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Accelerated UV weathering device based on integrating sphere technology

An ultraviolet (UV) weathering device based on integrating sphere technology has been designed, fabricated, and implemented for studying the accelerated weathering of polymers. This device has the capability of irradiating multiple test specimens with uniform, high intensity UV radiation while simultaneously subjecting them to a wide range of precisely and independently controlled temperature and relative humidity environments. This article describes the integrating sphere-based weathering system, its ability to precisely control temperature and relative humidity, and its ability to produce a highly uniform UV irradiance.

Relating laboratory and outdoor exposure of coatings: II. Effects of relative humidity on photodegradation and the apparent quantum yield of acrylic-melamine coatings

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.

Relating laboratory and outdoor exposures of acrylic melamine coatings. I. Cumulative damage model and laboratory exposure apparatus

A cumulative damage model and a laboratory apparatus are described for linking field and laboratory photodegradation results and for predicting the service life of polymeric materials exposed in the laboratory and field. The apparatus was designed to independently and precisely monitor and control in both space and time the three primary weathering factors causing polymeric materials to degrade when exposed in the field. These factors include temperature, relative humidity, and spectral ultraviolet radiation. A model acrylic melamine coating was exposed in the laboratory apparatus to each of 12 different spectral wavebands and four temperature and four relative humidity environments. The spectral dosage and material damage were measured for each exposure treatment and this data input into the cumulative damage model from which estimates of the spectral quantum yield were made. Variables affecting the accuracy of the measurements are discussed.

Ultraviolet Chambers Based on Integrating Spheres for Use in Artificial Weathering.

Laboratory ultraviolet (UV) chambers are widely used to obtain weathering data for a wide range of commercial polymer products including coatings, textiles, elastomers, plastics, and polymeric composites. Although numerous improvements have been made in the design of UV chambers over the last 80 years, the reproducibility of the exposure results from these chambers has remained elusive. This lack of reproducibility is attributed to systematic errors in their design, operation, and control which prevent direct comparisons of the performance of materials exposed in the same environment, comparisons of the performance of the same material exposed in different laboratories, and the comparison of field and laboratory results. This paper describes an innovative UV chamber design based on integrating sphere technology that greatly reduces the magnitude of these errors, as well as provides additional experimental capabilities.

Design, development, and testing of a hybrid in situ testing device for building joint sealant

The testing of sealant samples has been restricted to devices that either focus on fatiguing multiple samples or quantifying the mechanical properties of a single sample. This manuscript describes a device that combines these two instrumental designs: the ability to both fatigue and characterize multiple sealant samples at the same time. This device employs precise movement capability combined with a stiff loading frame and accurate force measurement for the characterization of five ASTM C719 sealant samples. The performance of this device is demonstrated by monitoring the changes in mechanical properties of silicone sealant during the first 90h of cure. A complete description of the apparatus, results from the study of curing and analysis is included.