Preparation of UHMWPE fiber

UHMWPE, also known as high-strength high-modulus polyethylene, is currently one of the world's high-performance materials. Due to its comprehensive excellent properties such as corrosion resistance, wear resistance and low density, it is currently used in military protection materials, military mechanical materials, aerospace equipment and other military fields. The development of high-performance fiber is the foundation of a country's military equipment, and the advanced material can lead to the advanced military technology, which has become an important material foundation for the construction of a powerful modern country, and occupies a decisive position in the field of military materials worldwide.

1.    Properties of UHMWPE fiber 

UHMWPE fiber has excellent comprehensive properties, its relative density is small, can float on water. And UHMWPE fiber is the strongest fiber in the world at present. Compared with steel, UHMWPE fiber is more than ten times stronger than high-quality steel. In addition, UHMWPE fiber also has strong corrosion resistance, chemical resistance, wear resistance and other properties, comprehensive performance, UHMWPE fiber in many important fields in China play an important role.

1.1 Excellent mechanical properties

Compared with other high-performance fibers, UHMWPE fiber density is second only to conventional PE fiber and polypropylene fiber, and it is the optimal fiber material with the smallest density among bulletproof materials. It can reduce the weight of the material and achieve a lightweight effect while ensuring better bulletproof performance.

Compared with other properties, the tensile strength of UHMWPE is only second to that of PBO and polyaryl ester fiber, and it is only 0.1 different from that of polyaryl ester fiber. It can be seen that UHMWPE has excellent tensile strength.

Compared with other fibers, the initial modulus is only second to PBO and carbon fiber, which indicates that the fiber has a relatively good resistance to damage tension and is not prone to deformation. It is a kind of characteristic fiber with ultra-high specific strength and specific modulus, which plays an important role in bulletproof material.

1.2  Electrical insulation performance

UHMWPE fiber reflectance radar wave phenomenon is very few, with high conduction efficiency, enhance the dielectric constant of composite materials. Although the dielectric constant and loss value of polyethylene are the least among other materials, UHMWPE fiber has the performance that traditional polyethylene fiber can't reach, and it has better effect than general materials, so it is the preferred material for radar radome, with high quality and light effect.

1. 3  Weather resistance and wear resistance

UHMWPE fiber has excellent weather resistance and can keep the original high performance unchanged after a long time of illumination and harsh environment. At the same time, UHMWPE fiber has higher wear resistance and bending fatigue resistance than aramid fiber in high performance materials, so the wear resistance of this fiber is better than other high performance fibers. Due to its high wear resistance and easy processing performance, it has a good application prospect in the industrial field.

1. 4  Chemical corrosion resistance

The internal structure of UHMWPE fiber is relatively tight. It is precisely because of the high crystallinity and orientation of the molecular chain inside the fiber that the fiber has a strong chemical inertia. Therefore, under the acid and base state or the high and low temperature state, the fiber can keep its original performance unchanged for a long time, and still adapt to and play its value in the harsh environment.

1. 5  Self-lubricating properties

UHMWPE material compared with other engineering materials, UHMWPE material has very low friction factor, low friction factor makes the fiber itself better self-lubricating performance, it is the best material in plastic materials under the condition of no lubricant, so UHMWPE material is widely used in engineering, with very high use value. UHMWPE fiber is used in the operation of the machine, compared to the traditional steel and brass under the operation of the lubricant is better. Therefore, compared with ordinary materials, UHMWPE fiber not only saves the raw material cost, but also guarantees the excellent performance effect, so it has a higher use value.

2.  Preparation method of UHMWPE fiber

2.1  Gel spinning method

There are many methods to prepare high performance UHMWPE fiber, but due to the reason of solvent itself, the preparation of UHMWPE fiber can not be achieved. Gel spinning is the most ideal method. Gel spinning method is different from general solution spinning or wet spinning, generally using high molecular weight polymers as raw material, made of semi dilute solution as spinning dope, flexible molecule chain solution to tangles in the semi dilute solution, and then spinning, crystallization, high tensile stretch chain, after extraction treatment to times the thermal stretching, which is made with high strength and high modulus fibers. The gel spinning method has the following basic characteristics: (1) ultra-high molecular weight polymer is used as raw material;(2) use semi-dilute solution as spinning stock; (3) hyperthermal stretching was carried out, and the tensile ratio was greater than 30.

2.2  Plasticizing melt spinning method

Melt spinning is made of polymer melt by melt spinning and extruding. Plasticized melt spinning is on the basis of melt spinning, adding an appropriate amount of diluent to the polymer melt for spinning, through the twin screw mixed solvent, and then extruded, soaked in the extraction agent, and then repeated stretching can finally get high strength and high modulus polyethylene fiber.

2.3  High pressure solid state extrusion method

The principle of extrusion forming is that granular solid solvent is added to the extruder, the material barrel containing solid solvent is heated to the melting temperature, so that the solid material is molten, the molten agent is transported to the head of the machine with a fixed shape, and then after cooling and shaping, the final product is solidified. High pressure solid extrusion method is on the basis of extrusion forming high pressure melting, forming solvent, then through the jet hole, and then high tensile, and finally get high molecular weight polyethylene.

2.4  Surface crystallization method

Due to the slow growth rate of fibrous crystal, this method is seldom used in the preparation of UHMWPE fiber.

Research progress of uhmwpe fiber

The idea of making high-strength fibers from ultra-high molecular weight 

polyethylene resins was born in the 1970s. Uhmwpe fiber has low density @ : 0.97 g/cm3). It is the fiber product with the highest specific strength and modulus at present, and it is an indispensable and important strategic material .Properties of uhmwpe fibers are as follows:

Mechanical properties in the process of gelatinized spinning, the quality and orientation of ultra-high molecular weight polyethylene fiber have been greatly improved by multistage super stretching, and the structure of folded chain polyethylene sheet has been transformed into straight chain structure, which greatly improves the strength and modulus of the fiber.

It is two times stronger than high-strength carbon fiber and 14 times stronger than steel.

Chemical medium corrosion resistance because of ultra-high molecular weight polyethylene fiber is a kind of non-polar materials, excluding polar group in molecular chain, contains only c, H, two kinds of elements, the surface under the action of tensile stress will produce a weak interface layer, and fiber surface into chemical inertness, therefore to acid, alkali and chemical reagent has a strong ability to resist corrosion. In addition, because the molecular chain does not contain double bond groups, heat and light aging resistance and other environmental stability is very good.

Ultra-high molecular weight polyethylene (uhmwpe) has the highest impact resistance of any plastic at present. It is 3 or 5 times higher than polycarbonate, which is known for its impact resistance .As uhmwpe fiber has high toughness, high modulus and high fracture energy, it has excellent bulletproof performance.

The water absorption rate of uhmwpe is the smallest in engineering plastics. It has excellent low temperature resistance, and still maintains good impact strength below freezing point. The minimum temperature can reach 1 269 ℃. The surface adsorption of uhmwpe is very weak.

Based on its excellent comprehensive performance, uhmwpe fiber has been widely used in many fields such as national defense, military industry, aerospace and so on. The fiber has good impact resistance and energy absorption, so it can be made into protective materials, helmets and body armor. The bulletproof vest made of uhmwpe fiber has the advantage of softness, and the bulletproof effect is better than that of aramid. In addition, the specific impact load value of ultra-high quality polyethylene fiber composite material is twice that of steel, and twice that of glass fiber and arrayon. Foreign bulletproof and riot helmets made of ultra-high molecular weight polyethylene fiber composites have become substitutes for steel helmets and aramid reinforced composite helmets. During the flight, shanyu fiber composite material has light weight, high strength and good impact resistance, which is suitable for wing tip structures of various aircraft. Uhmwpe could also be used for landing parachutes on space shuttles and for hanging heavy objects on airplanes, replacing traditional steel cables and synthetic fiber ropes.

Ultra high molecular weight polyethylene (uhmwpe) fiber is also favored in some civil fields.A rope made of this fibre breaks eight times as long under its own weight as a steel rope and twice as long as an aramid. Its rope is used for fixed anchor rope of supertanker, offshore operating platform and lighthouse, etc., which solves the problems of corrosion of steel cable and corrosion, hydrolysis and ultraviolet degradation of nylon and polyester cable, which cause the cable strength reduction and fracture and need to be replaced frequently. In terms of sporting goods, ultra-high molecular weight polyethylene fiber composite materials have been made into hard hats, fishing rods, rackets, bicycles, glide boards, etc., whose performance is better than traditional materials. Due to its excellent chemical inertia, uhmwpe can be used as medical devices such as sutures and artificial muscles in the field of biomedical materials. In terms of building materials, uhmwpe staple fiber reinforced cement composites can improve the toughness and impact resistance of cement.