The four most common types of polyethylene are described below:
- Ultra-High Molecular Weight Polyethylene (UHMWPE): UHMWPE has a linear molecular chain with no side branching. It has excellent abrasion resistance and is extremely tough, making it well suited to industrial applications. UHMWPE has much longer continuous molecular chains than other polyethylenes, hence the “ultra-high molecular weight” designation.
- High-Density Polythene (HDPE): HDPE material has a linear molecular chain with limited to no branching off the main chain. This allows the polymer chain to fold into a dense structure, allowing for higher packing efficiency and increased crystallinity when compared to LDPE. HDPE is a rigid material with good mechanical properties. It has an opaque appearance.
- Low-Density Polyethylene (LDPE): LDPE does not have the linear molecular structure of HDPE. Instead, the main carbon backbone can have additional branches that have the same form as the basic polyethylene molecule. These branches stop the molecular chain from folding into a densely packed structure, i.e. reducing its packing efficiency compared to the linear structure of HDPE. LDPE is softer than HDPE. It also tends to be transparent, and has low crystallinity.
- Linear Low-Density Polyethylene (LLDPE): LLDPE has a similar molecular structure to LDPE. However, its branches are significantly shorter than those found in LDPE. This means that the molecular chains do not entangle themselves as easily. LLDPE has good tensile strength and very high elongation. For that reason, it is often used in stretch films.
What Are the Benefits of Using Polyethylene?
Polyethylene’s many benefits include:
- Low cost and easy availability
- Can be used as electrical insulation
- Chemically resistant to solvents and dilute acids
- Easy to process for injection molding
- Tough and wear resistant
- Can be produced in strong, thin films
- Some grades are transparent
Is Polyethylene Suitable for Plastic Injection Molding?
Yes, polyethylene is widely used for plastic injection molding. It is one of the easiest materials to work with. Its processing ease makes it popular in other applications as well, such as blow molding and film extrusion. For more information, see our guide on Plastic Injection Molding.
Why is Polyethylene Used in Plastic?
Polyethylene is a thermoplastic and as such is not used in plastic but is rather a plastic itself.
Is Polyethylene Environmentally Friendly?
No, polyethylene is not environmentally friendly. Like most thermoplastics, polyethylene is produced as a crude oil processing by-product and is not biodegradable. In fact, a large percentage of plastic pollution is due to discarded polyethylene films and bags.
What Is the Difference Between Polyethylene and Polypropylene?
The difference between polypropylene (PP) and polyethylene (PE) is in the makeup of their polymeric chains. Polypropylene molecular chains are made from repeating propylene (C3H6)n monomers, whereas polyethylene chains are made from repeating ethylene (C2H4)n monomers.
What Is the Difference Between Polyethylene Terephthalate and Polyethylene?
Polyethylene (PE) and polyethylene terephthalate (PET) are entirely different polymers, manufactured differently, and used for different applications. PET, with the chemical formula (C10H8O4)n, is produced from the polymerization of ethylene glycol and terephthalic acid, while PE ((C2H4)n) is produced from the polymerization of ethylene. Polyethylene is often used for making plastic films or containers, whereas PET is more typically used in fibers. It is more commonly known as polyester. For more information, see our guide on Polyethylene Terephthalate.