He specializes in polymer additives, polymer processing and formulation, material durability and the development of sealants and coatings. Would you like to tell us about a lower price? If you are a seller for this product, would you like to suggest updates through seller support?
In spite of extensive efforts, material weathering testing still requires improvement. This book presents findings and opinions of experts in material degradation testing. The aim is to improve testing methods and procedures. Materials are presented to show that photochemical degradation rate depends on a combination of environmental factors such as UV radiation, temperature, humidity, rain, stress, and concentration of reactive pollutants.
The potential effect of each parameter of degradation on data gathered is discussed based on known results from a long experience in testing. This book contains data obtained in laboratories of the largest manufacturers of UV stabilizers and chemical companies that manufacture durable materials. The book gives details of testing procedures and choice of parameters of exposure which are crucial for obtaining laboratory results correlating with environmental performance of materials.
In addition to exposure conditions, the book contains many suggestions on sample preparation and post-exposure testing. The effective use of these methods shortens testing time of materials and determines acceleration rate of testing. The book also gives examples of complete, well-designed weathering experiments which may be used as patterns for selection of parameters and techniques for new studies.
The areas of research that still require more attention in future studies are clearly indicated. Read more Read less. Review "Everyone who is concerned about the durability of plastics Plastics Design Library Hardcover: William Andrew; 1 edition January 14, Language: Be the first to review this item Amazon Best Sellers Rank: Try the Kindle edition and experience these great reading features: Share your thoughts with other customers.
Write a customer review. There's a problem loading this menu right now. These modifications are often done in chemically irreversible ways. We want the products to be durable over their useful life but we also want theln to be returned to nature when we no longer need them. We hope that their disposal will not cause pollution. We need our water to be pure, our air to be safe to breath, and our soil to be uncontaminated. If we are to resolve them and continue to use synthetic materials responsibly, we must plan carefully and gain a complete understanding of how materials will perform and degrade.
In particular we must be able to understand how materials weather, what the by-products of weathering are and how materials can be transformed into non-polluting entities either through recycling or natural disposal. Terms such as "life cycle assessment", "recyclable", "biodegradable" and "lifetime warranty" slip easily off our tongues. We need to bring weathering testing to the point at which reliable testing and investigative studies can enable us to use these and related terms with con1plete confidence.
In spite of the efforts of research groups, standardization organizations and industry, there is much to be done to bring weathering testing to the level that will allow the results to predict the life of materials. There must be a willingness among the involved parties to cooperate and a con1prehensive body of information to support their efforts. This book is a contribution to the information base to assist the scientific efforts aimed at improving the knowledge of weathering. ChemTec Publishing and William Andrew will continue to supply infonnation to this field. In the year we will publish: One aim of this book is to provide a critical overview of methods and findings based on experimental work.
Another is to create an awareness of the effect of the combined action of all the weather variables on materials under study. The introductory chapter outlines experimental design techniques and equipment selection and etnphasizes the importance of selecting the basic parameters of weathering including: Throughout the book, the authors attempt to show that weathering is not only dependent on UV radiation but that the overall effect depends on the interplay of all parameters which create a unique sequence of events that will change if the parameters are changed.
The lack of correlation between laboratory and outdoor exposure is frequently caused by combinations of factors among which the improper selection of laboratory conditions is prime. After the introduction we discuss the choices available for outdoor weather testing. This relates laboratory tests to tests outdoors so that there may be correlation with natural conditions.
The importance of precise control of both UV spectral intensity, temperature and heat flow is demonstrated in Boxhammer's careful use of available equipment and by studies done on automotive components. The recent availability of the ClRA filters and the continued use of borosilicate filters now permits accurate duplication of solar radiation. The chapter by Summers and Rabinovitch shows how radiation wavelength impacts the performance of several polymers.
The manufacturers of weathering equipment can perfectly simulate the solar spectrum. Researchers now must take advantage of these developments. We show that failure to duplicate the solar spectrum invalidates the experiment. The failure is caused by energy input, temperature, moisture, and radiative effects.
These parameters should not differ in the experiment from that of natural exposure. We compare the two most common artificial light sources - xenon arc and fluorescent lamps. The automotive, textile, polymer and stabilizer industries use xenon arc which gives the full spectrum of solar radiation UV, visible, and near infrared.
Weathering of Plastics: testing to mirror real life performance (Plastics Design Library)
The use of fluorescent Preface ix lamps, which lack the spectral range ofthe xenon arc, should be discouraged except in special cases where the known mechanisms for degradation are triggered only by radiation between nm to nm. Several industries report problems stemming from studies done with fluorescent lamps which fail to correlate with actual outdoor exposure. Water spray during weathering studies has often been neglected. The reported work on co-polyester sheeting shows how complex material changes can be in the presence of water. More work is urgently needed to determine how hUlnidity and condensation influence material degradation.
Two contributions from the Edison Welding Institute have been included to den10nstrate the effect of infrared energy and how different materials absorb this energy differently. In particular, the inclusion of pigments complicates infrared absorption. The chapter by Hardcastle shows how an evaluation of performance requirements helps to define a method of predicting the Inaximum allowable service temperature of vinyls based on measurements of their solar reflectance.
Products in service operate under mechanical stress due both to residual stresses developed during the forn1ing process and to external stress in use. It has long been recognized that stress affects weathering but little has been done to evaluate the effect. Two chapters by White et ale propose methods of evaluating the effects of stress in weathering studies. These effects are complex since the initial stress distribution changes during exposure and this requires a knowledge of the kinetics of these changes.
A similar situation exists with respect to the effects of pollutants. We know they influence weathering but there are few studies that assess their influence. Paterna et ale examine gas fading of automotive components in the presence of nitrous oxides. More elaborate techniques must be developed to evaluate the combined effects of UV radiation, moisture, temperature and pollutants on products to sin1ulate outdoor applications.
It is unrealistic to study these influencing factors independently. Two studies on the effects of high energy radiation have been included to den10nstrate well defined projects which evaluated material failures and determined the activation energies of the degradation process for many materials, explained why degradation occurred in industrial sterilization, and determined how such degradation might be prevented.
Assessment of automotive clearcoats and nanocomposites show that current test methods are sufficiently accurate, sensitive and suitable to detect degradation at an early stage of exposure. This is another area where more investigative work is needed. The benefit of this approach lies in gaining information early in the product developn1ent process using the equivalent of natural conditions without depending on the use of high energy radiation, often employed in accelerated testing, which causes degradation mechanisms which would not normally occur.
Several contributors emphasize other complexities which must be dealt with in weathering studies. The materials themselves are complex. Many contain additives which interact with the host, the substrates and one another in a weathering situation. Conclusions may err if x Preface they are based on an inaccurate knowledge of the real composition of the material under study. Even the manufacturer may be unaware of the true composition as composite additives may have proprietary compositions which are not disclosed. Many fundamental studies are needed to investigate the interactions of multi-component systems and to unravel the effects of processing aids which may be added without knowledge of their effects or interactions.
Such practices may lead to unexpected and possibly, catastrophic, failures which would remain undetected in routine research and quality control operations. The stabilizer manufacturers have, as an industry, made a significant contribution to weathering testing methods. There are several chapters from these sources. They show that their reports to their customers are meticulous in relating the results of evaluations to the conditions of the test. Their approach is conservative in selecting both equipment and test conditions. The tests are expensive. They must relate to the real conditions of use and results should be comparable to those of prior tests.
The book concludes with an example of the type of ground work and planning that is required before routine analysis begins. Using work on automotive clearcoats, we demonstrate how information must be analyzed and categorized to provide a rationale for testing, defining performance requirements, exposure conditions, mechanisms of degradation and how best to observe and measure the changes in specimens.
Information gleaned from field performance is used to determine the appropriate laboratory simulations. If this preparatory work is not done the subsequent testing efforts are unlikely to yield useful data and be of little use in predicting future product performance. Manufacturers must operate to meet economic goals. Industry as a whole is becoming increasingly competitive and is continually seeking ways to rationalize production methods to improve econonlics.
Materials from different industries compete for the same markets. Durability has become one ofthe most important characteristics. The product is either made from an inherently durable material or it receives an external coating which gives the required durability. The first approach is more consistent with recycling processes which generally have difficulty in dealing with multi-component mixtures. As the understanding of weathering increases we may learn how to more frequently select a durable substrate which will not require the complication and cost initial and recycling of a surface coating.
The economic answer would seem to lie in making the investment in weathering research to avoid the costs of material replacement and material failures. I sincerely hope that this introductory volume will generate an increased interest in advancing these important studies and provide an inspiration to researchers to pursue weathering studies as both economically and environmentally important activities.
These failures not only affect custon1er perception of the abilities of manufacturers to deliver products designed for the required perfonnance, but also result in complaints and liabilities. We know from everyday practice that products do fail and examples such as paint peeling from cars, faded and discolored textiles and plastics, or various defective construction materials are con1ll1onplace.
Many of these failures are caused by the exposure of materials to the environmental conditions which include factors listed in Table 1. Two observations from this table are important: These variations n1ake testing in the natural conditions very difficult because only long-tenn testing results can average these variations in climatic conditions and thus results.
This is one reason underlining the need to test materials in a laboratory under conditions which can always be repeated. It is known from any type of study that if parameters of an experiment are not strictly controlled the results of study are meaningless. This, in turn, shows the need to choose adequate equipment and select proper parameters of testing.
These subjects are discussed below. There is also a need in the studies on the n1aterial durability to select a yardstick which can be used to obtain results in a numerical form pennitting comparison of the results. Here, two matters are important: The methods of specimen 2 Weathering of Plastics Table 1. Parameters of material degradation Parameter Typical range Comments UV radiation to nm UV radiation in this range is found in the sun radiation.
Product temperature is a parameter which must be selected for testing Rain o to Rain is important because it washes away components of material and deposits dissolved gases such as carbon dioxide, oxygen and pollutants e. These pollutants can be deposited by rain to become more aggressive degradants Stress variable Materials degrade more rapidly under the mechanical stress testing are discussed below in a separate section.
The reference standard of laboratory results is the material perfonnance under its nonnal conditions of use. This brings us back to the exposure to environmental conditions. The choices of selection of exposure sites and the conditions ofsuch exposure are omitted in this discussion. But, it should be borne in mind that the results of long-term testing of the same or similar materials in the weathering stations allow us to express the results of laboratory studies in the required form of years of product performance by correlating them with results of laboratory studies.
Planning durability testing of a material requires not only proper strategies to chose adequate methods of testing and exposure but reasons for testing should also be evaluated. They decide about effectiveness of material use and associated costs. At the same time, the importance of these factors puts even more stringent requirement on the quality of testing results. Having in mind that the results of testing affect decision making process of product selection and its economy of use, one must conduct these studies in a manner that gives assurance that the outcome of testing gives reliable information on product behavior in real life.
This introductory chapter gives a general overview of selection of testing conditions. This information is further elaborated in other pal1s of the book. UV radiation is, for most materials, the most important determinant of their durability and as such deserves considerable attention. Two factors help to quantify UV radiation: The solar cut-on wavelength is the lowest wavelength still available in the sun radiation.
The value of a solar cut-on varies with the season and it is commonly estimated at run in sununer and nm in winter. Below these cut-on values there is no radiation in daylight. Considering that the lower the wavelength, the higher the energy of radiation, the sun radiation is less damaging to material in winter than in summer.
What does happen if we perform the tests using radiation of a lower wavelength e. It can be expected that, since radiation at run has higher energy than at run, the damage of material should be more extensive because more radiant energy was applied. This faster degradation is not, by itself, precluding the lower radiation wavelength from use because we want to obtain test results faster. But, other question arises. Is the degradation process the same when we use radiation of a higher energy?
The answer is no. There are two reasons for this: The selective absorption means that any given material is capable of absorbing only at certain wavelengths but not at the others. These bands of absorption are the characteristic properties of any given material. For example, polycarbonate exposed to three wavelengths ofradiation ,, and run degraded extensively at nn1 because it does not absorb radiation at and Thus, radiation at run, having higher energy than radiation at run, was harmless because energy is used for degradation only when absorbed by the material.
On the other hand, if polycarbonate was exposed to radiation fron1 a lamp which had UV radiation in a range fron1 to such as for example mercury lamp , polycarbonate would show signs of degradation because it absorbs radiation at nn1 which does not exist in daylight the energy of 4 Weathering of Plastics radiation at a wavelength of run, which is present in daylight, is not sufficient to degrade bonds in polycarbonate.
The conclusion from the above is that no radiation below the solar cut-on nm should be present in the equipment used for testing. Many other examples of real n1aterials support this statement. Irradiance level is the second factor which determines energy of radiation. Irradiance is the rate with which sun or lamp energy falls on the surface ofn1aterial. It is expressed in Watts units of energy per surface area usually m 2 and a wavelength.
From this definition one may expect that the more energy falls on an object, the more damage can be expected providing that energy is absorbed. Two characteristic values of irradiance are used in practice. If irradiance in laboratory testing is above these values, test results may not be comparable with the results of exposure to natural environmental conditions. The use of higher irradiance values requires additional studies which prove good correlation between laboratory and natural exposures. In conclusion, irradiance setting at 0. The operation of an instrument under high energy levels speeds up the process ofdegradation but the results ofstudies may not reflect the performance characteristics of materials used under normal conditions.
In the last section, it will be shown that safe methods exist which allow for early detection of failure or acceleration of testing. The selection of higher irradiance usually requires that the preliminary experiments confirm that the mechanisms of material degradation were not affected by the high energy levels used for testing.
Air and product telnperature. Temperature of a sample during testing has impact on results. Typical samples tested in a laboratory have different colors. Therefore, they have different ability to absorb infrared energy. Figure 1 shows the difference in temperature between white and orange colored samples. Temperature depends on time of the day and color. Therefore, black sample, according to this rule, should be degrading 8 times faster than the white sample. It can be concluded that samples should be tested in their real temperatures, resulting from ambient air temperature, absorbed infrared energy, and cooling effect of water evaporation.
Temperature behind the sample on sunny day. Rain and relative hllidity. The amount of rain varies even more widely when one COlnpares dry climates e. This parameter is essential because many additives in plastics operate on the surface of materials. The most typical additives include UV stabilizers, antistatics, and biocides. There are also numerous other essential additives such as, for example, plasticizers which tend to migrate to the surface to equilibrate for the lost concentration. If excessive rain or condensation is selected then n1aterial loses its properties without correspondence to natural conditions.
Similar results are due to condensation if excessive humidity is used. Some polymers are also affected by moisture. Polymers such as polycarbonate, polyester, polyamide and many others hydrolyze in the presence of water. The hydrolysis is time-related and water concentration-related phenomenon therefore the increase in water supply to the sample changes mechanism of degradation. Excessive condensation and selection of excessive rain changes the mechanism of degradation making results of laboratory studies not comparable with the nonnal conditions of performance of materials.
Simulation of the pollutants influence is difficult to conduct in the laboratory equipment because of many different substances involved and their highly variable concen- 6 Weathering of Plastics tration. The combination with typical weathering studies is complicated by the fact that specialized equipment is needed for such studies operated under variable conditions and variable compositions of pollutants. For this reason these studies are not a part of main stream weathering studies.
Stress is an essential parameter of weathering considering that thermal and moisture movements in materials are found in practical applications and are known to affect the rates of degradation. Two aspects of stress interference can be considered: The existing sample holders allow to induce static stress to material exposed to radiation and other environmental conditions. This mode of testing is one of the methods to accelerate testing and frequently to obtain results which are common with material performance in normal applications. The stress applied should be selected based on the prior knowledge ofmaterial performance conditions.
At the same time, it should be considered that stress is an additional parameter of weathering therefore its introduction changes both rate and mechanisms of degradation. For this reasons, the effect of stress should be tested on well defined specimens. Based on the above discussion the suggested choices of main parameters are summarized in Table 2. This check list is useful in evaluation of laboratory equipment which can be used for testing giving high correlation with natural conditions.
The list of important considerations for the selection of laboratory equipment which performs testing under conditions that may give a high correlation with natural exposures in addition to full spectrum of visible and IR, the UV radiation wavelength is limited to to nm irradiance can be selected and controlled within the range 0. Effect of different filters on a light spectrum of a xenon lamp. This narrow focus is selected to concentrate on the capabilities of equipment to give reliable data which correlate with normal conditions under which products perform.
The equipment technology b b I. Three major sources of radiation are used: The source of radiation determines the conditions of sample exposure. A carbon arc is an older technology which is still in use for testing samples according to standards developed for this equipment. The majority of standards either specify testing equipment with a xenon lamp, a fluorescent lamp, or give the choice of both. In many existing standards, the equipment using a fluorescent lamp is given as an optional choice for fast or preliminary screening of samples because it is less costly and easier to maintain but also has numerous limitations.
Spectrum of fluorescent lamps compared with daylight radiation. COlnparison of temperature of colored samples. Figure 2 shows spectra of daylight and a xenon lamp equipped with filters. It is apparent that the daylight radiation from sun is very well simulated in all regions UV, visible, and also infrared range not shown on the graph. Filters such as ClRA and borosilicate glass provide radiation restricted to the range available in daylight. The fluorescent lamp of UVA type can match sun daylight between and run. Outside this range the lamp does not emit substantial levels of radiation.
This characteristic has implications on the results. First of all many materials absorb and degrade outside this range. Polyamide-6 nylon is one such example since it has substantial degradation when exposed to the radiation wavelength at run. Pigments are known to change colors in the visible range producing products of degradation which affect stability of resins. There are numerous other examples which can be found elsewhere. Samples exposed to an outdoor conditions and xenon lamp are degraded under different temperatures depending on their color.
The temperature of samples in a fluorescent light device can only be controlled by heating the chamber but this results in the same temperature for all the samples which differs from their exposure in normal conditions of their performance. Many confusing results were produced because of this discrepancy. The fluorescent devices do not have control over humidity.
Their controls can be in one oftwo positions: Water is delivered to samples by evaporation from reservoir and condensation of vapor on the surface of samples. This increases probability of washing away some vital components as was previously discussed. These three deficiencies combined with many other simplifications introduced to decrease the cost of construction are behind the designation of the machine as suitable for preliminary screening of samples. The preliminary screening results should always be compared with the results obtained from devices equipped with a xenon lamp in fully controlled equipment as discussed below or long-term weathering studies.
For reliable testing, equip- 10 Weathering of Plastics ment giving more operational controls and having environment similar to outdoors should be used. Figure 6 shows a schematic diagram ofWeather-Ometer which is equipped with a xenon lamp. The instrument provides full control ofUV radiation, air temperature control, rain and rain water control. All essential parameters can be selected by manual controls or from the computerized interfaces.
Input and output data can be acquired to the remote computer and automatically controlled. These instruments are equipped with diagnostic functions which help users in troubleshooting and returning equipment to normal operation mode. Suitable equipment which may satisfy any practical need is available. The instruments manufactured range from small benchtop instrunlents to large chanlbers which can accommodate large parts ofmachines e.
At the same time, benchtop instruments have limited controls over the environmental conditions under which experiment is conducted. The user should be aware of this limitations which may affect results of studies. In conclusion, selection of equipment for required precision of testing is a complicated process, which can be narrowed down to the analysis of elements essential to obtain results predicting material performance in natural conditions of their perfOTI11anCe as given in Table 2. But still there is a high potential for studies to fail ifexperiment is not designed properly.
We now outline the essential elements of the experiment design which serve a broad range of applications of weathering methods. British Standard BS Here are the most important points. The following major tasks must be performed: From the principle of similarity it is known that if conditions of degradation UV, temperature, humidity, rain, etc. The selection of equipment and its operating parameters, similar to encountered in real life, allows to omit tasks listed in points 3,4,5, 7, 8.
This limits our tasks to a much simplified process. Identify the perfornlance criteria. This first stage means that certain parameters ofproduct performance should be selected together with a time scale for their occurrence. Suppose that product should not yellow, crack, and lose tensile strength. These are the most essential parameters for this product performance.
Now, it is necessary to attach time values to these parameters. This time scale is constructed based on the product role in the marketplace. Products are divided by the length of time of service. For example, in construction industry, products are divided into five categories: The other parameters determining the time scale of performance are related to how this product is used in practice.
Products can be replaced, maintained, or designed for a long life without maintenance. In the first and the last case there is no cost associated with the product maintenance but only life titne and cost of replacement differ. These two elements of cost replacement or maintenance must be factored into product cost and thus reflected in the choice of time scale. The result of this task is a table of parameters of degradation yellowing, cracking, etc. Identify possible degradation echaniss. While the prediction of a mechanism is not con1pulsory in the experiment designed based on the similarity of conditions average UV, temperature, humidity, etc.
At the same time, it is still good practice to do this analysis at least once because it n1ay help to improve products based on the understanding which properties fail and why. Identify inlportant degrading paranleters. The identification of degrading parameters is not required if conditions in laboratory and outdoors are similar because all parameters work in combination.
The only help from such analysis may be that it allows to predict methods of stabilization to improve products. Identify the range ofchanges ofpeljormance criteria. The range of changes of performance criteria is analyzed as an additional check point if conditions in laboratory and 12 Weathering of Plastics outdoors differ.
- God, Did You Send This Mate to Me??
- Embedded Systems Hardware for Software Engineers?
- Michael Hanekes Funny Games: A Textual Examination (BSY Short Film Guides Book 1).
- Weathering of Plastics: Testing to Mirror Real Life Performance - Google Книги.
- Editorial Reviews.
By doing this analysis we want to find out if measured changes are not outside the normally observed range of changes in normal use of a product. In the controlled experiment the only significance of such analysis would be to establish frequency of testing and sensitivity of testing method but otherwise such analysis is not required. Postulate on how degradation can be increased in accelerated weathering tests. Because degradation occurs under very similar conditions it can be expected that an accelerated test induces the same changes as average climatic conditions should do.
Thus, the identified mechanisms of degradation in normal use are the same as mechanisms active in laboratory study which only is better controlled and run under repeatable conditions. This step is very essential. The most frequently asked question in accelerated test regards the degree or rate of acceleration. One source of acceleration is operation of equipment set at Miami conditions. This gives different acceleration factors for different geographic locations which may typically vary in a range from 2.
But, the acceleration depends much more on the method of observation testing. Conducting experiment under well controlled laboratory conditions gives us samples suitable for many sophisticated methods of analysis. If a sample is exposed outdoors, it does pickup dust particles which, residing on the surface, make sample unsuitable for many chemical analytical techniques which require clean surface for analysis.
These methods will only analyze dust. A simple example of acceleration can be given based on previous experiences. A material durability was measured by the time when cracks appear on the surface. When this material was exposed to outdoor conditions in Toronto, cracks were observed after 2 years of exposure by a simple visual inspection. Exposure in Weather-Ometer operated under conditions listed in Table 2 with in adiance of 0. The same specimens observed under stereo microscope allow to detect cracks after about h of exposure which gives an acceleration factor of If analysis of these samples was performed under SEM microscope enlarging cracks could be detected after 40 h of exposure in Weather-Ometer which gives an acceleration factor of There are many similar analytical techniques available for every type of analysis required to attain similar accelerations.
The importance of the method selection cannot be overemphasized. It is not only an acceleration factor which is important but also the method should be selected based on realistic criteria related to field observations of the product and available techniques which can detect and quantify these observations. It is always advisable to use methods which lead to answer in a shortest possible way. For example, if tensile strength is an important parameter indicative ofor important for its performance there is no need to look for chemical analysis which correlates with tensile strength but simply tensile strength should be determined unless one goal of 4 13 Basic Parameters in Weathering Studies studies is to detennine the mechanism of degradation for which chemical analysis gives supportive data.
Design and execute prelilninaly studies. Preliminary study and evaluation of its results are only critical when the conditions of exposure are different from outdoor environment.
Such experin1ent under well controlled conditions of exposure is only valuable if experimentation is made with various methods of chemical analysis and it is uncertain whether the method of testing is the right choice. Otherwise, it is possible to go directly to the analysis of material and COlnpare the data from laboratory studies with outdoor exposure to built predictive criteria and evidence for life predictions of material.
Such data are invaluable because they can be used in future for evaluation of reformulated products based on laboratory studies alone. There are other numerous factors related to weathering studies which cannot all be mentioned in one short paper. Many answers can be found in the specialized monograph on the subject. In conclusion, the effort was made here to show that simple approach to studies of weathering is possible.
This approach allows to concentrate on the essence of weathering studies which are meant to predict properties and durability of materials in the most efficient fashion. These studies are invaluable for both consumer and manufacturer alike. If conducted in a well planned experiment they will help in extending life of materials and prevent unnecessary and unexpected failures.
If attention is focused on the modification of parameters existing in the natural environment these studies will most likely fail in spite of the work done because common physical and chemical principles have been violated. Bond, Choices in the design of outdoor weathering tests. Durability of building elements, products, and components. Lee, Essential paratneters of degradation of automotive coatings. Masters and Laurence F. As a result, manufacturers and users need reliable weathering data on a wide range of materials and systems to aid in product development, materials selection, quality assurance, life cycle costing and warranty considerations.
Studies carried out through international organizations Jernberg et al; Masters; Sjostrom and and within organizations of specific industries such as construction or automotive Bauer; Bourke and Davies; Fischer and Ketola; Martin et al; Misev et al, Nichols and Darr, Shirayama, Wicks et al illustrate the increasing interest in durability performance of materials and systems, as well as the use of new and innovative approaches to life prediction. Accelerated tests, for example, have been widely used to shorten test times Wootton and have included test chatnbers large enough to accommodate full scale automobiles Severon In addition, Sjostrom's work points out increasing interest in drawing upon databases of actual in-service performance of buildings as a source of data to aid service life predictions.
But even with the rapid technological improvements in life prediction techniques, outdoor or natural exposures, accelerated weathering machines, evaluation techniques and database development there is often mystery, mistrust, and misunderstanding of weathering and durability data. The general principle of assessing the effect of weathering is to measure specific properties or performance attributes prior to 16 Weathering of Plastics and after weathering exposure.
The difference provides a measure of the change in the materials or systems caused by the weathering exposure. Outdoor exposure methods include both direct and under-glass exposure; the chamber tests include Carbon-arc, Xenon-arc, metal halide and fluorescent exposure; the accelerated outdoor exposures include Fresnel-reflecting mirror machines and various other exposure devices aimed at simulating in-use conditions. In addition, other factors such as air contaminants, oxygen, salt, etc. The parameters of weathering are variable. Thus, to better interpret results of weathering exposure tests and to compare results obtained from different sites or at different times, it is essential to measure the key weathering parameters.
Atlas Weathering Services G-roup AWSG , for example, measures and reports data on total and UV radiation at various test angles, air temperature, black and white panel temperature, time of wetness, rainfall, etc. It is obvious that many different clinlate zones are observed in the US; on a worldwide basis, even more zones can be identified.
With the worldwide marketing of many manufacturers, it is important to have weathering data which pertains to as many of the climate zones as possible.
However, most organizations which have weathering tests performed desire to limit the number of exposure sites used to reduce costs of testing. Traditionally, the plastics and coatings industries have addressed the above tradeoff by heavily using two extreme climates for outdoor or natural testing: Thus, US commercial exposure facilities have focused heavily upon Arizona and Florida and industry has assumed that Outdoor Weathering Tests.
Climates of the world. Climatological data - various locations Location Lat. Most often, test results from the subtropical area of South Florida are used as the weathering standard for building and construction materials and in the automotive industry. In addition to the hot, dry and hot, wet extremes, other frequently used climate zones for weathering are I seashore salt air , 2 industrial, 3 temperate and 4 freeze-thaw.
Often, the controlling specification or test method defines the exposure conditions. A frequently asked question pertains to the extrapolation of data obtained from one climate to other climates. One means of addressing this question is to compare specific climatological data, such as is done in Table 1, from various sites. For example, materials subject to degradation by radiant energy would be expected to degrade much more rapidly in climates with high radiant energy particularly high UV radiation. Another means of comparison is to use results from specific materials exposed in various climates.
For example, after investigating thirteen sites representing a wide variety of global climates, Bores Bores reported that the degradation rate of the coatings tested were dependent on the climate; and that reversal in ranking could occur depending upon the formulation. In other studies from Europe Helmen and Hess , it has been stated that, "I year outdoor exposure in Basel Central Europe is equivalent to approximately 6 months in Florida.
E tions of major industries. J two South Florida Test Service o: Climatic conditions in Miami, Florida. In addition to the hot, wet and hot, dry climates often used for materials weathering studies, materials are also often exposed in climates with cold winters and large temperature cycles. AWSG exposure facilities are available in Canada and Chicago, IL for such exposures and a number of research laboratories have exposure facilities in cold climates.
The following discussion is a description of the most commonly used exposure angles and exposure devices. The absence of any angle or exposure condition from the list does not preclude it from being a viable way to test materials or systems for durability to weathering. The differences between those listed are basic to the question of the choice of the environment under which the materials or systems are to be tested. Each angle change or change in the type of test rack will influence the radiant energy received by the sample, the wet periods it will endure, and the temperatures it will achieve.
To illustrate the effect ofexposure angle and test configuration on temperature ofthe test materials, typical temperatures for black and white automotive acrylics for six different types of exposures at Miami, FL are listed in Table 2. Temperatures presented are the highest and the lowest recorded and the average values from eight readings collected over a period of twelve months.
Dramatic changes in temperature can occur in a very short time with wind, cloud cover, time of day or rain. ASTM G24 under glass exposures are used for materials which normally will not be subjected to all elements ofweather while in service. Test specimens are placed 75 mm 3 in behind 2. Outdoor Weathering Tests 21 Test Fixtures: Figure 5 is a test building specifically designed for weather testing window systems. The building is air conditioned and heated to simulate in-service conditions. But such a test building could be altered to provide other orientations of exposure.
Weathering of Plastics: Testing to Mirror Life Performance (Plastics Design Library)
To reduce costs of expoFigure 5. For example, x mm 6 x 12 in specimens are mounted on anodized aluminum racks which typically have a 64 mm 2. Specimens may be exposed without the mask when the entire test surface is to be exposed. Test fixtures or racks may be constructed ofany material which will not interfere with the test, and which is suitable for geographical area in which they will be used. The distance above ground for the lowest section of the rack is dependent on the location. However, test specimens should be mounted at a sufficient height to avoid contact with vegetation and to prevent damage which might occur during area maintenance grass cutting, regraveling, weed control, etc.
The area surrounding the test site should be free of objects likely to shade the specimens during exposure. Ground cover in the immediate vicinity ofthe racks must be representative of the location; gravel for desert areas to reduce possible abrasion caused by blowing sand , and low-cut grass for most other areas. Roof top exposure set-ups are excluded from ground cover requirements. Standard Exposure Tilt Angles: All of the tilt angles listed below may be used for either direct or under glass exposures at any facing direction and with solid backing, expanded metal backing or without backing.
Figure 6 shows typical exposure racks used at an outdoor weathering site. Primarily used for environmental etch, and roofing materials. In the Miami area, there is no advantage in respect to total irradiation, and significant differences in test results have not been reported. Station latitude is specified for the exposure ofsome materials designed for solar energy conservation applications.
Vertical exposures are often used for testing residential and commercial construction materials such as siding, window and door profiles, etc. This exposure angle significantly reduces wet time and nonnally lowers the temperatures of specimens being tested. Vertical racks are designed to off-set test specimens to prevent contamination from wash-down from the specimen mounted above. Seasonal angle changes provide optimum exposure to radiant energy and nonnally result in higher temperatures, and may be applied to test all materials.
The above tilt angle listings represent those angles most commonly used; however, any fixed angle or variable angle change schedule may be specified by the client to meet special test conditions. In addition, rack fixtures may be turned to face directions other than due North or South. Outdoor Weathering Tests 23 Table 3. The Fresnel-reflector test machine, which is a follow-the-sun rack, has a ten-mirror collector array to concentrate sunlight onto an exposure area as described in ASTM G The machine is equipped with a blower to cool the test specimens.
The air is directed over and under the samples by an adjustable deflector along one side ofthe exposure area. This limits the increase in surface temperature of most materials to 10 0 e above the maximum surface temperature that would be reached by identically mounted samples exposed to direct sunlight at the same time and location without concentration. Exposures on these devices may be conducted with or without water application. Specimen spray schedules include day only rain simulation , night only dew simulation or day and night applications. The effective exposure area is x mm 5 x 48 in ; therefore, samples should not exceed mm 5 in in one dimension.
Like the Fresnel-reflector device, the equatorial tracking device follows the sun through the day and has a mast which allows the entire exposure area to be adjusted for seasonal variations in the solar altitude. The temperature of the samples is on average higher than those mounted in the same way on fixed racks because of the attitude of the sample to the sun, but will not be above the maximum recorded on anyone day. Typically, this unit is run between the hours of7 AM to 6 PM and locked into a fixed position at night or in very heavy winds.
In the desert, spray cycles may be added for controlled wet periods to the exposure program. A high confidence level cannot be established on test results which constantly change. The variability of weather does not lend itself to obtaining repeatable results. Ultraviolet sun hours UVSH nlay have served a purpose years ago but, with today's technology, it is an unrealistic unit for timing exposures. Examining the definition of an UVSH help make its shortcomings obvious. An UVSH is any cumulative 60 minutes when the intensity of inconling solar radiation is above 0.
Both statements are true, but few would want to dig a ditch one foot deep using the above definition. It could tum out to be a rather deep hole. A similar problem exists with using total irradiation measurements to time exposures. Neither UVSH nor total irradiation take into consideration the quality of sunlight. It is quite possible to monitor nearly the same amount ofUVSH and total irradiation on a day in December and a day in June. However, for the northern hemisphere, the ultraviolet content of June sunlight is at least twice that of December.
Summer sunlight may contain well over three times as much ultraviolet as winter sunlight. Whenever possible, it strongly recommended that outdoor exposure programs be timed either by total ultraviolet or by selected wavelength measurements. Either of these methods will reduce the effects of seasonal variations and improve repeatability in test results. The use of a reference material to time the length of an exposure is common. The materials vary fronl industry accepted standards such as AATCC Blue Woollightfastness standards in the textile field to metals of known corrosion rates for the coatings and steel industries.
Exposures are conducted for a given period of time under a specific condition until the standard material exhibits a predetennined color change or measurable degree of degradation. Equally common is the use of a known material specific to the company doing the testing. Included in the population ofeach test or return, these materials act as "clock" for the test lot, e. In some cases, reference materials are checked to gage the period of exposure when the test is conducted using a separate timing method of calendar days or sunlight measurements. It is also clear that, with outdoor or natural exposures, there are far more options for exposure, acceleration, and correlation studies than conventional laboratory environments offer.
- Weathering of Plastics: testing to mirror real life performance (Plastics Design Library).
- Going Dutch.
- Lorsque le brouillard tombe: Destin dun loup solitaire (French Edition)!
If there is a single point to be gained from this paper, it is to pay 26 Weathering of Plastics particular note to the variables associated with outdoor weathering. Plan for them when designing a test and review them when the exposure period is complete. The weathering of materials in a given climatic region for a year or two mayor may not provide an accurate picture of the materials' response to climate, the average environmental factors over centuries.
The infonnation gained is related to weather, periods of months or years. In an 18 month period in , Mian1i rainfall was more than one meter below recorded averages for the last years. Finally, there are two cautions that should be made in direct relation to weathering programs. First, the caution to ensure proper handling of the test specimens. Attention paid to curing times and packaging for shipping will reduce the chance of having your weathering program tum out to be a test for "durability of materials to shipping.
Without an appreciation for the multiple sets of criteria and conditions under which such things as gloss readings, visual ratings, or color units are recorded, the exercise of testing a product for its durability to weathering can be a waste of time and money. Journal of Coatings Technology, NBS Technical Note Outdoor Weathering Tests 27 Nichols, M. Journal of Coatings Technology Testing Technology International 1. Architectural Institute of Japan. Feedback froln Practice of Durability Data: Collection of In-Service Performance Data: Educational Series, Journal ofCoatings Technology Accelerated Weathering Specifications used in the Polymer Industry.
Proceedings ofPolymer Testing ' Rapra Technology Limited, UK. The reproduction ofapplications effects, on the one hand, as well as the precision and the speed on the other, are the key factors of a good accelerated weathering test. A great deal of tin1e and money are continuously spent by industry in scrutiny of these points in an effort to improve the quality of test design.
Concurrently, there has been an accompanying strong effort by instrument manufacturers concerning improved and evolving equipment technology. Compared to other simulation techniques, laboratory weathering devices that utilize filtered xenon arc light sources have the advantage of a full spectrum including all wavelengths that exist in sunlight; which, ifproperly filtered, can be modified to provide a spectnlm which closely resembles sunlight.
Improved measuring, controlling and calibration techniques ensure that critical physical paratneters are maintained at specific levels. But nevertheless, various types of instrumentation which employ different techniques to control and measure the test parameters in addition to their calibration regimes, must be investigated for their impact on test results. This is especially valid for test methods that are designed to simulate extreme environmental conditions, as for example, for the purpose of predicting the performance of automotive materials for interior applications.
Previous experimentation and reports in literature on the lightfastness of automotive textile materials 1 indicate that reliable test results can be obtained for these materials in different types of xenon arc instruments. In the present 30 Weathering of Plastics study several widely used automotive polymers were investigated in instruments which employ different technologies to control critical test parameters and correlation of test results will be discussed.
Especially in the field of test methods for automotive n1aterials, a major concern is the length of test time necessary for qualification tests. The ultraviolet portion of sunlight is known to have the greatest degradation effect on materials and can be used to accelerate the processes in one of two ways: The latter also increases the likelihood ofproducing results which may never occur during the service life of a real automobile.
Specific SAE-standards are based on the latter method. However, experimental work is ongoing for replacement by the methods based on filters that produce a better match for sunlight. Xenon-arc Radiation method 2: Determination of colorfastness 9 - for automotive interior materials which are based on "sunlight behind window glass" and increased levels of irradiance have already been included. The specified testing conditions listed in Table 1 are similar for the range of irradiance as well as temperature, taking into account the well known systematic differences between black standard and black panel temperature.
But nonetheless, further systematic investigations are still needed and have been conducted on a number of industrial polymeric materials for automotive interior applications in the instruments Xenotest Alpha and Xenotest Beta. The test results will be discussed. The irradiance on specimen area in laboratory instrumentation can be raised by either increasing the power of the lamp or decreasing the distance between the lamp and the sample surface.
Both approaches are used in different types of available instruments and both increase the irradiance of all wavelength proportionally. Thus the increased spectrum also contains increased levels of visible and infrared radiation as well as UV radiation. The increased infrared radiation can be problematic. However, over the last few years, instrumentation has been introduced that make it possible to control both black panel or black standard temperature, as is traditionally the case, as well as chamber air temperature.
This is an important innovation as it allows san1ples ofvarious colors, from dark to light, to be tested in accelerated weathering devices in a similar manner to that of outdoor testing.