Accelerated weathering tests limitations

Stabilized with 0.2% amine antioxidant High Density Polyethylene. Extrusion grades of hlgh-denslty polyethylene protected by 2.5% channel type black of 19 my particle size were exposed In a Weather-O-Meter for 10,000 hours without any evidence of serious mechanical damage, as measured by low temperature brittleness and elongation tests. This represents the useful limit In our accelerated weathering test, since as described In an earlier paper,(2) fllm-like deposits form on... 

Automation has been introduced to the traditional molybdate method for the determination of silica in spra)dng water for accelerated weathering test [7]. The spectrometer measures Mo-yellow at 400 nm (AA/217.5 nm) using ammonium molybdate and HCl. The results are processed by a CPU (arranged in a comparator circuit) to calculate Si02 concentration, alarms when the concentration reaches to the limit, and stops the weathering test automatically. 

Interpretations and Limitations of Accelerated Weathering Test Results... 

The mathematical methods used for interpolation and extrapolation of the data obtained from accelerated tests, as described in Chapters 8 and 9, include both the mechanistic and the empirical. Arrhenius formula, based on chemical rate kinetics and relating the rate of degradation to temperature, is used very widely. Where there are sufficient data, statistical methods can be applied and probabilities and confidence limits calculated. For many applications a high level of precision is unnecessary. The practitioners of accelerated weathering are only too keen to tell you of its quirks and inaccuracies, but this obscures... 

Table III. Slope of Erosion Data (mils loss x 10 /hr with 95% confidence limits) Accompanied by a T-test Probability (%) that a Statistical Difference Exists Between the Respective Slope for a Given Pollutant Type and Level vs. the Zero Pollutant Level, Based on Accelerated Weathering Data Collected at 400, 700, and 1,000 Hours Only (used, with permission, from Campbell et al. (12))...

R.P. Brown, T. Butler and S.W. Hawley, Ageing of Rubber—Accelerated Weathering and Ozone Test Results, Rapra Technology Limited, 2001. 

TGSting. No test is available that reliably predicts the exterior durability of coatings, partly due to the wide variety of environments and application conditions (see Weathering). The limitations of accelerated tests, the need for data based on actual field experience, and methods of building a database are described in Reference 23. Use of reliability theory using statistical distribution functions of material, process, and exposure parameters for predicting exterior durability of automotive coatings has been recommended (46). Reference 55 reviews various test methods. 

We surveyed and screened a number of candidate glazing matmals (5,6), which include a varirty of polyesters, fluoropolymers, and polycarbonates (PC), as well as acryhc, polyetherinride, poly ylene (PE), polystyrene, and polyvinyl chloride. Bas on accelerated screaiing tests, we find that fluoropolymers and acrylic arc UV weatherable, and all other materials tested lose transmittance and yellow. However, fluoropolymers are relatively expensive and realistically would be limited to use as thin-film glazings. Acryhc tends to be too brittle and exhibits thomal sag as a glazing candidate for solar collector apphcations. 

Fig. 5.1 Proposed methodology for predicting the service life of newer PVDF products. A general weathering model is used to understand the limitations of the linkages between accelerated and outdoor exposure testing and between different PVDF-based coating platforms, as well as to predict the outdoor performance of newer products...

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]. 

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