What is the high temperature resistance of polyethylene

What is the high temperature resistance of polyethylene?
① High temperature resistance characteristics of low-density polyethylene: Low density polyethylene (LDPE) is a widely used type of polyethylene with relatively low high temperature resistance. The continuous use temperature of conventional low-density polyethylene is between 60-80 ℃, and the short-term maximum temperature tolerance does not exceed 100 ℃. The common food cling film in daily life is mostly made of low-density polyethylene material. When used, if it comes into contact with hot oil just out of the pot and the temperature exceeds 100 ℃, the cling film will quickly soften, shrink, or even melt, producing harmful substances. In industrial production, water pipes made of low-density polyethylene, if used to transport hot water above 80 ℃, will experience significant deformation, decrease in pipe wall strength, and are prone to rupture and leakage during long-term use. When testing, place the low-density polyethylene sample in a constant temperature box at 90 ℃. After 24 hours, the sample will show slight signs of melting, indicating that it cannot be used stably at that temperature.
② High temperature resistance characteristics of high-density polyethylene: High density polyethylene (HDPE) has a more regular molecular structure and higher crystallinity, and its high temperature resistance is superior to low-density polyethylene. Its continuous use temperature can reach around 100 ℃, and it can withstand high temperatures of up to 120 ℃ in the short term. A household high-density polyethylene water storage tank can be used to hold boiling water at 100 ℃ without deformation or damage, and has good chemical stability without releasing harmful substances. In the industrial field, chemical storage tanks made of high-density polyethylene can be used to store corrosive liquids with temperatures not exceeding 100 ℃, such as low concentration acid-base solutions. Place the high-density polyethylene sample in a constant temperature environment of 110 ℃, and after 48 hours, the sample only shows slight discoloration without obvious deformation or melting, indicating that it has good stability within the temperature range of

.
③ High temperature resistance characteristics of linear low-density polyethylene: The high temperature resistance of linear low-density polyethylene (LLDPE) is between low-density and high-density, with a continuous use temperature of 70-90 ℃ and a short-term temperature tolerance of up to 110 ℃. The commonly used linear low-density polyethylene film in agricultural production can maintain a stable shape and prevent melting due to high temperatures, effectively providing insulation and moisture retention during high temperature weather in summer when the surface temperature can reach 60-70 ℃. If the plastic film is placed in boiling water at 100 ℃, it will soften after 30 minutes, but it will not melt immediately. In industry, films made of linear low-density polyethylene are used to package foods with high temperatures, such as freshly baked bread (at a temperature of about 80 ℃), which can maintain the packaging shape well and will not adhere to the food.
④ High temperature resistance characteristics of ultra-high molecular weight polyethylene: Ultra high molecular weight polyethylene (UHMWPE) has excellent mechanical properties, but its high temperature resistance is similar to high-density polyethylene, with a continuous use temperature of about 90-100 ℃ and a short-term tolerance temperature of 120 ℃. In construction machinery, sliders made of ultra-high molecular weight polyethylene are used for mechanical transmission parts in high-temperature environments, such as gearboxes with a temperature of about 90 ℃. The sliders can maintain good lubrication and wear resistance and will not fail due to high temperatures. If the slider is placed in a high temperature environment of 130 ℃, significant thermal deformation will occur after 1 hour, affecting its performance. In the food processing industry, conveyor tracks made of ultra-high molecular weight polyethylene can be used to transport food raw materials with temperatures not exceeding 100 ℃, without producing harmful substances due to high temperatures.
⑤ High temperature resistance characteristics of cross-linked polyethylene: Cross linked polyethylene (XLPE) crosslinks its molecular chains through chemical or physical methods, greatly improving its high temperature resistance. It can be continuously used at temperatures up to 120-150 ℃ and can withstand temperatures above 200 ℃ in the short term. In the wire and cable industry, cross-linked polyethylene is a commonly used insulation layer material for cables in high-temperature environments, such as cables near power plant boilers, where the ambient temperature can reach 130 ℃. The cross-linked polyethylene insulation layer can maintain stable insulation performance and will not age due to high temperatures. The cross-linked polyethylene hot water pipe for household use can be used to transport high-temperature hot water at 120 ℃, and long-term use will not cause deformation or leakage. During testing, the cross-linked polyethylene sample was placed in a constant temperature box at 150 ℃. After 72 hours, the sample showed no significant changes and still maintained good mechanical properties.
⑥ The influence of different processing methods on the high temperature resistance of polyethylene: Processing methods can change the high temperature resistance of polyethylene. Polyethylene products produced by injection molding have a tighter molecular arrangement during the molding process, resulting in a 5-10 ℃ higher high temperature resistance than those produced by blow molding. For example, injection molded high-density polyethylene water bottles can withstand boiling water at 100 ℃, while blow molded high-density polyethylene water bottles may experience slight deformation when filled with boiling water at 100 ℃. If extruded polyethylene pipes undergo subsequent heat treatment, their crystallinity can be improved and their high temperature resistance can be enhanced by 10-15 ℃. Agricultural extruded plastic film, after heat treatment, can extend its service life by more than 30% in high temperature environments in summer, and is less prone to cracking due to high temperature aging.