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Polyurethane versus Polyethylene

The world of plastics include materials made up of a wide variety of chemical compositions and characteristics, providing product designers numerous options to choose from. Depending on your design specifications, you may find some materials may be better suited due to their physical properties and manufacturing processes. For instance, polyurethane and polyethylene are two different types of plastics that are commonly found in a variety of applications. However, one material can offer designers more design freedom and higher, more robust properties. In this post, we will discuss the differences between polyurethane and polyethylene and when to choose the best material for your product design.

bigstock-Multiple-Plastic-Shopping-Bags-239117521-768x512What is Polyethylene?

Like ABS plastics, polyethylene (PE) is a material commonly found in many consumer goods. This flexible material is created through a very simple chemical structure that consists of hydrogen atoms and carbon atoms. Depending on the preferred density, polyethylene can be engineered to form either a linear or branched structure also commonly known as high-density polyethylene (HDPE) or low-density polyethylene (LDPE). While both materials stem from the same chemical composition, they each portray very different physical properties. HDPE is strong and stiff, while, LDPE is softer and more flexible. For example, HDPE can typically be found in toys, bins, and drainpipes, whereas, LDPE is often found in disposable gloves, bags, and plastic wrap to name a few.

What is polyurethane?

Polyurethanes are formed through the chemical reaction between a polyol and diisocyanate. Despite having a complex chemical structure, this unique material can allow engineers to tailor the urethane’s chemistry to meet specific design requirements. Polyurethanes can be custom formulated to be either soft and flexible as a cushion to something as hard and rigid like metal. Due to their adaptability, polyurethanes can be found in a wide variety of applications, from the bottom of your shoes to your favorite electronic devices.

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Differences Between Polyethylene & Polyurethane

While polyethylene and polyurethanes stem from the same plastics family, both materials differ in properties, types of products, and manufacturing processes. Starting with the chemical structure, polyethylene is a type of thermoplastic, while, polyurethanes are thermosets. Thermoplastics are typically injection molded products that can be melted and reformed. Thermosets, on the other hand, are molded through either a cast or reaction injection molded (RIM) process. Unlike thermoplastics, thermosets offer better performance under high temperatures while remaining in its permanent form. For additional information on thermosets versus thermoplastics, click here.

Due to their chemical and manufacturing differences, thermoset polyurethanes generally offer more robust physical properties than the two common types of polyethylene. Below is a chart to help breakdown the differences between thermoset polyurethane and thermoplastic polyethylene:

  Polyethylene     Polyurethane  
  • Solids and foams available
  • Can be custom formulated to meet exact design needs
  • Limited durometers can be achieved
  • Low resistance to heat
  • Higher durability; Able to withstand various temperatures from -80°F up to 300°F
  • Difficult to bond
  • Can bond to various subcomponents during the molding process
  • Can be made conductive with the use of carbon black

Which Material Should You Choose?

Depending on your design requirements, polyurethane and polyethylene can fit into a wide range of products and/ or components. However, thermoset polyurethanes can produce stronger, more robust products that can withstand most environmental conditions. For this reason, thermoset polyurethane are often preferred for applications that require very specific physical properties for better performance. Polyethylene, more so, best for products that have little to no importance in wear requirements. When evaluating between both materials, it is important to consider the application's requirements and manufacturing process to produce efficient products based on your design needs. To help narrow your material decisions, make sure to check out our blog posts on reaction injection molding (RIM), cast vs injection molding to find the perfect fit!     

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