Common types, properties, and applications of polyethylene (PE)

Polyethylene (PE) is one of the most popular thermoplastic materials. It has different crystal structures, called HDPE, LDPE, and LLDPE. This type of commodity plastic is produced through additive or free radical polymerization. It is used for a wide range of applications: plastic containers, bottles, bags, plastic toys, etc.
What is PE? Polyethylene or polyethylene is a type of polyolefin. It is usually abbreviated as PE. The chemical formula for PE is (C2H4) n. It is lightweight, durable, and one of the most commonly used plastics. Used for frozen food bags, bottles, grain liners, yogurt containers, etc. Looking around, all plastics with recycling codes 2 and 4 are made of PE. These plastics have different crystal structures.
How is PE made? Polyethylene is polymerized from ethylene (or ethylene) monomer. PE chains are generated through addition or free radical polymerization. Possible synthesis methods include Ziegler Natta polymerization and metallocene catalysis.

What are the common types of PE?
? Depending on their density and branching, different PE grades may have very different performance. Therefore, the classification of PE grades is as follows. Branched version of low-density polyethylene, linear low-density polyethylene (LLDPE), linear version of high-density polyethylene, ultra-high molecular weight polyethylene, cross-linked polyethylene (PEX or cross-linked polyethylene). In addition, other types of PE are also available, such as medium density polyethylene, ultra-low density polyethylene, high molecular weight polyethylene, metallocene polyethylene, and chlorinated polyethylene. How are the main types of PE compared?

What is High Density Polyethylene (HDPE)? High density polyethylene (HDPE) is an economically efficient thermoplastic with a linear structure. It has no branches or a low degree of branching. It has flexibility, translucency/wax like, and weather resistance. The chemical structure of high-density polyethylene is:
HDPE is harder due to its high crystallinity (>90%). This also means that its transparency is lower than that of LDPE and LLDPE versions. HDPE also exhibits toughness at low temperatures. HDPE is manufactured at low temperatures (70-300 ° C) and pressures (10-80 bar). It originates from two main technologies for producing HDPE, either by modifying natural gas (methane, ethane, propane mixture) or by catalytic cracking crude oil into gasoline: slurry polymerization or gas-phase polymerization. Characteristics of high-density polyethylene

1. Melting point of high-density polyethylene: 120-140 ° C. 2. Density of high-density polyethylene: 0.93 to 0.97 grams per cubic centimeter. 3 Chemical resistance of high-density polyethylene: Excellent resistance to most solvents, excellent resistance to alcohols, dilute acids, and bases, moderate resistance to oil and grease, poor resistance to hydrocarbons (aliphatic, aromatic, halogen) Continuous temperature: -50 ° C to+60 ° C, a relatively rigid material with useful temperature capability Compared with other forms of PE, the tensile strength is higher by 6 Low cost polymer with good processability Good low temperature resistance 8 Excellent electrical insulation performance 9 What are the disadvantages of HDPE with extremely low water absorption? Susceptible to stress cracking, with a stiffness lower than that of polypropylene, high forming shrinkage rate, poor UV resistance and heat resistance. High frequency welding and connection are impossible, but some grades have been cleverly upgraded and some improved performance configuration files have been provided. The excellent performance combination of high-density polyethylene makes HDPE an ideal material for various industries and applications. Some of the main uses of HDPE include:

packaging applications – HDPE is used in a variety of packaging applications, including Flat noodles, trays, milk and juice bottles, food packaging covers, jerry cans, barrels, industrial bulk containers, etc. In such applications, HDPE provides reasonable impact strength for the final product. Consumer goods - Low cost and ease of processing make HDPE the preferred material for various household/consumer goods such as trash cans, household items, ice packs, toys, etc. Fibers and Textiles - Due to its high tensile strength, HDPE is widely used in agricultural applications such as ropes, fishing nets and sports nets, as well as industrial and decorative fabrics. Other applications of HDPE include pipelines and fittings (for natural gas, water, sewage, drainage, sewage outlets, industrial applications, cable protection, steel pipe coatings, large inspection rooms, and pipeline sewage manholes), due to its excellent chemical and hydrolysis resistance, automotive fuel tanks, wiring and cable energy sheets, telecommunications cables. What is Low Density Polyethylene (LDPE)? Low density polyethylene (LDPE) is a semi-rigid polymer with low crystallinity (~50-60%). LDPE is composed of 400040000 carbon atoms and has many short branches. Compared to HDPE, it has a higher degree of short side chain and long side chain branching. The chemical structure of LDPE is:
How is LDPE manufactured? LDPE is produced under high pressure (1000-3000 Pa) and temperature (80-300 ° C). It is derived through a free radical polymerization process. The two basic processes for producing LDPE are: stirred high-pressure reactor, tubular reactor, and tubular reactor, which are increasingly prioritized over the high-pressure reactor route due to their higher ethylene conversion rate. What are the characteristics of LDPE?
1. Melting point of low-density polyethylene: 105 to 115 ° C. 2. Density of low-density polyethylene: 0.910-0.940 g/cm3. 3. Chemical resistance of low-density polyethylene: Good resistance to alcohols, dilute bases, and acids. Limited resistance to aliphatic and aromatic hydrocarbons, mineral oils, oxidants, and halogenated hydrocarbons. 4. Continuous temperature resistance up to 80 ° C and short-term resistance to 95 ° C. 5. Low cost polymer with good processability. 6 High low-temperature impact strength and good weather resistance Excellent electrical insulation performance 8 Extremely low water absorption rate of 9 What are the disadvantages of transparent LDPE film? The presence of more branching in polymer chains has brought certain drawbacks to the performance of LDPE. For example, it is prone to stress cracking with low strength, low stiffness, and the highest operating temperature. This limits its use in applications that require extreme temperatures. High breathability, especially carbon dioxide anti UV linear difference, highly flammable, high-frequency welding and connection cannot overcome these challenges. Several LDPE grades with improved performance have been developed, such as UV stability, high strength, anti adhesion, etc. What are the applications of LDPE? LDPE is mainly used for manufacturing containers, dispensing bottles, washing bottles, pipes, plastic bags for computer components, and various molding laboratory equipment. The most popular application of LDPE is plastic bags.
Packaging - Due to its low cost and good flexibility, LDPE is used in the packaging industry for pharmaceutical and extrusion bottles, bottle caps and caps, tamper proof, lining, garbage bags, food packaging films (frozen, dry goods, etc.), lamination, etc. Pipes and fittings - LDPE is used for manufacturing water pipes and hoses in the pipe and fittings industry due to its plasticity and low water absorption. Other applications include consumer goods - household items, flexible toys, agricultural films, wires and cables - secondary conductor insulators, cable sheaths. What is Linear Low Density Polyethylene (LLDPE)? The structure of linear low-density polyethylene (LLDPE) has a linear main chain with short and uniform branches (unlike the long branches of LDPE). These short branches can slide against each other when elongated, without entangling together like LPDE. It is structurally similar to LDPE. How is LLDPE manufactured? LLDPE is polymerized from ethylene (or ethane monomer) with 1-butene, as well as small amounts of 1-hexene and 1-octene. This process is carried out using Ziegler Natta or metallocene catalysts. In the current situation, LLDPE has been very successful in replacing LDPE due to the following characteristics. What are the characteristics of LLDPE? Very flexible, with high impact strength, semi transparent and natural milky white color, very suitable for mild and strong buffer solutions, with good chemical resistance, good water vapor and alcohol barrier properties, good stress cracking resistance and impact resistance. What are the applications of LLDPE? LLDPE is suitable for various film applications, such as general-purpose films, stretch films, clothing packaging, agricultural films, etc. What is ultra-high molecular weight polyethylene (UHMWPE)?

The molecular weight of ultra-high molecular weight polyethylene ranges from 3.5 to 7.5 million amu. This is about 10 times higher than HDPE resin. The appearance of HDPE and UHMWPE is similar. But UHMWPE is a tough, wear-resistant, and low-cost plastic. Suitable for industrial or manufacturing applications that may involve friction or wear. How is UHMWPE manufactured? UHMWPE is synthesized using metallocene catalysts and ethane units. These units are bonded together to form a UHMWPE structure. This structure has 100000 to 250000 monomer units per molecule. What are the characteristics of UHMWPE? It has excellent mechanical properties, such as high wear resistance, impact strength, and low friction coefficient. This material is almost entirely inert, therefore it is used in the most corrosive or corrosive environments at moderate temperatures. Even at high temperatures, it can resist various solvents, except for aromatic, halogenated hydrocarbons, and strongly oxidizing materials such as nitric acid. These special properties make the product suitable for a variety of high-performance applications. UHMWPE is suitable for high wear applications such as pipes, linings, silos, containers, and other equipment. Cross linked polyethylene (PEX or cross-linked polyethylene) high-density cross-linked PE is a form of polyethylene with a cross-linked structure. It is abbreviated as PEX or XLPE. It is designed specifically for critical applications.
How is cross-linked polyethylene manufactured? Cross linked polyethylene is made by reacting polyethylene with organic peroxides under high pressure. This will generate free radicals, leading to crosslinking of the polymer. Therefore, the resin is designed specifically for the following key applications: chemical storage pipeline systems, circulating radiation heating and cooling systems, and insulation of high-voltage cables. What are the characteristics of cross-linked polyethylene?

What are the characteristics of cross-linked polyethylene cables with high and low temperature resistance, high hydrolysis resistance, high electrical and insulation performance, high wear resistance, drinking water certification standards, high extrusion speed, lower cost, and stronger machinery on the production line? Cross linked polyethylene cable is by far the most popular cable, providing unlimited benefits in various electrical applications, thanks to its moisture resistance, stress resistance, and higher resistance to thermal deformation protection than other similar power cables. Especially when comparing cross-linked polyethylene and polyvinyl chloride cables, cross-linked polyethylene power cords have: longer service life, better heat resistance. cross-linked polyethylene power cords can usually withstand up to 260 ° C, have better tensile strength and impact resistance, and higher rated current. How to process PE plastic? Various forms of polyethylene can be used in injection molding, blow molding, extrusion and various film production processes, such as rolling or blown film extrusion. HDPE can be easily processed through injection molding, extrusion (pipes, blown and cast films, cables, etc.), blow molding, and rotational molding. As an ideal material for injection molding processes, it is mainly used for batch and continuous production. The most common processing technology used for LDPE is extrusion (pipe, blown film and cast film, cable, etc.). LDPE can also be processed through injection molding or rotational molding. UHMWPE is processed through compression molding, plunger extrusion, gel spinning and sintering. Conventional methods such as injection molding, blow molding, or extrusion molding are used because this material does not flow even at temperatures above its melting point. PE (mainly HDPE) is gradually becoming popular as a 3D printing material. Its strength, low density, and non toxicity make it an ideal choice for various 3D printed objects. In addition, recycled PE grades and bio based PE are also used for 3D printing processing. The absolute availability of PE has encouraged efforts to apply this material to additive manufacturing.

What type of PE is recyclable? The two main forms of resin identification codes for PE are LDPE and HDPE, which are essentially non biodegradable. They have made significant contributions to the world's plastic waste. Both forms of PE are recyclable. They are used for the production of non food bottles, outdoor application plastics, composting bins, etc. HDPE pipes are used for non potable water applications. For drinking water, HDPE can be used for hot and cold water service applications. In recent years, cross-linked PE has become popular in drinking water, but PEX requires special accessories and is not recyclable.