{"id":3142,"date":"2021-04-07T09:55:00","date_gmt":"2021-04-07T14:55:00","guid":{"rendered":"https:\/\/sybridge.com\/?p=3142"},"modified":"2024-05-20T16:20:37","modified_gmt":"2024-05-20T21:20:37","slug":"know-your-materials-polyethylene","status":"publish","type":"post","link":"https:\/\/sybridge.com\/know-your-materials-polyethylene\/","title":{"rendered":"Know Your Materials: Polyethylene (PE)"},"content":{"rendered":"\n

Originally published on fastradius.com on April 7, 2021<\/em><\/p>\n\n\n\n

Polyethylene (PE) is a variable crystalline thermoplastic<\/a> well known for its versatility. German chemist Hans von Pechmann discovered polyethylene by accident in 1898 when attempting to create a more stable version of diazomethane. Eric Fawcett and Reginald Gibson first synthesized polyethylene for industrial use in 1933, and large-scale production of low-density polyethylene began six years later. In the 1950s, catalysts were discovered that improved the polymerization aspect of polyethylene production, which jumpstarted high-density polyethylene production for the next twenty years and beyond.<\/p>\n\n\n\n

Today, polyethylene is a staple of the manufacturing industry, and over 100 million tons of it are produced annually. Here\u2019s everything you need to know about polyethylene, from how it\u2019s made to its best-fit applications.<\/p>\n\n\n\n

How is Polyethylene Made?<\/h2>\n\n\n\n

Polyethylene is made via the polymerization process. Hydrocarbon fuels are distilled into lighter groups called monomers, which are then brought into contact with a catalyst to start the polymerization process. Coordination polymerization, which involves metal chlorides and oxides, is most common, but polyethylene can also be produced using the radical polymerization process.<\/p>\n\n\n\n

Polyethylene is available in many types, grades, and formulations with different properties. The most common types of polyethylene can be broken up into branched versions, linear versions, and cross-linked polyethylenes. Popular branched versions include low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), while popular linear versions include high-density polyethylene (HDPE) and ultra-high-molecular-weight polyethylene (UHMWPE).<\/p>\n\n\n\n

LDPE<\/h3>\n\n\n\n

This semi-rigid, flexible thermoplastic has good weatherability, high-impact strength, and excellent electrical insulating properties. LDPE\u2019s unique flow properties make it ideal for making shopping bags and plastic films. Even though low-density polyethylene is highly ductile, it has a very low tensile strength, as evidenced by its stretchiness. Like HDPE, this material has poor heat-resistance \u2014 in fact, it\u2019s highly flammable \u2014 which limits its usage in high-temperature applications.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

LLDPE<\/h3>\n\n\n\n

This type of polyethylene is flexible with good stress, crack, impact, and chemical resistance. It also has a high impact strength. LLDPE is structurally similar to LDPE and can even replace it in some applications, but LLDPE has a few key advantages. LLDPE\u2019s properties can be altered by adjusting the polymer formula, and it\u2019s less labor-intensive to produce than LDPE. This polyethylene is primarily used to make different kinds of film.<\/p>\n\n\n\n

HDPE<\/h3>\n\n\n\n

In contrast to LDPE and LLDPE, high-density polyethylene has a linear structure and little to no branching. It\u2019s flexible but still rigid, weather-resistant, and holds up in the presence of low temperatures. HDPE has good UV resistance and is sometimes used in outdoor furniture. It also has a higher tensile strength than other forms of polyethylene. HDPE is frequently used in plastic milk cartons, garbage bins, cutting boards, and even laundry detergent bottles. However, it\u2019s prone to stress cracking and has poor heat-resistance.<\/p>\n\n\n\n

\"\"
Manufacturing HDPE bottles.<\/em><\/figcaption><\/figure>\n\n\n\n

UHMWPE<\/h3>\n\n\n\n

This is an extremely dense type of polyethylene \u2014 even denser than HDPE. This material can be spun into threads stronger than steel, and it\u2019s frequently used to create bulletproof vests and other high-performance equipment. It has excellent mechanical properties and is mostly inert, making it suitable for use in the most corrosive environments.<\/p>\n\n\n\n

XLPE<\/h3>\n\n\n\n

High-density cross-linked polyethylene (XLPE) is a cross-linked polyethylene designed specifically for critical applications like chemical storage pipework systems and insulation for high-voltage electrical cables. It\u2019s hydrolysis-resistant and potable water-approved with excellent abrasion resistance and electrical properties.<\/p>\n\n\n\n

Polyethylene Properties and Mechanical Specifications<\/h2>\n\n\n\n

Generally, polyethylenes have excellent chemical and impact resistance, good electrical properties, and a low coefficient of friction. They\u2019re also affordable, lightweight, and highly machinable. The mechanical properties of polyethylene will vary by type. For example, the mechanical specifications<\/a> for LDPE are as follows:<\/p>\n\n\n\n