Light is one of the important environmental factors that affect the anti-aging performance of plastic shell. The ultraviolet energy in sunlight is high and can destroy the chemical bonds in the plastic molecular chain. When plastic shell is exposed to sunlight for a long time, ultraviolet rays will cause the plastic to undergo photo-oxidation reaction, resulting in molecular chain breakage and degradation. For example, plastic shell made of polypropylene (PP) is prone to free radical reaction under ultraviolet irradiation, making the molecular structure unstable, and then discoloring and becoming brittle.
In addition, ultraviolet rays will accelerate the decomposition of additives in plastics and reduce their original anti-aging effect. Especially in areas with strong sunlight in summer, the intensity of ultraviolet radiation received by plastic shell is high, and the aging speed will be significantly accelerated. In order to resist the influence of ultraviolet rays, ultraviolet absorbers are usually added to plastics or materials with anti-ultraviolet coatings are used to reduce the damage of ultraviolet rays to plastic molecules and improve their anti-aging performance.
The effect of temperature on the anti-aging performance of plastic shell is also significant. High temperature environment will accelerate the chemical reaction rate of plastics, intensify the thermal motion of plastic molecules, and make molecular chains more likely to break and recombine. For example, at high temperatures, the ester bonds in the molecular chains of polycarbonate (PC) plastic shells are prone to hydrolysis, thereby reducing the strength and toughness of the material. In low-temperature environments, plastics become hard and brittle, with reduced toughness, and are prone to cracking or even rupture when subjected to external impact. When plastic shells are in an environment with frequent temperature changes for a long time, thermal expansion and contraction will cause stress inside the plastic. The repeated action of this stress will accelerate the fatigue aging of the plastic and shorten its service life. Therefore, when using plastic shells in different temperature environments, it is necessary to select suitable plastic materials and take corresponding insulation or heat preservation measures to reduce the adverse effects of temperature on its anti-aging properties.
Humidity is also a key environmental factor affecting the anti-aging properties of plastic shells. High humidity environments can cause plastics to absorb moisture. For some hydrophilic plastics (such as nylon), the absorption of water will cause changes in their size, and may also trigger hydrolysis reactions, destroy the molecular chain structure, and reduce material performance. In addition, humid environments are prone to mold growth, and molds will secrete enzymes and other substances during their growth. These substances can erode the surface of plastics and accelerate the aging and damage of plastics. When there are tiny cracks or holes on the surface of the plastic shell, moisture is more likely to penetrate into the interior, further aggravating the aging process. In order to cope with the influence of humidity, on the one hand, the plastic can be modified to reduce its water absorption; on the other hand, a moisture-proof coating can be applied to the surface of the plastic shell to isolate moisture from the plastic and improve its anti-aging ability in a humid environment.
Chemical substances in the air have an impact on the anti-aging performance of plastic shell that cannot be ignored. Industrial waste gas, acidic gases in automobile exhaust (such as sulfur dioxide, nitrogen oxides), and ozone in the air will react chemically with plastics. For example, ozone can react with double bonds in plastic molecules to cause cracks and powdering on the surface of the plastic. Some organic solvents, detergents and other chemicals may dissolve or swell the plastic, destroy its internal structure, and reduce its strength and hardness. In environments such as chemical plant areas and busy urban roads, plastic shells are at a higher risk of being eroded by chemicals and will age faster. Therefore, when using plastic shells in these special environments, it is necessary to select plastic materials with good chemical stability and regularly clean and protect the plastic shells to reduce damage to them by chemicals.
The interaction between mechanical stress and environmental factors will also accelerate the aging of plastic shells. When plastic shells are subjected to continuous mechanical stress (such as stretching, extrusion, vibration, etc.), microcracks will be generated inside them. Under the combined effect of environmental factors such as light, temperature, and humidity, these microcracks will gradually expand, causing the strength of the plastic shell to decrease and accelerating the aging process. For example, the plastic shell installed in the engine compartment of a vehicle, in addition to being affected by the high temperature environment, will also be subjected to mechanical stress due to the vibration of the engine. In this case, the plastic shell is more likely to age and crack. In order to reduce the impact of mechanical stress on the anti-aging performance of plastic shells, it is necessary to reasonably plan the structure during the design and installation process, reduce stress concentration, and adopt buffering, shock absorption and other measures to reduce the damage of mechanical stress to plastic shells.
Altitude and air pressure changes will also affect the anti-aging performance of plastic shells. In high-altitude areas, the air pressure is low, the air is thin, and the intensity of ultraviolet rays is relatively higher, which will accelerate the speed of light aging of plastics. At the same time, changes in air pressure may cause stress inside the plastic shell, especially for sealed plastic shells, where the pressure difference may cause the shell to deform or even break. In addition, the temperature difference between day and night in high altitude areas is large, and frequent thermal expansion and contraction will also accelerate the aging of plastics. Therefore, for plastic shells used in high altitude areas, special material selection and structural design need to be considered to enhance their resistance to ultraviolet rays, air pressure changes, and temperature differences to ensure their anti-aging performance and service life.
The microbial environment is also a potential factor affecting the anti-aging performance of plastic shells. In environments containing a large number of microorganisms such as soil and sewage, some microorganisms can use plastics as a carbon source for metabolic activities, and the secreted enzyme substances can decompose plastic molecular chains. For example, some bacteria and fungi can degrade biodegradable plastics, causing them to gradually lose strength and integrity. Even for non-biodegradable plastics, the surface will be eroded under the long-term action of microorganisms, resulting in performance degradation. For plastic shells used in special environments such as underground burial and underwater applications, it is necessary to consider the impact of microorganisms and choose plastic materials with resistance to microbial erosion, or perform special treatment on the plastic shell to inhibit the growth and erosion of microorganisms and improve its anti-aging performance.
