The “A Song of Ice and Fire”of the bulletproof world: the cold toughness of PE and the flame resistance of Kevlar

Properties and Applications of PE, or ultra-high molecular weight polyethylene, is a tasteless, odorless, and non-toxic milky-white waxy granule. It possesses excellent chemical stability, resisting the erosion of most acids and alkalis, but not resistant to oxidizing acids. At room temperature, PE is insoluble in common solvents, has low water absorption, and excellent electrical insulation. Due to its extremely high stability, low-temperature resistance, UV resistance, water resistance, and lightweight characteristics, PE has become an ideal choice for the manufacture of bulletproof equipment. However, PE's high-temperature resistance is relatively weak; the operating temperature must be controlled below 80℃. Exceeding this limit will cause its performance to degrade rapidly, and it may even melt above 150℃. Therefore, although PE bulletproof products can meet most usage scenarios, they are not suitable for high-temperature environments, such as the Middle East.

Kevlar Properties and Applications Kevlar, also known as aramid, was originally named "poly(p-phenylene terephthalamide)". This new material has attracted much attention due to its excellent physical properties. It has low density, high strength, excellent toughness, and superior high-temperature resistance. Even more remarkably, its strength is up to five times that of steel of the same weight, while its density is only one-fifth that of steel. These properties make Kevlar widely used in many fields, such as bulletproof equipment, construction, and electronic equipment. In addition, Kevlar also has advantages such as acid and alkali resistance, light weight, and high strength, further expanding its application range. In the military field, Kevlar is hailed as the "armor guardian," demonstrating its superior protective performance. Compared to PE, Kevlar performs better in terms of high-temperature resistance and creep resistance. However, Kevlar also has some shortcomings, such as degradation under ultraviolet radiation and susceptibility to hydrolysis. Even when stored in a dry environment, Kevlar will gradually absorb moisture from the air and undergo hydrolysis. Therefore, equipment made of Kevlar is not suitable for long-term use in environments with strong ultraviolet radiation or high humidity.