When to use HDPE vs. LLDPE Geomembrane?

When to use HDPE vs. LLDPE Geomembrane?

When first selecting a geomembrane material for a project, clients often come to us asking “What are the differences between HDPE and LLDPE geomembranes and which material should I choose for my project?” Both are commonly used in the industry, and visually look very similar, but they do have distinct properties and advantages. In this article, we will explore the advantages and disadvantages of both products:

HDPE – High Density Polyethylene 

vs  

LLDPE – Linear Low-Density Polyethylene

HDPE and LLDPE Molecular Configuration Differences and Its Impact on Material Properties

Both HDPE and LLDPE are part of the same family of materials, polyolefins, so they share some common attributes, but they differ in their final molecular structure and crystallinity. Crystallinity refers to the presence of regions where polymer chains pack efficiently into dense regions that are impervious to both oxygen and chemicals, conferring exceptional strength and resistances.

HDPE has a highly crystalline configuration, so its polymer chains are more orderly structured, resulting in a denser, stronger, and more resistant material. LLDPE has medium crystalline structure, meaning its polymers chains are less orderly than those of HDPE, resulting in a slight loss in strength and resistances, but gains greater flexibility. Other materials, like LDPE have even lower crystallinity while PVC has no crystallinity at all.

A good simple analogy to understand the difference between HDPE and LLDPE’s molecular structure is to imagine a carton box.

• HDPE’s carton box is filled with cubes, that can be neatly stacked next each other. This results in a tightly packed box with little room for any other element to infiltrate or break the order of the container. This illustrates how HDPE achieves its superior strength and resistances as it is difficult for particles to infiltrate and disrupt the denser HDPE configuration.
• LLDPE’s carton box is filled with both cubes and round spheres. Some areas contain neatly packed cubes liked HDPE, but every so often, the order is broken by the presence of spheres that don’t fit tidily into the box. While these breakages represent weakness points that can be attacked by other particles (like chemicals particles) causing a slight loss in strength and resistances compared to HDPE, it does allow LLDPE to have greater flexibility compared to the stiffer HDPE.

Box of cubes (HDPE)

Spheres cannot be packed as tightly or orderly

Differences Between HDPE and LLDPE

Let’s take a closer look at some of the difference between HDPE and LLDPE.

Material flexibility

Material flexibility is the main factor when comparing HDPE and LLDPE, with LLDPE being more flexible. LLDPE’s suppleness means it easily adapts to deformation or obstructions without losing material performance. This means LLDPE is ideal in applications where the geomembrane is subject to deformation or bending movements over time because such movements may take stiffer HDPE membranes above their yield point, cause the liner to be damaged and weaken the product. LLDPE materials can be subject to bending without damage.

Prefabrication

Because LLDPE is flexible and resistant to bends, it can be prefabricated into large panels in factory conditions. This signifies that all welding and testing for the LLDPE can be performed indoors, in controlled settings, without the effects of wind, dust or rain. The harder HDPE on the other hand must be entirely welded and tested at the jobsite. Depending on the thickness of the LLDPE geomembranes, panels of up to 25,000 SQM can be prefabricated into one. This is an advantage for smaller projects, because a single panel designed to the project specifics can be rapidly deployed and installed.

Tensile Strength and Puncture Resistance

HDPE is a tougher material than LLDPE. Comparing an HDPE and LLDPE liner of the same thickness, the HDPE geomembrane will have superior puncture resistance and tensile strength.

Chemical Resistance & UV Resistance

Over the years, HDPE has become the standard lining material for landfills, mining ponds, coal ash ponds and other environment protection projects because of this unparallel chemical and UV radiation resistances. Due to its higher crystallinity, HDPE will have the best resistance to any harsh chemicals. Even when exposed to tough conditions, HDPE can maintain its performance for decades.

Conclusion

In summary, if your material strength and resistances are important to your project and the liner won’t be subject to movements, then HDPE is be better choice, but if material flexibility and adaptability to displacements are key to your project, then the use of LLDPE needs to be explored.