Can Oxo-Biodegradable Plastic be Composted?

Before getting to the answer, let’s have some understanding about ‘biodegradable plastic’. There are two types of biodegradable plastic, its either oxo-biodegradable or hydro-biodegradable. These two are completely different technologies, with different purposes.

Oxo-biodegradable plastic (OBP) is made from polymers such as PE, and PP, and contains special ingredients which do not include any metals exceeding the prescribed limits [1]. OBP products are tested according to ASTM D6954 to prove that they are biodegradable and non-toxic. They can also be recycled during their useful life, and independent reports proving this are publicly available on the OPA website. Starch is not used in OBP.

Crop-based hydro-biodegradable plastic (HBP) (also loosely known as “bio-based plastics” or “bioplastics” or “compostable plastics”). These contain a high proportion of plant-based material, and are tested according to EN 13432 or ASTM D6400 to biodegrade in the special conditions found in industrial composting.

The main purpose of hydro-biodegradable plastic is to make bags which are used to carry compostable material to an industrial composting plant and which do not therefore have to be emptied there. Oxo-biodegradable plastic has in fact been trialled for this purpose in the UK and was found satisfactory by industrial composters, but it is not marketed for composting for the bizarre reason that it does not produce CO2 gas quickly enough to pass EN13432. The carbon in oxo-biodegradable plastic residues would therefore remain as a nutrient for the soil until it is returned to nature by the action of micro-organisms. 

In conclusion, a simple answer for the question would be YES, it is suitable for “in-vessel” composting at the higher temperatures required by the new EU animal by-products regulations, but it does not degrade quickly in low temperature “windrow” composting in which crop-based plastics do.

A side note, “Compostable” plastic does not convert into compost – it converts rapidly into CO2 gas (EN 13432 and ASTM D6400) which does nothing for the soil. [2]

References:

[1] EU Packaging Waste Directive 94/62/EC Art. 11 and Annex A.1.2 of EN13432

[2] Oxo-biodegradable Plastics Association: The new plastics economy