1.The choice of artificial accelerated aging test conditions
In the process of using polymer materials, various factors such as aging factors, climate environment, and others may play a role in their aging. If we know the main factors of aging in advance, we can select the test method.
We can determine the test method by considering the transport, storage and use environment of the material as well as its aging mechanism. For example, people mainly use rigid PVC profiles outdoors, which they make from PVC with stabilizers, pigments, and other additives. From the aging mechanism of polyvinyl chloride, polyvinyl chloride is easy to decompose by heat; from the use of environmental considerations; oxygen in the air, ultraviolet light, heat, moisture are the causes of profile aging.
Therefore, the national standard GB/T8814-2004 “doors, windows with unplasticised polyvinyl chloride (PVC-U) profiles”, both the provisions of the light and oxygen aging test method, the use of GB/T16422.2 “Plastics Laboratory Exposure Test Methods for Light Sources Part II: Xenon Arc Lamp” aging 4,000h or 6,000h, simulating the outdoor ultraviolet and visible light, temperature, humidity, rainfall and other factors, and so on. At the same time, but also provides for the thermal oxygen aging project: heated state, 150 ℃ placed 30min, visual observation of whether bubbles, cracks, pockmarks or separation phenomenon, in order to examine the heat resistance of the profile.
Another example is a product of competitiveness in the international market: foreign trade export shoes. In the process of use, the ultraviolet rays of the sun are the main cause of discolouration and fading of shoes, therefore, it is necessary to use the UV light box to carry out the yellowing resistance test.
The yellowing resistance test chamber commonly used for shoes uses a 30W UV lamp, positions the sample 20cm away from the light source, and observes the color change after 3 hours of irradiation. Meanwhile, in the process of transportation, the harsh environment of stuffy heat and humidity in the container will cause discolouration, spotting and even deterioration of the upper, sole and glue. Therefore, before loading and transporting, it is necessary to consider the moisture and heat aging test, simulate the high heat and humidity environment in the container, under the condition of 70℃ and 95% relative humidity, and observe the appearance and colour change after 48h test.
2.Artificial accelerated aging light source selection
Researchers commonly use an artificial accelerated aging test method that simulates laboratory light exposure in a test chamber with factors like light, oxygen, heat, and rainfall in an environment similar to the visible atmosphere. Among these simulation factors, the light source plays a crucial role. Experience shows that the wavelengths of sunlight that cause polymer materials to break the ring are mainly concentrated in ultraviolet light and some visible light.
Currently used artificial light source are trying to make in this wavelength range of the energy spectrum distribution curve and the sun spectrum close to the simulation and acceleration rate is the main basis for the choice of artificial light source. After about a century of development, the laboratory light source has a closed carbon arc lamp, sunlight-type carbon arc lamps, fluorescent ultraviolet lamps, xenon arc lamps, high-pressure mercury lamps and other light sources to choose from. The International Organisation for Standardisation (ISO) technical committees related to polymer materials mainly recommend the use of sunlight-type carbon arc lamps, fluorescent ultraviolet lamps, xenon arc lamps, three kinds of light sources.
01 Xenon arc lamp
Currently, researchers believe that the spectral energy distribution of the xenon arc lamp’s artificial light source is most similar to sunlight in the ultraviolet and visible parts. By selecting the correct filter, you can filter out most of the short-wave radiation in the sunlight that reaches the ground. Xenon lamps in the 1000nm ~ 1200nm infrared region there is a very strong radiation, will produce a lot of heat.
Therefore, it is necessary to choose a suitable cooling device to take away this part of the energy. Currently, there are two types of xenon lamp aging test equipment on the market: water-cooled and air-cooled. Generally speaking, the cooling effect of water-cooled xenon lamp device is better than air-cooled, but also more complex structure, the price is also more expensive. The xenon lamp is the lowest in terms of acceleration multiplier due to the fact that the energy of the UV part of the lamp increases less than the other two light sources.
Application: plastics industry, rubber industry, paint industry, dyes, pigments, textiles, etc.
Commonly used standards: GB/T 16422.2, ISO 4892-2, SAE J2527, ASTM G 155, ASTM D4459 and so on.
02Fluorescent UV Lamps
Theoretically, the short-wave energy of 300nm~400nm is the main factor causing aging. Increasing this part of energy can achieve the effect of a rapid test. Fluorescent UV lamps mainly concentrate their spectral distribution in the ultraviolet part, so they can achieve a high acceleration multiplier.
However, fluorescent UV lamps not only increase the UV energy in natural daylight, but also have radiant energy that is not present in natural daylight when measured on the earth’s surface, which can cause unnatural damage. In addition the fluorescent light source has no energy above 375 nm except for very narrow mercury spectral lines, so that materials sensitive to longer wavelengths of UV energy may not change as they would if exposed to natural daylight. As a result of these inherent shortcomings it can lead to unreliable results.
As a result, fluorescent UV lamps are poorly modelled. However, you can achieve rapid screening of specific materials by selecting the appropriate type of lamp because of its high acceleration multiplier.
Application: Widely applied to non-metallic materials, organic materials (e.g., coatings, paints, rubber, plastics and their products)
Commonly used standards: GB/T 16422.3, ISO 4892-3, ASTM G154, SAEJ 2020, IEC 61215 and so on.
03Sunlight-type carbon arc lamp
Sunlight-type carbon arc lamp is currently less used in China, but it is widely used in Japan as a light source, most of the JIS standards use sunlight-type carbon arc lamp. Many of our joint ventures with Japan’s automotive enterprises still recommend the use of this light source. Sunlight-type carbon arc lamp spectral energy distribution is also closer to sunlight, but in the 370nm ~ 390nm ultraviolet concentration to strengthen the simulation is not as good as the xenon lamp, accelerated multiplier between xenon and ultraviolet lamps.
Application: General daylight type weathering machine is more suitable for paint industry, automobile industry, construction industry, communication equipment, textile industry, dye chemical, rubber industry, etc. Now it is mainly used for testing of automobile materials, especially for Japanese enterprises.
Commonly used standards: GB/T 16422.4, GB/T 15255, ISO 4892-4, ASTM G152, JIS D0205 and so on.
Material aging test
Guogao Material Analysis and Testing Centre can determine the reliability index of materials through aging equipments such as Thermal Oxygen Aging Chamber, Xenon Lamp Aging Tester, Carbon Arc Aging Chamber and Ultraviolet Aging Chamber according to the test standards such as GB, ISO, ASTM and so on.
Service Process
Understand the customer’s real needs – test sample evaluation – design programme – analysis and testing – issue a report
3.Determination of test time
01Refer to the relevant product standards
Relevant product standards have made provisions for the aging test time, we just need to find the relevant standards, according to the time specified in the implementation of the line. Many national standards, industry standards have made provisions for this.
02Projections based on known correlations
Research shows that: through the colour and yellowing index changes to evaluate the colour stability of ABS, artificial accelerated aging and natural atmospheric exposure has a better correlation, the accelerated multiplier is about 7. If you want to understand a certain ABS material outdoor use after one year of colour changes, using the same test conditions, you can refer to the accelerated multiplier to determine the accelerated aging time of 365×24/7 = 1251h.
Researchers at home and abroad have conducted extensive research on the correlation between the question, leading to the derivation of many conversion relations. However, due to the diversity of polymer materials, different accelerated aging test equipment and methods, different time, regional climate variability leads to the complexity of the conversion relationship. Therefore, when choosing the conversion relationship, we must pay attention to the specific materials, aging equipment, test conditions, performance evaluation indexes and other factors to derive the correlation.
03Controlling the total amount of artificial accelerated ageing radiation to be comparable with the total amount of natural exposure radiation
For some products that lack corresponding standards or reference relevance, we can control the total amount of artificial accelerated aging radiation to be comparable to the total amount of natural exposure radiation, considering the radiation intensity of the actual use environment.
Example: How to control the total radiation of artificial accelerated aging
People use a plastic product to control the total artificial accelerated aging radiation equivalent to one year of outdoor exposure.
Step 1: As the product is a plastic product, and used outdoors, choose to use GB/T16422.2-1996 “plastic laboratory light source exposure test methods Part II: Xenon arc lamp” in the A method.
Test conditions are: irradiation intensity 0.50W/m2 (340nm), blackboard temperature 65 ℃, box temperature 40 ℃, 50% relative humidity, water spray time / no water spray time 18min/102min, continuous light;
The second step: the total amount of radiation in a year is about 5609MJ/m2, based on the comparison of artificial light sources and natural sunlight radiation spectral distribution of the international guidelines CIENo85-1989 (GB/T16422.1-1996 “Plastics Laboratory Light Exposure Test Methods Part I: Xenon Arc Lamp” cited); of which the ultraviolet region and the visible part of the region (300nm ~ 800nm) accounted for 62.2%, that is, the UV region and the visible part of the region (300nm ~ 800nm). ) accounts for 62.2%, i.e. 3489MJ/m2.
Step 3: According to GB/T16422.2-1996
With an irradiation intensity of 0.50W/m2 at 340nm, and an irradiation intensity of 550W/m2 in the infrared region and visible part (300nm ~ 800nm), we can calculate 3489X106/550 = 6.344X106s, which equals 1762h. According to this calculation method, the accelerated multiplication rate of about 5. As the natural aging is not a simple irradiation intensity of the iteration. Only in determining the sunlight is caused by the material.
4.The choice of performance evaluation index
Selection of performance evaluation index is mainly from the use of materials and the material itself characteristics of two aspects to consider.
4.1 According to the use of materials to determine the evaluation index for the same material, due to its different uses, may choose the evaluation index is also different. For instance, if using the same paint for decoration, you must focus on changing its appearance. GB/T1766-1995 “Rating of Aging of Color Paint and Varnish Coatings” specifies in detail the rating methods for various appearance changes such as gloss, color change, chalking, and gold flooding.
As for some functional coatings, such as anti-corrosion coatings, a certain degree of colour and appearance change is acceptable, when the evaluation index is selected, the main consideration is its cracking resistance, chalking degree and other aspects. When using the same polyvinyl chloride (PVC) for producing shoe uppers, one must consider its resistance to yellowing. In contrast, if using it for rainwater downpipes, the requirements for appearance changes are not high, but changes occur in the material’s physical and mechanical properties, with alterations in tensile strength being the main assessment index.
4.2 Determine the evaluation indexes according to the characteristics of the material itself In the case of the same material, the decline of different properties in the aging process is not equal. In other words, certain properties are sensitive to the environment and decline fast, which is the main factor causing material damage. When choosing evaluation indexes, select these sensitive properties. Research shows that: for most engineering plastics, impact strength is the one that changes more and decreases more significantly in the natural aging test detection.
Therefore, when conducting the aging test of engineering plastics, prioritize selecting the impact strength decline as the evaluation index. Impact strength is also quite sensitive to the aging of polypropylene, which is the main index to assess the aging performance. For polyethylene materials, the decrease in elongation at break is more obvious, and it is the evaluation index of priority consideration. One should select polyvinyl chloride for evaluation based on the actual situation because it experiences a rapid decrease in both tensile strength and impact strength.
The national standard GB/T8814-2004 “unplasticized polyvinyl chloride (PVC-U) profiles for doors and windows” selects an impact strength retention rate of ≥ 60% after aging as a qualified judgement indicator; while the light industry standard QB/T2480-2000 for hard polyvinyl chloride (PVC-U) rainwater pipes and fittings for construction selects a tensile strength retention rate of ≥ 80% after aging as a qualified judgement indicator.
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