Bioplastics, Part 1: Breaking Down PLA, PHA, & PHB

The world of bioplastics can feel a bit like alphabet soup...PLA. BPA-free. PHA. BPI-certified. PHB. L-M-N-O-P.

Let’s break this down.

The ABC’s of Bioplastics

To be considered a bioplastic, a material must be one of the following:

1. Biobased - Made from a renewable organic sources, such as corn starch or sugarcane
2. Biodegradable - Breaks down completely by natural means
3. Biobased AND Biodegradable

Companies have derived a host of materials from plant-based sources to create plastic alternatives. We see packaging containers and wrappings, straws, bags, bottles, and machine parts in agriculture, medicine, and auto manufacturing. Some can be waterproof, heat-resistant, or insulating.

Bioplastics may be molded, pressed, injected, and 3D printed. They take on many of the physical properties of petroleum-based plastics. Almost any product that’s traditionally plastic...can be made from bioplastics.

Together, bioplastics represent an exciting future: a reduced reliance on fossil fuels (oil) for plastic production.

The 3 Main Bioplastics

PLA - Polyactic Acid
Manufacturers start with natural sugars found in corn starch, cassava (yuca root), sugarcane or beets. Citric acid helps the sugars join in long-chain molecules, or polymers.

Added enzymes transform these long glucose polymers into dextrose, which microorganisms digest (ferment) into lactic acid. This sugar fermentation is similar to the one that gives sourdough bread its classic tangy nature.

Hang in there, chemistry class is almost over...

This lactic acid further transformed into rings of lactide. These rings are opened up and then stitched together to form polylactic acid polymers. These structures take on plastic-like qualities.

Now, creativity kicks in. Production facilities form utensils, packaging, and other products. 

Minnesota-based NatureWorks, a leading producer of PLA, sells their Ingeo product to plastic alternative brands we find in supermarkets.

PHA - Polyhydroxyalkanoate
Certain microorganisms produce PHAs when they are deprived of nutrients like nitrogen, oxygen, and phosphorus. Instead, they feed high levels of carbon, usually in the form of sugars or fats. They store carbon reserves as granules within their cell walls.

Electron microscope imaging shows PHA-producing bacteria. We see their carbon stores as white granules, stored within their cell walls. Credit: Department of Chemistry, UiT The Arctic University of Norway

Once they have other necessary nutrients needed to grow and reproduce, they can tap into this stored extra fuel. Before they do, companies collect these PHA carbon reserves for commercial use. 

The harvested PHA has a similar chemical structure as traditional, petroleum-based plastics. It can be combined, molded, injected and formed as needed.

Biodegradable and harmless to living tissues, PHA is perfect for medical applications, like dissolvable sutures, slings, bone plates, and even skin grafts. Outside of medicine, it’s often a substitute for single-use food packaging.

PHB - Polyhydroxybutyrate
A subclass of PHAs, PHB polymers also come from bacteria, which create and store carbon reserves (see PHA reference image). Production companies harvest PHBs, like PHAs, and create "plastic pellets" for a multitude of uses.

Pellets of the bacteria-produced PHB, which can then be injection molded or formed to whatever shape is needed.

They are also UV stable, so they can survive exposure to sunlight without breaking down quickly. This contrasts with PLAs (the polylactic acids we first introduced), which can be sensitive to sunlight.

PHB is not water-soluble and does not float. It also resists moisture and proves to be a decent aroma barrier. These qualities make it a great substitute for polypropylene (PP), a petroleum-based plastic commonly used for food packaging wrap. PHBs often work best as “mixed” copolymers for added elasticity and other plastic qualities.

Breaking Down Bioplastics (literally)

Many traditional petroleum-based plastics are light enough to remain suspended in the first three feet of the ocean surface. In this environment, heat and sunlight may break them down, but this creates another problem: microplastics.

These are so small they can be consumed by microscopic organisms, like plankton. Then they make their way up the food chain, even into the fish we enjoy.

With PLAs on the other hand, we see four typical degradation methods:

1. Recycling - Chemical or mechanical processes allow companies to reuse these bioplastics with virgin (new) PLAs. This is the best renewable option.
2. Composting - Within commercial or industrial facilities, this utilizes an initial chemical process followed by microbe digestions. It leaves only water and carbon dioxide as byproducts.
3. Incineration - Burning bioplastics releases no toxic chemicals or heavy chemicals, unlike petroleum-based plastics. This option is relatively safe, just wasteful.
4. Landfill - This environment rarely contains the right combination of moisture, oxygen and heat for biodegredation or composting processes. Dumping bioplastics makes them little better than traditional plastics in terms of lifespan. They may never fully decompose.

For PHAs and PHBs, various bacteria have proven effective in biodegradation. Some microbes are soil-based, others anaerobic, and others still, marine-based.

In the ocean, the density of bioplastics means they sink to the ocean floor. Some argue this could help facilitate natural biodegradation from microorganisms living on the seabed.

This is not the ideal environment for biodegradation, but it’s more promising than microplastics collecting in the open ocean.

A Final Thought

Many counties process bioplastics appropriately. This can make them a great alternative (without compromising quality) to the plastics we’ve grown accustomed to in our everyday lives.

That said, there are hidden truths behind bioplastics. Before committing to them, check out their Fuller Environmental Picture, the next post in our Bioplastics series.

🌊🌊🌊🌊🌊 

Our hope is to inspire people to perform their own small-scale beach cleanups whenever they visit our beautiful oceans. Every bit helps, so we hope you join the community and share your stories.

Thanks, and we’ll see you on the next wave!

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