There are three types of production methods: high-pressure (synthesized from ethylene by a high-pressure process with a synthesis pressure of 100-300 MPa, a temperature of 150-275°C, and 0.05%-0.1% oxygen or peroxide as a catalyst; the synthesis occurs either intermittently in stirred tanks or continuously in tubular reactors), low-pressure, and medium-pressure. The high-pressure method is used to produce low-density polyethylene, which was developed early and has so far accounted for about 2/3 of the total polyethylene production, but with the development of production technology and catalysts, its growth has lagged considerably behind that of the low-pressure method. As far as the low pressure method is concerned, there are slurry, solution and vapor phase methods. Slurry method is mainly used for the production of high-density polyethylene, while the solution method and gas-phase method can not only produce high-density polyethylene, but also through the addition of *** polymer monomer, the production of medium- and low-density polyethylene ethylene, also known as linear low-density polyethylene. In recent years, a variety of low-pressure process development. Medium-pressure method only Phillips is still used today, the production of mainly high-density polyethylene.
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Polyethylene characteristics
Polyethylene odorless, non-toxic, feel like wax, has excellent low temperature resistance (minimum use temperature up to -70 ~ -100 ℃), good chemical stability, can resist most of the acid and alkali erosion (does not tolerate oxidizing nature of the acid), insoluble in general solvents at room temperature, water absorption is small, but because of its linear molecules can be Slowly dissolved in some organic solvents, and does not dissolve, excellent electrical insulation properties; but polyethylene for the environmental stress (chemical and mechanical effects) is very sensitive, poor heat aging resistance.
The properties of polyethylene vary from species to species, depending mainly on the molecular structure and density.
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Types
(1) LDPE: low-density polyethylene, high-pressure polyethylene
(2) LLDPE: linear low-density polyethylene
(3) MDPE: medium-density polyethylene, bimodal resin
(4) HDPE: high-density polyethylene, low-pressure polyethylene
(5) UHMWPE: ultra-high molecular weight polyethylene
(6) modified polyethylene: CPE, crosslinked polyethylene (PEX)
(7) ethylene **** polymer: ethylene-propylene **** polymer (plastics), EVA, ethylene-butylene **** polymer, ethylene - other olefins (such as octene POE, cycloalkenecarbonyl) of **** polymer, ethylene - unsaturated ester ****polymers (EAA, EMAA, EEA, EMA, EMMA, EMAH)
Linear polyethylene with a molecular weight of 3,000,000-6,000,000 is known as Ultra High Molecular Weight Polyethylene (UHMWPE). UHMWPE is so strong that it can be used to make bulletproof vests.
The main methods: polyethylene liquid-phase method (also divided into solution method and slurry method) and gas-phase method (the type of phase of the material in the reactor). In China, the slurry method with Ziegler catalyst is mainly used.
Conditions and process description: purity of more than 99% of the ethylene in the presence of catalyst titanium tetrachloride and dichlorodiethylaluminum, in the pressure of 0.1-0.5MPa and the temperature of 65-75 ℃ gasoline polymerization to get the slurry of HDPE. The residual catalyst is destroyed by alcoholysis, neutralized, washed, and the gasoline and unpolymerized ethylene are recovered, and the product is obtained by drying and granulation.
Chemical name: polyethylene
English name: Polyethylene (PE for short)
Specific gravity: 0.94-0.96 g/cm3 Molding shrinkage: 1.5-3.6% Molding temperature: 140-220 ℃
Characteristics: corrosion resistance, excellent electrical insulation (especially high frequency insulation), can be Chlorination, chemical cross-linking, irradiation cross-linking modification, available glass fiber reinforced. Low-pressure polyethylene melting point, rigidity, hardness and strength, small water absorption, good electrical properties and radiation resistance; high-pressure polyethylene softness, elongation, impact strength and permeability is better; ultra-high molecular weight polyethylene high impact strength, fatigue resistance, wear resistance. Low-pressure polyethylene is suitable for the production of corrosion-resistant parts and insulating parts; high-pressure polyethylene is suitable for the production of film, etc.; ultra-high molecular weight polyethylene is suitable for the production of vibration damping, wear-resistant and transmission parts.
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Molding characteristics
1. Crystalline material, moisture absorption is small, do not need to be sufficiently dry, excellent fluidity and pressure-sensitive fluidity, molding is suitable for high-pressure injection, material temperature uniformity, fast filling speed, full pressure. It is not suitable to use direct gating to prevent uneven shrinkage and increased internal stress. Pay attention to choose the location of the gate to prevent shrinkage and deformation.
2. Shrinkage range and shrinkage value is large, the direction is obvious, easy to deformation warping. Cooling rate should be slow, the mold set up cold material cavity, and cooling system.
3. The heating time should not be too long, otherwise decomposition will occur.
4. Soft plastic parts have shallow side grooves, can be forced out of the mold.
5. Melt rupture may occur, should not be in contact with organic solvents to prevent cracking
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Polyethylene products
Product categories
Polyethylene (PE) is a general-purpose synthetic resins in the production of the largest varieties, including mainly low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), High-density polyethylene (HDPE) and some products with special properties.
Polyethylene physical properties
Polyethylene is a white waxy translucent material, flexible and tough, lighter than water, non-toxic, with superior dielectric properties. It is easy to burn and continues to burn after leaving fire. Water permeability is low, while the organic vapor permeability is large. The transparency of polyethylene decreases with the increase of crystallinity. Under a certain degree of crystallinity, the transparency improves with the increase of molecular weight. High-density polyethylene melting point range of 132-135oC, low-density polyethylene melting point is lower (112oC) and wide range.
It is insoluble in any known solvent at room temperature, and a small amount can be dissolved in solvents such as toluene, pentyl acetate polyethylene ester, trichloroethylene
Polyethylene Chemical Properties
Polyethylene has excellent chemical stability, and is resistant to hydrochloric acid, hydrofluoric acid, phosphoric acid, formic acid, amines, sodium hydroxide, potassium hydroxide and other chemicals at room temperature, and nitric acid and sulfuric acid are very sensitive to polyethylene. Nitric acid and sulfuric acid have strong destructive effect on polyethylene. Polyethylene is easy to photo-oxidation, thermal oxidation, ozone decomposition, easy to degrade under the action of ultraviolet rays, carbon black has excellent light shielding effect on polyethylene. Crosslinking, chain breaking, formation of unsaturated groups and other reflections can occur after radiation.
All kinds of polyethylene product use
High-pressure polyethylene: more than half of it is used for film products, followed by pipes, injection molding products, wire wrapping layer, etc.
Medium-low, low-pressure polyethylene: injection molding products and hollow products are mainly used.
Ultra-high-pressure polyethylene: due to the excellent comprehensive performance of ultra-high polymer polyethylene, it can be used as engineering plastics.
Melting point 140 degrees Celsius
Enthalpy of melting 292.88J/g
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Different densities of polyethylene
Overview
LDPE is the acronym for low-density polyethylene, i.e., low-density high-pressure polyethylene
HDPE is the acronym for high-density polyethylene, i.e., high-density low-pressure polyethylene.
The density of the two are different, the general density is greater than 0.94 for the HDPE, less than 0.925 for the LDPE, in between for the MDPE (medium density polyethylene).
LDPE (low-density high-pressure polyethylene): Sensory identification: soft to the touch: white and transparent, but the general transparency, combustion identification: burning flame on the yellow and blue; burning smoke, paraffin wax odor, melt drops, easy to draw
HDPE (high-density polyethylene): HDPE is a high degree of crystallinity, non-polar thermoplastic resin. The appearance of raw HDPE is milky white, with some degree of translucency in the micro-thin section.PE has excellent resistance to most household and industrial chemicals. Some types of chemicals are chemically corrosive, such as corrosive oxidizers (concentrated nitric acid), aromatic hydrocarbons (xylene) and halogenated hydrocarbons (carbon tetrachloride). The polymer is non-hygroscopic and has good water and vapor resistance for packaging applications.HDPE has very good electrical properties, particularly high dielectric strength, making it well suited for wire and cable. The medium to high molecular weight grades have excellent impact resistance at room temperature and even at low temperatures of -40 degrees Celsius.
Low-density polyethylene (LDPE)
It is usually produced by the high-pressure method (147.17-196.2MPa), so it is also called high-pressure polyethylene. Due to the high pressure method of production of polyethylene molecular chain contains more long and short branched chain (every 1000 carbon chain atoms contained in the average number of branched chain 21), so the degree of crystallinity is lower (45% -65%), density is smaller (0.910-0.925), lightweight, flexible, low-temperature resistance, impact resistance is better.LDPE is widely used in the production of film, tubing (soft), cable insulation and sheathing, Artificial leather and so on.
High-density polyethylene (HDPE)
Mainly low-pressure production, so it is also known as low-pressure polyethylene. HDPE molecule with fewer branched chains, high degree of crystallinity (85% -90%), high density (0.941-0.965), with a high operating temperature, hardness, mechanical strength and chemical resistance is better. Polyethylene is suitable for hollow blow molding, injection molding and extrusion of a variety of products (hard), such as a variety of containers, nets, packing tape, and can be used as a cable cladding, tubing, profiles, sheets and so on.
Polyethylene resin classification and properties
Types of polyethylene:
(1) LDPE: low-density polyethylene (also known as high-pressure polyethylene)
(2) LLDPE: Linear Low Density Polyethylene
(3) MDPE: Medium Density Polyethylene
(4) HDPE: High-Density Polyethylene (also known as low-pressure polyethylene)
(5) UHMWPE: ultra-high molecular weight polyethylene
(6) Modified polyethylene: chlorinated polyethylene (CPE), crosslinked polyethylene (PEX)
(7) Ethylene ****polymer: ethylene-propylene***polymer (plastics), EVA, ethylene-butene ****polymer, ethylene-other olefins (such as octene POE EVA, ethylene-butylene*** polymers, ethylene-other olefins (e.g. octene POE, cyclic olefins) **** polymers, ethylene-unsaturated ester **** polymers (EAA, EMAA, EEA, EMA, EMMA, EMAH). Polyethylene with a molecular weight of 3-6 million is called ultra-high molecular weight polyethylene (UHMWPE). UHMWPE is so strong that it can be used to make bulletproof vests.
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LDPE resin
Properties: tasteless, odorless, non-toxic, non-toxic, non-glossy surface, milky white waxy particles, density of about 0.920g/cm3, melting point of 130 ℃ ~ 145 ℃. Insoluble in water, slightly soluble in hydrocarbons, toluene and so on. It is resistant to the erosion of most acids and alkalis, with small water absorption, and can still maintain softness at low temperature, with high electric insulation.
Production process: there are mainly two kinds of high-pressure tube method and kettle method. From the current state of development, in order to reduce the reaction temperature and pressure, the tube method process is generally used in the low-temperature, high-activity initiator initiated polymerization system, high purity ethylene as the main raw material, propylene/propane, etc. for the density adjusting agent, the use of high-activity initiator in the polymerization reaction at about 200 ° C ~ 330 ° C, 150-300MPa conditions. The molten polymer initiated polymerization in the reactor must be cooled and separated at high, medium and low pressures. The high pressure circulating gas is cooled and separated and sent to the inlet of the ultra-high pressure (300MPa) compressor, the medium pressure circulating gas is cooled and separated and sent to the inlet of the high pressure (30MPa) compressor, and the low pressure circulating gas is cooled and separated and sent to the low pressure (0.5MPa) compressor for recycling. The molten polyethylene is separated from the high pressure and low pressure and then sent to the granulator for cutting granules in water. When granulating, the enterprise can add suitable additives according to different applications and the granules are packed and shipped out.
Use: injection molding, extrusion, blow molding and other processing methods. Mainly used as agricultural film, industrial packaging film, pharmaceutical and food packaging film, machinery parts, daily necessities, construction materials, wire, cable insulation, coating and synthetic paper.
Mechanical properties
Polyethylene mechanical properties in general, low tensile strength, creep resistance is not good, good impact resistance. Impact strength LDPE>LLDPE>HDPE, other mechanical properties LDPE<LLDPE<HDPE. mainly affected by the density, crystallinity and relative molecular mass, with the improvement of these indicators, its mechanical properties increase. Environmental stress cracking resistance is not good, but improves when the relative molecular mass increases. Good puncture resistance, of which LLDPE is the best.
Thermal Properties
Polyethylene's heat resistance is not high, and improves as relative molecular mass and crystallinity increase. Low temperature resistance is good, brittle temperature generally up to -50 ℃ below; and with the increase in relative molecular mass, the lowest up to -140 ℃. The coefficient of linear expansion of polyethylene is large, up to (20 ~ 24) × 10-5 / K. Thermal conductivity is high.
Electrical Properties
Because polyethylene has no polarity, so it has excellent electrical properties with low dielectric loss and high dielectric strength, i.e., it can be used as FM insulating material, corona-resistant plastics, and high-voltage insulating material.
Environmental properties
Polyethylene belongs to the alkane inert polymer, has good chemical stability. It is resistant to corrosion of aqueous solutions of acids, alkalis and salts at room temperature, but is not resistant to strong oxidizing agents such as fuming sulfuric acid, concentrated nitric acid and chromic acid. Polyethylene is insoluble in general solvents below 60 ℃, but with aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons and other long-term contact will be dissolved or cracked. After the temperature exceeds 60℃, it can be dissolved in a small amount in toluene, amyl acetate, trichloroethylene, turpentine, mineral oil
and paraffin; the temperature is higher than 100℃, it can be dissolved in tetrahydronaphthalene.
Because the polyethylene molecule contains a small number of double bonds and ether bonds, its weather resistance is not good, sun, rain will lead to
aging, need to add antioxidants and light stabilizers to improve.
Processing characteristics
Because of the good fluidity of LDPE, HDPE, processing temperature is low, the viscosity of the size of the moderate decomposition temperature is low, the high temperature of 300 ° C in the inert gas does not decompose, so it is a good processing performance of the plastic. However, the viscosity of LLDPE is slightly higher, need to increase the motor power by 20% to 30%; easy to melt rupture, need to increase the gap between the mouth mold and add processing aids; processing temperature is slightly higher, up to 200 to 215 ℃. Polyethylene's water absorption rate is low, before processing does not
need drying treatment.
Polyethylene melt belongs to the non-Newtonian fluid, viscosity fluctuations with the temperature change is small, and the shear rate of the increase in the decline of fast, and a linear relationship, which is the slowest decline in LLDPE.
Polyethylene products in the cooling process is easy to crystallize, therefore, in the process should pay attention to the mold temperature. In order to control the crystallinity of the products, so that they have different properties. Polyethylene has a large molding shrinkage, which must be considered when designing the mold.
Polyethylene melt flow rate and the relationship between the type of product is shown in the table below
Polyethylene melt flow rate and the relationship between the type of product
Application Melt flow rate, g/10min
LDPE LLDPE HDPE
Blow molded film
Repackaging film
Extrusion Flat Film
Monofilament, Flat Filament
Pipe, Profile
Hollow Blow Molded Containers
Cable Insulation
Injection Molded Products
Coating
Rotational Molding 0.3 ~ 8.0
0.1~1.0
1.4 ~ 2.5
-
0.1 ~5.0
0.3 ~0.5
0.2 ~0.4
1.5 ~50
20 ~200
0.75 ~20 0.3 ~3.3
0.1 ~1.6
2.5 ~4.0
1.0 ~2.0
0.2 ~2.0
0.3 ~1.0
0.4 ~1.0
2.3 ~50
3.3 ~11
1.0 ~25 0.5 ~8.0
3.0 ~6.
-
0.25 ~1.2
0.1 ~5.0
0.2 ~1.5
0.5 ~8.0
2.0 ~20
5.0 ~10
3.0 ~20
Polyethylene Uses
Polyethylene Uses
Polyethylene Uses
Polyethylene Uses
Polyethylene Uses
Polyethylene Uses
Polyethylene Uses Uses Percentage of resin Products
Film products 50% of LDPE
10% of HDPE
70% of LLDPE Used for food, daily necessities, vegetables, shrinkage, self-adhesive, garbage, and other lightweight packaging film, mulch film, trellis film, preservation film and so on.
Heavy packaging film, tear film, undershirt bags and so on.
Packaging film, garbage bag, fresh bag, ultra-thin ground film, etc.
Injection molded products 30% of HDPE
10% of LDPE
10% of LLDPE Daily necessities such as: pots, tubs, baskets, boxes, etc., around the box, corrugated boxes, thermos shells, cups, tables, toys and so on.
Hollow products HDPE-based barrels for food oil, alcohol, gasoline and chemical reagents, toys
Tubular products HDPE-based tubes for water supply, gas transmission, irrigation, threading, suction pipes, refills, and tubes used in cosmetics, medicines, shoe polish, toothpaste and so on.
Filament products HDPE for round filaments
HDPE and LLDPE for flat filaments Fishing nets, cables, industrial filters, civilian screens and so on.
Textile bags, cloth, tear film.
Cable products LDPE-based cable insulation and protection materials
Other products HDPE, LLDPE
LDPE Packing tape
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Production methods
Divided into three kinds of high-pressure, low-pressure, medium-pressure method. High-pressure method is used to produce low-density polyethylene, which was developed early, and the polyethylene produced by this method has so far accounted for about 2/3 of the total production of polyethylene, but with the development of production technology and catalysts, its growth rate has lagged behind that of the low-pressure method considerably. As far as the low pressure method is concerned, there are slurry, solution and vapor phase methods. The slurry method is mainly used for the production of high-density polyethylene, while the solution method and gas-phase method can not only produce high-density polyethylene, but also through the addition of *** polymerization monomer, the production of medium and low-density polyethylene, also known as linear low-density polyethylene. In recent years, a variety of low-pressure method process is developing rapidly. Medium-pressure method only Phillips is still used today, the production of mainly high-density polyethylene.
High-pressure method The use of oxygen or peroxide as an initiator, so that the polymerization of ethylene for low-density polyethylene method. Ethylene after two-stage compression into the reactor (Figure 3), under the pressure of 100-300MPa, temperature 200-300 ℃ and initiator polymerization for polyethylene, the reactants are separated by decompression, so that the unreacted ethylene recycling recycling, molten polyethylene in the addition of plastics additives extrusion pelleting. (See color chart)
The polymerization reactors used are tube reactor (tube length up to 2000m) and kettle reactor. Tubular process of one-way conversion rate of 20% to 34%, the annual production capacity of a single line of 100kt. kettle process of one-way conversion rate of 20% to 25%, the annual production capacity of a single line of 180kt.
Low-pressure method of slurry, solution and gas-phase method of the three kinds of, in addition to the solution method, the polymerization pressure of less than 2MPa. The general steps are catalyst preparation, ethylene polymerization, polymer separation and granulation.
①Slurry method The polyethylene generated is insoluble in solvent and slurry. Slurry method of polymerization conditions are mild, easy to operate, commonly used alkyl aluminum as an activator, hydrogen as molecular weight regulator, more kettle reactor. Polymer slurry from the polymerization kettle out of the flash kettle, gas-liquid separator to the powder dryer, and then go to granulation (Figure 4). The production process also includes steps such as solvent recovery and solvent refining. Products with different molecular weight distributions can be obtained by using different combinations of polymerization kettles in series or parallel.
② Solution method Polymerization is carried out in the solvent, but both ethylene and polyethylene are dissolved in the solvent, the reaction system is a homogeneous solution. Reaction temperature (≥ 140 ℃), pressure (4 ~ 5MPa) higher. Characterized by short polymerization time, high production intensity, can produce both high, medium and low three densities of polyethylene, can better control the nature of the product; but the solution method of polymer molecular weight is low, narrow molecular weight distribution, low solids content.
3 gas-phase method Ethylene polymerization in the gaseous state, generally using a fluidized bed reactor. The catalyst has two kinds of chromium and titanium systems, from the storage tank quantitatively added to the bed, with high-speed ethylene circulation to maintain the bed fluidization, and exclude the heat of polymerization reaction. The generated polyethylene is discharged from the bottom of the reactor (Figure 5). The reactor pressure is about 2 MPa and the temperature is 85 to 100°C. Gas-phase method is the most important method of production line type low-density polyethylene Polyethylene, gas-phase method eliminates the solvent recovery and polymer drying and other processes, and than the solution method to save investment of 15% and operating costs of 10%. For the traditional high-pressure method of 30% of the investment, operating costs of 1 / 6. Therefore, the rapid development. But the gas phase method in product quality and variety of products to be further improved.
Medium-pressure method Using chromium catalyst loaded on silica gel, in the ring tube reactor, the polymerization of ethylene under medium pressure, the production of high-density polyethylene.
Processing and Application It can be processed by blow molding, extrusion, injection molding, etc. It is widely used in the manufacture of films, hollow products, fibers and daily miscellaneous products. In actual production, in order to improve the stability of polyethylene to ultraviolet light and oxidation, improve processing and use of performance, need to add a small amount of plastic additives. Commonly used ultraviolet absorber for o-hydroxy benzophenone or its alkoxy derivatives, etc., carbon black is an excellent ultraviolet shielding agent. In addition, also add antioxidants, lubricants, coloring agents, etc., so that the polyethylene application range is more expanded.
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Polyethylene resin production methods and processes
Polyethylene production methods: polyethylene can be divided into high-pressure, medium-pressure, low-pressure method according to polymerization pressure; according to the medium can be divided into slurry method, solution method, gas-phase method.
The main production process: At present, the world has a lot of companies with polyethylene technology, there are 7 companies with LDPE technology, 10 companies with LLDPE and full density technology, and 12 companies with HDPE technology. From the point of view of technological development, LDPE produced by high pressure method is the most technologically mature method in the production of PE resin, and both kettle method and pipe method process technology have matured, and at present, these two kinds of production process technology coexist at the same time. Foreign companies generally use low-temperature high-activity catalyst initiated polymerization system, which can reduce the reaction temperature and pressure.
High-pressure method to produce LDPE will be large-scale, tube direction. The low-pressure method of producing HDPE and LLDPE, mainly using titanium and complex catalysts, Europe and Japan mostly use titanium catalysts, while the United States mostly use complex catalysts.
Currently the world's main application of polyethylene production technology *** with 11 kinds, China's PE production process has 8 kinds.
(1) High-pressure tubular and kettle reaction process
(2) Mitsui Chemical low-pressure sludge CX process
(3) BP gas-phase method Innovene production process
(4) Chevron-Philippines double ring tube reactor LPE process
(5) Nordic Chemical North Star (Bastar) bimodal process
(6) Low Pressure Gas Phase Unipol Process
(7) Bassel Polyolefins Hostalen Process
(8) Sclartech Solution Process
Catalyst Technology: Catalysts are the key part of the PE process, and are the focal point of its technological development. In particular, metallocene catalysts were industrialized in the United States in 1991, which made PE production technology enter a new stage of development.
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Domestic and foreign polyethylene industry status
At present, the world's major PE manufacturers have mostly been involved in the metallocene PE (mPE) production field, such as Dow Chemical, Eastman, Asahi Kasei, Atofina, Chevron - Phillips and other companies.
Japan's Asahi Kasei Chemical purchased Dow Chemical's metallocene catalyst patent Insite, using the slurry production process to produce metallocene high-density polyethylene (mHDPE), the brand Creolex. mPE due to superior performance, mPE 1995 into the commercialization of the development of the world since the consumption of mPE resin doubled every year. It is expected that by 2010, the global mPE production capacity will reach 17 million tons, of which: mLLDPE for 7 polyethylene 00 million tons, mHDPE for 6 million tons.
Currently PE catalysts have been developed to the third generation, Japan's Mitsui Chemicals and Dow Chemical cooperation to develop a new generation of metallocene (Post-metallocene) catalysts. Unlike traditional metallocene and Z-N type catalysts, this catalyst enables polar monomers such as methyl methacrylate and vinyl acetate to polymerize with olefins***, which can be used to develop new polyolefin resins with adhesion, oil resistance and gas barrier properties.
China attaches great importance to PE production technology, PE production technology innovation has been included in the national technology innovation program projects. For domestic PE production to gas-phase process-based, product grade switching difficulties, transition materials, more problems, in recent years, the domestic PE production enterprises have carried out to the existing polyethylene production technology based on technological transformation, gas-phase polyethylene condensation, super-condensation process and slurry method of polyethylene external recycling process development work, and achieved results.
Currently, most of China's Uuipol process production units have been converted and expanded using domestic condensation technology, the output has exceeded the unit's original design capacity of 120% to 200%.
Film more than half of the total output of low-density polyethylene by blow molding made of film, this film has good transparency and a certain degree of tensile strength, widely used as a variety of food, clothing, pharmaceuticals, fertilizers, packaging materials for industrial products, as well as agricultural film (see color chart). Can also be extruded into a composite film for packaging heavy objects. since 1975, high-density polyethylene film has also been developed, its high strength, low temperature resistance, moisture, and has good printability and processability. Linear low-density polyethylene's biggest use is also made of film, its strength, toughness are better than low-density polyethylene, puncture resistance and rigidity is also better, although less transparent, still slightly better than high-density polyethylene. In addition, it can be extruded and coated with polyethylene coating on paper, aluminum foil or other plastic films to make polymer composite materials.
Hollow products High-density polyethylene strength is high, suitable for hollow products. Available blow molding method into bottles, barrels, tanks, tanks and other containers, or casting method to make tanks and storage tanks and other large containers.
Pipe sheet Extrusion method can produce polyethylene pipe, high-density polyethylene pipe with high strength, suitable for underground laying. Extruded sheet can be secondary processing. Can also be used to foam extrusion and foam injection method of high-density polyethylene made of low-foam, as table boards and building materials (see polymer materials for construction).
Fiber Chinese called ethylene, generally low-pressure polyethylene as raw material, spun into synthetic fibers. Polyethylene is mainly used in the production of fishing nets and ropes, or spun into staple fibers used as flocculent, can also be used for industrial acid and alkali resistant fabrics. Has developed a super-high-strength polyethylene fiber (strength up to 3 ~ 4GPa), can be used as bulletproof undershirts, automobiles and marine operations with composite materials.
Miscellaneous goods Produced by injection molding method of miscellaneous goods, including daily sundries, artificial flowers, turnover box (see color), small containers, bicycles and tractors, parts and so on. High-density polyethylene is used to manufacture structural parts.
Polyethylene modification Polyethylene modification varieties are mainly chlorinated polyethylene, chlorosulphonated polyethylene, cross-linked polyethylene and **** mixed modified varieties.
Chlorinated polyethylene Chlorine partially replaces the hydrogen atoms in the polyethylene and obtained by random chlorination. Chlorination is carried out under the initiation of light or peroxide, and is mainly produced industrially by aqueous phase suspension method. Due to the molecular weight of raw polyethylene and its distribution, the degree of branching and the degree of chlorination after chlorination, the distribution of chlorine atoms and the degree of residual crystallinity are different, we can get the chlorinated polyethylene from rubbery to hard plastic. The main use is as a modifier of polyvinyl chloride to improve the impact resistance of polyvinyl chloride. Chlorinated polyethylene itself can also be used as electrical insulation materials and ground materials.
Chlorosulfonated polyethylene When polyethylene and sulfur dioxide-containing chlorine, part of the hydrogen atom in the molecule is replaced by chlorine and a small amount of sulfonyl chloride (-SO2Cl) group, you get chlorosulfonated polyethylene. The main industrial production method is the suspension method. Chlorosulfonated polyethylene is ozone-resistant, chemical-resistant, oil-resistant, heat-resistant, light-resistant, abrasion-resistant and tensile strength is better, is a comprehensive performance of good elastomers, can be used to make food contact equipment parts.
Crosslinked polyethylene The use of radiation (X-rays, electron rays or ultraviolet irradiation, etc.) or chemical methods (peroxide or silicone crosslinking) to make the linear polyethylene to become a network or the body type of crosslinked polyethylene. The silicone cross-linking method is simple, with low operating costs, and the molding and cross-linking can be carried out in steps, so blow molding and injection molding are preferred. Cross-linked polyethylene heat resistance, resistance to environmental stress cracking and mechanical properties are greater than polyethylene, suitable for large pipes, cables and wires, as well as rotomolded products.
Polyethylene **** mixing modification of linear low-density polyethylene and low-density polyethylene blending, can be used for processing film and other products, product performance than low-density polyethylene. Polyethylene and ethylene propylene rubber **** mixing can be produced for a wide range of thermoplastic elastomers.
Metallocene polyethylene
Metallocene polyethylene is a novel thermoplastic, is the most important technological progress in the polyolefin industry in the 90's, following the LLDPE production technology after an important innovation. Because it is the use of metallocene (MAO) as a polymerization catalyst to produce polyethylene, therefore, in terms of performance and the traditional Ziegler-Natta catalyst polymerization of PE has a significant difference. Metallocene catalyst for the synthesis of metallocene polyethylene unique excellent performance and application, caused the market's general concern, many of the world's leading large-scale petrochemical companies invested huge human and material resources competing for the development and research, and become a polyolefin industry and even the entire plastics industry's hot topic.
Early, metallocene catalysts for ethylene polymerization can only get the wax-like material with molecular weight of 2~30,000, and the catalytic activity is not high, which is of no practical significance, and thus has not attracted much attention and promotion. Until 1980, Professor Kaminsky of the University of Hamburg, Germany, found that the combination of **** catalysts with dichlocene zirconium chloride (CP2ZrCl2) and methylaluminoxane (MAO) was used to carry out the polymerization of ethylene in toluene solution, and the catalytic activity could be as high as 106g-PE/g-Zr, and the speed of the reaction was comparable to that of enzyme reaction speed.MAO is a high degree of chimerical methylalumina synthesized by dimethylaluminum and water under the condition of the conditions outside the polymerization system. Professor Kaminsky's discovery injected vitality into metallocene catalyst research, attracting many companies to participate in the development and research, and considerable progress has been made. 1991 Exxon realized metallocene catalysts for industrial production of polyolefins for the first time, producing the first batch of metallocene polyethylene (mPE), whose trade name is "Exact", and the first batch of "mPE" was made by Exxon. The name is "Exact".
Metallocene polyolefin is the fastest growing and more mature mPE, the main varieties are linear low density polyethylene (LLDPE) and very low density polyethylene (VLDPE). mPE has two series, one is the film grade mainly targeting the packaging field, and the other is the plasticizer called POP (Polyolefine Plastmer) which is made of octene-1 as **** polymer monomer. Polyolefine Plastmer). mPE film grade has a lower melting point and obvious melting zone, and in terms of toughness, transparency, hot adhesion, heat sealing temperature, low odor, etc. significantly better than traditional polyethylene, can be used for the production of heavy-duty bags, metal trash can liners, food packaging, stretch film, etc..
At present, metallocene linear low-density polyethylene consumption accounted for about 15% of the total consumption of linear low-density polyethylene, and it is expected that this proportion will reach 22% by 2010. According to statistics, the current annual production of metallocene polyethylene in the world is about more than 15 million tons, of which the products used in the field of food packaging accounted for about 36% of the total consumption, non-food packaging accounted for about 47%, and other aspects (pharmaceuticals, automotive and construction, etc.) accounted for about 17%.
Polyethylene in the synthetic resin in the largest production, the fastest development, the most active varieties of development, whether to achieve the high performance of polyethylene, depends largely on the performance of the catalyst. Metallocene catalyst has excellent catalytic *** polymerization ability, it can make most *** polymer and ethylene *** polymerization, and can make the polar monomer catalytic polymerization, and the use of traditional catalysts is difficult to achieve; in the cyclic allylene polymerization, traditional catalysts can only be open-ring polymerization, and the use of metallocene catalysts can be double-bond addition polymerization.