PE flat bags are mainly made of polyethylene, and their weather resistance in high temperature environments depends first on the molecular structure and type of polyethylene. Low-density polyethylene (LDPE) is relatively soft and flexible, but its melting point is low, generally around 105-115℃. In high temperature environments, PE flat bags made of LDPE are prone to softening and deformation. When the temperature approaches or exceeds its melting point, the bag will lose its original shape, and even become sticky or damaged. The molecular chains of high-density polyethylene (HDPE) are closely arranged, with a high degree of crystallinity and a melting point of usually 125-135℃. Compared with LDPE, its dimensional stability and rigidity at high temperatures are better, but in continuous high temperature environments, flat bags made of HDPE will also experience a certain degree of performance degradation, such as reduced hardness and weakened toughness. Long-term exposure to high temperatures may also cause molecular chain breakage, affecting the bag's load-bearing capacity and service life.
High temperature environments will accelerate the oxidation process of PE flat bags and have a negative impact on their weather resistance. When PE flat bags are exposed to high temperatures, oxygen in the air is more likely to react with polyethylene molecules, causing oxidative degradation. During the oxidation process, the carbon-carbon bonds in the polyethylene molecular chain are destroyed, generating functional groups such as carbonyl and carboxyl, resulting in a decrease in the mechanical properties of the material. For example, PE flat bags, which originally have good tensile strength and toughness, will gradually become brittle under high-temperature oxidation, and may break if they are gently pulled. Moreover, the oxidation reaction will also change the appearance of the PE flat bag, making the color darker and losing its luster, reducing its performance and aesthetics. In order to slow down the oxidation process, antioxidants are usually added to the PE raw materials. These antioxidants can capture free radicals and prevent further oxidation reactions, thereby improving the weather resistance of PE flat bags in high temperature environments.
The synergistic effect of high temperature environment and ultraviolet rays will further aggravate the aging of PE flat bags. The ultraviolet energy in sunlight is high, which can destroy the chemical bonds in the polyethylene molecular chain, while high temperature will accelerate the thermal motion of molecules, making the molecular chain easier to break. In the hot summer environment with strong sunlight, PE flat bags are simultaneously affected by high temperature and ultraviolet rays, and the aging rate will be significantly accelerated. Ultraviolet rays can trigger the photo-oxidation reaction of PE flat bags and produce free radicals. These free radicals combine with oxygen to further accelerate the degradation of the molecular chain. At this time, even PE flat bags with added antioxidants may find it difficult to resist this synergistic destruction, resulting in discoloration, brittleness, and a significant decrease in strength of the bag, which seriously affects its normal use. Therefore, when using PE flat bags in outdoor high-temperature environments, effective protective measures need to be taken, such as avoiding direct sunlight and using materials with UV resistance.
The production process also has an important influence on the weather resistance of PE flat bags in high-temperature environments. In the film blowing process, the control of parameters such as temperature and blowing ratio is directly related to the quality and performance of PE flat bags. If the film blowing temperature is too high, it will cause the polyethylene molecules to degrade, making the mechanical properties of the flat bag made worse and more easily damaged in a high-temperature environment; and if the blowing ratio is unreasonable, the film thickness will be uneven, and the thin parts will be more likely to break at high temperatures. In addition, the ink and printing method used in the printing process will also affect the weather resistance of the flat bag. Some inks may fade, fall off, or even react chemically with PE materials at high temperatures, reducing the strength and stability of flat bags. Therefore, optimizing production process parameters and selecting appropriate inks and printing methods are important ways to improve the weather resistance of PE flat bags in high temperature environments.
The thickness and structural design of PE flat bags also affect their weather resistance in high temperature environments. Thicker PE flat bags usually have better heat resistance and mechanical strength, and can resist the effects of high temperatures to a certain extent. Because thicker materials can disperse heat and reduce the damage to the molecular structure caused by local overheating. At the same time, reasonable structural design, such as adding reinforcing ribs and adopting multi-layer composite structures, can also improve the high temperature resistance of flat bags. Multi-layer composite structures can combine materials with different properties. For example, the outer layer uses materials with UV resistance and heat resistance, and the inner layer uses food-grade safety materials. This can not only meet the use requirements in high temperature environments, but also ensure the safety of packaged items. However, increasing thickness and optimizing structure may increase production costs, and a balance needs to be struck between performance and cost.
The humidity conditions in high temperature environments will also have a certain impact on the weather resistance of PE flat bags. Although polyethylene itself has good waterproof properties, in a high-temperature environment with high humidity, moisture may condense on the surface of the PE flat bag to form a water film. Water at high temperatures will accelerate some chemical reactions. For example, when there are impurities or additives on the surface of the flat bag, water may promote these substances to react with polyethylene, thereby affecting the performance of the flat bag. In addition, high-humidity environments are prone to mold growth, and substances such as enzymes secreted by molds may corrode the PE flat bag, especially for flat bags used in food packaging and other fields. Mold erosion not only affects the physical properties of the bag, but may also pose a threat to food safety. Therefore, when using PE flat bags in high-temperature and high-humidity environments, attention should be paid to moisture-proof and mildew-proof treatment.
In order to improve the weather resistance of PE flat bags in high-temperature environments, in addition to the aforementioned methods of adding antioxidants, anti-ultraviolet agents, and optimizing production processes, new materials and technologies can also be used. For example, using cross-linked polyethylene materials, chemical bonds are formed between polyethylene molecular chains through cross-linking reactions, which enhances the intermolecular forces and improves the heat resistance and mechanical properties of the material. In addition, nanocomposite technology is also an effective means to improve the weather resistance of PE flat bags. Adding nanoparticles to polyethylene can improve the material's barrier properties, mechanical properties and heat resistance. At the same time, strengthening the use of PE flat bags in high temperature environments, avoiding long-term exposure to high temperature environments, and reasonable storage and use can also effectively extend their service life and improve their weather resistance in high temperature environments.
