Ultra-high molecular weight polyethylene

UHMWPE has excellent wear resistance, good low-temperature impact resistance, self-lubrication, non-toxicity, water resistance, and chemical resistance. Its heat resistance is better than that of common PE. However, its disadvantages include low heat resistance (heat distortion temperature), poor processability, and inferior outer surface hardness, rigidity, and creep resistance compared to general engineering plastics. Its coefficient of expansion is relatively large. UHMWPE has poor fluidity and extremely high viscosity in the molten state. It is a high-viscosity elastomer with a rubber-like appearance. In the early days, it could only be formed by pressing and sintering methods. Currently, it can also be processed by extrusion, injection molding and blow molding. The mechanical properties of UPE boards are higher than those of common high-density polyethylene. It features outstanding impact resistance, stress crack resistance, high-temperature creep resistance, low friction coefficient, self-lubrication, excellent chemical corrosion resistance, fatigue resistance, noise damping, nuclear radiation resistance, etc. Operating temperature: 100-110℃. It has good cold resistance and can be used at -269℃. The product with a density of 0.935g/cm ³ and a molecular weight of 2 million has a tensile strength at break of 40MPa, an elongation at break of 350%, a flexural elastic modulus of 600MPa, and cannot be broken by the notched impact of a cantilever beam. The wear (MPC method) is 20mm. UPE plates can replace carbon steel, stainless steel, bronze and other materials in the textile, papermaking, food machinery, transportation, medical, coal mining, chemical and other sectors. Such as impact-resistant and wear-resistant parts in the textile industry, such as shuttles, shuttling rods, gears, couplings, sweeping rods, buffer blocks, eccentric blocks, rod shaft sleeves, and swing effects. In the paper industry, it is used to make box covers, wipers, compaction components, joints, sealing shafts of transmission machinery, deflector wheels, filters, etc., which are similar to polyamide and polytetrafluoroethylene. Its wear resistance exceeds that of carbon steel. It is also used to make gears, bearings, bearing shells, star wheels, valves, pumps, guide rails, sealing packing, equipment linings, sliding plates, artificial joints, ropes, etc. Linings of hoppers, silos and chutes used in the transportation industry for powdery materials.

Wear resistance performance

Water absorption characteristics

Low-density characteristic

Ultra-high molecular weight polyethylene (UHMW-PE) is a thermoplastic engineering plastic with a linear structure and excellent comprehensive performance.

The development of ultra-high molecular weight polyethylene has been very rapid. Before the 1980s, the world's average annual growth rate was 8.5%. After entering the 1980s, the growth rate reached as high as 15% to 20%. The average annual growth rate in our country is above 30%. In 1978, the global consumption was 12,000 to 12,500 tons, while by 1990, the global demand was approximately 50,000 tons, of which the United States accounted for 70%. From 2007 to 2009, China gradually became the world's engineering plastics factory, and the development of the ultra-high molecular weight polyethylene industry was particularly rapid. The following is the development history:

The basic theory about ultra-high molecular weight polyethylene fibers was first proposed in the 1930s.

The emergence of gel spinning and plasticized spinning has led to significant technological breakthroughs in ultra-high molecular weight polyethylene. In the 1970s, Capaccio and Ward from the University of Leeds in the UK first successfully developed high-molecular-weight polyethylene fibers with a molecular weight of 100,000. It was successfully developed and put into industrial production in China in 1964. In 1975, the Netherlands invented the Gelspinning method using decanaphthalene as the solvent and successfully prepared UHMWPE fibers. A patent was applied for in 1979. After ten years of diligent research, it was confirmed that the gel spinning method is an effective way to manufacture high-strength polyethylene fibers and has industrialization prospects. In 1983, Japan produced ultra-high molecular weight polyethylene fibers by using the gel extrusion superstretching method with paraffin as the solvent. In China, ultra-high molecular weight polyethylene pipes were listed in the National Key Promotion Plan for scientific and technological Achievements by the Ministry of Science and Technology's Document No. 056 of the Ministry of Science and Technology (2000) in 2001, and they belong to new materials and new products in the chemical industry. The National Development and Reform Commission and the Ministry of Science and Technology have listed ultra-high molecular weight polyethylene pipes as key high-tech industry projects to be prioritized for development at present.

Identification method

Ultra-high molecular weight polyethylene is a kind of high-molecular compound that is difficult to process and has extremely strong wear resistance, self-lubrication, relatively high strength, stable chemical properties and strong anti-aging performance. Therefore, when distinguishing genuine from fake high-molecular polyethylene, it is necessary to pay attention to these characteristics of it. The specific identification methods are as follows:

Weighing rule: The specific gravity of products made of pure ultra-high molecular weight polyethylene is between 0.93 and 0.95, with a relatively low density, allowing them to float on water. If it is not pure polyethylene material, it will sink to the bottom of the water.

2. Temperature measurement: Pure ultra-high molecular weight polyethylene products will not melt or deform at 200 degrees Celsius, but will become soft. If it is not pure ultra-high molecular weight polyethylene material, it will deform at 200 degrees Celsius.

3. Visual inspection method: The surface of genuine ultra-high molecular weight polyethylene is flat, uniform, smooth and the density of the cut surface is very uniform. If it is not pure polyethylene material, the color is dull and the density is uneven.

4. Edge testing method: The flanged end face of pure ultra-high molecular weight polyethylene is round, uniform and smooth. If it is not pure polyethylene material, there will be cracks on the flanged end face, and there will be slag shedding during flanging after heating.

Forming processing

Due to the fact that the viscosity of ultra-high molecular weight polyethylene (UHMW-PE) in the molten state is as high as 108Pa*s and its fluidity is extremely poor, and its melt index is almost zero, it is very difficult to process it by general mechanical processing methods. The processing technology of ultra-high molecular weight polyethylene (UHMW-PE) has developed rapidly. Through the transformation of common processing equipment, UHMW-PE has evolved from the initial press-sintering molding to extrusion, blow molding, injection molding and molding by other special methods.

Pressing and sintering

Pressing sintering is the most primitive processing method for ultra-high molecular weight polyethylene (UHMW-PE). This method has a rather low production efficiency and is prone to oxidation and degradation. To enhance production efficiency, the direct electric heating method can be adopted

(2) The ultra-high-speed fusion processing method uses a bladder-type mixer, with the maximum rotational speed of the blades reaching 150m/s, enabling the material to rise to the processing temperature within just a few seconds.

2. Extrusion molding

Extrusion molding equipment mainly includes plunger extruders, single-screw extruders and twin-screw extruders. Twin-screw extrusion mostly adopts twin-screw extruders rotating in the same direction.

In the 1960s, plunger extruders were mostly used. In the mid-1970s, Japan, the United States, West Germany and other countries successively developed single-screw extrusion processes. Mitsui Petrochemical Corporation of Japan first achieved success in round rod extrusion technology in 1974. At the end of 1994, China developed a special single-screw extruder for Φ45 ultra-high molecular weight polyethylene (UHMW-PE), and achieved the success of an industrial production line for Φ65 single-screw extruded pipes in 1997.

(3) Injection molding

Mitsui Petrochemical Corporation of Japan developed the injection molding process in 1974 and commercialized it in 1976. Later, it also developed the reciprocating screw injection molding technology. In 1985, the Hoechst Company in the United States also achieved the screw injection molding process of ultra-high molecular weight polyethylene (UHMW-PE). In 1983, China modified the domestic XS-ZY-125A injection machine and successfully injected ultra-high molecular weight polyethylene (UHMW-PE) rollers for beer canning production lines and shaft sleeves for water pumps. In 1985, it also successfully injected medical artificial joints, etc.

(4) Blow molding

When processing ultra-high molecular weight polyethylene (UHMW-PE), after the material is extruded from the die, a certain degree of retraction occurs due to elastic recovery, and there is almost no sagging phenomenon. Therefore, it creates favorable conditions for the blow molding of hollow containers, especially large containers such as oil tanks and large barrels. Blow molding of ultra-high molecular weight polyethylene (UHMW-PE) can also lead to high-performance films with balanced strength in the longitudinal and transverse directions, thereby solving the long-standing problem of inconsistent strength in the longitudinal and transverse directions of HDPE films, which is prone to longitudinal damage.

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