This article will discuss important considerations when choosing a polymer liner for environmental applications, the drawbacks of PVC, and the benefits of using strengthened polymers such as high-density polyethylene (HDPE).
Polymers, or plastics, are considered among the greatest inventions of our generation. Its introduction marked the first time humans did not rely on nature’s metal, stone, wood, and bone for production. Plastics were the perfect complement to our industrialized society, enabling a new level of manufacturing that supported the spread of material wealth across the globe (1). Unfortunately, the rapid proliferation of plastics led to unexpected uses.
The material’s low cost and ease of manufacturing, for instance, meant that plastics were often used in disposable products like grocery bags, straws, milk cartons, and six-pack rings. And unlike the disposable product’s short-term use, once dumped in nature it can take several hundred years to decompose—even based on optimistic estimates (2). The widespread use and dumping of disposable plastic products have led to an environmental crisis headlined by rapidly filling landfills and the Great Pacific Garbage Patch (3).
But the same materials being used to pollute the Earth unintentionally can help protect it. For decades, polymer liners made with polyvinyl chloride (PVC) and polyethylene (PE) have been used to separate landfill contents from the surrounding ecology. And environmental non-profits such as the Ocean Cleanup are designing autonomous systems made with plastic to help collect and recycle plastic waste (4).
PVC liner for environmental applications
Modern landfills have two design phases: before construction and before closure. In both phases, engineers turn to polymer liners to help prevent the landfill’s contents from leaking into the surrounding environment. Engineers use PVC liners to create a very-low permeability barrier against waste fluids or leachate. For the liner to do its job effectively, it must maintain performance throughout a long service life spanning multiple decades.
Therefore, the best liners in environmental applications provide very-low permeability, high resistance to chemical degradation, high durability, and flexibility. Most of these properties are determined by the polymer’s molecular structure and the liner’s thickness. The polymer’s molecular structure determines the polymer’s tensile strength, density, and permeability. The thickness of the liner affects overall strength, weight, flexibility, and cost, with the liner’s permeability directly proportional to its thickness.
For each landfill design phase, choosing a polymer and the liner’s thickness should be among the first steps (5).
The drawbacks of using PVC liners in environmental applications
Some polymers are better suited for environmental applications than others. While known for their ease of use, PVC liners are not naturally flexible and rely on additives like phthalates for their flexibility. PVC can also contain traces of bisphenol A (BPA) and can release dioxins. The National Institutes of Health (NIH) lists phthalates, BPA, and dioxins as toxins that cause adverse health effects and are suspected endocrine disruptors (6). In addition to being harmful, PVC additives can leach out over time, causing embrittlement of the liner.
It is also important to note that the permeability of a PVC is about two orders of magnitude higher than an equivalent thickness of HDPE, which means any contaminants in the landfill are more likely to seep through the PVC liner over time, potentially causing soil and groundwater contamination. In place of PVC liners, engineers can use HDPE liners. HDPE liners provide many of the same benefits as PVC but are non-toxic and made with a very easy polymer to recycle (7).
Using HDPE liner in environmental applications
HDPE is a unique configuration of polyethylene that exhibits minimal branching of its polymer chains and is, therefore, more rigid and has a higher density when compared with linear low-density polyethylene (LLDPE). Like a PVC liner, an HDPE liner will also confer several benefits regardless of its thickness, such as its high resistance to corrosion and long-term ultraviolet (UV) resistance.
Additionally, the chemical resistance of HDPE is among the best of commonly used lining materials and far better than PVC, especially against acids, bases, and hydrocarbons. The low-temperature characteristics of HDPE are also better. While PVC can become brittle at -40°C, it requires a temperature closer to -90°C to have the same effect on HDPE.
- 1. https://www.sciencehistory.org/the-history-and-future-of-plastics
- 2. https://www.nationalgeographic.com/magazine/2018/06/plastic-planet-waste-pollution-trash-crisis/.
- 3. https://en.wikipedia.org/wiki/Great_Pacific_garbage_patch
- 4. https://theoceancleanup.com/milestones/system001/
- 5. Topliff, CR, “Uses and Installation of HDPE Liner to Reduce Soil Erosion and Prevent Water Loss.” West Texas A&M. (2018). Accessed on June 2019. https://wtamu-ir.tdl.org/handle/11310/153.
- 6. https://toxtown.nlm.nih.gov/chemicals-and-contaminants/polyvinyl-chloride-pvc
- 7. https://www.azocleantech.com/article.aspx?ArticleID=255