Ultra-high molecular weight polyethylene (UHMWPE) fiber, also known as high-strength high-modulus polyethylene fiber, is currently the fiber with the highest specific strength and specific modulus in the world; it is spun from polyethylene with a molecular weight of 1 million to 5 million.
The three major high-performance fibers in the world today are aramid, carbon fiber and ultra-high molecular weight polyethylene (UHMWPE) fiber. At present in China, only a small amount of aramid is produced because of technical issues; carbon fiber is still at the experimental and initial production stage, and its products can only be used in fields such as wear-resistant fillers; since Tongyizhong achieved a breakthrough in key production technology in 1994, multiple industrial production bases for ultra-high molecular weight polyethylene fiber have been established in China.
Performance Characteristics
1. High specific strength and high specific modulus. The specific strength is more than ten times that of steel wire of the same cross-section, and the specific modulus is second only to top-grade carbon fiber.
2. Low fiber density. The density is 0.97-0.98 g/cm3, so the fiber can float on water.
3. Low elongation at break and high work of rupture, with a strong ability to absorb energy, thus giving outstanding impact resistance and cut resistance.
4. Resistance to ultraviolet radiation, protection against neutrons and gamma rays, high specific energy absorption, low dielectric constant and high electromagnetic wave transmittance.
5. Resistance to chemical corrosion and abrasion, with a long flexural life.
Physical Properties:
Density: 0.97-0.98 g/cm3. Lower than the density of water, so it can float on water.
Strength: 2.8-4 N/tex.
Modulus: 91-140 N/tex.
Elongation: 3.5%-3.7%.
Its impact energy absorption is nearly twice that of para-aramid fiber, and it offers good abrasion resistance and a low coefficient of friction, but its melting point under stress is only 145-160 degrees C.
Research and Development Status at Home and Abroad
At present, only three companies abroad can produce ultra-high molecular weight polyethylene fiber on an industrial scale: DSM of the Netherlands, Honeywell of the United States and Toyobo of Japan, with a combined annual output of less than 9,000 tons.
There are certain differences in the application structure of ultra-high molecular weight polyethylene fiber between Europe and the United States on the one hand and Japan on the other. In Europe and the United States it is mainly used for ballistic vests and weaponry, accounting for 60%-70% of the total, followed by ropes and cables at 20%, fishing nets at 5% and protective equipment at 5%; in Japan it is mainly used for ropes and cables, fishing nets and protective products, especially cut-resistant gloves, and its use in the painting process of automobile production has reached one quarter of total demand for ultra-high molecular weight polyethylene fiber.
China began research on ultra-high molecular weight polyethylene fiber in 1985. Donghua University and the Yancheng Institute of Super-Strength Polymer Materials Engineering Technology joined the research effort successively and achieved a series of major theoretical breakthroughs. Enterprises then invested in pilot testing and small-scale industrial production, and after years of unremitting effort the fiber’s performance has now reached an intermediate international level with distinctive features of its own, with some products entering the stage of large-scale production. At present, five domestic producers manufacture ultra-high molecular weight polyethylene fiber, namely Shanghai Research Institute of Chemical Industry, Zhengzhou Antai Protection Technology Co., Ltd., Beijing Tongyizhong Special Fiber Technology Development Co., Ltd., Hunan Zhongtai Special Equipment Co., Ltd., Ningbo Dacheng New Material Co., Ltd. and Shandong Aidi Polymer Materials Co., Ltd., and all have achieved considerable results. In addition, there are Wuxi Fukun Chemical Co., Ltd., Jiujiang Zhongke Xinxing New Materials Co., Ltd., Shanghai Lianle Chemical Technology Co., Ltd. and Anhui Tejiajin Fine Chemical Co., Ltd., among others.
Application Fields
National Defense
Because of the fiber’s good impact resistance and high specific energy absorption, it can be made into protective clothing, helmets and ballistic materials for military use, such as armor protection plates for helicopters, tanks and ships, protective radome covers for radar, missile domes, ballistic vests, stab-resistant clothing and shields, among which ballistic vests are the most notable application. It is lightweight and soft, and its ballistic performance is better than that of aramid, and it has now become the main fiber occupying the U.S. ballistic vest market. In addition, the specific ballistic load value U/p of ultra-high molecular weight polyethylene fiber composite is 10 times that of steel and more than twice that of glass fiber and aramid. Abroad, ballistic and riot helmets made from resin composites reinforced with this fiber have become substitutes for steel helmets and aramid-reinforced composite helmets.
Aviation
In aerospace engineering, because the fiber composite is lightweight, high-strength and has good impact resistance, it is suitable for the wingtip structures of various aircraft, spacecraft structures and float-equipped aircraft. The fiber can also be used for the deceleration parachutes of space shuttle landings and for ropes suspending heavy objects on aircraft, replacing traditional steel wire ropes and synthetic fiber ropes, and its development has been unusually rapid.
Civilian Applications
(1)Applications in ropes and cables:Ropes, cables, sails and fishing gear made from this fiber are suitable for marine engineering, which was the fiber’s original use. They are widely used for ropes, heavy-duty ropes, salvage ropes, tow ropes, sailboat lines and fishing line, among others. A rope made from this fiber has a breaking length under its own weight 8 times that of steel rope and 2 times that of aramid. Such ropes are used as mooring lines for supertankers, offshore operating platforms and lighthouses, solving the problems encountered with steel cables, which rust, and with nylon and polyester cables, where corrosion, hydrolysis and ultraviolet degradation reduce rope strength and cause breakage, requiring frequent replacement.
(2)Sports equipment and supplies:In sporting goods, this fiber has been made into safety helmets, skis, sailboards, fishing rods, rackets and parts for bicycles, hang gliders and ultra-light aircraft, with better performance than traditional materials.
(3)Use as a biomaterial:This fiber-reinforced composite is used for dental tray materials, medical implants and plastic surgery sutures, among other applications. It has good biocompatibility and durability as well as high stability, does not cause allergies, and has been used in clinical applications. It is also used for medical gloves and other medical measures.
(4)In industry, this fiber and its composites can be used for pressure vessels, conveyor belts, filter materials and automotive buffer plates; in construction they can be used for wall and partition structures, and as a reinforcing cement composite it can improve the toughness of cement and enhance its impact resistance.