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With China Plastic Machinery
With China Plastic Machinery
High-density polyethylene is a polymer formed by the polymerization of ethylene under specific conditions and catalysts. It is also known as low-pressure polyethylene. It is a highly crystalline, non-polar thermoplastic resin and one of the five general-purpose plastics. The chemical formula is (CH-CH)n. It is an odorless, tasteless, non-toxic white powder or semicircular particles with a melting point of 131¡ãC and a density of 0.942g/cm3-0.950g/cm3. It has a high use temperature, hardness, mechanical strength and corrosion resistance. It can be prepared by slurry method, gas phase method and other methods.
High-density polyethylene has many applications such as food packaging film and beverage bottles, making sports equipment such as dance mats, preparing cable sheath materials, medical equipment, orthopedic implants, and sand-proof nets. High-density polyethylene is more diversified in production equipment and process routes, but because it is a flammable substance, its dust can burn and explode in the air, so attention should be paid to fire protection and storage and transportation safety.
In 1953, the research on high-density polyethylene made its first breakthrough. Professor Ziegler, a West German chemist, polymerized high-density polyethylene under normal pressure for the first time. This method was called Ziegler high-density polyethylene, also known as low-pressure high-density polyethylene, and was later applied to the company's production. In 1954, the Philips method and standard oil method for preparing high-density polyethylene were born. It is also called medium-pressure polyethylene. HDPE produced by Ziegler process, Phillips process and standard oil process is called the first generation of HDPE.
In the late 1960s, the research on high-density polyethylene achieved a second breakthrough. The Belgian Solvay Company improved the original Ziegler catalyst and pioneered a high-efficiency catalyst (the catalytic activity is dozens of times higher than that of the old Ziegler process). In the 1970s, in addition to the Solvay process, there were more than ten processes such as the Hoechst process in West Germany, the National Mining Company process (DSM) in the Netherlands, the Montedison process in Italy, the Phillips Particle Process in the United States, and the UCC Gas Process.
In the 1980s, researchers from Fujikura Electric Wire Co., Ltd. in Japan chemically modified HDPE and found that the DC breakdown strength could be greatly improved after introducing a small amount of polar groups on the main chain of HDPE. After the modification of HDPE, HDPE was widely used as an insulating material for overhead power cables.
High-density polyethylene is the highest density polyethylene, with the molecular formula (CH-CH)n, odorless, tasteless, non-toxic white powder or semi-circular particles, melting point of 131¡ãC, high melting point, good thermal properties, low glass transition temperature; good chemical resistance, low permeability, density of 0.942g/cm3-0.950g/cm3, close molecular arrangement, minimum degree of branching, high crystallinity, tensile strength of 20-35MPa, impact strength (notch) of 2-30kPa¡¤m, breakdown field strength of 18-20kV/mm.
HDPE is almost unaffected by most common chemicals, water, solvents, acids, detergents and cleaning fluids. It is durable and water-resistant, can be sterilized by boiling, can withstand most strong inorganic acids and alkalis, and has excellent resistance to natural chemicals found in the soil. HDPE plastic is also easy to recycle, helping to prevent non-biodegradable waste from entering landfills, while also reducing plastic production by up to 50%.
HDPE and ethylene-vinyl acetate copolymer resins can be used to prepare cable sheathing materials with higher mechanical properties. The flame retardancy of HDPE high-voltage cable sheaths can also be improved. HDPE/IFR composites doped with intumescent flame retardants IFR (APP and TT4) are prepared by hot pressing, which effectively improves the flame retardancy of HDPE high-voltage cable sheaths. The introduction of a small amount of polar groups on the main chain of HDPE can greatly improve the DC breakdown strength. Some organic molecules can also be added as voltage stabilizers to improve the electrical properties of HDPE. For example, azo compounds have the effect of inhibiting partial discharge.
High-density polyethylene (PE-HD) plastic pipes have the advantages of heat resistance, aging resistance, high mechanical strength, etc., and meet the requirements of relevant international and national standards. Therefore, the seawater system of nuclear power plants often uses high-density polyethylene for its seawater corrosion resistance and bioerosion resistance. It is used as a substitute for steel pipes in the seawater system of coastal nuclear power plants. High-density polyethylene has also been used in nuclear-grade pipeline systems of nuclear power plants. For example, the Catawba Nuclear Power Plant and Callaway Nuclear Power Plant in the United States have successively replaced generator hydrogen coolers and emergency diesel engine cooling water system steel pipes with HDPE pipes.
High-density polyethylene has poor thermal conductivity. It can be melt-blended with boron nitride (BN) to prepare HDPE/BN composite materials with high thermal conductivity. As a thermoplastic resin, high-density polyethylene has the advantage of being formaldehyde-free and is often used as an adhesive to prepare poplar plywood. Special high-density polyethylene resin is compounded with a large amount of limestone and other additives to prepare "stone paper", which can not only be written and printed, but also has the tear resistance, folding resistance and waterproof properties of plastic packaging.
HDPE has the characteristics of low moisture absorption, chemical resistance, recyclability and low bacterial retention rate. It can be used as medical catheters, films, connectors, laboratory equipment, catheters, intravenous infusion bags, masks, equipment housings, drug delivery components, packaging, etc. Some special HDPE, such as ultra-high molecular weight polyethylene (UHMWPE), can also be used as orthopedic implants, such as knee or hip replacements.
In daily life, high-density polyethylene can be used as food and beverage containers, plastic bottles, shampoo and conditioner bottles, etc., and can also be used as trash cans, recycling bins, plastic containers, etc. It has many applications. High-density polyethylene films are mainly used in vest bags, garbage bags, shopping bags, food bags, heavy packaging bags, multi-layer structural films, etc. The largest amount is garbage bags, shopping bags and food bags.
High-density polyethylene has been modified to have the advantages of high wear resistance and impact resistance. It can be used to make sports equipment such as dance mats. The use of HDPE, carbon fiber and stearic acid to prepare HDPE/CF composite materials will have higher mechanical properties and wear resistance.
The US Food and Drug Administration announced that waste plastics within 50km of the coast can be used as OceanBound resin raw materials to prepare high-density polyethylene for food packaging. High-density polyethylene can also be made into anti-sand nets. To prevent the aging of high-density polyethylene materials, antioxidants and light and heat stabilizers can be added to them to improve the light and heat stability of the materials and prevent the further decomposition of hydroperoxides. In landfills, high-density polyethylene (HDPE) membranes can be used to build anti-seepage systems to prevent leachate leakage, thereby protecting the safety of soil and groundwater.
This process uses high-purity ethylene as raw material, propylene and 1-butene as comonomers, hexane as solvent, and uses a high-efficiency catalyst for low-pressure polymerization. The slurry obtained by the polymerization is separated, dried, mixed and granulated to obtain various HDPE products with excellent performance. This method can freely control the composition distribution of the polymer by adjusting the comonomer inserted into the polymer chain.
Ethylene monomer, gasoline as solvent, titanium tetrachloride as catalyst, diethylaluminum monochloride as activator can also be used, polymerization reaction occurs under certain pressure and temperature conditions, and it is esterified with alcohol. The product is washed with water, neutralized, separated from gasoline, recovered from solvent, dried and granulated.
In this method, the raw gas is passed into a purification tower for purification to remove trace impurities such as water, oxygen, and carbon dioxide, and then enters the reactor after preheating. At the same time, the catalyst is automatically added to the reactor in batches by the catalyst feeding system, and the raw material is polymerized under the action of the catalyst.
High-density polyethylene is produced by using a gas phase fluidized bed process, ethylene as raw material, 1-butene or 1-hexene as comonomer, isopentane as induced coolant, and chromium, titanium, and metallocene catalysts.
Use recycled high-density polyethylene plastic as raw material, and prepare polyethylene wax by solvent-assisted pyrolysis. That is, add a corresponding proportion of solvent to the high-density polyethylene in the autoclave to crack the high-density polyethylene, and obtain polyethylene wax by extraction, filtration and drying. The recycled high-density polyethylene plastic can also be co-catalyzed with baked bamboo to produce light aromatics, that is, the bamboo is pre-treated to increase its carbon content and then expanded to prepare a multi-level pore molecular sieve catalyst, and finally co-catalyzed pyrolysis is used to obtain light aromatics.
When preparing concrete, HDPE particles can be added to it to prepare HDPE fiber concrete, which can effectively improve the cracking ductility and impact resistance of concrete, and has a high elastic modulus, compressive strength and durability.
The solid phase stretching method is used to perform secondary processing on waste high-density polyethylene. Under high temperature pressing and stretching conditions at different temperatures, high-density polyethylene forms a shredded crystal structure, and the yield strength of the material reaches a maximum of about 104MPa, which is 354% higher than the yield strength value of the unstretched sample (22.87MPa).
HDPE is an inert polymer that does not react with acidic or alkaline substances. The molecular formula is (CH-CH)n, with polyethylene chains as the skeleton. The molecular weight and distribution of high-density polyethylene determine its properties. The more low molecular weight content, the greater the crystallinity. The melt flow rate (MFR) is inversely proportional to the weight average molecular weight (-Mw). The larger the weight average molecular weight, the more sensitive it is to shear rate. The larger the molecular weight distribution index (PI), the higher the tensile strength, but the impact performance decreases. The molecular chain and other polyethylene chains are spatially distributed on the main line and finally connected to the methyl group. The linear structure of HDPE has almost no branches, few and short side chains, and the molecular chain is easy to stack into thicker lamellae during the crystallization process, with a crystallinity of >80%. Compared with other types of polyethylene, HDPE has higher density and strength. This is entirely due to its molecular structure and chain length.
High-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/cm3. Fire and high temperature should be strictly prohibited, and corresponding fire-fighting facilities should be equipped.
When storing, high-density polyethylene should be double-packed in woven bags on the outside and polyethylene film bags on the inside. It should be stored in a ventilated and dry warehouse. It should not be piled in the open air, and should be kept away from direct sunlight and fire sources. During transportation, it should be prevented from being scratched, rainproof, and sun-proof. It should not be mixed with pollutants such as sand, metal, and coal, and should not be mixed with flammable items.
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