Research on commonly used aging test methods for plastics

During the use, processing and storage of plastics, due to various external factors, such as light, oxygen, heat, radiation, odor, rain, mold, bacteria, etc., the chemical structure is destroyed, so that the original excellent performance. loss, a phenomenon commonly known as aging. The main manifestations of plastic aging are discoloration and cracks in appearance, and physical and chemical properties such as mechanical properties and electrical properties. The aging test can be roughly divided into two categories: one is natural exposure aging, and the other is artificial aging test. They are introduced separately here. 1. Natural exposure aging The natural exposure aging test is an aging test under natural environment conditions. Commonly used methods for plastics are: 1. Atmospheric exposure test GB/T3681-2000 (neq ISO877:1994) Atmospheric exposure test method for plastics GB/T17603-1998 (equivalent to ASTM D5272-1992) Outdoor exposure test method for photodegradable plastics 2 . Indirect exposure test under sunlight filtered by glass plate GB/T14519-1993 (refer to ISO877:1976) Indirect exposure test method of plastics under sunlight filtered by glass plate The natural exposure aging test is relatively close to the actual use environment of the material, according to its The results obtained are more reliable for the weather resistance evaluation of materials, and the results of artificial climate test should also be verified by natural aging test, so natural aging is a basic method. However, the natural aging test has a slow speed, a long period, and is greatly affected by environmental factors, so its application range is limited. Now we use more laboratory artificial simulation methods to accelerate aging. 2. Artificial aging test (1) Laboratory light source exposure test for plastics The laboratory light source (artificial climate) exposure test is an artificial accelerated aging test method that simulates and strengthens the main factors in the atmospheric environment. Results of routine atmospheric exposure. This method simulates five main factors in the atmospheric environment: sunlight, air () air, temperature, and rainfall. Among them, sunlight is the most important. A. Light source The principle of light source selection is: the spectral characteristics of the artificial light source should be similar to the wavelength that is most sensitive to the aging and damage of the material, and it should be considered in combination with the purpose of the test and the use environment of the material. Studies have shown that the radiation in the near-ultraviolet region (300~400nm) wavelength range of sunlight is the main factor that causes plastic aging and degradation. Usually in addition, the radiation intensity increases, and the aging rate of the material increases. Therefore, the closer the energy spectrum distribution of artificial light sources in the ultraviolet region is to the spectral lines of the sun in this region, the better the simulation of the light source will be. Currently, three light sources are recommended internationally: xenon arc lamp, carbon arc lamp, and fluorescent ultraviolet lamp. 1. Xenon arc lamp: The spectral range of xenon arc lamp is ultraviolet, visible and infrared radiation with wavelengths greater than 270nm. After appropriate filtering, its spectral energy distribution is most similar to the ultraviolet-visible part of sunlight. Therefore, the spectral irradiance distribution of the xenon arc lamp is the best simulation of the current artificial light source, but the increase of the ultraviolet distribution of the xenon arc lamp is less, so the aging doubling rate is lower. 2. Carbon arc lamp: The spectral energy distribution of carbon arc lamp is relatively close to sunlight, but the ultraviolet rays are more concentrated between the wavelengths of 370~390nm. Although the simulation performance of the carbon arc lamp is not as good as that of the xenon lamp, the doubling rate is higher than that of the xenon lamp. The Japanese standard is used more. 3. Fluorescent UV lamps Fluorescent UV lamps emit a considerable part of the light energy with wavelengths below 300 nm, which changes the mechanism of material aging and degradation reaction, so the simulation is poor, but the doubling rate is high. B. Test temperature The selection of air temperature is based on the highest temperature in the environment where the material is used, which is slightly higher than that, usually around 50°C. The selection of xenon lamp blackboard temperature is based on the maximum temperature of the material surface in the use environment of the material, and it is slightly higher than it, more than 63±3 ℃, of course, other temperatures can also be selected. However, the irradiation temperature of the sample should not be too high, especially for materials that are sensitive to temperature. Because the temperature is too high, the test results may not be mainly photo-oxidative aging, but the result of thermal effects, such as: PVC. Therefore, care should be taken to prevent the sample from overheating when the xenon lamp is aging, and the air flow should be strengthened for the open carbon arc lamp to avoid excessive temperature rise. C. Relative humidity The influence of relative humidity on the aging of materials varies depending on the variety of materials. It is based on the annual average relative humidity of the material in the environment where it is used, and is usually selected in the range of 50-70%. D. The selection of the rainfall cycle is based on the rainfall of the natural climate. International rainfall time/non-rainfall time should be 18min/102min or 12min/48min, 3min/17min, 5min/25min. However, the moisture in the form of condensation may have a greater impact on the accelerated exposure test, so the exposure in the light and dark cycle often requires a specified condensation time. Distilled or deionized water is used for artificial aging rainfall. Minerals in the water may stain the surface of the sample.​​
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