Warm Global Customers
With China Plastic Machinery
With China Plastic Machinery
Low-density polyethylene (LDPE) is the lightest variety of polyethylene resin except ultra-low-density polyethylene. Low-density polyethylene is milky white, tasteless, odorless, non-toxic, and matte wax particles. The density range is 0.910-0.925g/cm3; the molecular formula is (C2H4)n.
Low-density polyethylene is mainly used as agricultural film, industrial packaging film, mechanical parts, daily necessities, building materials, wire, cable insulation, coating and synthetic paper, etc. Harmful substances can be precipitated above 110¡ãC, and it is not recommended to store high-temperature food.
In 1933, the British Imperial Chemical Industries conducted a reaction between ethylene and acetaldehyde at a pressure of 200MPa and 170¡ãC, and found that white wax was attached to the reactor wall. This is the earliest polyethylene. In 1934, Fawcett and Gibson first reported the relevant synthesis technology and published a patent for polyethylene production in 1937. From 1937 to 1939, the company conducted research on the synthesis of polyethylene under high pressure induced by trace oxygen and completed the pilot test. In 1939, Imperial Chemical Industries built the world's first LDPE industrial plant with an annual output of 100 tons, and the product was used as an insulating material for cables and radars. In 1941, DuPont and Union Carbide of the United States successively introduced the LDPE production technology of Imperial Chemical Industries of the United Kingdom and put it into production in 1943. Now there are 135 companies in 38 countries in the world using 22 process flows to produce LDPE.
¢Ù Low-density polyethylene is a milky white, tasteless, odorless, non-toxic, matte waxy particle with a molecular formula of (C2H4)n and a structural formula of [-CH2-CH2-]n. The density range is 0.910-0.925g/cm3. It is the lightest variety of polyethylene resin except ultra-low-density polyethylene. Its molecular structure is a branched molecule with long and short branches on the main chain, with about 20 to 30 ethyl, butyl or longer branches per 1,000 carbon atoms on the main chain. The molecular arrangement is relatively loose. Compared with high-density polyethylene and medium-density polyethylene, the crystallinity (55% to 65%) and softening point (90 to 100¡ãC) are lower, and the melt flow rate is wider (MFR = 0.2 to 80g/10min). ¢Ú It has good chemical stability, can withstand acid, alkali and salt aqueous solutions, and can withstand general organic solvents below 60¡ãC. It also has good cold resistance and can remain stable at -70 to -80¡ãC. It has good electrical properties, with low conductivity, small dielectric constant, low dielectric loss tangent and high dielectric strength. However, its heat resistance, oxidation resistance and light aging resistance are poor. It is often necessary to add antioxidants and ultraviolet absorbers to the application formula to improve its aging resistance. ¢Û It has good softness, extensibility, transparency, processability and a certain degree of air permeability, but its mechanical strength is lower than that of high-density polyethylene and linear low-density polyethylene. Its moisture permeability is also poor. Its adhesion, bonding and printing properties are poor and can only be improved after chemical erosion and corona treatment. Its physical and mechanical properties also vary depending on its use. See Table 2-1-3-1. ¢Ü Low-density polyethylene is a flammable substance, and its dust can burn and explode in the air. The combustion temperature is 625-650¡æ, and the combustion concentration in the air is 85-370g/m3. Therefore, fire and high temperature must be strictly prohibited during transportation and storage.
(2) LDPE is a typical crystalline polymer with a crystallinity of 55%~65% and a melting point of 105~126¡æ;
(3) LDPE is a non-polar material, easy to carry static electricity, and has low surface energy. Therefore, it should be corona treated before printing and lamination to increase the surface energy. During processing, attention should be paid to anti-static to avoid static electricity accumulation affecting the quality of the product or electric spark discharge, causing fire;
(4) LDPE has excellent transparency and heat sealing properties, and can be widely used in the production of transparent low-temperature frozen packaging products;
(5) LDPE has excellent moisture barrier properties and is a high-quality raw material for making dry food or packaging items that require good moisture-proof properties. However, LDPE has a large gas barrier property and is easy to pass through various gases;
(6) Although LDPE has a certain degree of oil and fat resistance, its oil and fat resistance and organic solvent resistance are not as good as polypropylene. Therefore, when the thickness is small, it is not suitable for long-term storage of gasoline, alcohol, grease, etc. When using LDPE, the thickness should preferably be more than 50mm;
(7) LDPE is flammable. When burning, the flame is smokeless and colorless, and there is a burning drip phenomenon and candle gas, which is a characteristic for identification.
LDPE has a wide range of uses and can be used as various films and injection molding and blow molding products. ¢Ù Packaging film: divided into food packaging film and non-food packaging film. The latter is used for industrial padding, transport bags, shrink film packaging, soft products and light industrial product outer packaging bags, and the manufacture of garbage bags, construction and agricultural films, etc., which is the largest LDPE usage. ¢Ú Injection molding products: Injection molding products are the second largest use of LDPE. The main injection molding products include daily necessities (caps, artificial flowers, sealed containers, kitchen supplies, buckets), toys, stationery and light industrial product containers. ¢Û Composite film (tubes, plates, bottles): Another major use of LDPE is extrusion coating and composite film. LDPE is a composite of paper, cardboard, fiberboard, aluminum foil, nylon, polypropylene, ethylene-vinyl alcohol copolymer film and other plastic films, which are widely used in food, medicine soft packaging, moisture-proof packaging, chemical product packaging, vacuum and deoxygenation packaging. ¢Ü Wires and cables: mainly used for communication wires and power cables. Such as telephone cable sheaths, submarine cables, signal device cables; power cables are mainly used as wiring cables in high-voltage transmission lines. ¢Ý Other uses: blow molding various containers, foam products, buoys. Extrusion of pipes and fittings (drinking water pipes, drainage pipes). Rotational molding to manufacture large-sized and complex-shaped products. In addition, it can be used as coatings, synthetic paper, belts (narrow belts, tablecloths, ropes, fishing nets, etc.). LDPE is used in the military industry, mainly to manufacture composite film moisture-proof packaging and military special packaging. Such as ammunition packaging, large weapon envelope packaging, and packaging of advanced military instruments and missiles to prevent damage from electromagnetic radiation in space. Packaging and storage. The product is packed in polyethylene heavy packaging film bags, and can be packed in polypropylene woven bags as outer packaging according to user needs. The net weight of each bag is (25¡À0.25) kg. The product should be stored in a clean and dry warehouse and can be transported by train, car, ship, etc. During storage and transportation, attention should be paid to fire prevention, waterproofing, sun protection, dust prevention and pollution prevention. The transportation tools should be kept clean and dry, and there should be no sharp objects such as nails, and there should be a shed or tarpaulin.
The method for large-scale industrial production of low-density polyethylene is to obtain the product by free radical polymerization of high-purity ethylene at 98-343MPa and 150-330¡æ in the presence of trace oxygen (or air), organic or inorganic peroxides and other initiators. In terms of production methods, according to the different polymerization reactors used, it is often divided into two categories: kettle method and tubular method. The polymerization reactor used in the kettle method is a high-pressure reactor with a stirrer. The initiator is mostly an organic peroxide. The reaction pressure is usually lower than that of the tubular method, about 98-245MPa, the reaction temperature is about 150-300¡æ, and the single-pass conversion rate is 20%-25%. The polymerization reactor used in the tubular method is a hollow long tube with a tube length of up to 1400m. The initiator is oxygen (or air), the pressure is 196-343MPa, the temperature is 250-330¡æ, and the single-pass conversion rate is 20%-34%.
Consumption quota: Different types of low-density polyethylene produced by different methods have different consumption quotas. As far as the kettle polymerization method is concerned, each ton of product consumes 1030kg of polymerization-grade ethylene, 0.30kg of initiator CP-02 (tert-butyl perbenzoate), a small amount of CP-10 (3,5,5-trimethylhexanoyl peroxide), solvent LP-14 (normal alkane), etc.
After mixing high-purity fresh ethylene with unreacted ethylene circulating gas, the mixture is pressurized twice to 112.7-215.6MPa and then fed into an abatement reactor, into which a trace amount of organic peroxide initiator is injected. In the presence of the initiator, ethylene is polymerized at 107.8-196MPa and 160-285¡ãC to obtain low-density polyethylene. After the obtained low-density polyethylene and unreacted ethylene are cooled to a certain temperature, the unreacted ethylene is separated through a high-pressure separator and a low-pressure separator, and then enters the circulation system and is mixed with fresh ethylene for use. The molten polymer separated from the low-pressure separator is mixed with an appropriate amount of additives and then extruded and granulated to obtain a granular product.
Fresh high-purity ethylene is mixed with circulating gas ethylene from the low-pressure separator and sent to the primary compressor, where the pressure is increased to 24.5-29.4MPa. At the same time, initiator oxygen (or air) and relative molecular mass regulator are added. After primary compression, the material is mixed with the circulating ethylene from the high-pressure separator, and then compressed to a pressure of more than 245MPa by the secondary compressor and sent to the tubular polymerization reactor for polymerization under the action of the initiator. The polymerization temperature is 250-330¡æ. The reaction product is separated from the unreacted ethylene by the high-pressure separator and the low-pressure separator, and sent to the secondary compressor and the primary compressor for recycling. The obtained polymer is extruded, pelletized and dried to obtain the product.
LDPE (Low-Density Polyethylene): This material is often used for cling film and plastic film on the market. It is not heat-resistant. Qualified PE cling film will melt when the temperature exceeds 110¡ãC. When food is wrapped in cling film and heated, the fat in the food can easily dissolve the harmful substances in the cling film. Low-density polyethylene is a flammable substance, and its dust can burn and explode in the air.
Before heating food in the microwave, the LDPE cling film should be removed. Fire and high temperature must be strictly prohibited during the transportation and storage of LDPE.
Eyes: First check whether the victim has contact lenses. If so, remove them. Rinse the victim's eyes with water or saline for 20 to 30 minutes, and call the hospital or poison control center at the same time. Do not put any ointment, oil or medicine into the victim's eyes without the doctor's explicit instructions. Take the victim to a hospital immediately after flushing of the eyes, even if no symptoms (such as redness or irritation) occur.
Skin: Immediately flush affected skin with water while removing and isolating all contaminated clothing. Gently and thoroughly wash all affected skin areas with soap and water. If symptoms such as redness or irritation occur, call a doctor immediately and prepare to transport the victim to a hospital for treatment.
Inhalation: Immediately leave the contaminated area; breathe fresh air deeply. If symptoms occur (such as wheezing, coughing, shortness of breath, or burning sensation in the mouth, throat, or chest), call a doctor and prepare to transport the victim to a hospital. Provide appropriate respiratory protection for rescuers entering unknown environments. Self-contained breathing apparatus (SCBA) should be used whenever possible; if unavailable, use a level of protection greater than or equal to that recommended in the protective suit.
Ingestion: Do not induce vomiting. If the victim is conscious and not convulsing, give 1 or 2 cups of water to dilute the chemical and call a hospital or poison control center immediately. Be prepared to transport the victim to a hospital if a doctor recommends. If the victim is convulsing or unconscious, do not take anything orally, make sure the victim's airway is open, and lay the victim on his side with his head lower than his body. Do not induce vomiting. Send the victim to the hospital immediately.
No. 4 LDPE: plastic wrap, plastic bags, tube packaging for toothpaste, etc. (avoid high temperatures and should not come into contact with greasy foods). The triangle formed by three arrows means "recyclable and reusable", but it is not a sign of whether it can be reused. In China, it is not mandatory to mark plastic products with recycling signs. Some regular large brand companies have recently begun to mark recycling signs to facilitate the recycling of plastic products.
If you are interested in our company and machine, feel free to contact our sales engineer. We will contact you as soon as possible.