HDPE (high-density polyethylene) is a widely used thermoplastic that possesses numerous advantageous properties, such as rigidity and excellent chemical resistance. Although part of the polyethylene family, HDPE has a molecular density that is much higher than that of its standard counterpart, which gives it unique mechanical properties. In this article, we will discuss the main advantages of HDPE and explore the various industries that make the most of this impressive polymer.
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The main advantages of HDPE
Resistant to chemicals
Characterized by a high resistance to corrosion, HDPE is an ideal material for manufacturing storage containers for liquids, food and chemical products with varying pH levels. Thanks to this feature, it can maintain its properties when in contact with chemicals, thus remaining safe and effective.
Certified food grade
Many industries choose HDPE for food and beverage storage because it meets FDA sanitary standards. Safe for contact with foodstuffs and easy to clean, HDPE is a wise choice for food environments where safety standards are an important issue.
Durable and lightweight
The density of HDPE ranges from 941 kg/m3 to 965 kg/m3 depending on its formulation. By comparison, although aluminum is considered extremely light, it has a density of kg/m3, nearly 2.8 times heavier than HDPE. For many applications where weight reduction is crucial, the light weight of high-density polyethylene is a decisive advantage.
UV resistant
UV resistance is an essential property that ensures the optimum service life of parts and components that are primarily used outside. Unlike other plastics, HDPE has several UV-resistant formulations. This makes it ideal for outdoor applications, such as playground equipment made of HDPE that contains a UV stabilizer mixed with its resin.
Easily machinable and weldable
High-density polyethylene can easily be machined or welded. These durable, strong welds make it possible to design larger projects, such as large watertight tank liners used to store important volumes of liquids.
Does not absorb moisture
Zero moisture absorption is an essential property for materials used for liquid and food storage. For this reason, HDPE is an excellent choice when designing storage tanks and other products intended for outdoor use because it does not absorb moisture even when subjected to prolonged contact with fluids.
The main areas of use for HPDE
Food
Several HDPE formulations comply with FDA and European standards and are therefore approved for direct contact with food. For example, SANALITE®, an HDPE designed specifically for the food industry, is used almost exclusively in the manufacturing of rigid, durable and easy-to-clean cutting boards. It is food safe and does not damage knife blades.
HDPE is also an excellent option for environments regulated by strict sanitary standards. For example, AGROMUR, an HDPE formulation approved by Agriculture and Agri-Food Canada, is used primarily in the design of wall panels.
Medical and pharmaceutical
High-density polyethylene is often used in the medical field, as it does not absorb moisture and offers excellent chemical resistance. Nontoxic and food grade, HDPE is ideal for work surfaces or storage units such as medical containers. Some formulations that contain certain plastic additives also have antibacterial properties.
Chemical
Because of its high chemical resistance and weldability, HDPE is a material of choice for the design of bottles, containers and tanks intended for chemical products. It is also used to produce corrosion-resistant liners. High-density polyethylene is compatible with many products including
Low concentration acids
Certain concentrated acids (pH 1&#;3)
Several alcohols
Bases and alkalis (pH 11&#;14)
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Construction
As mentioned earlier, HDPE does not absorb water and can be easily welded. This explains its popularity with pipe manufacturers. Several properties of HDPE make it a perfect material for designing lightweight, rigid and durable piping systems.
Maritime
HDPE is also used in the maritime industry. For example, SEABOARD&#;, a formulation of HDPE, is used to design boat components and pool equipment (benches, seats, doors, handles, etc.). This HDPE formulation also possesses effective UV resistance.
What are the limitations of HDPE?
Mechanical stress
HDPE is not well suited for applications subjected to high levels of mechanical stress&#;friction, compression, impacts; UHMW may be a better choice for these types of environments. Nylons could also be considered since they have excellent mechanical properties and are especially known for their superior compressive strength.
To determine which plastic range is best suited to your needs, consult our articles:
To learn more about the differences between HDPE and UHMW: What is the difference between UHMW and HDPE?
To learn about the benefits and applications of high performance nylons: The Applications and Advantages of High-Performance Nylons
Heat
HDPE is unsuitable for high heat applications, as it can only withstand continuous temperatures of up to 180 °F (82.2 °C). Fortunately, a few specialized polymers do offer excellent heat resistance: PTFE, PVDF, PEI and PAI.
To learn more, take a look at our top 5 heat resistant plastics by clicking here!
HDPE comes in many formulations based on brand and specific application, but generally, the types of HDPE are broken into two grades based on density: 300 grade and 500 grade (where the number denotes the material density). Both types come in either white or black colors, but 500 grades can typically be colored into any desired hue.
HDPE can be manufactured specially-formulated for different applications. Below is a list of some types of HDPE blended for specific environments or situations in mind:
- Cutting board HDPE
- Enhanced Stiffness HDPE
- UV stabilized HDPE
- Engravable HDPE
- Antimicrobial HDPE
- Woodgrain HDPE
- Injection Molding HDPE
and more.
Polyethylene vs. High Density Polyethylene
Polyethylene is the general name to denote all plastics formed from the (C2H4)n monomer, while High Density Polyethylene is a specific form of polyethylene that has been formulated to be denser, more linear in chain structure, and stronger than other forms. Polyethylene encompasses all the possible types such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ultrahigh molecular weight polyethylene (UHMWPE), as well as others. In industry, polyethylene is the class of materials, while HDPE is a specific instance of that class of polymers.
To learn more, see our guide on What is Polyethylene.
High Density Polyethylene (HDPE) vs Low Density Polyethylene (LDPE)
HDPE and LDPE are built from the same monomer units, but are functionally two different polyethylene materials. HDPE has a more linear chain structure, making it stronger, denser, and stiffer than low-density polyethylene (LDPE). LDPE is more flexible for this reason and has a lower crystallinity. Both materials are recyclable, however, they cannot be recycled together as LDPE tends to soften quickly and gum up recycling machinery. LDPE Is weak to heat, succumbing to decreases in density after temperatures beyond 20 °C, while HDPE can remain functional through high temperatures like 100 °C. HDPE has overall better mechanical and chemical resistances, but both are generally weak to oxidizing agents and select hydrocarbons. LDPE is more transparent than HDPE, and both are easily worked and are considered a waterproof material.
Deciding on which polyethylene polymer works best for a given application depends on budget, intended material properties, and special considerations. It is impossible to say if HDPE or LDPE is best (as both are highly popular), but both have cases for their use beyond strength and resistance comparisons. If price is the determining factor, then LDPE wins out; if looking to create a structural part, HDPE will probably be the better choice.
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