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The difference between ultra high molecular weight polyethylene raw materials and various polyethylene (PE) plastic raw materials

Aug 07, 2019

The difference between ultra high molecular weight polyethylene raw materials and various polyethylene (PE) plastic raw materials


Mainly from the production process and use to distinguish:


High pressure: using polymerization grade ethylene as raw material, using oxygen (or air) or organic peroxide as catalyst, in the tubular reactor tank reactor, using 130-280Mpa

It is formed by superhigh pressure and high temperature process of about 300 degrees Celsius.


Low pressure: using high purity ethylene as raw material, propylene or 1-butene as comonomer, alkane as solvent, in the presence of high activity catalyst, using a certain temperature (65-85) and pressure (0.1-0.7Mpa) The solution polymerization is carried out, followed by separation, drying, kneading, and granulation.


Uses:

High pressure: suitable for extrusion, blow molding, injection, vacuum, molding, coating and rotary molding, etc., manufacturing food security film, light film packaging film for agricultural film industry, general transparent film, sheet, wire, cable sheath, Guan Cai, chemical containers, synthetic paper, foamed products, etc.


Low pressure: mainly used for blow molding, manufacturing various bottles, cans, barrels and containers for injection molding, manufacturing pots, baskets, baskets, totes and industrial machinery parts, for extrusion molding various pipes, films, Weaving bag narrow wire, monofilament, etc.


LDPE (Chinese name: low density high pressure polyethylene): Sensory identification: soft handfeel: white transparent, but the transparency is general, combustion identification: yellow and blue on the burning flame; smokeless when burning, smell of paraffin, melt and drip, easy Drawing

LLDPE (Linear Low Density Polyethylene) Linear Low Density Polyethylene is structurally different from conventional low density polyethylene because of the absence of long chain branching. The linearity of LLDPE depends on the different manufacturing processes of LLDPE and LDPE. LLDPE is typically formed by copolymerization of ethylene with higher a olefins such as butene, hexene or octene at lower temperatures and pressures. The LLDPE polymer produced by the copolymerization process has a narrower molecular weight distribution than the general LDPE, and has a linear structure to have different rheological properties. The melt flow characteristics of LLDPE are suitable for the new process, especially with the film extrusion process, which can produce high quality LLDPE products. LLDPE is used in all conventional polyethylene markets to enhance tensile, penetration, impact and tear resistance properties, making LLDPE suitable for use as a film. Its excellent resistance to environmental stress cracking, low temperature impact resistance and warpage resistance make LLDPE attractive for pipe, sheet extrusion and all molding applications. The latest application of LLDPE is as a mulch for the lining of waste landfills and waste ponds. Higher tensile strength, penetration resistance, tear resistance and increased elongation are characteristics of LLDPE, making it particularly suitable for film making. If hexene or octene is used instead of butene as a comonomer, even the impact resistance and tear resistance can be greatly improved. The hexene and octene LLDPE resins are improved to 300% in impact and tear properties for a given resin at the same melt index and density. The longer side chains of hexene and octene resins act like a "knot" molecule between the chains, improving the toughness of the compound.


HDPE (High Density Polyethylene): HDPE is a highly crystalline, non-polar thermoplastic resin. The original HDPE has a milky white appearance and a semi-transparent shape in a thin section. PE has excellent resistance to most of the characteristics of living and industrial chemicals. Certain types of chemicals can cause chemical corrosion, such as corrosive oxidants (concentrated nitric acid), aromatic hydrocarbons (xylene), and halogenated hydrocarbons (carbon tetrachloride). The polymer is non-hygroscopic and has good water vapor resistance and can be used for packaging purposes. HDPE has excellent electrical properties, especially high dielectric strength, making it suitable for wire and cable. Medium to high molecular weight grades have excellent impact resistance, both at normal temperatures and even at low temperatures of -40F





Referred to as PE, it is a thermoplastic resin obtained by polymerization of ethylene. Industrially, copolymers of ethylene and a small amount of an α-olefin are also included. Polyethylene is odorless, non-toxic, feels like wax, has excellent low temperature resistance (minimum use temperature can reach -70~-100°C), good chemical stability, and can resist most acid and alkali corrosion (not resistant to oxidizing properties) The acid is insoluble in common solvents at normal temperature, has low water absorption and excellent electrical insulation properties; however, polyethylene is very sensitive to environmental stress (chemical and mechanical action) and has poor heat aging resistance. The nature of polyethylene varies from species to species and depends primarily on molecular structure and density. Products of different densities (0.91 to 0.96 g/cm3) can be obtained by different production methods. Polyethylene can be processed by conventional thermoplastic molding methods (see plastic processing). It is widely used in the manufacture of films, containers, pipes, monofilaments, wires and cables, daily necessities, etc., and can be used as high-frequency insulation materials for televisions, radars, etc. With the development of petrochemical industry, polyethylene production has developed rapidly, and its output accounts for about 1/4 of the total output of plastics. In 1983, the world's total polyethylene production capacity was 24.65 Mt, and the capacity of equipment under construction was 3.16 Mt.


Polyethylene is the most simple polymer and the most widely used polymer material. It is made up of repeated –CH2– units. Polyethylene is formed by addition polymerization of ethylene (CH2=CH2).


The properties of polyethylene depend on how it is polymerized. High-density polyethylene (HDPE) is formed by polymerization of Ziegler-Natta under moderate pressure (15-30 atmospheres) under the catalysis of organic compounds. The polyethylene molecules polymerized under such conditions are linear and have a long molecular chain with a molecular weight of several hundred thousand. If it is at high pressure (100-300 MPa), high temperature (190-210 ° C), free radical polymerization under peroxide catalysis, the production of low density polyethylene (LDPE), which is branched structure.


Polymerization pressure: high pressure, medium pressure, low pressure;


Polymerization implementation method: slurry method, solution method, gas phase method;


Product density: high density, medium density, low density, linear low density;


Product molecular weight: low molecular weight, common molecular weight, ultra high molecular weight.


Polyethylene properties


Polyethylene is odorless, non-toxic, feels like wax, has excellent low temperature resistance (minimum use temperature can reach -70~-100°C), good chemical stability, and can resist most acid and alkali corrosion (not resistant to oxidizing properties) The acid is insoluble in common solvents at normal temperature, has low water absorption and excellent electrical insulation properties; however, polyethylene is very sensitive to environmental stress (chemical and mechanical action) and has poor heat aging resistance.


The nature of polyethylene varies from species to species and depends primarily on molecular structure and density.


Type of polyethylene


(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, cross-linked polyethylene (PEX)


(7) Ethylene copolymer: copolymer of ethylene-propylene copolymer (plastic), EVA, ethylene-butene copolymer, ethylene-other olefin (such as octene POE, cyclic olefin), ethylene-unsaturated ester copolymer ( EAA, EMAA, EEA, EMA, EMMA, EMAH)


Linear polyethylene having a molecular weight of 3,000,000-6,000,000 is called ultra high molecular weight polyethylene (UHMWPE). Ultra high molecular weight polyethylene is very strong and can be used as a body armor.


The main method:


The liquid phase method (also divided into a solution method and a slurry method) and a gas phase method (the type of phase of the material in the reactor). China mainly uses the slurry method of Ziegler catalyst.


Conditions and Process Description: Ethylene with a purity of 99% or more is polymerized in a gasoline having a pressure of 0.1-0.5 MPa and a temperature of 65-75 ° C in the presence of a catalyst of titanium tetrachloride and diethylaluminum chloride to obtain a slurry of HDPE. The residual catalyst is destroyed by alcoholysis, neutralized, washed with water, and gasoline and unpolymerized ethylene are recovered, dried, and granulated to obtain a product.


HDPE and LDPE are different types of PE, different production methods, can produce HDPE and LDPE:

The production method is divided into three types: high pressure method, low pressure method and medium pressure method. The high-pressure method is used to produce low-density polyethylene. This method was developed early. Polyethylene produced by this method has accounted for about 2/3 of the total output of polyethylene, but with the development of production technology and catalyst, its growth rate has been Far behind the low pressure law. The low pressure method has a slurry method, a solution method, and a gas phase method in terms of its implementation method. The slurry method is mainly used to produce high-density polyethylene, while the solution method and the gas phase method can not only produce high-density polyethylene, but also produce medium- and low-density polyethylene by adding comonomer, also known as linear low-density polyethylene. Ethylene. In recent years, various low pressure process technologies have developed rapidly. The medium pressure method is still only used by Philips, and the main production is high density polyethylene.


The liquid phase method (also divided into a solution method and a slurry method) and a gas phase method (the type of phase of the material in the reactor). China mainly uses the slurry method of Ziegler catalyst.


Conditions and Process Description: Ethylene with a purity of 99% or more is polymerized in a gasoline having a pressure of 0.1-0.5 MPa and a temperature of 65-75 ° C in the presence of a catalyst of titanium tetrachloride and diethylaluminum chloride to obtain a slurry of HDPE. The residual catalyst is destroyed by alcoholysis, neutralized, washed with water, and gasoline and unpolymerized ethylene are recovered, dried, and granulated to obtain a product.