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Ultra-high molecular weight polyethylene (UHMWPE) is a polyethylene with a linear structure and a relative molecular mass of more than 1.5 million. It can be used for a long time at a temperature of -269~80¡æ.
The melting point of ultra-high molecular weight polyethylene is 147¡æ, and the use temperature can be between 80~90¡æ. Its advantages are: excellent friction resistance, lubricity, impact resistance, chemical resistance, and low temperature resistance. Due to its low friction coefficient and self-lubrication, it can be used to prepare artificial joints. It can provide high impact resistance for composite laminates even at low temperatures and is a good raw material for bulletproof vests.
Ultra-high molecular weight polyethylene was first industrialized by Alied Chemical Company in the United States in 1957. Since then, Hoechst Company in Germany, Hereules Company in the United States, Mitsui Petrochemical Company in Japan, etc. have successively invested in industrial production and focused on developing its application. With the expansion of application fields and the continuous improvement of processing technology, the application scope of UHMWPE has continued to expand, and demand has also increased accordingly. According to incomplete statistics, the world consumption in 1978 was 12,000 to 12,500 tons, and increased to about 50,000 tons in 1990, of which the United States accounted for 70%; in 2012, the world demand reached 180,000 tons/year, and it is growing at an annual rate of 3%.
Ultra-high molecular weight polyethylene (UHMW-PE) is a thermoplastic engineering plastic with a linear structure and excellent comprehensive properties.
Its development is very rapid. Before the 1980s, the world's average annual growth rate was 8.5%. After entering the 1980s, the growth rate was as high as 15% to 20%. China's average annual growth rate is above 30%. In 1978, the world consumption was 12,000 to 12,500 tons, and by 1990, the world demand was about 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 ultra-molecular weight polyethylene industry developed very rapidly. The following is the development history:
In the 1930s, the basic theory of ultra-high molecular weight polyethylene fiber was first proposed;
The emergence of gel spinning and plasticized spinning methods made major breakthroughs in the technology of ultra-high molecular weight polyethylene;
In the 1970s, Capaccio and Ward of the University of Leeds in the UK first successfully developed high molecular weight polyethylene fibers with a molecular weight of 100,000;
In 1964, China successfully developed and put it into industrial production;
In 1975, the Netherlands invented the gel spinning method (Gelspinning) using decahydronaphthalene as a solvent, successfully prepared UHMWPE fibers, and applied for a patent in 1979. After ten years of hard research, it was confirmed that the gel spinning method is an effective method for manufacturing high-strength polyethylene fibers and has a promising industrialization prospect; in 1983, Japan adopted the gel extrusion super-stretching method, using paraffin as a solvent to produce ultra-high molecular weight polyethylene fibers; in China, ultra-high molecular weight polyethylene pipes were listed as a national key promotion plan for scientific and technological achievements by the Ministry of Science and Technology in Document No. (2000) 056 in 2001, and are new materials and new products in the chemical industry. The State Planning Commission and the Ministry of Science and Technology listed ultra-high molecular weight polyethylene pipes as a key high-tech industry project with current priority development.
Ultra-high molecular weight polyethylene is a polymer compound that is difficult to process, and has super wear resistance, self-lubrication, high strength, stable chemical properties, and strong anti-aging performance. Therefore, when distinguishing true and false polymer polyethylene, you must pay attention to its characteristics. The specific identification method is as follows:
1. Weighing rule: The specific gravity of products made of pure ultra-high molecular weight polyethylene is between 0.93-0.95, the density is small, and it can float on the water surface. If it is not a 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 a pure ultra-high molecular weight polyethylene material, it will be deformed at 200 degrees Celsius.
3. Visual method: The surface of a real ultra-high molecular weight polyethylene is flat, uniform, smooth, and the cross-sectional density is very uniform. If it is not a pure polyethylene material, the color is dull and the density is uneven.
4. Edge test method: The flanged end face of pure ultra-high molecular weight polyethylene is round, uniform and smooth. If it is not pure polyethylene material, the flanged end face will have cracks, and slag will fall off when the flange is heated.
Since the viscosity of ultra-high molecular weight polyethylene (UHMW-PE) in the molten state is as high as 108Pa*s, its fluidity is extremely poor, and its melt index is almost zero, it is difficult to process it using general mechanical processing methods. The processing technology of ultra-high molecular weight polyethylene (UHMW-PE) has developed rapidly. Through the transformation of ordinary processing equipment, ultra-high molecular weight polyethylene (UHMW-PE) has developed from the initial pressing-sintering molding to extrusion, blow molding, injection molding and other special molding methods.
1. Pressing and sintering
(1) Pressing and sintering is the most primitive processing method for ultra-high molecular weight polyethylene (UHMW-PE). This method has low production efficiency and is prone to oxidation and degradation. In order to improve production efficiency, direct electric heating can be used.
(2) Ultra-high-speed sintering processing method, using a blade mixer, the maximum speed of the blade rotation can reach 150m/s, so that the material can be raised to the processing temperature in just a few seconds.
2. Extrusion molding
Extrusion molding equipment mainly includes plunger extruder, single screw extruder and twin screw extruder. Twin screw extruder mostly uses co-rotating twin screw extruder.
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 technology. Japan's Mitsui Petrochemical Company first achieved success in round rod extrusion technology in 1974. China developed a ¦µ45 type ultra-high molecular weight polyethylene (UHMW-PE) special single screw extruder at the end of 1994, and successfully achieved the ¦µ65 type single screw extrusion pipe industrial production line in 1997.
(3) Injection molding
Mitsui Petrochemical Company of Japan developed the injection molding process in 1974 and commercialized it in 1976. Later, it developed the reciprocating screw injection molding technology. In 1985, Hoechst Company of the United States also realized 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) wheels and shaft sleeves for water pumps for beer canning production lines. In 1985, it 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, it will shrink to a certain extent due to elastic recovery, and almost no sagging will occur, so it creates favorable conditions for the blow molding of hollow containers, especially large containers such as oil tanks and barrels. Ultra-high molecular weight polyethylene (UHMW-PE) blow molding can also produce high-performance films with balanced strength in the longitudinal and transverse directions, thus solving the long-standing problem of HDPE film with inconsistent strength in the longitudinal and transverse directions, which is easy to cause longitudinal damage.
1. Gel spinning
(1) Development process
The preparation of high-strength, high-modulus polyethylene fibers using gel spinning-ultra-stretching technology is a novel spinning method that appeared in the late 1970s. The Dutch DSM company first applied for a patent in 1979, and then Allied Company of the United States, Toyobo-DSM Company jointly established by Japan and the Netherlands, and Mitsui Company of Japan all achieved industrial production. The Chemical Fiber Institute of China Textile University began research on this project in 1985, gradually formed its own technology, and produced high-performance ultra-high molecular weight polyethylene (UHMW-PE) fibers.
(2) Spinning process
The ultra-high molecular weight polyethylene (UHMW-PE) gel spinning process is briefly described as follows: dissolve ultra-high molecular weight polyethylene (UHMW-PE) in an appropriate solvent to make a semi-dilute solution, extrude it through a spinneret, and then quench the spinning solution with air or water to solidify it into gelatin filaments. In the gelatin filaments, almost all the solvent is contained therein, so the untangled state of the ultra-high molecular weight polyethylene (UHMW-PE) macromolecular chain is well maintained, and the decrease in the solution temperature leads to the formation of ultra-high molecular weight polyethylene (UHMW-PE) folded chain lamellae in the gel. In this way, the macromolecular chains can be fully oriented and highly crystallized by super-heat stretching the gelatin filaments, and then the macromolecules in the folded chain are transformed into straight chains, thereby producing high-strength and high-modulus fibers.
(3) Application
Ultra-high molecular weight polyethylene (UHMW-PE) fiber is the third generation of special fiber in the world today. It has a strength of up to 30.8cN/dtex, the highest specific strength among chemical fibers, and has excellent properties such as good wear resistance, impact resistance, corrosion resistance, and light resistance. It can be directly made into ropes, cables, fishing nets and various fabrics: bulletproof vests and clothes, cut-resistant gloves, etc., among which the bulletproof effect of bulletproof vests is better than aramid. Internationally, ultra-high molecular weight polyethylene (UHMW-PE) fibers have been woven into ropes of different deniers, replacing traditional steel cables and synthetic fiber ropes. Ultra-high molecular weight polyethylene (UHMW-PE) fiber composite materials have been used in the military as armored weapon shells, radar protective shell covers, helmets, etc.; in sports equipment, they have been made into bowstrings, sleds, and water skis.
2. Lubricated extrusion (injection)
Lubricated extrusion (injection) molding technology is to form a lubricating layer between the extruded (injected) material and the mold wall, thereby reducing the shear rate difference between each point of the material, reducing the deformation of the product, and at the same time being able to achieve the extrusion (injection) speed of high-viscosity polymers under low temperature and low energy consumption conditions. There are two main methods to produce a lubricating layer: self-lubrication and co-lubrication.
(1) Self-lubricating extrusion (injection)
The self-lubricating extrusion (injection) of ultra-high molecular weight polyethylene (UHMW-PE) is to add an appropriate amount of external lubricant to it to reduce the friction and shear between the polymer molecules and the metal mold wall, improve the uniformity of material flow, demolding effect and extrusion quality. External lubricants mainly include higher fatty acids, compound fats, silicone resins, paraffin and other low molecular weight resins. Before extrusion (injection) processing, the lubricant is first mixed into the material together with other processing aids. During production, the lubricant in the material seeps out to form a lubricating layer, realizing self-lubricating extrusion (injection).
There is a patent report: 70 parts of paraffin oil, 30 parts of ultra-high molecular weight polyethylene (UHMW-PE) and 1 part of oxygen-phase silica (highly dispersed silica gel) are mixed and granulated, and can be smoothly extruded (injected) at a temperature of 190¡ãC.
(2) Co-lubricated extrusion (injection)
There are two situations for the co-lubricated extrusion (injection) of ultra-high molecular weight polyethylene (UHMW-PE). One is to use the gap method to press the lubricant into the mold to form a lubricating layer between the inner surface of the mold cavity and the molten material; the other is to blend it with a low-viscosity resin to make it part of the product.
For example: when producing ultra-high molecular weight polyethylene (UHMW-PE) sheets, SH200 silicone oil is delivered to the mold cavity by a metering pump as a lubricant. The appearance quality of the resulting product is significantly improved, especially due to the small extrusion deformation and increased tensile strength.
Roller forming is a solid-state processing method, that is, high pressure is applied to ultra-high molecular weight polyethylene (UHMW-PE) below its melting point, and particles are effectively fused together through particle deformation. The main equipment is a rotating wheel with a screw groove and a bow-shaped slider with a tongue groove, which is perpendicular to the screw groove. During the processing, the friction between the material and the wall is effectively utilized, and the pressure generated is sufficient to deform the ultra-high molecular weight polyethylene (UHMW-PE) particles. A heating support is installed at the end of the machine base to extrude the material through the die. If this roller pressing device is used in conjunction with an extruder, the processing process can be continuous.
When the ultra-high molecular weight polyethylene (UHMW-PE) resin powder is heated for a short period of 1min to 30min between 140¡æ and 275¡æ, it is found that some physical properties of ultra-high molecular weight polyethylene (UHMW-PE) are unexpectedly greatly improved. Compared with the unheat-treated UHMW-PE products, the products pressed from heat-treated UHMW-PE powder have better physical properties and transparency, and the surface smoothness and low-temperature mechanical properties of the products are greatly improved.
Using radio frequency to process ultra-high molecular weight polyethylene (UHMW-PE) is a new processing method. It is to evenly mix ultra-high molecular weight polyethylene (UHMW-PE) powder and carbon black powder with high dielectric loss, and irradiate it with radio frequency. The heat generated can soften the surface of ultra-high molecular weight polyethylene (UHMW-PE) powder, so that it can be consolidated under a certain pressure. This method can be used to mold thick and large parts in a few minutes, and its processing efficiency is many times higher than that of conventional ultra-high molecular weight polyethylene (UHMW-PE) molding.
Ultra-high molecular weight polyethylene (UHMW-PE) is dissolved in a volatile solvent, extruded continuously, and then subjected to a thermoreversible gel/crystallization process to form a wet gel membrane, and the solvent is evaporated to dry the membrane. Due to the formed skeleton structure, the shrinkage of the gel is limited, and micropores are generated during the drying process. The maximum porosity is achieved by biaxial stretching without destroying the complete porous structure. This material can be used as waterproof, oxygen-permeable fabrics and chemical-resistant clothing, as well as ultrafiltration/microfiltration membranes, composite films and battery separators. Compared with other methods, the porous ultra-high molecular weight polyethylene (UHMW-PE) membrane prepared by this method has the best comprehensive properties such as pore size, strength and thickness.
Compared with other engineering plastics, ultra-high molecular weight polyethylene (UHMW-PE) has the disadvantages of low surface hardness and heat deformation temperature, poor bending strength and creep performance. This is due to the molecular structure and molecular aggregation of ultra-high molecular weight polyethylene (UHMW-PE), which can be improved by filling and cross-linking.
Ultra-high molecular weight polyethylene (UHMW-PE) is filled and modified with glass beads, glass fibers, mica, talc, silicon dioxide, aluminum oxide, molybdenum disulfide, carbon black, etc., which can improve the surface hardness, stiffness, creep, bending strength, and heat deformation temperature. After treatment with a coupling agent, the effect is more obvious. For example, glass beads after filling treatment can increase the heat deformation temperature by 30¡ãC.
Glass beads, glass fibers, mica, talc, etc. can improve hardness, stiffness and temperature resistance; molybdenum disulfide, silicone oil and special wax can reduce the friction factor, thereby further improving self-lubrication; carbon black or metal powder can improve antistatic and electrical conductivity and heat transfer. However, the impact strength decreases slightly after filler modification. If the content is controlled within 40%, ultra-high molecular weight polyethylene (UHMW-PE) still has a fairly high impact strength.
The molecular chain of ultra-high molecular weight polyethylene (UHMW-PE) resin is relatively long, which is easily broken by shear force or degraded by heat. Therefore, lower processing temperature, shorter processing time and reduced shear are very necessary.
In order to solve the processing problem of ultra-high molecular weight polyethylene (UHMW-PE), in addition to special design of ordinary molding machinery, the resin formula can also be improved: blending with other resins or adding flow modifiers so that it can be molded on ordinary extruders and injection molding machines. This is the lubricated extrusion (injection) introduced in 2.2.2.
Blending is the most effective, simplest and most practical way to improve the melt fluidity of ultra-high molecular weight polyethylene (UHMW-PE). This technology is mostly found in patent literature. The second component used in blending mainly refers to low melting point, low viscosity resins, including LDPE, HDPE, PP, polyester, etc. Among them, medium molecular weight PE (molecular weight 400,000-600,000) and low molecular weight PE (molecular weight <400,000) are more commonly used. When the blending system is heated above the melting point, the ultra-high molecular weight polyethylene (UHMW-PE) resin will be suspended in the liquid phase of the second component resin to form an extrudable and injectable suspension material.
(1) Blending with low and medium molecular weight PE
UHMW-PE blending with low molecular weight LDPE (molecular weight 1,000-20,000, with 5,000-12,000 as the best) can significantly improve its molding processability, but at the same time it will reduce mechanical properties such as tensile strength and flexural elasticity. HDPE can also significantly improve the processing fluidity of ultra-high molecular weight polyethylene (UHMW-PE), but it will also cause a decrease in performance such as impact strength and friction resistance. In order to maintain the mechanical properties of ultra-high molecular weight polyethylene (UHMW-PE) blends at a high level, an effective compensation method is to add PE nucleating agents, such as benzoic acid, benzoate, stearate, adipate, etc., which can enhance the PE crystallinity and finely homogenize the spherulite size to effectively prevent the decline of mechanical properties. A patent pointed out that adding a small amount of fine nucleating agent wollastonite (with a particle size range of 5nm to 50nm and a surface area of 100m2/g to 400m2/g) to the ultra-high molecular weight polyethylene (UHMW-PE)/HDPE blend system can well compensate for the reduction in mechanical properties.
(2) Blending morphology
Although the chemical structure of ultra-high molecular weight polyethylene (UHMW-PE) is similar to that of other types of PE, it is difficult for their blends to form a uniform morphology under general melt mixing equipment and conditions. This may be related to the large difference in viscosity between the components. In the ultra-high molecular weight polyethylene (UHMW-PE)/LDPE blend obtained by ordinary single-screw mixing, the two components crystallize separately and cannot form a eutectic. The ultra-high molecular weight polyethylene (UHMW-PE) is basically dispersed in the LDPE matrix in the form of filler. Long-term treatment of the melt and mixing using a twin-roll plasticizer can strengthen the interaction between the two components and further improve the performance, but the eutectic morphology cannot be formed.
Vadhar found that when a two-step blending method is used, that is, the ultra-high molecular weight polyethylene (UHMW-PE) is first melted at high temperature, and then cooled to a lower temperature and LLDPE is added for blending, a blend that forms a eutectic can be obtained. Vadher also obtained an ultra-high molecular weight polyethylene (UHMW-PE)/LLDPE blend that can form a eutectic by using a solution blending method.
(3) Mechanical strength of the blend
For the ultra-high molecular weight polyethylene (UHMW-PE)/PE system without the addition of a nucleating agent, larger spherulites will be formed during the cooling process. There are obvious interfaces between the spherulites, and there are internal stresses caused by different molecular chain arrangements on these interfaces, which will lead to the generation of cracks. Therefore, compared with the matrix polymer, the tensile strength of the blend is often reduced. When impacted by external force, cracks will quickly develop along the spherulite interface and eventually break, thus causing a decrease in impact strength.
Flow improvers promote the disentanglement of long-chain molecules and play a lubricating role between macromolecules, changing the energy transfer between macromolecular chains, making segment displacement easier and improving the fluidity of polymers.
Flow improvers used in ultra-high molecular weight polyethylene (UHMW-PE) mainly refer to aliphatic hydrocarbons and their derivatives. Aliphatic hydrocarbons include: n-alkanes with more than 22 carbon atoms and mixtures of lower alkanes with them as the main component; paraffin wax obtained by petroleum splitting and refining, etc. Its derivatives refer to fatty acids, fatty alcohols, fatty acid esters, fatty aldehydes, fatty ketones, fatty amides, fatty thiols, etc., which have aliphatic hydrocarbon groups at the end and one or more (preferably one or two) carboxyl groups, hydroxyl groups, ester groups, carbonyl groups, aminoformyl groups, thiol groups, etc. inside; fatty acids, fatty alcohols, fatty acid esters, fatty aldehydes, fatty ketones, fatty amides, fatty thiols, etc., with carbon atoms greater than 8 (preferably 12 to 50) and molecular weights of 130 to 2000 (preferably 200 to 800). For example, fatty acids include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, etc.
China has prepared an effective flow agent (MS2), which can significantly improve the flowability of ultra-high molecular weight polyethylene (UHMW-PE) by adding a small amount (0.6% to 0.8%), lowering its melting point by as much as 10¡ãC, and can be injection molded on ordinary injection molding machines with only a slight decrease in tensile strength.
In addition, the modification of ultra-high molecular weight polyethylene (UHMW-PE) with styrene and its derivatives can not only improve the processing performance and make the products easy to extrude, but also maintain the excellent friction resistance and chemical corrosion resistance of ultra-high molecular weight polyethylene (UHMW-PE); 1,1-diphenylacetylene, styrene derivatives, and tetralin can all make ultra-high molecular weight polyethylene (UHMW-PE) obtain excellent processing performance, while making the material have higher impact strength and wear resistance.
Crosslinking is to improve morphological stability, creep resistance and environmental stress cracking. Through crosslinking, the crystallinity of ultra-high molecular weight polyethylene (UHMW-PE) decreases, and the toughness that was hidden is re-appeared. Crosslinking can be divided into chemical crosslinking and radiation crosslinking. Chemical crosslinking is to add appropriate crosslinking agents to ultra-high molecular weight polyethylene (UHMW-PE) and crosslinking occurs during the melting process. Radiation crosslinking is to use electron beams or gamma rays to directly irradiate ultra-high molecular weight polyethylene (UHMW-PE) products to crosslink molecules. The chemical crosslinking of ultra-high molecular weight polyethylene (UHMW-PE) is divided into peroxide crosslinking and coupling agent crosslinking.
The peroxide crosslinking process is divided into three steps: mixing, molding and crosslinking. During mixing, ultra-high molecular weight polyethylene (UHMW-PE) and peroxide are melt-blended. Ultra-high molecular weight polyethylene (UHMW-PE) produces free radicals under the action of peroxide, and the free radicals couple to produce crosslinking. In this step, the temperature should not be too high to prevent the resin from being completely crosslinked. After mixing, a continuously crosslinkable ultra-high molecular weight polyethylene (UHMW-PE) with a very low degree of crosslinking is obtained, which is molded into a product at a higher temperature than mixing and then crosslinked.
After peroxide crosslinking, ultra-high molecular weight polyethylene (UHMW-PE) is different in structure from thermoplastics, thermosetting plastics and vulcanized rubber. It has a body structure but is not completely crosslinked. Therefore, it has the characteristics of all three in terms of performance, that is, it has thermoplasticity and excellent hardness, toughness and stress cracking resistance.
It has been reported abroad that 2,5-dimethyl-2,5-diperoxy tert-butyl hexyne-3 is used as a crosslinking agent, but it is difficult to find in China. Tsinghua University used cheap and readily available diisopropylbenzene peroxide (DCP) as a crosslinking agent for research and found that when the amount of DCP is less than 1%, the impact strength can be increased by 15% to 20% compared with pure ultra-high molecular weight polyethylene (UHMW-PE), especially when the amount of DCP is 0.25%, the impact strength can be increased by 48%. With the increase of DCP dosage, the heat deformation temperature increases, and it can be used for heat-resistant pipes in water heating systems.
Ultra-high molecular weight polyethylene (UHMW-PE) mainly uses two types of silane coupling agents: vinyl siloxane and allyl siloxane, commonly used are vinyl trimethoxy silane and vinyl triethoxy silane. Coupling agents generally rely on peroxides to initiate, and DCP is commonly used. The catalyst generally uses organic tin derivatives.
The first step in the molding process of silane cross-linked ultra-high molecular weight polyethylene (UHMW-PE) is to decompose the peroxide into highly chemically active free radicals by heating. These free radicals capture the hydrogen atoms in the polymer molecules to turn the polymer main chain into active free radicals, and then produce a grafting reaction with silane. The grafted ultra-high molecular weight polyethylene (UHMW-PE) undergoes hydrolysis and condensation under the action of water and silanol condensation catalyst to form cross-linked bonds to obtain silane cross-linked ultra-high molecular weight polyethylene (UHMW-PE).
Under the action of a certain dose of electron rays or gamma rays, part of the main chain or side chain in the molecular structure of ultra-high molecular weight polyethylene (UHMW-PE) may be cut off by the rays, generating a certain number of free radicals. These free radicals combine with each other to form cross-linked chains, transforming the linear molecular structure of ultra-high molecular weight polyethylene (UHMW-PE) into a network macromolecular structure. After a certain dose of irradiation, the physical properties of ultra-high molecular weight polyethylene (UHMW-PE) such as creep, oil immersion and hardness are improved to a certain extent.
Using gamma rays to irradiate artificial ultra-high molecular weight polyethylene (UHMW-PE) joints, cross-linking them while disinfecting them, can enhance the hardness and hydrophilicity of artificial joints, and improve creep resistance, thereby extending their service life.
Studies have shown that combining irradiation with PTFE grafting can also improve the wear and creep behavior of ultra-high molecular weight polyethylene (UHMW-PE). This material has tissue tolerance and is suitable for in vivo transplantation.
Liquid crystal polymer in-situ composite materials refer to blends of thermotropic liquid crystal polymers (TLCP) and thermoplastic resins. During the melt processing, due to the rigidity of the TLCP molecular structure, this blend can spontaneously orient itself in the flow direction under the action of the force field, resulting in obvious shear thinning behavior, and forming a reinforcing phase with an oriented structure in situ in the matrix resin, that is, in-situ fiberization, thereby strengthening the thermoplastic resin and improving processing fluidity. Zhao Anchi and others from Tsinghua University have achieved significant results in improving the processing performance of ultra-high molecular weight polyethylene (UHMW-PE) by using in-situ composite technology.
Ultra-high molecular weight polyethylene (UHMW-PE) modified with TLCP not only improves the fluidity during processing, but also can be easily processed using conventional thermoplastic processing technology and general equipment, and can maintain high tensile strength and impact strength, and also greatly improves wear resistance.
The polymerization filling process in polymer synthesis is a new polymerization method, which is to treat the filler to form an active center on the surface of its particles, and to allow ethylene, propylene and other olefin monomers to polymerize on the surface of the filler particles during the polymerization process to form a resin that tightly wraps the particles, and finally obtain a composite material with unique properties. In addition to the properties of a blended composite material, it also has its own characteristics: first, it does not need to melt the polyethylene resin, and can maintain the shape of the filler to prepare a powdery or fibrous composite material; second, the composite material is not limited by the filler/resin composition ratio, and the filler content can generally be set arbitrarily; in addition, the resulting composite material is a uniform composition, which is not limited by the filler specific gravity and shape.
Compared with hot melt blended materials, the filler particles in the ultra-high molecular weight polyethylene (UHMW-PE) composites prepared by the polymerization filling process are well dispersed, and the interface bonding between the particles and the polymer matrix is also good. This makes the tensile strength and impact strength of the composite material not much different from those of ul
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