At present, the commonly used bulletproof composite materials in the market can be divided into aromatic polyamide (aramid) fiber composite materials and ultra-high molecular weight polyethylene (UHMWPE) fiber composite materials according to the type of material. The specific strength and specific modulus of aramid fiber are 10 times higher than that of steel, while the specific strength of ultr
The Reason Why UHMWPE is Widely Used in Military Defense
At present, the commonly used bulletproof composite materials in the market can be divided into aromatic polyamide (aramid) fiber composite materials and ultra-high molecular weight polyethylene (UHMWPE) fiber composite materials according to the type of material. The specific strength and specific modulus of aramid fiber are 10 times higher than that of steel, while the specific strength of ultra-high molecular weight polyethylene fiber is about 1.5 times higher than that of aramid fiber. Both can be widely used in the fields of national defense equipment and special civilian products. UHMWPE composite materials, due to their good impact toughness and absorption of energy compared to impact, are currently the highest among composite materials and are widely used in bulletproof vests, bulletproof inserts, and armor. According to statistics, 70% of ultra-high molecular weight polyethylene fibers in the United States are used in fields such as bulletproof vests, helmets, armor, and aerospace. The development of high-performance fibers has become a reflection of a country's comprehensive strength and an important material foundation for building a modern strong country.
UHMWPE: Ultra high Molecular Weight Polyethylene is a linear structure of PE (polyethylene), which is a thermoplastic engineering plastic with excellent comprehensive properties. Unbranched linear polyethylene with a molecular weight exceeding 1.5 million, commonly ranging from 1 million to 6 million, can even reach up to 10 million, and has a chain length and molecular weight 10-20 times and 20-30 times that of high-density polyethylene (HDPE), respectively.
UHMWPE has unparalleled performance advantages and is a new type of thermoplastic engineering plastic. Currently, there is no single polymer material that combines so many excellent properties and can become the "king of plastics".
UHMWPE has advantages such as low friction coefficient, low wear, excellent chemical resistance, impact resistance, pressure resistance, frost resistance, insulation, self-lubricating, scaling resistance, stress cracking resistance, and renewability. Among them, wear resistance, low temperature resistance, corrosion resistance, self lubrication, and impact resistance are the highest among all plastics.
(1) Low density and good flexibility: UHMWPE has a density 56% lower than PTFE, 33% lower than POM, and 30% lower than PBTP, which is relatively low compared to other engineering plastics. And ultra-high molecular weight polyethylene pipes have a low density, only 1/8 of steel pipes. Easy to use, able to bend and lay, with good flexibility, it can be used easily and quickly.
(2) Wear resistance: Wear resistance can be matched with polytetrafluoroethylene (PTFE) as a super wear-resistant thermoplastic resin. Compared with other engineering plastics, the sand abrasion index of UHMWPE is only 1/5 of PA66, and 1/10 of HEPE and PVC. The wear resistance of UHMWPE is directly proportional to its molecular weight, and the higher the molecular weight, the better its wear resistance. The wear resistance of ultra-high molecular weight polyethylene pipes is 4-7 times higher than that of steel pipes and stainless steel pipes when conveying various slurries, and about 10 times higher than that of polyvinyl chloride pipes and polyethylene pipes, greatly improving the service life of pipelines.
(3) Self lubrication: UHMWPE has an extremely low coefficient of friction (0.05~0.11), therefore it has excellent self-lubricating properties. Compared with other engineering plastics, the dynamic friction coefficient of UHMWPE is 1/2 of PA66 and POM under water lubrication conditions, second only to polytetrafluoroethylene (PTFE), which has the best self-lubricating properties among plastics, under no lubrication conditions. Therefore, in the field of tribology, UHMWPE is known as a friction material with very ideal cost/performance.
(4) Impact resistance: Compared with other engineering plastics, the impact strength of UHMWPE is about twice that of impact resistant PC, 5 times that of ABS, more than 10 times that of POM and PBTP, 10 times that of nylon 66, 20 times that of polyvinyl chloride, and 4 times that of polyethylene. The impact resistance is so high that it is difficult to fracture using the usual impact testing method. Its impact strength increases with the increase of molecular weight, reaching its maximum value at a molecular weight of 1.5 million, and then gradually decreases as the molecular weight continues to increase. Excellent impact strength can also be maintained in liquid nitrogen (-195 ℃), a characteristic that other plastics do not have. UHMWPE has excellent impact energy absorption, with the highest impact energy absorption value among all plastics, resulting in excellent noise damping performance and excellent sound reduction effect.
(5) Chemical corrosion resistance: Based on ultra-high molecular weight polyethylene, it is a saturated molecular group structure with extremely high chemical stability. In addition to strong oxidizing acids, it can withstand various corrosive media (acid, alkali, salt) and organic media (excluding solvents) within a certain temperature and concentration range. Immersion in 80 organic solvents at 20 ℃ and 80 ℃ for 30 days resulted in no abnormal appearance and almost no change in other physical properties.
(6) Tensile strength: UHMWPE has incomparable ultra-high tensile strength due to its essential structural characteristics towards tensile orientation. Therefore, ultra-high elastic modulus and strength fibers can be obtained by gel spinning, with tensile strength up to 3~3.5GPa and tensile elastic modulus up to 100~125GPa; The fiber specific strength is the highest among all commercialized fibers to date, 4 times greater than carbon fiber, 10 times greater than steel wire, and 50% greater than aramid fiber.
(7) Weather resistance and aging resistance: on the one hand, because there are few unsaturated molecular chains in ultrahigh pipeline molecular chains, the molecular weight is large; On the other hand, the service life of UHMWPE pipeline is much longer than that of ordinary polyethylene pipeline due to the addition of anti-aging agent. The low-temperature embrittlement temperature of ultra-high molecular weight polyethylene pipes is extremely low, and they can be safely used within -60 ℃ to 40 ℃. There is no need to take special protective measures during winter construction, and pipe embrittlement will not occur. UHMWPE has excellent low-temperature resistance and ductility even at liquid helium temperatures (-269 ℃), making it suitable for use as a low-temperature resistant component in the nuclear industry.
(8) Low water absorption: UHMWPE has a very low water absorption rate; Generally less than 0.01%, only 1% of PA66, so drying treatment is generally not necessary before forming and processing.
(9) Non stick: The surface adsorption capacity of UHMWPE is very weak, and its anti stick ability is second only to PTFE, which has the best non stick ability among plastics. Therefore, the surface of the product is not easy to stick with other materials. Ultra high molecular weight polyethylene has self-lubricating and non adhesive properties, no scaling, low friction coefficient, corrosion resistance, wear resistance, and therefore low flow resistance, which can maintain flow rate and flow rate for a long time without decreasing.
(10) Flame retardancy: Used in special industries for fire-resistant environments, modified with flame retardants, manufactured with special processing techniques, overcoming the inherent flammability of ultra-high molecular weight polyethylene and possessing flame retardant properties.
(11) Hygienic and non-toxic: UHMWPE is hygienic and non-toxic, fully compliant with the standards of the Japanese Health Association, and recognized by the US Food and Drug Administration and the US Department of Agriculture for use in contact with food and drugs.
Due to its numerous excellent properties, ultra-high molecular weight polyethylene fibers have shown great advantages in the high-performance fiber market, including mooring ropes in offshore oil fields and high-performance lightweight composite materials. They play a crucial role in modern warfare, aviation, aerospace, maritime defense equipment, and other fields.
In terms of national defense and military equipment, due to its good impact resistance and high energy absorption, this fiber can be used in military applications to make protective clothing, helmets, and bulletproof materials, such as armor plates for helicopters, tanks, and ships, radar protective casings, missile covers, bulletproof vests, stab proof vests, shields, parachutes, etc. Among them, the application of bulletproof vests is the most eye-catching. It has the advantages of softness and better bulletproof effect than aramid, and has now become the main fiber occupying the US 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. Bulletproof and riot helmets made of resin composite materials reinforced with this fiber have become substitutes for steel helmets and aramid reinforced composite helmets abroad.
In aerospace engineering, due to its lightweight, high strength, and good impact resistance, this fiber composite material is suitable for various aircraft wing tip structures, spacecraft structures, and buoy aircraft. This fiber can also be used as a deceleration parachute for space shuttle landings and as a rope for hanging heavy objects on airplanes, replacing traditional steel and synthetic fiber ropes. Its development speed is exceptionally fast.
In the civilian field, ropes, cables, sails, and fishing gear made of this fiber are suitable for marine engineering. The fracture length under its own weight is 8 times that of steel ropes and 2 times that of aramid. This rope is used as a fixed anchor rope for super oil tankers, ocean operation platforms, lighthouses, etc. It solves the problems of corrosion, hydrolysis, and UV degradation caused by steel cables and nylon and polyester cables in the past, which lead to a decrease in cable strength and breakage, and require frequent replacement.
In industrial applications, this fiber and its composite materials can be used as pressure vessels, conveyor belts, filtering materials, automotive buffer plates, etc; In terms of architecture, it can be used as a wall, partition structure, etc. Using it as a reinforced cement composite material can improve the toughness of cement and enhance its impact resistance. Due to its excellent wear resistance and impact resistance, UHMWPE is widely used in the mechanical manufacturing industry. It can produce various mechanical components such as gears, camshafts, impellers, rollers, pulleys, bearings, bushings, bushings, shafts, gaskets, sealing gaskets, elastic couplings, screws, etc.