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Bioplastic Standards 101

by Green Plastics


The website greenbiz.com recently published an article called “Improved Standards Needed for Bioplastic Claims.”  The gist of the article is just what the title says: there is a lack of standards for biodegradable plastics, and that causes problems.

But to anyone who is new to the field and interested in learning more, this leaves open a whole host of questions.

  • Who creates standards? Who enforces them?
  • How are standards actually measured?
  • What do these standards actually define, anyway?

This article will give a brief answer to each of these questions, and point you in the right direction for finding out more. It will also highlight an important conclusion: The big problem in the “green plastics” industry today isn’t a lack of standards; it is the misuse and misunderstanding of existing standards by producers, consumers, politicians and the media.


Let’s start with the last question first.

What do these standards actually define, anyway?

You have probably seen phrases like “Our plastic products meet the ASTM D6400 standard for compostability.”

In this case, ASTM D6400 is the name of a document that defines two things:

  • A set of scientific tests that can be used to measure properties of a plastic
  • A set of criteria (threshold values) that these measurements must meet for the plastic to be considered “compostable”.

This kind of standard is called a specification. A specification is an explicit set of requirements that have to be satisfied by a material, product, system, or service, to be designated with a particular label. A specification lets you answer a “YES/NO” question about a material. In the case of ASTM D6400, the question is: “Is this material compostable?”

Not all standards are specifications, however. For example, ASTM D5338 defines a way of measuring aerobic biodegradation of a plastic under laboratory composting conditions. This document describes:

  • An exact scientific experimental procedure you can execute to carry out a test
  • An exact way of measuring and calculating the results of the test.

This kind of standard is called a test method. A test method is a definitive procedure that can be applied to a material to produce a test result. A test method gives you an objective way of obtaining a measurement, but does not answer any kind of “YES/NO” question. It is impossible to “pass” or “fail” or “conform to” a standard that is a test method.

This is one of the most misunderstood and abused issues when it comes to claims about “biodegradability.” Many companies claim that their products “conform to” an ASTM standard for biodegradability, or “pass” the ASTM test for biodegradability, or “can be defined as biodegradable” based on an ASTM standard. All of these claims are incorrect.

ASTM has defined several tests for biodegradability, using different methods and under different conditions. ASTM D5338 is just one of them. Another one is ASTM D5988, which tests aerobic biodegradation in soil. ASTM D5511 is a test for anaerobic biodegradation within a device called a “high-solids anaerobic digestion unit.” There are tests for many different types of biodegradation under many different conditions.

But the key fact is: None of the tests for biodegradability produce a “pass/fail” result.

Instead, when a material is tested for biodegradability using an ASTM test method, the result looks something like this:

astm5988 data graph


Here we see four different materials represented by four different curves. The y-axis is the percent of the material that has biodegraded (measured according to the instructions in the standard), and the x-axis is time. Obviously, some of these materials are more biodegradable than others, and at least one of them can probably be called “non-biodegradable” according to this test.

But do any of these materials qualify as being “fully biodegradable”? The blend between LDPE and starch was 30% biodegraded after 90 days, but is that enough that it should get the label “biodegradable”? The pure starch foam reached 80% after 90 days, but is that enough? Is there any way of telling whether any of these would reach 100%, given enough time? Should it even need to reach 100% to deserve the label “biodegradable”? How high does it need to get? How quickly should it happen?

The ASTM D5988 does not address any of these questions. The fact that a company says it has “tested its material using ASTM D5988” does not answer any of these questions, either. This standard is just a method for producing a graph like the one you see above. It gives no guidelines for what threshold is “good enough” for anything.

How are standards actually measured?

So how does one actually come up with a graph like the one in the example above?

Consider ASTM D5338 as an example. The full title of this standard is “Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions.” An important feature of this test is that it measures aerobic biodegradation.

Aerobic biodegradation is a process where microbes use oxygen to break down the plastic material into smaller compounds. The microbes use a chemical process that takes carbon atoms out of the plastic material and combine them with oxygen to make carbon dioxide (CO2). This process is also sometimes called “aerobic respiration” because it is like breathing: oxygen in, carbon-dioxide out.

As a plastic (aerobically) biodegrades, it produces CO2. You can actually measure how much carbon has been removed from the material and converted into CO2 by measuring the amount of CO2 that has been released over time. The ASTM D5338 test describes a procedure that involves putting a plastic into laboratory composting conditions, trapping the released CO2 into a solution, and titrating that solution with an acid in order to measure how much CO2 has been released over time.

This measure of CO2 can be used to measure the percentage of carbon in the original plastic that has been converted by the microbes, yielding the y-axis on the graph presented earlier (% biodegradation). For a excellent, slightly technical but still introductory, explanation of this test, check out the article “Fundamental Principles and Concepts of Biodegradability” by Ramani Narayan.

What about compostability?

The ASTM D6400 specification for compostability is a pass/fail test with three parts. All three parts have to be passed for a material to meet the specification.

  • The material has to reach 60% biodegradation within 180 days
  • The residue has to have disintegrated so that the size of the remaining pieces are under a maximum threshold
  • The residue has to contain less than certain specified limits of heavy metals and other contaminants.

Each of these criteria has a Test Method associated with it, which tells exactly how to measure whether the material has met the requirement. In the case of the first part (biodegradation), the Test Method to be used is either ASTM D5338 or D6340. Both of these tests are methods for testing aerobic biodegradation in under laboratory composting conditions.

Now that you know the details of how the D6400 is actually defined, you know that it is extremely specific in what it measures and how it measures it.

Is the D6400 Specification too limited?

The article “Improved Standards Needed for Bioplastic Claims” raises a number of objections about D6400 and its definition of compostability:

  • This standard can only be used to measure aerobic biodegradation; what about anaerobic biodegradation?
  • This standard is based on laboratory composting conditions, which often differ from real-world industrial composting conditions

Another recent article, “Compostable in Theory, But Not in Practice,” raises similar concerns.

  • Real-world composting facilities often don’t meet the conditions described by D6400
  • Some composting facilities ship the residue off to landfills after only 60-90 days, making the D6400 cut-off of 180 days suspect

These observations have been put forward as criticisms of the D6400 Specification. However, they are all are based on a false assumption:

The D6400 specification was never meant to be universal test for whether something is “biodegradable.”

This point cannot be stressed enough. D6400 is a test for the compostability of aerobically biodegradable plastics in a very specific composting environment. Not all things that are biodegradable fulfill D6400…. and they are not meant to. Not all things that fulfill D6400 will biodegrade under all conditions…. and they are not meant to. The specification was not designed to answer questions like “Will this plastic biodegrade in the composting facility nearest my home?” or “Will this plastic biodegrade under all circumstances?”

The problem is not with the standard, but with the people who are pushing D6400 as if it were the “golden test” for a product being eco-friendly. This has been picked up in the media, and even by politicians. Consider California Senate Bill 1454. This bill would have made it illegal for products to claim biodegradability unless they’re compostable per ASTM D6400. This created quite an uproar, especially among people who would like to pursue multiple end-of-life options for plastics, including anaerobic biodegradation in landfills. But most importantly, the law was based on a misunderstanding. It was based on the assumption that the one and only Gold Standard for measuring whether something is “biodegradable” is the ASTM D6400. And that assumption just isn’t true.

Moreover, the ASTM organization knows this. They already have put into play more specifications for labeling materials as biodegradable or compostable under more varied conditions:

  • ASTM D7081 is a Specification that can be used to answer the question: “is this plastic biodegradable in marine waters and sediments?”
  • ASTM D6868 is a Specification that can be used to answer the question: “is this plastic coating compostable in municipal and industrial composting facilities?”

They are also working on new ones all the time, like the New Specification for Aerobically Biodegradable Plastics in Soil Environment. Will it be helpful to add even more specifications to the the ASTM repertoire, allowing products to demonstrate objectively that they meet requirements under a more varied set of conditions? Of course it would; and the ASTM is currently working toward that goal.

Although this effort is laudable, it won’t actually fix the real problem at hand: the misuse of the standards that already exist. When politicians propose laws like CB 1454, and when companies announce that their products have “passed” the ASTM 5338 Test for Biodegradability, these are based on deep misunderstandings of what these standards are and how they should be used. That is the first and foremost issue that has to be addressed.

Who creates standards? Who enforces them?

Standards are produced by organizations. Many standards organizations are very general, producing standards for a wide range of industries. For example, the American Society for Testing and Materials (ASTM) has committees that produce standards for industries ranging from thermal insulation to sports equipment to homeland security. ISO is the international standards organization, with a broad range of committees spanning subjects from psychological assessment to the production of ball bearings. There are also standards organizations that specialize in particular topics or fields. You may have heard of the Internet Engineering Task Force (IETF) or the World Wide Web Consortium (W3C), both of which produce standards associated with browsers, web pages, file types and file transfer, and other processes and procedures related to the internet.

The organizations are not government bodies, and they are not manufacturers within any industry. Usually, the members are volunteers: experts on a topic who choose to join the committee responsible for standards related to that topic. The experts can work for a company in an industry, or can be academics that perform research and teach about a topic.

The most important thing to understand about standards organizations: They have no power.

ASTM or any of the other standards organizations that are out there have absolutely no ability to enforce any of their standards. The organizations have no legal or political status. This is why (for example) different browsers always display website slightly differently, and some websites only work with certain browsers. The are standards out there that describe how websites should be coded and how browsers should display them; but there is nobody who forces Microsoft or Firefox or Google to meet these standards when they build their browsers, and there is nobody who forces you to meet the standards when you build a website.

The ASTM group that oversees standards related to biodegradable plastics is Subcommittee D20.96. They have published 23 active standards related to green plastics: some are test methods, some are specifications, others simply define terminology or suggested procedures. The people on this committee include industry professionals, researchers, and academics. They are all volunteers.

They have no control over politicians who try to create legislation about “biodegradability”. They have no control over companies that claim that Test Methods for biodegradability can be used to “certify” that a product is biodegradable. They have no control over a media that constantly muddies the water by treating terms like “biodegradable, “compostable” and “environmentally-friendly” as if they were interchangeable.

The best that a standards organization can do is provide rules that define when to use a label, and when not to use it.

That is exactly what they are doing. The rest is in the hands of the producers and consumers, the media and the politicians. The rest is in your hands, and mine.

Can you spot the problems?

Here are some examples of problematic claims that you have probably seen if you’ve spent time online looking at the topic of bioplastics.

These are not bad companies. These examples don’t mean that the companies are somehow sinister or that their products are bad. In many cases, the products are biodegradable or compostable and entirely deserve the title of “green plastics.” But in each specific case shown below, the terminology is technically incorrect or misleading.



PROBLEM: ASTM D6400 is a specification for compostability, not biodegradability. There is no such thing as a specification for biodegradability.



PROBLEM: ASTM D5209 and D5338 are not specifications (i.e. a list of requirements to be satisfied by materials), they are tests (i.e. procedures that result in a measurement). They can determine the rate of biodegradation, and the degree of biodegradation, of a material; but they do not determine whether a material meets any particular requirement, and have nothing to do with certification. Also, ASTM does not use phrases like “safe for the environment.”



PROBLEM: First, to give credit where credit is due: this notice is better than most. It specifically talks about meeting the standards for “compostable” plastics and not “meeting the standards for biodegradable plastics” (which is an error: biodegradability is something you can measure the degree of, but it isn’t a threshold you can “meet”). Also, it specifically mentions that it was certified by a third-party agency (BPI) that confirmed the tests, rather than implying that meeting the tests is enough for certifications. (You can’t do your own tests and certify yourself: just because a material passed the test doesn’t mean it is certified, if the test was not done by an independent agency.)

However, ASTM D6866 is not a specification, it is only a test. As a result, it doesn’t make sense to talk about “meeting the requirements” for D6866, because a test tells you how to get a measurement: it does not tell you what a “required” measurement is to pass or fail.



PROBLEM: ASTM D5511 is not a “certification” (NO standards are certifications, because a certification is the result of having the results of a test determined by a third party) and is not even a specification: it is only a test. This standard defines a procedure to permit the determination of the rate and degree of anaerobic biodegradability of plastic products when placed in a high-solids anaerobic digester for the production of compost from municipal solid waste. It does not provide any threshold that must be met to “qualify” as biodegradable.

Have you seen other examples? Email us the URL, and we will post it here and give you credit for the find.


The Federal Trade Commission in the United States has recently been grappling with the issue of environmental claims that companies make about their products. When a company says that their product is “environmentally sound,” what does it mean? How can you measure it? How can you tell if they are lying? What about if they say their product is “sustainable” or “eco-friendly”? When their competitor says that they are lying, how can you tell who is right? If nobody agrees on how to measure it, then how can you know whether a company is accurately representing its product?

The purpose of having standards is to make sure that people can agree on measurements and terminology. Standards allow us to be sure that a company that reports a measurement or uses a label means exactly what we think it means. But this only works when everyone understands what the standards are, and uses them correctly.

Terminology that is technically incorrect or misleading–even by good companies that are putting out good products–muddies the water and makes the use of standards more difficult. The biggest problem facing the “bioplastics industry” or the field of green plastics in generally is not a lack of Standards per se: it is the mis-use, mis-application, and mis-understanding of Standards by producers, consumers, politicians, and the media.

Comments (1)

  1. harbecinc says:

    This is a great read. What has changed in the last 2 years?

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