How Much Do You Know about UHMWPE Used in Bulletproof Equipment?

Ultra-high molecular weight polyethylene fiber, referred to as UHMWPE fiber, also known as high-strength high-module polyethylene fiber, is an unbranched linear polyethylene with a molecular weight of more than 1.5 million. The general viscosity average molecular weight is more than 1.5 million, and the weight average molecular weight is more than 3 million.

Together with carbon fiber and aramid, it is known as the "three major high-tech fibers in the world". Ultra-high molecular weight polyethylene fiber is the strongest and toughest fiber in the world. It has the highest specific strength and ballistic resistance among industrialized fiber materials. It has ultra-high strength, ultra-high modulus, low density, wear resistance, and low temperature resistance. , UV resistance, shielding resistance, good flexibility, high impact energy absorption and resistance to strong acid, strong alkali, chemical corrosion and many other excellent properties. In view of its light weight, high strength, and high specific energy absorption, it has gradually replaced aramid fiber and become the fiber of choice in the field of individual bulletproof. It is currently the main material for manufacturing bulletproof vests and bulletproof helmets.

Production Process

Ultra-high molecular weight polyethylene, referred to as UHMWPE, is polymerized from ethylene. The production process is similar to the production process of ordinary high-density polyethylene. It is made by using Ziegler catalyst to polymerize ethylene under certain conditions.

The gel spinning-superdrawing method for industrial production of UHMWPE fibers is divided into two process routes: dry method and wet method according to the different solvents used. Dry-process products have high strength and stable quality, and are high-end products. The wet method is a mid- to low-end product.

Performance characteristics

Excellent mechanical properties: Under the same linear density, the tensile strength of ultra-high molecular weight polyethylene fiber is 15 times that of steel wire rope. It is 40% higher than aramid fiber, which is also one of the "three major high-tech fibers in the world", and 10 times higher than high-quality steel fiber and ordinary chemical fiber. Compared with steel, E-glass, nylon, polyamine, carbon fiber and boron fiber, its strength and modulus are higher than these fibers, and it has the highest strength among materials of the same quality.

Excellent impact resistance: Ultra-high molecular weight polyethylene fiber has excellent impact resistance. Its ability to absorb energy and resist impact during the deformation and shaping process is better than that of the "three major high-tech fibers in the world". Aramid fiber and carbon fiber are both high. Compared with polyamide, aramid, E-glass fiber, carbon fiber, and aramid, ultra-high molecular weight polyethylene fiber has a higher specific energy absorption than the total impact.

Excellent wear resistance: Comparing the friction coefficient of reinforced plastics of ultra-high molecular weight polyethylene fiber with carbon fiber and aramid fiber, the wear resistance and bending fatigue of ultra-high molecular weight polyethylene fiber are much higher than those of carbon fiber and aramid fiber. fiber. Therefore, its wear resistance is better than other high-performance fibers. Also because of its superior wear resistance and bending resistance, its processing performance is also relatively superior, and it is easy to be made into other composite materials and fabrics.

Chemical corrosion resistance: Ultra-high molecular weight polyethylene fiber has a relatively simple chemical structure and relatively stable chemical properties. Most chemical substances are not easy to corrode it. Only a few organic solutions can slightly swell it, and its The loss of mechanical properties is less than 10%. The strength retention rates of ultra-high molecular weight polyethylene fibers and aramid fibers in different chemical media were compared. The corrosion resistance of ultra-high molecular weight polyethylene fiber is significantly higher than that of aramid fiber. Its property and structure are particularly stable in acids, alkalis, and salts, and its strength is only lost in sodium hypochlorite solution.

Good optical resistance: Because the chemical structure of ultra-high molecular weight polyethylene fiber is stable, its light resistance is also the most superior among high-tech fibers. Aramid fibers are not UV resistant and should only be used when avoiding direct sunlight. Comparing ultra-high molecular weight polyethylene fibers with nylon, high-modulus and low-modulus aramids, the strength retention rate of ultra-high molecular weight polyethylene fibers is significantly higher than that of other fibers.

Other properties: Ultra-high molecular weight polyethylene fiber also has good hydrophobic properties, water and moisture resistance, electrical insulation properties and long tortuous life. It has outstanding water resistance and low temperature resistance and a small specific gravity. It is the only high-tech fiber that can float on water and is an ideal low-temperature material.

Disadvantages: lower melting point. During its processing, the temperature cannot exceed 130°C, otherwise it will cause creep phenomenon and shorten its service life due to the weak inter-molecular chain force between ultra-high molecular weight polyethylene fibers. There are no dye groups on the ultra-high molecular weight polyethylene fiber, which makes it poor in wettability. It is difficult for dyes to penetrate into the fiber, resulting in poor dyeability. These shortcomings affect the scope of its application fields.

Application areas

National defense field: Because the fiber has good impact resistance and large specific energy absorption, it can be made into protective clothing, helmets, and bulletproof materials in the military, such as armor protection plates for helicopters, tanks, and ships, and radar protection. Shell covers, missile covers, body armor, stab-proof vests, shields, etc. Among them, the application of body armor is the most eye-catching. Taking advantage of its low dielectric constant, low dielectric loss, and high sonar transmittance, it is used in antenna fairings, missile covers, radar protective shell covers, etc. It has the advantage of being lightweight and has a better bulletproof effect than aramid. It has now become the main fiber occupying the U.S. bulletproof vest market. In addition, the specific impact load value U/p of ultra-high molecular weight polyethylene fiber composite materials is 10 times that of steel and more than twice that of glass fiber and aramid.

Aviation field: In aerospace engineering, due to its lightweight, high strength and good impact resistance, the fiber composite material is suitable for wingtip structures of various aircraft, spacecraft structures and buoy aircraft. The fiber can also be used as a deceleration parachute for space shuttle landings and as a rope for suspending heavy objects on aircraft, replacing traditional steel cables and synthetic fiber ropes. Its development is extremely rapid.

Industrial field: In industry, the fiber and its composite materials can be used as pressure-resistant containers, conveyor belts, filter materials, automobile buffer plates, etc.; in construction, it can be used as walls, partition structures, etc., and it can be used as reinforced cement composites. Materials can improve the toughness of cement and increase its impact resistance. Due to its excellent wear resistance and impact resistance, it is widely used in the machinery manufacturing industry and can be used to make various gears, cams, impellers, rollers, pulleys, bearings, bearing bushes, bushings, cut shafts, gaskets, etc. Seals, elastic couplings, screws and other mechanical parts.

Civilian field

Applications in ropes and cables: Ropes, cables, sails and fishing gear made of this fiber are suitable for marine engineering and are the original use of this fiber. It is widely used in negative-load ropes, heavy-duty ropes, rescue ropes, towing ropes, sailing ropes and fishing lines. The breaking length of a rope made of this fiber under its own weight is 8 times that of a steel rope and 2 times that of aramid. This rope is used as a fixed anchor rope for supertankers, marine operating platforms, lighthouses, etc. It solves the problems of rust encountered in the past using steel cables and corrosion, hydrolysis, ultraviolet degradation, etc. caused by nylon and polyester cables, resulting in reduced strength and breakage of the cables. , the problem of frequent replacement.

Sports equipment and supplies: Sports supplies have been made into helmets, skis, sailboards, fishing rods, rackets and bicycles, gliding boards, ultra-light aircraft parts, etc., and their performance is better than traditional materials.

Used as biomaterials: This fiber-reinforced composite material is used in dental tray materials, medical implants, plastic sutures, etc. It has good biocompatibility and durability, high stability, and will not cause allergies. Has been used clinically. It is also used in medical gloves and other medical measures.