Polyethylene (PE) is the most common plastic material. All types of polyethylene are variants on the basic chemical formula (C₂H₄)H₂. Different types are formed by varying the amount of C₂H₄ compound. Most polyethylene grades are known for their excellent chemical resistance and electrical insulation, strength, and light weight. Polyethylene is a thermoplastic, meaning it softens to a molten state when heated and hardens when cooled. They have the ability to endure many heating and cooling cycles without changes to the chemical makeup of the material. Various polyethylene grades are made from crude oil. Ethylene is created by heating petroleum (naphtha) in a controlled environment until ethylene is released and then transformed into polyethylene. Polyethylene is inexpensive, flexible, durable, and chemically resistant.

Types of Polyethylene Resins

Polyethylene may take several different forms with differing densities and mechanical properties based on its molecular structure. The three main types are high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDE). 

The basic repeating unit for all types of polyethylene.

LDPE is used to form a variety of commodity packaging applications, such as films for food wrapping and packaging. High density (HDPE) and ultra-high molecular weight polyethylene (UHMW PE) have good friction and mechanical properties and are used in containers, medical devices, wear parts, and engineered components. In comparison to other plastic resins, polyethylenes have low strength, hardness, and rigidity, but have high ductility, impact strength, and low surface friction.

High density polyethylene (HDPE) is used in a variety of applications and industries where excellent impact resistance, high tensile strength, low moisture absorption, and chemical/corrosion resistance properties are required.

Low density polyethylene (LDPE) has a density range of 0.910–0.940 g/cm³. This results in a lower tensile strength and increased ductility. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap.

Very low density polyethylene (VLDPE) has a density range of 0.880–0.915 g/cm³. VLDPEs are used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap. They are also employed as impact modifiers when blended with other polymers.

Linear low density polyethylene (LLDPE) has a density range of 0.915–0.925 g/cm³. LLDPE has a higher tensile strength than LDPE, as well as higher impact and puncture resistance. LLDPE is used in packaging for film, bags, sheets, and industrial applications for cable coverings, containers, and pipe.

High molecular weight polyethylene (HMWPE) is commonly used for wear parts and abrasion resistant components in the conveyor and materials handling industry.

Ultra high molecular weight polyethylene (UHMWPE) provides a unique combination of low friction surface, high impact strength, and wear/corrosion resistance. UHMWPE  provides performance at temperatures down to -30°C. It is an excellent general-purpose plastic with self lubricating properties.

Cross-linked polyethylene (PEX or XLPE) is a medium- to high-density polyethylene containing cross-linked bonds in the molecular structure The cross linking changes the thermoplastic material into a thermoset. Cross-linked polyethylene has higher temperature resistance properties and improved chemical resistance.