Bio-plastics: is not gold all that glitters

It shouldn’t be a surprise that there is often confusion when talking about bio-plastics, In this post we will clarify some terms and also shed some light on the cons of bio-plastics.

Let’s start by listing some of the different types of plastic:

- Degradable: All plastic is degradable, even traditional plastic, however not all degrade at the same speed.

Some additives to traditional plastics make them degrade more quickly. Photodegradable plastic breaks down more readily in sunlight; oxo-degradable plastic disintegrates more quickly when exposed to heat and light.

- Biodegradable: Biodegradable plastic can be broken down completely into water, carbon dioxide and compost by microorganisms under the right conditions.

- Compostable: Compostable plastic will biodegrade in a compost site. Microorganisms break it down into carbon dioxide, water, inorganic compounds and biomass at the same rate as other organic materials in the compost pile, leaving no toxic residue.

If we turn our focus now to bio-plastics, we can identify two main types:

- PLA (polyactic acid): Typically made from the sugars in corn or potato starch, or sugarcane. It is biodegradable, carbon-neutral and edible.

PLA can look and behave like polyethylene (used in plastic films, packing and bottles), polystyrene (plastic cutlery) or polypropylene (packaging, textiles).

- PHA (polyhydroxyalkanoate): Made by microorganisms that produce plastic from organic materials. The microbes are deprived of nutrients like nitrogen or oxygen, but given high levels of carbon.

They produce PHA as carbon reserves, which they store in granules until they have more of the other nutrients they need to grow and reproduce. Companies can then harvest the microbe-made plastic.

Because it is biodegradable and will not harm living tissue, PHA is often used for medical applications such as sutures, slings, bone plates and skin substitutes.

Now that we have clarified some of the different types of bio-plastic, let’s address the controversy.

While bio-plastics are generally considered to be more eco-friendly than traditional plastics this isn’t necessarily true when the materials’ life cycles were taken into consideration.

Bio-plastics production results in greater amounts of pollutants, due to the fertilisers and pesticides used in growing the crops and the chemical processing needed to turn organic material into plastic.

While the biodegradability of bio-plastics is an advantage, most need high temperature industrial composting facilities to break down and very few cities have the infrastructure needed to deal with them.; as a result, bio-plastics often end up in landfills where, deprived of oxygen, they may release methane, a greenhouse gas 23 times more potent than carbon dioxide.

When bio-plastics are not discarded properly, they can contaminate batches of recycled plastic and harm recycling infrastructure. If bio-plastic contaminates recycled plastic, the entire lot could be rejected and end up in a landfill. So separate recycling streams are necessary to be able to properly discard bio-plastics.

Another point is the fact that the land required for bio-plastics competes with food production because the crops that produce bio-plastics can also be used to feed people. In addition, the water and petroleum used to run the farm has a greater carbon footprint.

Finally, at the moment bio-plastics are still relatively expensive, 20 to 50 percent more costly than fossil fuel based plastics because of the complex process used to convert corn or sugarcane into the building blocks for the final product.

In summary, right now, it’s hard to claim that bio-plastics are more environmentally friendly than traditional plastics when all aspects of their life cycle are considered: land use, pesticides and herbicides, energy consumption, water use, greenhouse gas and methane emissions, biodegradability, "recyclability" and more, but as researchers around the world work to develop greener varieties and more efficient production processes, bio-plastics do hold promise to help lessen plastic pollution and reduce our carbon footprint.