis of the durability of materials. First Published Online: 14 Oct 2010
... However, these three factors can be simulated in controlled, laboratory weathering tests to assess the lifespan of the coatings. Often, automobile coatings are also subjected to corrosive gasses and microorganisms; these degradation factors are usually only recreated in laboratory tests for special application situations [55]. ...
Article
Full-text available
Automotive coatings and the processes used to coat automobile surfaces exemplify the avant-garde of technologies that are capable of producing durable surfaces, exceeding customers’ expectations of appearance, maximizing efficiency, and meeting environmental regulations. These accomplishments are rooted in 100 years of experience, trial-and-error approaches, technique and technology advancements, and theoretical assessments. Because of advancements directed at understanding the how, why, when, and where of automobile coatings, the progress in controlling droplets and their deposition attributes, and the development of new technologies and paint chemistries, a comprehensive and up-to-date review of automobile coatings and coating technologies was considered to be of value to industrial practitioners and researchers. Overall, the critical performance factors driving the development and use of advanced automotive coatings and coating technologies are (a) aesthetic characteristics; (b) corrosion protection; (c) mass production; (d) cost and environmental requirements; and (e) appearance and durability. Although the relative importance of each of these factors is debatable, the perfection of any one at the expense of another would be unacceptable. Hence, new developments in automotive coatings are described and discussed in the following review, and then related to improvements in production technologies and paints. Modern automotive coating procedures are also discussed in detail. Finally, an extrapolation into the future of automotive coating is offered with a view of the developments and technologies needed for an increasingly efficient and more sustainable coatings industry.
... The earlier research studies on deterioration and corrosion (related with air pollution) have mostly been concerned with the SO 2 effects on painted metals [7,8,9,13]. The influence of acid rains as a catalyst of metal corrosion is well known. ...
Article
Full-text available
The paper provides the basic characterization of the principal agents that affect the durability of building materials and the description of the degradation mechanisms. The degradation factors are classified according to their nature (mechanical, electromagnetic, thermal, chemical and biological agents) as well as to their origin (atmosphere, ground etc.). The interactions between materials and climatic factors with pollutants are very complex and many variables are involved. Deposition of pollutants onto surfaces depends on concentrations of the atmospheric pollutants as well as the climate including the microclimate next to a surface. In case the pollutants are on the surface, interactions will vary depending on the amount of exposure, the reactivity of different materials and the amount of moisture. General effects and their causes include surface material cracking, splitting, spalling, softening and staining, due to salt or water crystallizations and acid-base chemical dissolution reactions. The article focuses on the specific problems connected with the atmospheric pollution and climatic effects on building materials, new accelerated ageing tests, including the simulation of atmospheric acidic precipitations.
... The coatings are often tested using standardized methods, such as the salt fog, the climatic chamber, the Q-UV chamber, thermal cycling, etc., and, in some cases, a combination of these methods is proposed. Many accelerated ageing cycles are used in practice to try to find a balance between various tests and obtain the most natural possible exposition [18]; however, very often, there is not a good correlation between accelerated ageing tests and degradation in a natural environment [19]. Research is still in progress in order to find reliable protocols and/or techniques to better understand organic coating degradation [20][21][22][23][24][25][26][27][28][29]. ...
Article
Full-text available
Three different coated steel systems were aged in natural or artificial seawater, in neutral salt spray (NSS), and using alternate immersion tests in order to evaluate the aggressiveness of the different ageing conditions. Commercial epoxy coatings were applied onto steel (S355NL), hot-galvanized steel (HDG), and Zn-Al15 thermal spraying coated steel. The defect-free systems were immersed in artificial seawater at 35 °C for 1085 days and in natural seawater for 1200 days and were characterized by electrochemical impedance spectroscopy (EIS). Panels with artificial defects were immersed for 180 days in artificial seawater and, regarding adhesion, were evaluated according to ISO 16276-2. In parallel, the three coated systems were submitted to cyclic neutral salt spray (NSS) for 1440 h: defect-free panels were regularly evaluated by EIS, while the degree or corrosion was measured onto panels with artificial defect. After NSS, defect-free panels were immersed in artificial seawater at 35 °C for further EIS investigations. Finally, alternate immersion tests were performed for 860 days for the three defect-free coated systems and for 84 days for panels with a defect. The results showed that, for defect-free panels, immersions in natural or artificial seawater and NSS did not allowed us to distinguish the three different systems that show excellent anticorrosion properties. However, during the alternate immersion test, the organic coating system applied onto HDG presented blisters, showing a greater sensitivity to this test than the two other systems. For panels with a defect, NSS allowed to age the coatings more rapidly than monotone conditions, and the coating system applied onto steel presented the highest degree of corrosion. Meanwhile, the coating systems applied onto HDG and the thermal spray metallic coating showed similar behavior. During the alternate immersion test, the three coated systems with a defect showed clearly different behaviors, therefore it was possible to rank the three systems. Finally, it appeared that the alternate immersion test was the most aggressive condition. It was then proposed that a realistic thermal cycling and an artificial defect are needed when performing ageing tests of thick marine organic coating systems in order to properly rank/evaluate the different systems.
... Other aspects of formulation as the type and level of pigments, crosslinkers and additives could impair the durability performances. The use of light stabilising additives, as UV absorbers (UVAs) or Hindered Amine Light Stabilizers (HALS) retards the photo-oxidation process resulting in more durable coatings ( Boxhammer, 2001 ;Hua, Li, Gao, & Zhao, 2009 ;Lee & Kim, 2006 ;Maetens, 2007 ;Malshe & Waghoo, 2004Osterhold & Gl ö ckner, 2001 ;Schulz, Trubiroha, Schernau, & Baumgart, 2000 ;Wicks, Jones, & Pappas, 1999 ;Yang et al., 2001 ). ...
Article
One of the most common strategy to protect metallic substrates from corrosion is the use of organic coatings. The accurate prediction of long-term performances of this protective system is a very important issue for the coating industry. Outdoor exposure of organic coatings can produce the loss of their aesthetic and anticorrosion properties because of weathering conditions: sunlight, temperature, water, oxygen and pollutants. Coating service life is generally evaluated by using laboratory tests simulating in accelerated way the natural conditions (temperature, UV radiation, moisture, condensation, pollution). It is well known that it is difficult to find a clear correlation between natural exposure and artificial weathering. The time of exposure in a natural site is not sufficient to define the weathering conditions; it is important to consider different environmental parameters affecting the organic coating properties (energy from UV radiation, wet time, temperature). In this work the change of aesthetic and protective properties of organic coatings was investigated. Different systems were studied: epoxy-polyester and polyester coatings crosslinked with different hardeners. The coatings have distinct surface finishes and colours with particular aesthetic effects. The samples were exposed in Trento area (alpine region, north of Italy), monitoring all meteorological parameters. The same samples were artificially weathered by a cyclic test consisting of 72 h of UV exposure (ASTM G154 UVA, 340 nm) and 72 h of salt spray chamber exposure (ASTM B117, 5% NaCl, 35°C, 100% relative humi­dity). The aesthetic degradation was evaluated by gloss and colour variation measurements; the surface chemical changes were studied by FTIR analysis. Environmental scanning electron microscopy was used to obtain some information about morphological characteristics of the exposed surfaces. The degradation of protective properties was studied by electrochemical impedance spectroscopy. Different results have been obtained for aesthetic and protective properties. Concerning gloss and colour variations, a good relationship was found between artificial and natural tests. When considering the protective properties, laboratory test results were more aggressive due to the salt spray environment in which the samples have been exposed.
... HNO 3 ) may have severe impacts on climate, environment, and human health. For instance, reaction of NO x and sulphur dioxide in the presence of moisture produces acid rain (Likens and Bormann, 1974;Welburn, 1988), which corrodes cars (Schulz et al., 2000;Samie et al., 2007), buildings and historical monuments (Cheng et al., 1987;Schuster et al., 1994;Bravo et al., 2006) and makes streams and lakes acidic, hence uninhabitable for fish (Minns et al., 1986). Reaction of NO x and ammonia with other substances generates particles and nitric acid (HNO 3 ). ...
Article
Full-text available
This study examines the contribution of pollutants (NOx and HNO3) from Highveld on pollution in Cape Town. For the study, we analyzed observation data (2001–2008) from the City of Cape Town air quality network and regional climate model (RegCM4) simulations (2001–2004) over southern Africa. The model accounts for the influence of complex topography, atmospheric condition, and chemical reactions among the atmospheric gases in simulating the emission and transport of the pollutants over southern Africa. The model results show that north-easterly flows can transport pollutants (especially HNO3) at low level (surface – 850 hPa) from Highveld to Cape Town. And in April, a tongue of high concentration of NOx and HNO3 extends from Highveld to Cape Town along southern coast. The study shows two dominant paths through which pollutants from Mpumalanga Highveld are transported to Cape Town. The first path follows the borders of South Africa, Botswana and Namibia, and along Western Cape to Cape Town while the second path is moves southward over South Africa to the south coast and then eastward along south coast to Cape Town.
... Moreover, there are different parameters which may affect the clear-coat surface chemistry and can directly influence the anti-corrosive performance of this layer during their exposure to outdoor factors [8]. These mainly include weathering environments (e.g., UV radiation from sunlight, water and humidity, acid rain, hot-cold shocks) [9][10][11] and biological materials (e.g., bird droppings, raw eggs, tree gum, insect bodies) [2,4,[12][13][14][15][16][17]. In response to this, a variety of exposure methods and test protocols have been developed to anticipate the long-term weathering behavior of coating failure and predict performance [10-12, 15, 18-23]. ...
Article
Full-text available
There are different aggressive biological materials which may potentially deposit on a painted automotive body surface during its service life, causing possible local damage, loss of appearance and loss of protective aspects of the system. In this study, the effect of two types of aggressive biological materials on a painted automotive body surface, i.e., natural bird droppings and raw eggs were studied and subsequently explained in more detail. Furthermore, two different testing conditions approaches including indoor and outdoor were utilized in order to investigate the surface roughness, R a , and also to study the behavior of biologically degraded automotive body surface at nano-level scale. The effects of these biological materials on a painted automotive body surface and its appearance were investigated by Atomic Force Microscopy (AFM) and a stylus-based inductive gauge (Taly-surf®, from Taylor Hobson, Inc.), having electromagnetic control of the contact force. Engaged vertically on the top of the specimens, the force could be set much lower than the weight. Results showed that natural bird droppings and raw eggs have a dramatic effect on the appearance and surface roughness of a painted automotive surface body. It was also found that the degradation which occurred due to the natural bird droppings was more severe than that of the samples exposed to raw eggs.
... Acidic environments are good catalysts for both hydrolysis and photo-oxidation. Schulz et al. mentioned the acidic rain (sulfur dioxide uptake (SO 2 $ H 2 SO 4 )) as one of the most important factors of acidic catalyst [23]. Sampers also exposed the fact that the performance of HALS can be drastically reduced in the presence of acids or pesticides [24]. ...
... In order to simulate degradation of coatings for outdoor applications as closely as possible, other environmental stress types have to be added, for example, acid rain simulation. Recently, new accelerated weathering tests including acid rain were introduced [10][11][12]. ...
Article
A new weathering device was designed and constructed for conducting accelerated tests on coatings for life data analysis. The commercial device was equipped with eight separate thermally insulated chambers, where eight weathering tests can be carried out simultaneously. The following stress types important for polymer ageing can be controlled in the apparatus: UV, temperature, humidity and pollutants. The apparatus, together with the Service Life Prediction methodology, have already been successfully tested for the degradation of aircraft coatings regarding loss of gloss, where sulfuric acid aerosol was used to simulate the post-eruption stratosphere conditions. Instead of sulfuric acid aerosol, acid rain, sodium chloride or other salts or gaseous pollutants could be added. This is, as far as we know, a truly unique instrument and it opens many new opportunities for the future of artificial weathering of coatings.
... Outdoor mechanical factors [1][2][3][4][5][6][7], weathering environments (e.g. sunlight, humidity, acid rain) [8][9][10] and biological substances (e.g. tree gum, bird dropping and insect body) impose different kinds of degradations to automotive clearcoats during their service life [11][12][13][14][15][16][17][18]. ...
Article
Acrylic/melamine based automotive clearcoats were prepared by inclusion of functional and conventional additives. The conventional additives used were based on polysiloxane chains without any reactive groups. On the other hand, the functional additives were based on polyacrylate and polysiloxane backbones. The additives were added to the clearcoat formulations at different concentrations. Surface tension, optical properties and rheological behaviors of the clearcoats were studied by tensiometer, gonio-spectrophotometer, rheometric mechanical spectrometer (RMS) and Brookfield techniques. Results showed that addition of both conventional and functional additives reduced the surface tension of the clearcoat up to a certain value of the additive concentration. It was seen that functional additives could reduce surface tension much greater than the conventional ones. The coating clarity and transparency were not affected in presence of conventional additives. However, the functional additives, especially the one having higher molecular weight, reduced the coating transparency. The clearcoat viscosity was increased using functional additives. A shear thickening behavior of the clearcoats loaded with functional additives was seen. The conventional additives did not change the clearcoat viscosity. It was concluded that the additive functionality, molecular weight and chemical structure were influential parameters affecting the final properties.
... However, these three factors can be simulated in controlled, laboratory weathering tests to assess the lifespan of the coatings. Often, automobile coatings are also subjected to corrosive gasses and microorganisms; these degradation factors are usually only recreated in laboratory tests for special application situations [55]. ...
Article
Automotive spray painting is among the most sophisticated and controlled industrial painting operations currently performed. Nevertheless, improvements in it are still sought in efforts to minimize the costs, the energy use and the environmental impacts. One compelling aspect of improvement is the paint transfer efficiency, i.e. the amount of paint that remains on a vehicle relative to the amount supplied to the paint applicator during coating operations, because currently it has been estimated that the overall paint transfer efficiency in the automotive industry is between 50% and 60%. Hence, this review assesses current automotive spray coating technologies with respect to their transfer efficiencies and discusses the fundamental and operational parameters that influence it. A comprehensive characterization of paint spray applicators (air sprayers, high-volume low-pressure sprayers, airless sprayers, air-assisted airless sprayers, rotary bell atomizers, electrostatic sprayers, and effervescent atomizers) is included. Some problems associated with evaluating and improving their paint transfer efficiencies are discussed. Also, the potential of and the technology needs for developing these applicators are considered.
... The Taj Mahal in India, the Colosseum in Rome and monuments in Krakow, Poland are continuing to deteriorate. Cologne Cathedral, Notre Dame, Westminster Abbey in Sweden, medieval stained glass windows have been affected by acid rain (Schulz, et al, 2000). It is a similar case with architectural products in urban centres of South-Eastern Nigeria where virtually all external building finishes have continued to deteriorate immediately after three rainy seasons of application. ...
Article
Full-text available
External building finishes play a vital role by increasing the durability of external structure, protecting against climatic hazards and providing aesthetic expression. The rate of deterioration of external finishes in South-East Nigeria is alarming. This development calls for investigation as most of the finishes could no longer serve the purpose for which they were programmed. This research investigates buildings in Owerri, Aba and Enugu towns. The research is aimed at providing criteria for specification of external finishes that will ensure sustainability of architectural design. The objectives were to: document the existing finishes; determine the climatic factors that affect the finishes; determine the nature and extent of deterioration; and develop a criteria for specification. The methodology involved field investigations using questionnaires, oral interviews and observations. The study population was 2,830 building units and 2,830 consumers while the sample population was 1887 buildings and 1887 consumers. The result revealed as follows: average of 93% of buildings had deteriorated finishes; temperature change ranging from 26 oC - 32 oC; high rainfall ranging from 2000 mm - 4000 mm; solar radiation intensity ranging from 151W/m2- 186W/m2. The research further revealed eight categories of finishes used as follows: stone based finishes-3%; wood based finishes-2%; cement based finishes-5%; glass panels- 8%; aluminium panels-5%; synthetic fibres-3%, Clay based-2% and paints-72%. The research recommends for architects specifying environmentally sensitive finishes in their design such as stone based finishes, glass and aluminium panels and clay based.
... Although generally aiming at acceleration, no acceleration factor compared with any outdoor exposure can be generalized for different polymers. There are various objectives in the conceptual design of such artificial weathering tests: e.g., the determination of acceleration factors [21], the comparison of the ranking of different materials in regard to aging effects [22,23], or the identification of potential failure locations for components. ...
Article
Full-text available
The potential release of hazardous substances from polymer-based products is currently in the focus of environmental policy. Environmental simulations are applied to expose such products to selected aging conditions and to investigate release processes. Commonly applied aging exposure types such as solar and UV radiation in combination with water contact, corrosive gases, and soil contact as well as expected general effects on polymers and additional ingredients of polymer-based products are described. The release of substances is based on mass-transfer processes to the material surfaces. Experimental approaches to investigate transport processes that are caused by water contact are presented. For tailoring the tests, relevant aging exposure types and release quantification methods must be combined appropriately. Several studies on the release of hazardous substances such as metals, polyaromatic hydrocarbons, flame retardants, antioxidants, and carbon nanotubes from polymers are summarized exemplarily. Differences between natural and artificial exposure tests are discussed and demonstrated for the release of flame retardants from several polymers and for biocides from paints. Requirements and limitations to apply results from short-term artificial environmental exposure tests to predict long-term environmental behavior of polymers are presented.
... The evaluation of these and other coating properties is essential in order to obtain constantly high quality level for coating products. The standard methods for quality control of coatings on steel sheets contain salt spray test, climatic chamber test, QUV chamber test or thermal cycling [4]. Most of these methods end up in a visual inspection of the coating. ...
Article
The effect of humidity on the glass transition temperature of coatings is well known and analyzed. In this study, an analysis method is introduced for analyzing coil-coated metal sheets submerged in water and water/methyl ethyl ketone (MEK) by using an immersion cell coupled to a DMA. For this purpose, a model polyurethane acrylate coating was applied to zinc/magnesium-coated steel plates and measured before and after immersion in water and water/MEK by DMA and immersion cell. The results show a shift of glass transition temperature from 138 to 13 °C of the coating by storing the coated steel plates under water and immersion testing. A time-dependent diffusion of water from the cell into the coating until saturation can be observed. An increasing concentration of MEK within the immersion cell results in a greater shift of the glass transition temperature. Overall, the immersion cell seems to be a useful tool for in situ characterization of the behavior of coil coating varnishes in liquid environment (Foster et al. in Prog Organ Coat 51:244–249, 2004, van der Wel et al. in Prog Organ Coat 37:1–14, 1999).
... Several researchers investigated the durability of the coatings [17][18][19]. However, the research on the longstanding fire resistant to fire retardant coatings is comparatively limited. ...
Article
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The aim of this work is to study corrosion behaviour of intumescent coating and the primer on steel substrate before and after a fire test. The coated steel substrates were subjected to fire in a furnace at 950oC for a variable duration ranging from 30, 45, 90 and 120 min. All coated steel substrates were also subjected to corrosion test by immersing them in 5% NaCl solution, for 15 min and three months duration using Electrochemical Impedance Spectroscopy (EIS). The specimen’s impedance before fire test and before immersion was 4.37x108Ω.cm2 . After 15 min exposure to NaCl, this value was reduced by 26, 53, 60 and 65% for specimens fired for 30, 45, 90 and 120 min, respectively. Further reduction in the impedance by 97.6, 97.8, 97.9 and 98.9% for samples fired for 30, 45, 90 and 120 min, respectively, were measured after three months in 5% NaCl immersion.
... The acidic environment created by gums may also account for the occurrence of such accelerated etching phenomenon. It has been found that, acidic solutions can affect and catalyze the hydrolysis reactions in the same way [20,21]. Several researchers have studied this condition for acrylic melamine, in terms of degradation caused by ''acid rain'', which is also a very common phenomenon. ...
Article
Full-text available
In this work the effects of natural gum and its simulated compound (Arabic gum) on an acrylic based clear coat applied on different basecoats were studied. The experiments were conducted at various aging processes to simulate the real outdoor conditions by the aid of different analytical techniques including optical microscopy, scanning electron microscopy, ATR-FTIR spectroscopy, DMTA and micro hardness measurements, by which the chemical and mechanical responses of the system were investigated. Results showed that, Arabic and natural gums, due to their sticky nature in the slurry state, can strongly attach to the clear coat surface and perform a significant stress during the drying process. It was shown that, this stress was responsible for the surface cracks produced by gums, indicating a physical degradation mechanism. However, it was revealed that, biological materials could also affect the clear coat chemically. In addition, different surface cracks produced by gums on the clear coat applied on silver and black basecoats were observed and attributed to their surface chemistry and mechanical properties differences. It was shown that different amounts of aluminum flakes existed in the basecoat layers of silver and black system can effectively influence the curing degree of the clear coats applied on the se systems. This leads to different cross-linking density, toughness and surface chemistries. Therefore, different interactions of clear coats and gums, as well as stress distribution and relaxation behaviors of these two systems were found effective in such degradations. Comparison of the mechanical properties and visual effects of gums on clear coats indicated a more severe degradation under the post aging, due to the greater effect of UV light. KeywordsArabic gum-Acrylic/melamine-Cross-linking density-Physical and chemical degradations
... Aesthetic damages can also occur such as efflorescence of soluble salts on the surfaces of porous walls, changes of colour paint staining and peeling (Ken et al 2010 andEvelyn et al., 2005). Damp walls may also provide ground, and encourage fungus attack and unpleasant odours (Folorunso, and Ahmad, 2013;Schulz et al.,2000). Parapet buildings are characterized by all these enumerated problems and therefore should be discouraged in the tropical zone. ...
Article
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Abstract With the wave of oil boom of 1970s in Nigerian, Veteran Architects imported into the country modern parapet style of architecture which gained popularity in both public and private sectors in the building industry, neglecting the peculiarities of tropical climate. The research is aimed at investigating the performance of these parapet buildings in Owerri, Enugu and Aba in South-Eastern Nigeria, as most of these buildings could no longer serve the functional, structural and aesthetic purposes for which they were built, with the view to evolving environmentally sensitive design. The objectives were: to determine the prevailing tropical climatic condition and architectural characters of this style of architecture; to determine the nature of deterioration and the extent of post-occupancy modifications and to determine the architectural characters that are sensitive to the prevailing tropical climate. The methodological approach was field investigation involving observations, questionnaire, and oral interviews. The study population was 1032 buildings and 1032 users with the sample size of 688 buildings and 688 users. The result revealed that the parapet buildings are characterized by extremely low pitch flat roof with less than 100 which has no respect to the prevailing climatic condition of the area. The result further revealed that 75.1 percent of the buildings had undergone post-occupancy modifications as a result of alarming deterioration of external and internal building cladding and roof structures causing leakages and wetness of interior. The research recommends for architects designing extremely 250 minimum high pitch roof with 750mm minimum deep eave projection sensitive to the prevailing tropical climatic condition. Keywords: Performance Appraisal, Parapet Building, Environment, Design, Climatic Factor Introduction Right from
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Pigmented epoxy coatings were UV degraded for various periods at elevated pressures (1–100bar) and investigated with dielectric sorption analysis (DSA). Differences in dynamics of absorption behaviour for degraded polymer occurred due to increased hydrophilicity, crosslinking and porosity. Degradation at all pressures showed desorption, caused by swelling of the coating and shrinking of pore size. The amount of water sorption and desorption rose linearly from 1bar to 50bar and from 50bar on no further increase in degradation was found. Longer degradation times at 100bar also resulted in a linear trend. At lower frequencies double peaks were found as a result of water desorption, polymer relaxation, water–hydrophilic cluster interactions and polymer swelling, indicating a frequency dependence. The double peak could be fitted by two independent curves, whereas a single exponential term sufficed to fit the desorption of water for all frequencies. Pressure is clearly an accelerating degradation parameter in combination with an UV source.
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For polypropylene of varied stabilization, spectral sensitivity as well as temperature dependence of irradiation caused crack formation was determined in artificial irradiation tests. UV radiant exposure HUV necessary to generate crack formation was measured both in spectrally dispersed irradiation and artificial irradiation in a Fluorescent UV lamp device. Dependencies were fitted to a plateau function and an Arrhenius function, respectively, to describe the action of irradiation by response functions. Applied to weather data from Phoenix, the results were compared with respective outdoor exposure results.
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As the results of a 14 weeks outdoor exposure of a series of automotive coatings in South Florida, the panels were found to be overgrown with an almost closed layer of mildew. Pinholes remained as permanent surface damage after removing the mildew mycelium. The extent of the damage differed in dependence of the kind of the coating. By tracing the images and profiles of the coating surfaces systematically over all phases of weathering and the subsequent cleaning procedure, a connection between formation of pinholes and mildew growth could be found. Outdoor weathering tests in other regions of Florida as well as in Europe and Australia showed that pinholes caused by mildew attack could also be found in all other locations, but always to a lower extent than in South Florida. The standardised mildew tests EN ISO 846 and MIL-STD 810F for laboratory exposure failed to reproduce the formation of pinholes.
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This paper presents a study into the impact of environmental weathering on the chemometric classification of automotive clear coats. These studies were conducted using attenuated total reflectance infrared spectroscopy, in conjunction with a chemometric model capable of predicting the country of vehicle manufacture for a sample based upon its infrared spectrum. Testing of three samples exposed to environmental conditions found the model to be robust to weathering over at least an eight-month period. However, analysis of 12 samples of unknown prior history found that extreme degradation over at least a 10-year period, or the presence of a post-manufacture (respray) coating, could result in misclassification when relying solely on analysis of the clear coat. It is therefore important that cross-sections comprising the full layer sequence of the paint system are obtained wherever possible, as analysis of the underlying layers may give more comprehensive characterisation.
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The effect of relative humidity (RH) from ≪1% to 90% on the photodegradation and quantum efficiency for a partially-methylated melamine acrylic coating exposed to UV/50°C condition has been investigated. The UV source is supplied by two 1000 W Xenon arc solar simulators and the relative humidities are provided by specially designed humidity generators, which control relative humidity in the 0 to 90% range to within <3% of the measured values. Radiation absorbed in the coating and degradation of the films are measured by UV-visible and Fourier transform infrared spectroscopies, respectively. The degradation at a particular RH/UV condition consists of four different modes: reactions taken place during post curing, hydrolysis due to water in the film at a particular RH, photodegradation, and moisture-enhanced photodegradation. Total degradation, hydrolysis, and moisture-enhanced photodegradation increase with increasing RH. At low relative humidities, photodegradation is an important degradation mode but hydrolysis dominates the degradation at high RH levels. Moisture in the film is found to increase the quantum efficiency of acrylic melamine coating photodegradation.
Article
The protective properties of organic coated galvanised steel for outdoor applications are generally evaluated by means of accelerated laboratory tests, including electrochemical techniques.An open question is how these accelerated tests can be correlated with natural exposure in different environments.It is well known that many papers did not found any significant correlation between the natural exposure and laboratory tests. In this paper we propose a different approach. The starting point is the consideration to define the natural weathering by monitoring a few different environmental parameters affecting the organic coatings properties (energy from UV radiation, wet time, temperature, etc.), and not just considering the time of exposure.We studied two different galvanised materials: Zn and Zn–Al coatings, three different primers and one top coat. The samples were exposed for 12 months in three different natural environments: Trento (Italy), alpine region, Marseille (France) by the Mediterranean sea and Daytona (USA), a humid tropical environment. At the same time all the meteorological parameters were collected.The coatings weathering was evaluated in the laboratory after some different accelerated tests (salt spray chamber, UV exposure, cyclic test) and after natural exposure. A correlation between the “natural stresses” and the “artificial stresses” was investigated.
Chapter
One way to realize a higher throughput in weathering consists in applying more sensitive means of detection. Within the group of luminescence techniques, which are generally characterized by high sensitivity, chemiluminescence (CL) is investigated as a possible candidate. Its usefulness in evaluating weathering effects and the limitations in correlating the effects of weathering tests at early stages to those at later stages commonly used for established macroscopic detection will be discussed. Also, principles in the correlation between shortening weathering tests and field exposure are highlighted.
Article
The protective properties of organic coatings for outdoor applications are generally evaluated by means of accelerated laboratory tests, including electrochemical techniques. The coatings are stressed by different mechanical, chemical, thermal loads and the effects on the protective properties can be measured by using well established electrochemical techniques, like electrochemical impedance spectroscopy, electrochemical noise, etc. An open question is how these accelerated tests can be correlated with natural exposure in different environments.
Article
Acrylic-melamine coatings are known to be susceptible to hydrolysis when exposed to water or humid environments. The mode and specific pathways for hydrolytic degradation of acrylic-melamine coatings exposed to water vapor in the absence of ultraviolet light are presented. Samples of a partially methylated melamine-acrylic coating applied to CaF2 substrates were subjected to five different relative humidity levels ranging from approximately 0 to 90% at 50°C. Coating degradation was measured with transmission Fourier transform infrared spectroscopy (FTIR) and tapping mode atomic force microscopy (AFM). In humid environments, partially methylated melamine-acrylic coatings undergo hydrolysis readily, causing considerable material loss and formation of mainly primary amines and carboxylic acids. The rate of hydrolysis increases with increasing RH. Hydrolytic degradation of acrylic-melamine coatings is an inhomogeneous process in which pits form, deepen, and enlarge with exposure. Such localized degradation mode suggests that hydrolysis of this material is an autocatalytic progression where acidic degradation products formed in the pits catalyze and accelerate the hydrolysis reactions.
Article
There are various biological materials which may repetitively deposit on a painted automotive body during its service life, causing possible local defects. This study is an attempt to reveal the mechanism of degradation caused by bird-droppings and to compare the performance of clearcoats having various resin/hardener ratios. Two different testing methods varying in aging conditions, of the effect of natural bird-droppings, were applied to two types of clearcoats. Variations in chemical structure were characterized by the aid of FTIR spectroscopy and DMTA analysis. Also, in order to establish an experimentally viable procedure to assess such an effect, synthetic countertype of bird-droppings (pancreatin) was used to simulate this natural phenomenon.The results revealed that a digestive enzyme (lipase) present in bird-droppings, can induce the hydrolysis reaction of coating polymer leading to a locally distributed etched surface. It was also found that the clearcoat containing higher ratios of melamine cross-linker had poorer performance against bird-droppings in spite of having a greater cross-linking density.
Article
Acrylic-melamine/urethane thermosets are widely used as topcoat materials in the automotive industry. End users and manufacturers require an accurate prediction of the service life of these materials. Despite the significant interest in the topic of service life prediction, no overview of the subject has been presented. This article characterises the influence of light, oxygen and water on these thermosets in an effort to improve the procedures used to evaluate the degradation. Degradation was tracked using two spectroscopic and one mechanical degradation criteria. Based on the evolution of these criteria under artificial and natural ageing, four accelerated ageing devices (SEPAP 12/24, SEPAP ’water spray’, WOM and QUV-B) were used. The results were used to calculate the acceleration factor between natural and artificial weathering to allow for a true service life prediction of these thermosets.
Article
Chemiluminescence (CL) is a sensitive method of investigating the thermo-oxidative stability of polymers in the early stages of degradation. Therefore, CL measurements were applied to different automotive coatings to evaluate their degradation behavior during artificial weathering. In this work, CL measurements were carried out for different automotive coatings to follow their degradation behavior during artificial weathering. The CL emission depends on sample-specific parameters like stabilizer, matrix, or hardener; experimental parameters like the oxygen partial pressure; and exposure parameters like the duration of weathering. The potential of CL could be demonstrated by classifying materials into categories of good, medium, and low degradation performance at a much earlier stage of weathering exposure than in combination with the usual visual detection of weathering effects.
Article
Full-text available
The essential function of exterior walls is to provide a continuous barrier to the exterior environmental conditions. The decay of the building facades is accelerated by atmospheric pollution and acidic precipitation. For determining of the impact of atmospheric pollution on the building facade face materials, the tests examining the impact of the cyclic moisturing‐drying have been carried out with the use of acidic water solution to imitate acidic rain. The results of the experiments demonstrated that water solutions have greater destructive effects on the paint film by penetrating through it into the plaster base, thus forming new derivatives in it, which increase water absorption in the plaster base. In order to improve the standard testing on weather resistance of facing building materials, which does not ignore the impact of the atmospheric pollution, for localities where acidic precipitations are frequent, the climatic tests should also include the deteriorating effect of acidic water solutions on facing materials. The results of the experiments will be used for a creation of the prognostic method which will lead to the establishment of a new accelerated climatic ageing test cycle meant for determining a more reliable prognosis of the durability of materials.
Article
An increasing normal load scratch test was employed to study the scratch behavior of acrylic coatings. The effects of weathering and substrate surface roughness on the interfacial adhesion of acrylic-coated thermoplastic polyolefin (TPO) systems were investigated. The increasing load test gives valuable information regarding the onset location to failure and the critical normal load for interfacial delamination. Both flatbed scanner and scanning electron microscope are utilized to characterize the scratch-induced damage mechanism of the coated TPO system. An increase in weathering time and in surface roughness of the virgin TPO leads to the increase in scratch resistance of acrylic coating. In addition, with increasing weathering time there is an increase in discoloration, while a decrease in gloss occurs. The correlation between the change of scratch coefficient of friction and the onset location of interfacial delamination is discussed.
Article
This paper reports the results of an experimental study of the degradation in fire protection performance of intumescent coating for steel elements after different times of accelerated weathering aging. The physical and chemical changes of the coatings during the aging process were investigated. The surface of the aged samples was found to become rough, powdered and embrittled, the fire resistance time decreased and the char layer morphology changed significantly. After 480 h of aging, the aging ratio was 39.8%, and 60% of the pore sizes in the char layer were over 300 μm. The sample aged for 600 h had almost no protective effect for the substrate and the adhesive strength was only 0.30 MPa. Due to the oxidation, decomposition and hydrolysis reactions in the main components of the coating, the components and the compositions of the coating change during the aging period. Therefore, the synergistic expansion reaction may not occur between the ingredients when heated, leading to the deterioration of the fire resistance performance of the coating. There is a linear dependence between the contact angle of the coating surface and the aging ratio of y = 116.71–1.36x. This result could be used to determine the aging ratio of the coating used for a period of time.
Article
Natural weathering of polystyrene (PS) was performed at six exposure sites with various climate types along the coastal line from China to Europe, including Qionghai (typical hot-humid climate), Sansha (island hot-humid climate), Chennai (savanna hot-humid climate), Jeddah (xerothermic climate), Sanary-sur-Mer (mediterranean climate), Hoek van Holland (warm-temperate climate). The chemical structure, morphology and color changes of PS after weathering were characterized by FTIR, DSC, SEM and Color spectrometer, and relative weathering severity of different climates on PS were compared. Results show that Sansha has the highest severity value while the severity value of Hoek van Holland is the lowest. The degradation degree of PS at the sites of Qionghai, Sansha, and Chennai is higher than that at other sites, resulted in a deterioration of the optical properties and serious damage of the sample surface. In the xerothermic climate, the optical properties of PS decrease drastically during the process of natural weathering, while only slight change in hydroxyl index and carbonyl index is observed, and micrographic surface does not differ from the surface of un-weathered materials. For other climates, the degradation degree was low, resulting in a relative slow change of optical properties and long time for the appearance of surface defects. In order to quantify the relative severity of these climates, a mathematic model was proposed based on the basic degradation principle of polymer materials, which could predict the failure time of PS. The failure time was predicted by the model using gloss loss of PS as failure index, with an accuracy up to 99.2%.
Article
Full-text available
This paper studies the influence of temperature on the corrosion rate of coated AA6111 aluminum alloy used in vehicle bodies under static and vibration states. The vibration test system was collected laboratory and used for testing of five different types of paints (EASI, Numix, Lesonal, DENSO and Polaron paints) in the 5 % NaCl solution using immersion test method. Lesonal paint provided the best corrosion protection, while DENSO paints show large values of corrosion rate, other coatings exhibit moderate values. Model of paints corrosion was developed to characterize the corrosion processes occur at the surfaces. It is found that corrosion rate obtained at vibration cases is larger than static cases and vibration effect on the coating protection rate.
Chapter
Exterior durability of coatings refers to their resistance against the deleterious effects of outdoor exposure, which include changes of modulus, loss of strength, embrittlement, discoloration, loss of adhesion, chalking, loss of gloss, and environmental etching. To achieve good exterior durability, functional groups in a coating that are vulnerable to hydrogen abstraction should be avoided or minimized. An entire branch of durability science is devoted to service life prediction (SLP). This chapter discusses SLP in detail, and focuses on the changes in chemical composition that occur during the exterior exposure of coatings. A major step toward formulation of a coating with exterior durability is to start with binders that resist photooxidation and hydrolysis. Data on the long-term weathering performance of coatings must be generated via tests that accelerate the rate of degradation in order to facilitate formulation changes and incremental improvements. This data can be generated via some different approaches. The chapter discusses theses approaches.
Article
This study examined the effects of artificial acid rain on the color change, the gloss and the morphology of several kinds of coatings used for exterior wood construction panels. The lightness, redness, yellowness and color difference of the coated panels changed with the treatment of artificial acid rain. In particular, a much more pronounced degradation in water-borne natural paint was observed than in the other types of coating as the treatment time increased, due to acid hydrolysis of the water-borne paint. The color change in the coated panel might be associated with the presence of chromophores and auxochromes. The gloss of the semitransparent penetrating oil-base stains (light brown) and natural varnish significantly decreased with increasing artificial acid rain treatment. SEM images and CLSM images showed increasing degradation of the coated surface with increasing treatment time of artificial acid rain.
Article
Silver is used for the production of the reflective surface of the solar concentrators due to its optical properties and good durability. However, in particular conditions, e.g. when exposed in presence of ozone and pollutants containing sulphur compounds, corrosion attacks might occur. In this work the potential of the Atomic Layer Deposition (ALD) technique to deposit thin and compact ceramic films to shield the silver reflective film against weathering was investigated. Al2O3 films applied onto glass samples coated with a physical vapor deposited silver film were applied by means of Atomic Layer Deposition to increase its durability during outdoor exposure. The effect of a different number of self-terminating gas–surface reactions in the ALD chamber (which lead to different thickness of the deposits) was investigated. The appearance and the physical properties of the coatings were explored by means of FE-SEM observations and ToF-SIMS analyses. The corrosion protection properties of the Al2O3 deposits were investigated by means of electrochemical techniques such as potentiodynamic curves and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of the different samples was characterized. The electrochemical measurements revealed that a ∼80 nm thick Al2O3 deposit is able to decrease up to two orders of magnitude the corrosion current compared to the bare silver substrate.
Article
Full-text available
Acid corrosion may cause the deterioration of the fire resistance of the intumescent fire retardant coatings, especially for the coatings used in the acid polluted environment. This paper reported the results of an experimental study of degradation in fire protection performance of intumescent coating for steel elements after different times of immersion in the hydrochloric acid solution. After acid erosion, the thickness of the coating thinned, the surface became rough and had cracks and broken holes. The size of the pores in the char layer was larger and uneven, and some ‘cement’ parts were formed in the char layer. The TG/DTG results showed in the low temperature stage the curve was relatively flat. In the medium temperature stage, the number of the weight loss troughs decreased; the shape of the troughs simplified; and the top weight loss rate increased. In the high temperature stage, the troughs near 593 °C flattened gradually, and the top weight loss rate became smaller, while the top weight loss rate became larger around 674 °C. And there were significant changes in the thermal dynamic parameters. A prediction method of remained fire resistance property for the acid erosion coatings was proposed, by comprehensively considering the physical and chemical characteristics change trends of the corroded coating. And this method can be a reference for the fire safety evaluation of the built protected steel structure.
Article
This study examined the effects of exposure to thermal ageing and weathering conditions on the scratch resistance of an uncoated thermoplastic polyolefin system over a period of 1800 h. A flatbed scanner and scanning electron microscopy were used to observe the surface characterization and morphology for the scratch-induced damage of the aged TPO systems. The number of oxygen containing polar functional groups, amount of talc, crystallinity and discoloration on the TPO surface increase with increasing ageing time. At the same time, the number of hydrocarbon groups decreases. These findings suggest that the hydrocarbon groups locally undergo oxidation on the TPO surface due to thermal ageing and weathering. The abovementioned changes lead to an increase in scratch resistance and performance.
Article
Acid corrosion may cause the deterioration of the fire resistance of the intumescent fire retardant coatings. This paper reported the results of an experimental study of degradation in fire protection performance of intumescent coating for steel elements after different times of immersion in the hydrochloric acid solution. The morphology, the equivalent thermal resistance, and the changes of the elements and groups contained on the surface of the coatings were investigated. The corrosion mechanism was as follows: when the coating was immersed in the acid solution, the ammonium polyphosphate (APP), pentaerythritol (PER), and melamine (MEL) underwent the process of acid catalyzed hydrolysis, dissolution, and chemical reaction, which led the change of the content ratio of the compositions and caused the deterioration of the coating fire resistance. A prediction method of the remaining fire resistance property for the acid corrosion coatings was proposed, by comprehensively considering the physical and chemical characteristic changing trends of the corroded coating.
Article
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.
Article
To examine the action of acid atmospheric precipitation on the light stabilisers in automotive coatings two common clearcoat types (TSA and 2K-PU) blended with commercially available HALS and UVA were subjected to artificial weathering (Acid Dew and Fog test and Acid-free weathering test) and natural weathering outdoors in Jacksonville, FL. Tracing gloss and haze during weathering the test results showed that the influence of acid stress on the long-term performance of the clearcoats depended on the kind of the stabilisation system.
Article
As form a part of way to improve the durability of concrete placed on deleterious environments such as acidic rivers, sewage wastewater, and sewer system, the paper presented here is the results of experimental immersion test, and for the test solution, 2% sulfuric acid solution was prepared. Also for the test specimens, 10% of silica fume, 60% of blast furnace slag and 20% of fly ash were used as partial replaced cemenetious materials for OPC and they were symbolized as OPC, SF10, BFS60 and FA20. XRD, SEM and EDS analysis were employed for evaluation technique. From the result of EDS analysis of cement paste at 91 days of immersion, the detected major chemical elements were Ca and S and they are assumed as composing elements of gypsum. Additionally, form the XRD analysis result, gypsum was confirmed with intensity. As the other evaluation items, compressive strength, weight change, and carbonation depth were measured for mortar specimens and BFS60 mortar showed the lowest weight change. Furthermore, in case of reduction in compressive strength, BFS60 resulted with most small reduction rate but no evidences to know the differences between specimens were confirmed from the carbonation test.
Article
Pure polystyrene (PS) was subjected to natural weathering in Qionghai (QH) and Ruoqiang (RQ) of China, representing hot and humid climate and xerothermic climate respectively. The degradation profile of pure PS was studied by Fourier Transform Infrared (FTIR) Spectroscopy, Differential Scanning Calorimetry (DSC), Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS) and Spectrophotometer. Artificial accelerated weathering tests protocol A and B were carried out to simulate hot and humid climate and xerothermic climate respectively. Results show that pure PS degrade slowly at the initial stage and then become faster. Color shift could be an appropriate indicator for evaluating simulated effect of artificial accelerated weathering and protocol A simulate hot and humid climate perfectly while protocol B turns out weak for xerothermic climate.
Article
Ten high-quality polyurethane clear coats used for automotive finishing were examined to study the effect of formulation and application process to their environmental etch resistance. The tests were carried out using the acid dew and fog accelerated artificial weathering test. The coating formulation showed a strong influence on the weatherability of the water-borne clear coats.
Article
Modern automotive basecoat/clearcoat enamels are expected to maintain their attractive appearance over the life of the vehicle with no catastrophic failures such as cracks or delaminations. Ensuring the durability of automotive topcoat requires an understanding of the relationships between exposure conditions, the chemical changes that can occur in the various coating layers, and potential failure modes. This paper reviews those relationships with particular emphasis on the chemistry and mechanisms of coating degradation and stabilization. The key factors that affect topcoat appearance durability are as follows: resistance of clearcoat to acid attack and hydrolysis; intrinsic clearcoat photostability (free radical formation rates); nature of photooxidative pathway in the clearcoat (e.g., chain scission versus crosslink formation); effectiveness of hindered amine light stabilizer; permanence of ultraviolet light absorbers; and photostability of basecoat and primer. These factors are discussed in terms of specific coating chemistries. The effects of application variables as well as protocols for evaluating performance are discussed.
Article
During the summer of 1988, General Motors Research Laboratories operated a mobile atmospheric research laboratory in Jacksonville, Florida to determine the cause of environmentally- related damage that occurs on automotive finishes In many parts of the U.S. The damage occurs as circular, elliptical, or irregular spots that appear as deposits or precipitates. The results of the present study show that a wetting event (rain or dew) is a prerequisite for damage to occur. Sulfuric acid contained in the rain or dew reacts on surfaces with drydeposited calcium which Is a common constituent of soli. As the droplets evaporate, a calcium sulfate precipitate forms on horizontal surfaces around the perimeter of the droplet. Subsequent washing of the surface may remove the precipitate, but on clearcoats, where the calcium sulfate was present, scars remain.
Article
Environmental etch damage to automotive coatings, and scratch and mar of these coatings are an important element of customer satisfaction as well as a significant warranty repair consideration for automotive companies. The conditions that result in environmental etch are examined and a laboratory test proposed. Data from this test are compared to automotive hoods exposed in Florida. The performance of various crosslinking chemistries is discussed and the requirements for improved environmental etch are outlined. Scratch and mar performance of these systems is also reviewed. We have found that coatings respond to physical stress by elastic recovery, by plastic flow and by brittle fracture. Classifying types of damage in this way is important for understanding the chemistry needed for improved scratch and mar of coatings.
Article
The extent of penetration of an acidic solution into a melamine-acrylic coating, the bulk changes in the thermal properties of the coating, and the chemistry and kinetics of acid degradation were investigated. Fluorescent microscopy experiments showed that significant penetration of the clearcoat occurs rapidly with acidic solutions. Thermal analysis of a matrix of samples exposed to a variety of conditions showed that significant differences occurred as a function of time, temperature, and acid concentration. Infrared analysis showed unreacted excess alkoxy-methyl melamine was hydrolyzed first, followed by the hydrolysis of the crosslinks. Acidic solutions are able to penetrate the coating in a short time. Once in the coating, chemical reactions occur which result in degradation of the crosslinked network causing a change in the thermal properties and the appearance of the coating materials. The reaction is hydrolysis of the crosslinks followed by either destruction or leaching of the crosslinking material.
Article
The acid etch and water spot resistance of conventional acrylic/melamine and polyester/melamine automotive clearcoats are significantly improved by ambient air ultraviolet irradiation of freshly cured coatings. Infrared and NMR analysis of cured films and model compounds indicate that surface photochemical oxidation of the melamine NRCH2OR linkage to a urethane NRCO2R occurs in the coating under these irradiation conditions.
Northwestern society for coating technology and Montreal society for coatings technology
Northwestern society for coating technology and Montreal society for coatings technology, J. Coat. Technol. 67 (1995) 19.
  • D R Bauer
D.R. Bauer, J. Coat. Technol. 66 (1994) 57.
  • U Schulz
  • P Trubiroha
  • T Engbert
  • T Klimmasch
U. Schulz, P. Trubiroha, T. Engbert, T. Klimmasch, Eur. Coat. J. 1/2 (1999) 18.
  • U Schulz
  • P Trubiroha
  • W Zwick
U. Schulz, P. Trubiroha, W. Zwick, Welt der Farben 10 (1997) 23.
  • W R Rodgers
  • G D Garner
  • G D Cheever
W.R. Rodgers, G.D. Garner, G.D. Cheever, J. Coat. Technol. 70 (1998) 83.
  • G T Wolff
  • W R Rodgers
  • D C Collins
  • M H Verma
  • C A Wong
G.T. Wolff, W.R. Rodgers, D.C. Collins, M.H. Verma, C.A. Wong, J. Air Waste Manage. Assoc. 40 (1990) 1638.
  • P H Lamers
  • B K Johnston
  • W H Tyger
P.H. Lamers, B.K. Johnston, W.H. Tyger, Polym. Degr. Stab. 55 (1997) 309.