Polymer materials in its synthesis, storage and processing and final application at all stages may deteriorate, that is, the performance of the material deteriorates, such as yellowing, relative molecular mass decline, product surface cracking, luster loss, more serious is resulting in impact strength, flexion strength, tensile strength and elongation and other mechanical properties decreased significantly. Thus affecting the normal use of polymer material products. This phenomenon is called the chemical aging of plastics, referred to as aging. From a chemical point of view, plastic materials, whether natural or synthetic, have a certain molecular structure, some parts of which have some weak bonds, these weak bonds naturally become a breakthrough in chemical reactions. The essence of plastic aging is nothing more than a chemical reaction, that is, a chemical reaction (such as oxidation reaction) with weak bonds as a starting point and a series of chemical reactions. It can be caused by many causes, such as heat, ultraviolet light, mechanical stress, high-energy radiation, electric fields, etc., can be a single factor, or a combination of factors. The result is that the molecular structure of the polymer material changes and the relative molecular mass decreases or produces crosslinking, so that the material performance deteriorates and can not be used.
The most common factors causing aging are heat and ultraviolet light, because the environment in which plastics are exposed most from production, storage, processing to product use is heat and sunlight (ultraviolet light). The study of plastic aging caused by these two types of environments is of particular importance to practical operators.
Maximum activation wavelength of common polymers
Why do burn-in tests?
1. Screening of materials and formulas
2. Comparison between competitors
3. Seek failure mechanism
4, improve aging resistance
5. Life expectancy
The advantages and disadvantages of outdoor exposure
Outdoor direct exposure refers to direct exposure to sunlight and other climatic conditions, and is the most direct way to assess the weatherability of materials.
Advantages:
It's a good match
Simple and easy to operate
Low absolute cost
Weaknesses:
Usually the period is very long
Global climate diversity
The sensitivity of different samples is different in different climates
1. Xenon lamp light aging test method → Xenon aging test chamber ← Click here learn more!
Xenon arc lamps simulate the full spectrum of sunlight, which includes ultraviolet, visible and infrared light spectra. Filtered xenon arc lamps are the best source for testing the light stability of products such as pigments, dyes and inks, which are sensitive to long-wave light in sunlight and visible light. Xenon arc lamps can precisely adjust their spectral energy distribution and can simulate natural light under a variety of conditions, from sunlight outside the atmosphere to sunlight through a glass window. In addition, by changing the radiation intensity, temperature, humidity and other parameters of the xenon lamp, you can simulate the use of different products, such as inside and outside the car. Figure 3 shows the spectral comparison between different irradiance of xenon lamp and natural light, in which the light intensity of 0.55W /m2 is the closest to natural light. At present, the use of xenon lamp for artificial accelerated aging test has become a preferred and general optical aging test method, and there are many corresponding xenon lamp aging test methods, such as ISO, ASTM, SAE J, GM and so on.
2. Ultraviolet fluorescent light aging test method → UV aging test chamber ← Click here learn more!
The fluorescent UV lamp is a low-pressure mercury lamp with a wavelength of 254nm. The energy distribution of the fluorescent UV lamp depends on the emission spectrum generated by the phosphorus coexistence and the diffusion of the glass tube. Fluorescent lamps are divided into UVA and UVB, and your exposure application determines which type of UV lamp should be used. The following table is the classification and scope of application of UV lamps.
Features:
UVA:
Features: UVA lamps are particularly useful for comparing different types of polymer tests. Since UVA lamps do not have any output below the 295 nm cutoff point of normal sunlight, they generally degrade the material less quickly than UVB lamps. However, they generally yield a better correlation to actual outdoor aging.
Main lamp type:
UVA-340: The UVA-340 provides optimal simulation of sunlight in the region of the critical short wave at 365 nm down to the sunlight cutoff point at 295 nm. Peak emission at 340 nanometers. The UVA-340 lamps are particularly useful for comparative testing of different formulations.
UVA-351: UVA-351 mimics the ultraviolet part of sunlight passing through a window pane. This is most effective for indoor applications, especially replicating the loss of polymers that occurs in window environments. This lamp is widely used in home appliance coatings and automotive interior coatings.
UVB:
Features: UVB lamps are widely used for quick and economical testing of durable materials. There are currently two types of UVB lamps. They produce the same wavelength of ultraviolet light, but the total energy produced is different. All UVB lamps emit short wavelengths of ultraviolet light, 295 nanometers below the sunlight cutoff point. Although this is a short-wave UV-accelerated test, it can sometimes lead to abnormal results.
Main lamp type:
Uvb-313el: The UVB-313EL is the most widely used QUV lamp for UVB exposure. It is very useful in maximizing acceleration for testing of very durable products such as automotive coatings and roofing materials. UVB-313EL lamps are also often used in QC applications.
QFS-40: This is the original QUV lamp. The QFS-40 lamp has been used for many years and is still specified for use in many test methods, especially in the automotive coatings class. The QFS-40 is best used in the QUV/ basic variant.
Standards for optical burn-in testing
ASTM G154/G53 Fluorescent UV Lamp Exposure test Procedure for non-metallic materials
ASTM D4329-05 Fluorescent UV Exposure test for plastics
ASTM D4674-02a Accelerated Color Fastness Testing of Plastics Exposed to indoor office environments
ISO 4892-3: 2006 Plastics - Exposure to laboratory light sources - fluorescent ultraviolet lamps
GB/T 16422.3-1997 Exposure tests for laboratory light sources in plastics - fluorescent ultraviolet lamp
ASTM G155/G26 Xenon Lamp exposure test for non-metallic materials
ASTM D2565-99(2008) Exposure to plastic cylinder lamps for outdoor use
ASTM D4459-06 Indoor Xenon Exposure by Plastic lamp
ISO 4892-2: 2006 Plastics - Exposure to laboratory light sources - Xenon lamps
GB/T 16422.2:1999 Exposure test for plastics laboratory light source - Xenon lamp