High-density polyethylene (HDPE) is one of the most versatile petroleum-based thermoplastics in manufacturing. Its unique combination of properties, including cost-effectiveness and recyclability (identified with the symbol #2), makes it a valuable choice across a wide range of industries.
In this post, we’ll discuss what HDPE is, how it’s made, and its history, as well as its properties and applications.
What is HDPE?
HDPE is a petroleum-based thermoplastic polymer made from the monomer ethylene (C₂H₄), and its chemical formula is (C₂H₄)ₙ with “n” representing the number of repeating units. It differs from other types of polyethylene due to its linear molecular structure and minimal branching. The polymer chains pack closely together, resulting in a highly crystalline, dense, and strong plastic.
What is the history of HDPE, and how is it made?
Earlier findings of polyethylene in the 1930s marked the beginning of HDPE’s history. In the early 1950s, the expansion of a new catalytic process by Phillips Petroleum researchers, along with the independent catalyst-based low-pressure operation by Erhard Holzkamp and Karl Ziegler, led to the commercial production of high-density polyethylene. Branded as Marlex, this new form of polyethylene gained favor during the mid-1950s, coinciding with the rise of the hula hoop fad. It was also a popular material in various applications, including plastic bottles and pipes.
The primary raw material for HDPE is ethylene. This material comes from petroleum or natural gas. Occasionally, co-monomer additives, such as butene, hexene, or octene, can tailor the polymer’s properties. Additives like UV stabilizers, antioxidants, and colorants can enhance performance.
Manufacturing HDPE through polymerization of ethylene using advanced Ziegler-Natta or chromium-based catalysts. There are three primary methods.
- Slurry Polymerization: In a hydrocarbon diluent, the polymerization of ethylene produces an HDPE powder.
- Gas-Phase Polymerization: In a fluid bed reactor, the polymerization of ethylene gas creates HDPE.
- Solution Polymerization: A solvent dissolves ethylene, and polymerization takes place in the liquid phase.
After polymerization, high-density polyethylene undergoes additional refinement through the process of extrusion. At this phase, pipes, sheets, and films are formed, as well as injection molding pellets for containers and toys, and blow molding for bottles, and rotational molding for large hollow items.
What are the properties of HDPE?
Popular because it offers an interesting balance of characteristics from sustainability to physical properties, including:
- Biological & Corrosion Resistance: This material does not support biological growth and is resistant to rust.
- Chemical Resistance: This material exhibits resistance to a wide range of chemicals, including acids, bases, and various solvents.
- Highly Recyclable: Globally, HDPE is one of the most recycled plastics.
- Impact & Abrasion Resistance: HDPE can withstand harsh environments and outdoor exposure.
- Low Water Absorption: HDPE is an exceptional moisture barrier.
- Strength-to-Weight Ratio: HDPE exhibits higher strength and rigidity compared to other plastics, for example, LDPE.
- Weatherability & UV Resistance: High-density polyethylene resists rain, sunlight, and extreme temperature changes without degrading.
The following table is information from AZO Materials:
| Property | Value |
|---|---|
|
Density (g/cm³) |
0.96 |
|
Surface Hardness |
SD68 |
|
Tensile Strength (MPa) |
32 |
|
Flexural Modulus (GPa) |
1.25 |
|
Notched Izod (kJ/m) |
0.15 |
|
Linear Expansion (/°C x 10-5) |
12 |
|
Elongation @ Break (%) |
150 |
|
Strain @ Yield (%) |
15 |
|
Maximum Operating Temperature (°C) |
55 |
|
Water Absorption (%) |
0.02 |
|
Oxygen Index (%) |
17 |
|
Flammability UL94 |
HB |
|
Volume Resistivity (log ohm.cm) |
17 |
|
Dielectric Strength (MV/m) |
22 |
|
HDT @ 0.45 MPa (°C) |
75 |
|
HDT @ 1.80 MPa (°C) |
46 |
|
Melting Temperature Range (°C) |
120 – 180 |
|
Mould Shrinkage (%) |
3 |
|
Mould Temperature Range (°C) |
30 – 70 |
What industries benefit from HDPE?
Known for its versatility, its use in many applications across industries is everyday due to properties, such as:
Agriculture & Marine
Agriculture Solutions: HDPE is invaluable for irrigation pipes, water storage solutions, and fertilizer delivery systems, due to its minimal water absorption and chemical-resistant properties.
Marine Environments: A good material for producing parts resistant to saltwater corrosion and low water absorption. Examples of applications for HDPE include floating structures, such as rafts, piers, and boat components.
Construction and Infrastructure
Building Materials: HDPE provides moisture control and energy efficiency in construction when used as house wraps and vapor barriers. Another place it can be found is in greenhouses.
Piping Systems: Critical for transporting water, wastewater, gas, and chemicals through pipes due to HDPE’s resistance to corrosion and chemicals.
Consumer Goods
Everyday Products: HDPE is a normal material for cutting boards, food storage containers, trash cans, and recycling bins. Playground equipment also utilizes it due to its outstanding properties.
Industrial & Automotive
Heavy-Duty Applications: Chemical tanks, industrial containers, automotive fuel tanks, and bumpers all benefit from HDPE’s chemical resistance, moisture resistance, and strength-to-weight ratio.
Medical & Healthcare
Medical Devices & Packaging: HDPE’s non-toxic and chemically resistant nature makes it a trusted material in the medical industry for packaging. Pharmaceuticals, such as over-the-counter pill bottles and specific medical devices, are also made from HDPE. Its safety features are a vital characteristic for these applications, ensuring the integrity of the packaged items.
Packaging
Containers & Bottles: Known for producing bottles and containers for milk, water, and juice, HDPE also creates bottles for detergents and cleaning chemicals.
Food Storage Solutions: Thin films are ideal for wrapping food items, while molded containers are standard for food storage.
Flexible Packaging: Mailing envelopes and other flexible packaging materials utilize HDPE due to its lightweight yet strong properties.
FAQs
HDPE, or High-Density Polyethylene, is a durable and versatile plastic used in numerous applications.
HDPE, or high-density polyethylene, is primarily composed of carbon and hydrogen atoms, forming a durable and versatile plastic material.
Packaging, containers, pipes, and construction materials.
Yes, HDPE (High-Density Polyethylene) is considered food safe. It is a non-toxic, durable plastic commonly used for food containers and packaging.
Cutting HDPE can be done using a variety of methods, including saws, routers, and hot wire cutters. Select the suitable tool based on the part’s thickness and complexity.
Yes, HDPE can be 3D printed using specialized printers and filaments designed for this material.
