ASTM D6954-24: Plastic Biodegradability

Using oxo-biodegradable technology can prevent future contributions to the accumulation of plastic waste that has escaped into the environment. Oxo-biodegradable plastic serves as a solution to littered plastic because it is recyclable and will degrade without releasing methane. ASTM D6954-24: Standard Guide For Exposing And Testing Plastics That Degrade In The Environment By A Combination Of Oxidation And Biodegradation provides guidelines to measure the degradability of oxo-biodegradable plastics.

Oxo-Degradable vs Oxo-Biodegradable Plastic

It is important to note that oxo-biodegradable plastic is not the same as oxo-degradable plastic. Oxo-degradable plastic does not biodegrade but breaks into microplastics which are then released into the environment and cause significant harm, especially to ocean life. They quickly fragment in smaller and smaller pieces (i.e., microplastics) that do not break down at the molecular or polymer level like biodegradable and compostable plastics. The resulting microplastics are left in the environment indefinitely until they fully break down over a very long period of time. They can be recycled but not composted.

By contrast, oxo-biodegradation means degradation resulting from oxidative and cell-mediated phenomena, either simultaneously or successively. The plastic degrades by oxidation until its molecular weight is low enough to be accessible to bacteria and fungi, who then recycle it back into nature. These plastics are tested for degradation, biodegradation, and ecotoxicity according to ASTM D6954-24.

What Is ASTM D6954?

ASTM D6954-24 provides a framework to compare and rank the controlled laboratory rates of oxo-biodegradable plastics. Specifically, the standard’s framework compares the degradation and degree of physical property losses of polymers by thermal and photooxidation processes as well as the biodegradation and ecological impacts in defined applications and disposal environments after degradation. Disposal environments range from exposure in soil, landfill, water, and municipal or industrial compost in which thermal oxidation may occur and land cover and agricultural use in which photooxidation may also occur. These environments may be compared and ranked using standard biometric test methods and measuring carbon dioxide evolution.

The standard is used to compare and rank the rate and degree of thermal oxidative degradation of a plastic material relatively to a molecular weight range that can be established as biodegradable in a chosen environment. Moreover, ASTM D6954-24 uses a tiered criteria-based approach to assess the consecutive oxidation and biodegradability of plastic products and ecological impacts in defined applications. Each tier in includes objectives and a summary that presents test methods, method principles, test duration, and interpretation of results. Here are the three tiers:

• Tier 1: Measuring by both thermal and photooxidation processes and other abiotic processes
• Tier 2: Measuring biodegradation
• Tier 3: Assessing ecological impact of the products from these processes

The tiered approach is chosen in the laboratory for convenient separation of oxidative degradation, biodegradation, and ecological impact stages even though in the real world all three are likely to be concurrent rather than consecutive.

How Do Oxo-Biodegradable Plastics Work?

Oxo-biodegradable plastics are a type of plastic that biodegrade faster in the presence of oxygen, transforming into the harmless, biodegradable matter within a few months to a few years. They are made of petroleum-based raw materials and a small number of metal salts. The metal makes it possible for the molecular structure of plastic to break down when exposed to heat and oxygen. 

Over time, the oxo-biodegradable plastic comes to a state where microorganisms can process it into water, carbon dioxide, and biomass. This shortens the degradation from centuries to months or a couple of years. The degradation time differs depending on the measure of exposure to degradation elements like sunlight, heat, humidity, and microorganisms.

ASTM D6954-24: Standard Guide For Exposing And Testing Plastics That Degrade In The Environment By A Combination Of Oxidation And Biodegradation is available on the ANSI Webstore.