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Building on our previous introduction to bio-plastics, this article focuses on quadrants 1 & 2 of the image below to further explain biodegradable vs. compostable when it comes to skincare containers
Once you understand the differences between petroleum-based and bio-based plastics and which ones are biodegradable, there is still further complexity when discussing biodegradability and compostability. There is no global standardization for how to test or judge materials as being compostable or not.
Biodegradability means that a substance is able to decompose with the help of microorganisms. The fact that something is biodegradable says nothing about the timeline on which that occurs or whether or not the by-products on the way to decomposition are completely safe for the environment (i.e. methane production from biodegrading substances in landfills is harmful, also things like BPA are toxins that leach out). Non-plastic natural materials like cork or a bamboo toothbrush will biodegrade over a reasonable timeframe depending on temperature and levels of moisture and oxygen.
Compostable describes a substance that can biodegrade into natural elements in a compost environment. The process usually takes about 60-180 days. The ASTM (American Society for Testing and Materials) defines compostable as anything that undergoes degradation by biological processes to yield CO2, water, inorganic compounds, and biomass at a rate consistent with other compostable materials and leaves no visible, distinguishable, or toxic residue.
So... compostable products are all biodegradable. However, biodegradable products are not all able to be composted.
When consumers see the words "biodegradable" on a packaging label, it can create false reassurance. Throwing these substances in the trash and allowing them to get to the landfill will result in eventual biodegradation; what often isn't clearly communicated is the timeline. Depending on the chemical structure and origin of the material as well as mechanical properties like thickness, the timeline to full biodegradation may be unacceptably long.
Within the category of compostable materials, there is yet another distinction: that of industrial versus home compostability. Simply explained, the conditions needed to compost some materials in a timely fashion can only be created in a specific, controlled environment. Industrial composting occurs when various factors are managed in a controlled fashion: temperature (typically 40–60°C/104-140oF), moisture and oxygen content, particle size, the carbon-to-nitrogen ratio, and the amount of turning. The products of industrial composting are CO2, water, and compost. The compost includes nutrients, and can be returned to the agricultural environment as a beneficial soil enhancer.
Currently, rigid skincare containers that are advertised as compostable are generally only able to undergo the process in industrial conditions. Many of these are PLA, which we discuss below. However, newer materials that biodegrade much more readily in the natural environment (when industrial composting isn't available) are hopefully going to become more available.
Global cultural change is not rapid.
The distinction between biodegradable and compostable can create opportunities, but also issues. As manufacturers find new ways to accelerate or improve recyclability, biodegradation and compostability, there needs to be constant re-evaluation and monitoring for unintended effects of consequences.
An example of this is "oxo-degradable" plastic. These products have biodegradable materials mixed into the non-biodegradable plastic structure to allow more rapid degradation. The problem is that this accelerated breakdown creates microplastics rapidly (degradation, not biodegradation) before biodegradation starts. Second generation materials (labelled as oxo-biodegradable) exist that work by degrading rapidly, but also allowing bacteria to start biodegradation simultaneously. At bareLUXE™, we have utilized a small amount of oxo-biodegradable plastic in our shipping materials, but we are keeping our eyes on the data/technology to determine if we need to change products.
A second example that illustrates the differences between biodegradability and compostability can be found when comparing PLA to PHA.
PLA (poly lactic acid) initially took the bio-plastic world by storm. Both bio-based and biodegradable, PLA is made from corn, sugarcane, potatoes, and other sources. PHA (polyhydroxyalkanoate) is the exciting up-and-comer. Also bio-based and biodegradable, PHA is made from corn and other sources. Both PLA and PHA can be used as substitutes for various traditional plastics (i.e. PET, PP). The two have entirely different chemical structures due to the way they are synthesized.
A challenge with PLA is that, though biodegradable, it will still take ~100+ years to fully disappear in the landfill. Industrial composting is necessary and it carries with it the risk of contaminating the plastic recycling chain if disposed of incorrectly. If it's mass-produced with incomplete or misleading disposal instructions (and if consumers just think it's fine to replace single-use plastics with it and move on), we are just going to end up with a huge PLA buildup in our landfills - not clearly an improvement, though still likely slightly better on a mass-scale due to the fact manufacturing carbon footprint is lower and resources used are renewable.
PHA, on the other hand, can be structurally modified depending on the product that it is used for. This allows a bit more "designability" when taking end-of-life disposal into account. It still isn't recyclable through normal streams, but it is definitely industrially compostable and some versions are able to be composted rapidly in the home environment. Biodegradation in the landfill environment appears to be much faster than PLA, but PHA use is still quite limited to know certainties.
It is very likely that future solutions will be hybrid materials that build upon most or all the technologies to date. We want to start a skincare container revolution and are working to completely eliminate plastic plus integrate newer, novel materials into our container options.
GreenPeace: biodegradable plastics facts
National Geographic article on bioplastics
Plastics Europe Factsheet