PET vs PLA: Which is the Better Choice for Sustainable Packaging?

First Published: May 3, 2024
PET vs PLA: Which is the Better Choice for Sustainable Packaging?

PET vs PLA

The quest for more environmentally friendly packaging solutions, two materials have emerged as frontrunners: PET (polyethylene terephthalate) and PLA (polylactic acid). Both have their advantages and drawbacks, and the choice between them ultimately depends on the specific requirements and priorities of the packaging application. In this article, we’ll explore the key differences between PET and PLA, their sustainability credentials, and factors to consider when choosing one over the other.

According to the National Library of Medicine, PET accounted for 44.7% of single-serve beverage packaging in the US in 2021. In comparison, aluminum cans accounted for 39%, glass for 11%, and high-density polyethylene (HDPE) for 3.4%.

What is PET?

PET is a widely used plastic derived from petroleum-based resources. It is known for its clarity, strength, and lightweight properties, making it a popular choice for beverage bottles, food containers, and other packaging applications. While PET is technically recyclable, a significant portion of PET packaging still ends up in landfills or the environment due to inefficient recycling practices.

What is PLA?

PLA, on the other hand, is a bioplastic derived from renewable resources such as corn, sugarcane, or cassava. It is biodegradable under specific conditions (industrial composting facilities with appropriate heat and moisture levels) and has similar properties to traditional plastics in terms of transparency and durability.

Packaging Performance

In addition to sustainability considerations, what is the difference in how the two materials perform at their main job of being effective packaging materials?

Barrier Properties:
PET has excellent barrier properties against gases like oxygen, carbon dioxide, and moisture vapor. This makes it ideal for packaging foods, beverages, and other products that require an extended shelf life by preventing spoilage and maintaining freshness.

PLA, on the other hand, has lower barrier properties compared to PET, which can limit its application in certain packaging scenarios where a high barrier is necessary.

Thermal Resistance:
PET exhibits superior thermal resistance, with the ability to withstand higher temperatures without deforming or losing its structural integrity. This makes it suitable for packaging products that may be exposed to high heat during manufacturing, transportation, or end-use, such as hot-fill beverage containers or microwavable food trays.

PLA has a lower melting point and can deform or degrade at higher temperatures, limiting its use in applications requiring high heat resistance.

Impact Strength and Rigidity:
Both PET and PLA are relatively rigid materials, but PET generally exhibits better impact strength and resistance to cracking or shattering. This makes PET a preferred choice for packaging applications where the containers or bottles may be subjected to rough handling or drop impacts during transportation and distribution.

PLA, while still reasonably durable, may be more prone to cracking or breaking under similar impact forces.

Clarity and Transparency:
PET is known for its exceptional clarity and transparency, making it an attractive choice for packaging applications where product visibility is desirable, such as clear beverage bottles or clamshell containers. PLA can also be produced in a clear or transparent form, but it may have a slightly more opaque or hazy appearance compared to PET.

Chemical Resistance:
PET is resistant to many chemicals, including acids, bases, and solvents, making it suitable for packaging certain chemical products or household cleaners.

PLA, being a more natural and biodegradable material, may exhibit lower chemical resistance and could be susceptible to degradation when exposed to certain chemicals or harsh environments.

These differences in performance characteristics should be carefully evaluated when selecting between PET and PLA for specific packaging applications.

Sustainability Comparison

Raw Materials:
PET is derived from non-renewable fossil fuels, while PLA is made from renewable plant-based sources, giving PLA an advantage in terms of resource sustainability.

Production Process:
The production of PET involves more energy-intensive processes and generates higher greenhouse gas emissions compared to PLA, which has a relatively lower carbon footprint.

End-of-Life Options:
PET can be recycled, but the recycling rates are often low due to various challenges. PLA, on the other hand, is biodegradable and compostable under specific conditions, offering a more sustainable end-of-life option.

PET Recycling Process:

Collection and Sorting: Used PET containers and packaging are collected from various sources, such as curbside recycling programs, drop-off centers, and deposit return systems. The collected materials are then sorted to separate PET from other plastics and contaminants.

Cleaning and Grinding: The sorted PET containers are cleaned to remove any residual contents, labels, or other contaminants. This can involve various processes like air classifiers, water baths, and chemical washes. The cleaned PET is then ground into small flakes or pellets.

Decontamination and Purification: The PET flakes or pellets undergo additional cleaning and decontamination processes to remove any remaining impurities or contaminants. This can involve processes like hot wash baths, friction washing, and chemical treatments.

Extrusion and Pelletization: The cleaned and decontaminated PET flakes are melted and extruded into continuous strands, which are then cooled and cut into small pellets. These recycled PET (rPET) pellets can be used as raw material for new PET products.

Manufacturing: The rPET pellets are melted and processed using injection molding, blow molding, or other manufacturing techniques to create new PET products, such as bottles, containers, fibers, or other packaging materials.

PLA Recycling & Composting Process:

Collection and Sorting: PLA packaging materials need to be separated from other plastics and waste streams during collection and sorting processes. This is crucial because PLA requires specific composting conditions and cannot be effectively recycled with traditional plastic recycling methods.

Industrial Composting: Sorted PLA packaging materials are sent to industrial composting facilities that provide the necessary conditions for PLA biodegradation. These facilities maintain specific temperature, moisture, and oxygen levels to facilitate the breakdown of PLA by microorganisms.

Not every community has the required facilities to compost PLA materials.

Composting Process: PLA packaging is mixed with other organic materials, such as food waste and yard trimmings in the composting facility. The controlled temperature and moisture levels, along with the presence of microorganisms, facilitate the breakdown of PLA into carbon dioxide, water, and biomass.

Curing and Screening: After the composting process is complete, the resulting compost undergoes a curing phase to stabilize and mature the material. The cured compost is then screened to remove any remaining non-biodegradable contaminants.

End Product: The final product is a nutrient-rich compost that can be used as a soil amendment or fertilizer for agricultural and landscaping applications.

It’s important to note that while PET recycling is a well-established process, the infrastructure for PLA composting and recycling is still developing in many regions. Effective collection and separation of PLA from other waste streams remain a significant challenge for widespread PLA recycling.

It’s also worth mentioning that some companies are exploring chemical recycling methods for PLA. These methods could potentially allow the material to be broken down into its molecular building blocks and repolymerized into new PLA products, similar to traditional plastic recycling processes.

Carbon Footprint:
Studies have shown that PLA generally has a lower carbon footprint than PET when considering the entire life cycle, from raw material extraction to disposal.

Factors to Consider

While PLA may seem like the more sustainable choice based on the above comparisons, there are several factors to consider when choosing between PET and PLA for packaging applications:

Cost: PLA is generally more expensive than PET, which can be a barrier for some applications, especially those with tight budgets.

Performance Requirements: As detailed above, PET has better performance characteristics and would be preferred for applications requiring higher heat resistance or barrier properties than PLA.

Recycling Infrastructure: In areas with well-established PET recycling facilities, PET may be a more practical choice, as PLA requires specific industrial composting facilities for proper disposal.

Product Shelf Life: For products with longer shelf lives, the durability and barrier properties of PET may make it a better choice compared to PLA, which can degrade over time.

Conclusion

Both PET and PLA have their advantages and drawbacks when it comes to sustainable packaging. PLA offers a more environmentally friendly option in terms of raw materials and end-of-life disposal, while PET may be more suitable for certain applications due to its performance characteristics and existing recycling infrastructure.

Ultimately, the choice between PET and PLA should be based on carefully evaluating the specific product requirements, sustainability goals, and available resources.

As sustainable packaging solutions evolve, it’s important to consider the broader environmental impact and seek innovative ways to reduce waste and promote a circular economy.

As an example, I recently saw an article at Plastics Today that looked at a Korean brand that was launching a labelless PLA bottle which is to be managed via a circular recycling system. I’ve written about labelless packaging for beverages here and here.

Further Reading

Polyethylene Terephthalate (PET) Bottle-to-Bottle Recycling from NIH.gov

PLA or PETr – which is best for food packaging?

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