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Über dieses Buch

This book defines the current state-of-the-art for predicting the lifetime of plastics exposed to weather and outlines the future research needed to advance this important field of study. Coverage includes progress in developing new science and test methods to determine how materials respond to weather exposure. This book is ideal for researchers and professionals working in the field of service life prediction.

This book also:

Examines numerous consensus standards that affect commercial products allowing readers to see the future of standards related to service life prediction

Provides scientific foundation for latest commercially viable instruments

Presents groundbreaking research including the blueprint of a new test method that will significantly shorten the service life prediction process time

Covers two of the latest verified predictive models, which demonstrate realized-potential to transform the field

Inhaltsverzeichnis

Frontmatter

Chapter 1. Predicting Elevated Temperature Ratings of Polymeric Materials

Abstract
Product development cycles have become shorter with time, with companies standing to gain significantly by making their products available to the marketplace faster than what was typical to expect in the past. Even with this speed, producers need to comply with all quality and safety requirements, and consumers expect no less on these attributes. To this end, product developers and manufacturers have to work closely with their design teams to understand the customer’s demands and to meet the product’s performance, quality, and safety requirements. Specifically with safety, manufacturers have to understand end-use requirements as well as design a product that is expected to comply with all aspects of third-party safety certification. Faster cannot be synonymous with a loss in safety. Thus, speed in getting new products without loss of safety is a basic expectation of the marketplace and of society at large.
Noé P. Navarro

Chapter 2. Laboratory-Based Predictions of Weathering in Outdoor Environments over the Entire Degradation Pathway

Abstract
A useful estimate of outdoor service life for a material or product based on laboratory weathering experiments requires a careful assessment of the degradation pathways that result from exposure. Furthermore, converting real-world conditions into parameters that serve as inputs to models based on the accelerated weathering stresses of radiation, heat, and moisture is not trivial. In an effort to study these relationships, a model material was weathered under accelerated conditions in the laboratory, from which mathematical formulas were derived to describe the resultant photodegradation rate as a function of irradiance and temperature. Calculations for a specific geographical location yielded degradation as a function of time that exhibited excellent agreement with actual outdoor weathering results over the entire degradation period. Variations on the method of calculation proved the mathematical model to be robust. Investigation of chemical degradation in the model material revealed the possibility of more than one reaction pathway. Such behavior is readily apparent in other polymer systems we have studied, wherein the exposure conditions employed can lead to a lack of synchronization of changes in the material or can produce significantly different degradation pathways, both of which affect lifetime estimates.
Kenneth M. White, David M. Burns, Travis Q. Gregar

Chapter 3. Hydrolysis Kinetics and Lifetime Prediction for Polycarbonate and Polyesters in Solar Energy Applications

Abstract
The hydrolysis kinetics of polyesters and BPA polycarbonate appear to be second order in water, that is, second order in relative humidity (RH). This finding, combined with activation energies for hydrolysis, was used in a service life prediction model for a photovoltaic (PV) module front sheet application. The modeling process involves: (1) finding finely time-parsed climatic data for a benchmark location, (2) calculating module temperature and RH from the climatic data, and (3) applying the kinetics to determine the amount of degradation that occurs in 1 year relative to accelerated laboratory conditions, 85 °C and 85 % RH in this case. Acceleration factors under laboratory conditions are very high, especially for poly(ethylene terephthalate) (PET), leading to predicted lifetimes of several centuries if hydrolysis is the only degradation mode. The model was tested for sensitivity to assumptions and experimental uncertainties, and hydrolysis can be considered unimportant in this solar energy application. Concerns about PET suitability on the basis of its relatively short embrittlement times in the 85 °C/85 % RH damp heat test are unfounded.
James E. Pickett

Chapter 4. A Kinetic Model for Predicting Polymeric Neutron Shieldings Lifetime

Abstract
Polymers are widely used in radioactive material transport/storage casks. Their neutron shielding ability relies mostly on their concentrations in hydrogen atoms which slow down neutrons. However, in-service high temperatures are responsible for H abstraction decreasing polymers shielding capability. Therefore, their long-term properties must be accurately predicted. In this regard, a multi-year R&D program has been set up to elucidate oxidation mechanisms of neutron shielding materials and develop a nonempirical lifetime prediction methodology. This paper deals with accelerated aging tests and modeling of a vinylester based neutron shielding product, commercially known as TN Vyal B™. Samples are exposed to various temperatures up to 160 °C and O2 partial pressure and analyzed using various experimental techniques. Basically, thin free films are fully oxidized while thick samples show the diffusion-limited oxidation (DLO): a superficial layer is oxidized whereas the core is not affected. Therefore, to investigate the long-term properties, it is obvious that DLO phenomenon must be taken into account by coupling both oxidation kinetic and oxygen diffusion. In our case, there is a good agreement between simulated weight losses and oxidation thicknesses. Based on degradation assessment and design temperature of dry storage casks, TN Vyal B™ excellent resistance can be confirmed.
F. Nizeyimana, H. Issard

Chapter 5. How Can We Effectively Use Accelerated Methods to Predict the Decorative Properties of PVDF-Based Coatings?: A Practical Approach

Abstract
Poly(vinylidene fluoride) (PVDF) resins are the dominant component of some of the most weatherable commercially available decorative coatings. These coatings can have color retention and chalk resistance service lifetimes of decades. We have recently outlined a quantitative service life prediction model for the decorative properties of coatings of this type (Wood K (2009) A quantitative model for the prediction of gloss retention, color change, and chalking for poly(vinylidene fluoride)/acrylic blends. In: Proceedings of 4th European weathering symposium, Budapest, Hungary, Sept 2009). The model is based on the “contraction” theory of gloss loss and chalking, coupled with simple assumptions about the photochemical kinetics of two-resin hybrid systems where one resin (PVDF) is much more weatherable than the other (in this case, an acrylic). Because different mechanisms account for gloss loss, color change, and chalking, the relative rates of change for each of these properties can be different, in accordance with experimental observations. We outline a methodology that uses insights from the model, empirical data from accelerated tests, and long-term weathering test data from solvent-based baked PVDF coatings, to predict the service life of new waterborne no-bake PVDF coatings.
Kurt A. Wood

Chapter 6. Accelerated Testing: Understanding Experimental Design and Error Propagation

Abstract
One of the most challenging tasks for the designer of a durable product is developing an understanding of the long-term performance of the product in the context of normal aging and degradation. Typically, the intended lifetime of the product is years to decades, making empirical determinations of performance degradation over that time span impractical. The ability to make reliable estimations of product performance over long periods of time based on measurements made over a relatively short time period becomes an important need for the designer.
Kevin White, Joel Forman

Chapter 7. The Effect of Non-radiation Factors on the Weathering of Silicone Hardcoats

Abstract
In the course of many years of developing thermally cured hardcoat systems at Momentive Performance Materials Inc. (MPM), it has been observed that model predictions of time to failure for coatings subjected to cycled temperature, humidity, and radiation are not always accurate. Particularly in systems where cracking failures occur sooner than adhesion failures, these models seem to break down. This paper reviews the results from ongoing experiments at MPM that attempt to decouple the radiation factor from the typical weathering exposure conditions of a hardcoat system on a polycarbonate substrate. The goal is to identify a “best case” or “entitlement” lifetime for a coating that has not experienced any photodegradation. Additionally, these experiments provide direction as to which factors are most critical in driving cracking failure in hardcoat systems. Discovery of the driving forces for crack propagation in these systems should enable a new model to be derived that would be a better predictor of real-world failure.
Jennifer David, Robert Hayes

Chapter 8. Thermal Aging of Polyolefin and Effect of Pre-irradiation of γ Ray on Degradation

Abstract
The temperature dependence of the thermal aging of ethylene-propylene elastomer (EPR) pure vulcanized and linear low-density polyethylene (LLDPE) was studied using various methods. The activation energy obtained by the measurement of chemiluminescence (CL) of EPR at the constant temperature ranging from 60 to 160 °C was 82.7 kJ/mol. The rate constant of thermal molecular chain scission of EPR was calculated from the chemical relaxation curves measured at constant temperature ranging from 80 to 140 °C. The activation energy was 110 kJ/mol. The total carbonyl concentration increased logarithmically with increased thermal aging from 60 to 160 °C; the activation energy of the rate constant of the carbonyl accumulation was 95.8 kJ/mol. Pre-irradiation on EPR increased the count of CL, the rate of molecular chain scission, and the rate of accumulation of C=O, but the pre-irradiation did not change the values of these activation energies. The weight change of LLDPE resulting from thermal aging was studied at constant temperatures ranging from 90 to 170 °C. Three stages were observed including induction, the weight increase, and the weight decrease period. The activation energy for the induction period was 136 kJ/mol and was 105 kJ/mol for the weight increase. The addition of antioxidant reagent increased the induction period of LLDPE in all of the temperatures, but the activation energy of the induction period was not changed.
When LLDPE was irradiated up to 320 kGy, the induction period of weight change of the sample by thermal aging was remarkably shortened. The mechanism of this result was considered to be as follows. The irradiation of LLDPE in air accumulated hydroperoxide in the samples, which initiated autoxidation of LLDPE rapidly with applying heat.
Masayuki Ito

Chapter 9. Test Method Development for Outdoor Exposure and Accelerated Weathering of Vinyl Siding Specimens

Abstract
This chapter provides an overview of extensive research conducted by the Vinyl Siding Institute (VSI) on the development of new test methods for exterior plastic building products. The purpose of the VSI study was to develop an accelerated testing protocol for use in certifying materials.
This chapter describes the development of an outdoor certification test program and subsequent efforts to create an accelerated weathering test method that could be used to predict the results of the outdoor protocol with a high degree of accuracy. Outdoor weathering tests were conducted in Florida, Arizona, and the northern temperate locations to obtain baseline data for comparison. This part of the research led to the development and subsequent publication of ASTM D6864.
Accelerated laboratory tests were performed in Fluorescent UV/condensation test apparatus and xenon arc test chambers. The process involved the examination of multiple types of equipment, multiple cycles, and multiple conditions, and comparing the various results to the outdoor exposures. Testing suggested that for this particular material, one method was more suitable than the other. The proposed method was verified with repeat testing and rugged statistical analysis. Round robin testing was conducted to determine repeatability and reproducibility.
Although the proposed accelerated method was not adopted into the VSI’s certification program, its results demonstrated high rank-order correlation with outdoor test results, giving the user much greater confidence that materials passing the accelerated test will pass the outdoor test. The accelerated method, therefore, is useful during research and development because it provides a fast and reliable method for evaluating small formula changes. It is useful for selecting formulations to include in a 2-year certification test.
Jeffrey P. Quill, Sean P. Fowler

Chapter 10. Shelf Life Assessment of Poly(ethylene-co-vinyl acetate) and Polyester Polyol Resins Used as Adhesives

Abstract
The thermal stability and ageing properties of Vinamul 3161 poly(ethylene-co-vinyl acetate) and AS1160 polyester polyol resins have been investigated in support of shelf life assessment and also to identify storage conditions that may extend product life. These resins are typically used in the production of adhesives for specialised applications either as binders for filler particles or to minimise the relative movement of materials in multi-material assemblies. Our studies confirm that both these resins are susceptible to moisture and hydrolysis chemistry which potentially limits shelf life. The EVA resin readily accumulates acetic acid through hydrolysis of the pendent acetate groups which increases both the acidity (pH) and volatile outgassing characteristics of the material. The temperature sensitivity of pH combined with Arrhenius kinetics was used to identify a useful shelf life for EVA in conditions representative of normal storage conditions. In a separate set of experiments, relatively short-term thermally accelerated ageing studies have been carried out on AS1160 polyester polyol to investigate sensitivity to humidity, temperature and open/close ageing conditions. This material is hygroscopic, readily accumulates moisture and is susceptible to chain scission with molecular weight changes linked to the hydrolysis-esterification equilibrium. These changes do not however adversely impact adhesive bond strength allowing the resin to be potentially used significantly beyond the manufacturer recommended shelf life limit.
Mogon Patel, Laura Pilon, Peter Beavis, Paul Morrell, Niaz Khan, Anil Kumar, Julie Etheridge, Tim Cartwright, Gregory Von White

Chapter 11. Ultra-Accelerated Weathering II: Considerations for Accelerated Data-Based Weathering Service Life Predictions

Abstract
This paper discusses the effect of varying UV intensity on weathering degradation rates of materials. The effects of increasing intensities of solar UV on materials obeying strict reciprocity and materials deviating from strict reciprocity are considered. A second new high-intensity natural UV weathering device is introduced based on ASTM G90. The paper presents data from two materials degrading under different intensities of UV and compares natural weathering with data obtained at increasing levels of UV intensity with implications on SLP calculations.
Henry K. Hardcastle

Chapter 12. Quantitative Mapping of Mechanisms for Photoinitiated Coating Degradation

Abstract
This work concerns the mathematical modeling of photoinitiated coating degradation. Using experimental evidence available, some of the most important assumptions underlying existing models for thermoset coatings are analyzed and suggestions for further work provided. A modeling approach that can be used to implement the various effects of water on the degradation mechanisms of cross-linked coatings is also presented and experiments to test the approach are suggested. Additionally, simulations with an existing degradation model for an epoxy–amine coating are used to map the influence of model parameters on the lag time (i.e., the time passing prior to the onset of erosion) and the stable erosion rate. The simulation results can be used in the optimization of UV radiation-induced intercoat adhesion losses, which are often observed in multilayer coating systems based on top coated epoxy coatings. Finally, potential directions for future experimental research in the field are outlined.
Søren Kiil

Chapter 13. Accelerated Service Life Testing of Photovoltaic Modules

Abstract
Temperature, temperature cycling, water and UV radiation are considered as main degradation factors for PV modules by causing hydrolysis and photodegradation of polymeric components and corrosion of glass and of metallic components like grids and interconnectors.
The temperature is very important for the degradation of the PV modules, because it determines at least the reaction rate for the degradation processes caused by the other degradation factors (e.g.hydrolysis by humidity and photodegradation by UV light). Modelling of the service life of modules applied in different climatic regions requires knowledge about the transient temperature load. A model, which allows calculating the module temperature as function of the ambient temperature, the global irradiation and the wind speed, facilitates the use of any time series of climatic data for a climatic region of interest. This data could be provided by weather services, test reference years or via the Internet.
The microclimatic stress level of UV radiation and moisture on the PV modules is modelled as function of the module temperature and the important climatic parameters. Simple time transformation functions were used for the design of appropriate accelerated service life tests. The evaluated testing times differ up to an order of magnitude for different climatic locations, depending on the kinetics of the dominant degradation processes.
Michael Koehl

Chapter 14. Polypropylene Numerical Photoageing Simulation by Dose–Response Functions with Respect to Irradiation and Temperature: ViPQuali Project

Abstract
The aim of the joint project ViPQuali (Virtual Product Qualification) was to describe a component’s ageing behaviour in a given environment, by numerical simulation.
Having chosen polypropylene (PP) as the material, which does not show sensitivity to moisture, the relevant weathering parameters of the dose–response functions could be limited to spectral irradiance and temperature.
In artificial irradiation tests, for PP plates of varied stabiliser content, spectral sensitivity as well as temperature dependence of irradiation-caused crack formation was quantified. For that purpose, samples were exposed both to artificial weathering tests at various constant temperatures and to spectrally resolved irradiation. The temperature dependence could be modelled by an Arrhenius fit. For fitting the spectral sensitivity, a plateau function was chosen. Subsequently, the stabiliser content was parameterised and extrapolated.
The formed dose–response functions were incorporated into a Computational Fluid Dynamics (CFD) software program, simulating the environment of a sample within a Phoenix-exposed IP/DP (Instrument Panel/Door Panel box) box, based on sun position and weather conditions, including radiation interactions. Observed local effects as well as the general ageing advance of PP hats are compared with respect to simulation and experiment.
Resulting from this project, for this most simple example of PP of varied stabiliser content, the time to failure can be estimated for each weathering exposure environment with known time-resolved irradiance and temperature conditions.
Anja Geburtig, Volker Wachtendorf, Peter Trubiroha, Matthias Zäh, Artur Schönlein, Axel Müller, Teodora Vatahska, Gerhard Manier, Thomas Reichert

Chapter 15. Impact of Environmental Factors on Polymeric Films Used in Protective Glazing Systems

Abstract
Accelerated and natural aging of safety films used in protective glazing systems was investigated by the use of Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy, and tensile tests. Accelerated conditions involved simultaneous exposure of specimens to ultraviolet (UV) radiation between 295 and 450 nm and each of four temperature/relative humidity (RH) environments, i.e., (a) 30 °C at <1 % RH, (b) 30 °C at 80 % RH, (c) 55 °C at <1 % RH, and (d) 55 °C at 80 % RH. Outdoor weathering was performed in Gaithersburg, MD, in two different time periods. FTIR spectra indicate that different exposure conditions have no consequence on the nature and the proportions of the oxidation products, suggesting that similar degradation mechanisms were operative under all outdoor and indoor conditions. In the accelerated exposure, the rate of degradation is found to be influenced dominantly by UV radiation. The combination of UV radiation and temperature results in a cumulative effect, producing more rapid degradation. Analogous to the chemical changes, post-yield mechanical behaviors (such as strain hardening modulus and elongation to break) are markedly reduced, while the Young’s modulus is minimally affected. Photodegradation leads finally to instability in the polymer’s necking behavior and embrittlement, which is explained in terms of chain scissions of the tie molecules in the amorphous region. Samples subjected to outdoor weathering exhibit significantly slower photodegradation, but the degradation mechanism is the same so higher doses of environmental factors can be used to provide reliable acceleration in short-term aging tests.
Kar Tean Tan, Christopher White, Donald Hunston, Aaron Forster, Deborah Stanley, Amy Langhorst, Patrick Gaume

Backmatter

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