Oxo Biodegradable - Standards Applicability

Standards Applicability

OXO plastic degrades in the presence of oxygen, and the process is accelerated by UV and heat. It can be recycled during its useful life with normal plastic. It is not designed to be compostable in industrial composting facilities according to ASTM D6400 or EN13432, but it can be composted in an in-vessel process.

The oxidation process takes longer than the 180 day period required by ASTM D6400 and similar standards for compostable plastics such as EN13432 and ISO 17088. This short time is necessary for compostable plastics because industrial composting has a short timescale, and is not the same as degradation in the environment. A leaf is generally considered to be biodegradable but it will not pass the composting standards, due to the 180 day limit in ASTM D6400. (Indeed, materials which do comply with ASTM D6400, EN13432, Australian 4736 and ISO 17088 cannot properly be described as "compostable." This is because those standards require them to convert substantially to CO2 gas within 180 days. You cannot therefore make them into compost - only into CO2 gas. This contributes to climate-change, but does nothing for the soil.)

There is a Standard Guide (ASTM D6954) which specifies procedures to test degradability, biodegradability, and non-toxicity, and with which a properly designed and manufactured oxo product complies. The ASTM D6954 Standard Guide is a 2-tier test procedure to determine whether a plastic could be marketed as "biodegradable". The Standard Guide references ASTM D5510 Test Specification which determines the usable life of the OXO plastic through Thermal Degradation. Secondly it also references ASTM D5208 which is used to determine the usable life based on UV degradation. These two test procedure in combination make up Tier 1 of the testing process for verifying that an OXO plastic is degradable. After Tier 1 is complete and the OXO plastic has been shown to be significantly degraded (usually done by FT-IR to show the new spectra peak at around the 1730 wavelength) the testing can move on to the Tier 2 procedure. The Standards used for Tier 2 testing are either ASTM D5338 or ISO 17556. These are both testing for the conversion of carbon in the polymer to CO₂ in a controlled compost environment. After 60% carbon is converted from the sample the OXO plastic is said to be biodegradable. Although ASTM D6954-04 is a Standard Guide (as opposed to a Standard Specification) it does provide pass / fail criteria and therefore is useful in deciding whether a plastic could be marketed as "biodegradable".

ASTM D6400 is a Standard Specification, but is appropriate only for the special conditions found in industrial composting. There is no need to refer to a Standard Specification unless a specific disposal route (e.g.: composting), is envisaged.

Another reference document has recently been published by the French standards organisation AFNOR. This document AC.51 808 offers a well researched method to test oxo-biodegradable plastics based on usage and climate conditions. It introduces a new testing method for the biodegradation of polymer using selected micro-organisms and measuring ATP and ADP by chimiluminescence. This method brings a new approach as tests are done at 37°C which is much more relevant to outdoor conditions than ASTM D6400 or EN 13432 done at 58°C plus The micro-organisms are identified based on the environment where the plastic will be disposed which is not the case with the CO2-evolution method.

This French document is so far the most interesting one for predicting the behaviour of an oxo plastic in case of littering. This test method provides as well an ecotoxicity testing method to ensure that fragments in the environment, pending complete biodegradation, are not toxic.