Decomposition temperature and melting point of polyethylene

In terms of the decomposition temperature of polyethylene, generally speaking, in an anaerobic environment, polyethylene begins to decompose at around 300 ℃ -400 ℃. This is because as the temperature increases, the chemical bonds of polyethylene molecular chains begin to break, leading to the destruction and degradation of the molecular structure. The melting point of low-density polyethylene is relatively low, around 105 ℃ -115 ℃, because its molecular chains contain many short branches, have relatively low crystallinity, and weak intermolecular bonding, so it can melt at relatively low temperatures. The decomposition process of polyethylene is relatively complex. In an aerobic environment, the decomposition temperature may decrease, and oxidation decomposition may begin at around 250 ℃. The oxidation reaction accelerates the breakage of molecular chains, promoting the faster decomposition of polyethylene. The melting point of linear low-density polyethylene is between high-density polyethylene and low-density polyethylene, usually between 120 ℃ and 125 ℃. Its molecular structure determines its crystallization performance and melting point range.
The decomposition temperature of polyethylene is also related to the heating rate. The faster the heating rate, the higher the temperature at which polyethylene begins to decompose. This is because during rapid heating, molecules do not have enough time to undergo sufficient thermal motion and structural changes. The melting point of ultra-high molecular weight polyethylene is relatively high, reaching 130 ℃ -137 ℃. This is due to its long molecular chain, stronger intermolecular interactions, more complete crystallization, and the need for higher energy to break down the crystalline structure and achieve melting. From the perspective of thermogravimetric analysis, the mass of polyethylene gradually decreases after reaching the decomposition temperature, and the rate of mass loss accelerates at 400 ℃ -500 ℃, reflecting the process of polyethylene molecules decomposing into small molecules in large quantities. The melting point of polyethylene is also affected by factors such as additives. For example, after adding certain nucleating agents, the crystallization rate of polyethylene accelerates, the crystallinity increases, and the melting point may rise by 2 ℃ 5 ℃.
In industrial production, understanding the decomposition temperature and melting point of polyethylene is crucial. For example, in injection molding processes, the temperature needs to be controlled within a range slightly higher than the melting point, generally 10-20 ℃ higher than the melting point, to ensure good fluidity of polyethylene materials and avoid decomposition caused by excessive temperature.