Outdoor test approach

Suggested test conditions that cover both "indoor and "outdoor environments are given in Table 7. It can reasonably be argued both for and against using the same humidity for indoor and outdoor testing. Since most chambers have been set up to operate stably at 70 or 75 % RH, one possible approach is to do all corrosive gas exposure testing at this RH but, for outdoor simulations, to follow the... 

The experimental data presented herein are the result of exploratory research aimed at bracketing the necessary moisture and inoculum loads for effective pilot-scale distributed upgrading of wheat straw stems for production of straw-thermoplastic composites (4,15). An exploratory approach was chosen for these tests because full-scale outdoor systems having few environmental controls would be difficult if not impossible to closely control. Both temperature and moisture levels vary owing to variations in heat,... 

If the chemical composition of the samples is known or at least partly known (in a stepwise TIE approach) or existing data allow for QSAR calculation, the samples can be ranked by TUs. Arts et al. (2006) studied, in 12 outdoor ditch mesocosms, the effects of sequential contamination with 5 pesticides in a regression design. They applied dosages equivalent with 0.2%, 1%, and 5% of the predicted environmental concentration (PEC) subsequently over 17 weeks. Endpoints recorded over 30 weeks included community composition of macroinvertebrates, plankton, and macrophytes, and leaf litter decomposition as functional ecosystem parameters. TUs were calculated in relation to acute toxicity data for the most sensitive standard species Daphnia magna and Lemna minor. Principal response curves (PRCs), a special form of constrained PCA, and Williams test (NOEC, class 2 LOEC) were used to identify the most sensitive taxa. Next to direct effects on certain species, also indirect effects, for example, how the change in abundance of a sensitive species affects the abundance of another, more tolerant species, can be detected only in mesocosm or in situ experiments. All observed effects were summarized in effect classes in a descriptive manner. 

Because of the deficiencies of single-species toxicity tests, alternative approaches are being evolved to address the structural and functional processes of an ecosystem. Multispecies tests include the use of laboratory microcosms, outdoor ponds, experimental streams, and enclosures. There are no standardized procedures for these tests. They are conducted with plant and animal species obtained from laboratory cultures and biota collected from natural sources. They can be conducted indoors or outdoors. The toxic effects, in addition to those used for single-species tests, are determined for structural parameters, such as community similarity, diversity, and density, and for functional parameters, such as community respiration and photosynthesis. Effects on these parameters are reported as the NOEC and LOEC. 

The oxidative deterioration of most commercial polymers when exposed to sunlight has restricted their use in outdoor applications. A novel approach to the problem of predicting 20-year performance for such materials in solar photovoltaic devices has been developed in our laboratories. The process of photooxidation has been described by a qualitative model, in terms of elementary reactions with corresponding rates. A numerical integration procedure on the computer provides the predicted values of all species concentration terms over time, without any further assumptions. In principle, once the model has been verified with experimental data from accelerated and/or outdoor exposures of appropriate materials, we can have some confidence in the necessary numerical extrapolation of the solutions to very extended time periods. Moreover, manipulation of this computer model affords a novel and relatively simple means of testing common theories related to photooxidation and stabilization. The computations are derived from a chosen input block based on the literature where data are available and on experience gained from other studies of polymer photochemical reactions. Despite the problems associated with a somewhat arbitrary choice of rate constants for certain reactions, it is hoped that the study can unravel some of the complexity of the process, resolve some of the contentious issues and point the way for further experimentation. 

There have been many other empirical approaches to predict service life from accelerated test results, some based on relations between change in polymer properties and exposure variables (78). A simple empirical method of estimating lifetimes by comparison with control materials has recently been proposed (79). The method consists of exposing the test materials in the laboratory accelerated test device simultaneously with several control materials with similar composition and construction to the test material and having a range of failure times outdoors. It requires, as do all service life methods, that the accelerated test produce the same failure modes as natural exposure. In addition, rank correlation between the two exposures should be very high. If these conditions prevail and the service life of the control materials is well defined, the service life of the test material can be bracketed by two control materials. 

This paper outlines how this quantitative weathering model can be used, first to better understand the linkages between natural and accelerated testing and, second, to predict outdoor gloss and color retention, as well as chalk resistance, for waterborne coatings based on new PVDF-acrylic hybrid latex materials. A general methodology for this approach is depicted in Fig. 5.1. 

Outdoor weathering offers three approaches for exposing test bodies to weathering ... 

It is common practice to expose vehicles for at least one year to dry-hot and/or humid-warm extreme climates. In order to maximize radiation loads during exposure, it is necessary to orient the test objects appropriately to the sun. To accelerate outdoor weathering, there are special devices that increase the solar radiation impacting the surface to be tested per unit of time. One approach is to use electric motors to turn the test object to follow the course of the sun, or to use EMMAQUA to bundle solar radiation (s. Section 2.2.3.1). Here it is very important to ensure that the maximum temperatures affecting the vehicle do not exceed set limits [208]. 

It is also possible to run tests outdoors using containers filled up with soil. This makes the recovery of the samples easier. A possible example of this approach is to perform the soil burial test in plastic flower pots (60 x 20 x 20 cm) placed outdoors [61]. 

Three laboratory tests for exfciiation corrositHi testing were perfonned representing two approaches to testing. The first approach emphasizes simplicity and bottom line results—-the EXCO immersion test The second approach attempts to reproduce the envinm-mental factors contributing to corrosivity and materials behavior—represented by the SO2 salt fog test and MASTMAASIS salt fog test Characteristics of these test environments are shown in Thble 3. Neutral salt fog conditions (ASTM B 117) and outdoor exposure (service) conditions are givm fm comparison. 

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