I. Introduction
Polymer materials are widely used in various fields such as aerospace, automobile manufacturing, shoemaking and textiles due to their excellent performance, which has played a great role in promoting the development of the national economy. However, in recent years, with the increasing requirements for materials in various fields Higher and higher, the aging problem of polymer materials is also becoming more and more prominent. During the use of polymer materials, they are easily affected by many environmental factors such as sunlight, rain, temperature, oxygen, moisture, and sand and dust, resulting in yellowing and brittleness. , mechanical properties decline, shortened service life and other aging phenomena, which have seriously restricted the further application and development of polymer materials. Studying the aging of polymer materials is of great importance for evaluating the performance of polymer materials, predicting the service life of polymer materials, actively taking measures to slow down the aging of polymer materials, and for the modification of polymer materials and the development of new materials. Practical significance. At present, there are many aging test methods for studying polymer materials, mainly including climate aging test, ultraviolet aging test, ozone aging test, hot air aging test, high and low temperature alternating aging test, damp heat aging test, medium aging test, salt spray aging test etc.
2. Weather aging test
The so-called climate aging test is to expose the polymer material test sample to the atmospheric environment, so as to obtain the aging law of the material sample under the atmospheric environment exposure, analyze the performance of the polymer material, and predict its service life. . The weather aging test can be divided into two types, one of which is the natural exposure test, which is to expose the test sample of the polymer material to the real atmospheric environment to obtain the aging behavior of the material in the real environment. The aging information obtained is the most accurate, and it is the most effective method to obtain the aging behavior of polymer materials, but this test method takes a long time and is time-consuming and labor-intensive. Atmospheric exposure tests for more than one year have been conducted in Florida, the United States, Wanning, Mohe, and Wuhan in China. The other is the artificial climate aging test. The artificial climate aging test refers to the aging test method in which people simulate the real atmospheric environment conditions indoors or strengthen a certain environmental factor to obtain the aging behavior of materials in a short time. Also known as artificial simulated aging or artificial accelerated aging. Artificial weathering is usually carried out in an artificial weathering box. Commonly used artificial weathering chambers mainly include xenon lamp weathering chambers, fluorescent lamp weathering chambers and carbon arc lamp weathering chambers. These kinds of climate aging test chambers simulate or strengthen the natural environmental factors from the main climatic factors such as light, temperature, humidity, rain or condensation to achieve material aging [1]. In addition, the aging test of materials should be carried out according to certain test standards.
3. UV aging test
Ultraviolet light in sunlight, because its light energy is equivalent to the bond energy of polymer chemical bonds, can cause the breakage of polymer compound chains, which is the main factor leading to the aging and degradation of polymer materials. The ultraviolet aging test refers to the test method that exposes the polymer material aging test sample under the ultraviolet light field, so as to obtain the aging behavior and law of the polymer material. Usually the ultraviolet aging test will stipulate that the ultraviolet region and the irradiation intensity, such as 40W/m2, are within the wavelength range of 300nm-400nm. The light sources used in the UV aging test usually include xenon lamps, fluorescent lamps, tritium lamps and deuterium lamps. Among them, the xenon lamp can simulate the solar spectrum very well, and the fluorescent lamp can simulate the ultraviolet spectrum in sunlight very well. The energy provided by the tritium lamp is relatively low. Strong, generally used for accelerated aging tests.
4. Ozone aging test
Ozone is an extremely rare gas in the atmosphere, but it is extremely destructive to polymer materials. Ozone can irreversibly react with unsaturated bonds and reducing groups in the chemical structure of polymer materials, resulting in high Molecular materials undergo oxidative degradation, thus losing their use value. Especially for rubber materials containing double bonds, it shows extremely strong destructive power. Ozone has a strong activity, it can decompose the more active atomic oxygen, and chemically react with the double bond in the rubber molecule, causing the rubber to age, crack and become brittle [1]. The ozone aging test of polymer materials is usually carried out in the ozone aging test chamber. The ozone is provided by the ozone generator, and its concentration can be adjusted by mixing with air through the mixer. The concentration of ozone is generally determined according to the environmental conditions in which the material is actually used. . In addition, the temperature, humidity and other factors in the ozone aging box can also be adjusted, so as to achieve the purpose of the test, and obtain the ozone aging resistance of the material and the ozone aging behavior and law.
5. Hot air aging test
Heat is one of the main factors leading to the aging of polymer materials. Heat can accelerate the movement of polymer chains, resulting in the breakage of polymer chains, the generation of active free radicals, and the occurrence of free radical chain reactions, resulting in degradation or crossover of polymers. Lian, the hot air aging test is one of the main test methods to evaluate polymer materials and study the aging resistance of polymer materials, and it is usually carried out in a constant temperature blast drying test box. The temperature in the drying box can be set according to the test requirements. The polymer material is exposed to the dryness and is regularly sampled and tested to obtain the aging behavior and law of the polymer material, so as to modify the polymer material in a targeted manner. improve its performance.
This hot air aging test, also known as "high temperature aging test", is a commonly used method for testing the aging resistance of polymers.
6. Temperature alternating aging test
Temperature is another important factor leading to the aging of polymer materials. For polymer adhesives, high temperature can accelerate the movement rate of polymer adhesive chains, and low temperature can cause internal stress in polymer adhesives. Alternation leads to chain breakage of the polymer adhesive and aging degradation. For rubber, high temperature can accelerate the thermal movement of molecular chains and cause rubber to crosslink, while low temperature can cause rubber molecular chains to freeze, making them brittle, reducing elasticity and aging. The high and low temperature alternating aging test is an aging test method for evaluating the temperature resistance of polymer materials. It is usually carried out in a temperature alternating aging test chamber, from a certain temperature T1 (usually room temperature) to a certain temperature at a constant heating rate. T2, maintain the temperature of T2 for a certain period of time, then cool down to a certain temperature T3 at a constant cooling rate, maintain the temperature of T3 for a certain period of time, and then raise the temperature to T1, this is a temperature cycle. The length of the cycle can be determined according to the specific test requirements.
7. Damp heat aging test
Damp heat aging test is an effective method to evaluate the aging resistance of polymer materials in high humidity and high temperature environment. In a high-humidity environment, moisture can penetrate into the polymer material, causing swelling of the polymer material, hydrolysis of some hydrophilic groups, and aging degradation of the polymer material. In addition, the penetration of moisture into the polymer material can also lead to the dissolution and migration of additives in the polymer material, such as plasticizers, compounding agents and other substances, affecting the mechanical properties of the polymer material. Under the action of high heat, the heat can promote the penetration of water. The heat promotes the movement of polymer chains, reduces the intermolecular force, promotes the penetration of water, and accelerates the degradation of polymer materials [1]. Different polymer materials have different formulations, so their damp heat aging mechanisms are also different. When performing damp heat aging tests, different aging standards should be selected according to different polymer materials. The damp heat aging test is usually carried out in the damp heat aging test chamber, and the temperature and humidity can be set according to the test requirements.
Eight, medium aging test
Some polymer materials need to be soaked in a certain medium for a long time during use. For example, polymer materials on equipment that have been engaged in offshore operations or seabed operations for a long time need to be soaked in seawater for a long time. Fuel oil, etc., all of which require polymer materials to have strong resistance to medium aging. Anti-medium aging test is a commonly used test method to evaluate the anti-aging performance of polymer materials and predict its life in a certain medium. The medium used in the aging test can be prepared according to the specific environment in which the polymer material is used. It can be artificial seawater, salt water, rainwater, acid-base solution, fuel oil, and other organic solvents.
9. Conclusion
In addition to the above aging test methods for polymer materials, there are also various aging test methods such as salt spray aging test, mildew resistance test, and cold resistance test [2]. Although there are many aging test methods for polymer materials, specific aging tests At the same time, it is also necessary to select the appropriate aging test method according to the environment in which the polymer material is used, the category of the polymer material, and the purpose of the test, so as to properly evaluate the performance of the polymer material and reasonably predict its service life. Provide more effective information.
