Does your compostable bag really contain corn?

Compostable bags contain a mixture of polymers that are specially blended to produce a material that is both strong and biodegradable. They’re not all manufactured the same, which is why you must look for international certification to verify what you’re buying is indeed home compostable.

Let’s break it down and take a look at what they’re really made from.

It all begins with corn. Compostable material typically contains a plant-based polymer (such as corn-starch, casava or sugarcane) plus other necessary polymers (usually PBAT and PLA). We’ll look at each ingredient but let’s start with the corn-starch used in our bags.

Corn is an annual crop - meaning that it completes its whole lifecycle within one growing season. Because it’s able to be easily regrown, and can be harvested again next season, it’s considered highly renewable.

Furthermore, the corn we use is sourced from GMO-free regions and the kernels are what’s called “third-grade”. First grade corn is used for human consumption, grade two is used in animal feed products, and grade three…well that would otherwise be left to rot. So we’re reclaiming an otherwise wasted by-product and putting it to good use.

That’s the traditionally farmed ingredient explained – now for the technical stuff.

PLA stands for polylactic acid. It’s a fully biodegradable thermoplastic polymer consisting of renewable raw materials. It biodegrades entirely because its origins are natural and microorganisms can feed on it. If you’ve ever had surgery that required screws, rods or implants there’s a good chance that PLA was used - it’s commonly used in medical implants and 3D printing.

The other core ingredient is PBAT, which stands for polybutyrate adipate terephthalate. Again this component is biodegradable and will leave behind no toxic residues but, unfortunately, it’s derived from petrochemicals (and is therefore not renewable).

PBAT is the binding agent used in plant-based compostable products - and it also helps them decompose. One day we hope to find a non-oil derived resin that could replace PBAT, but until then PBAT is necessary in the production of compostable products.

So there we have it: compostable bags made from GMO-free corn starch, PLA and PBAT. These bags will decompose in your home compost heap and return to carbon dioxide and water without leaving behind any harmful residues.

Ecopack compostable bin liners are all certified to strict international standards and we go so far as to use non-toxic inks in the printing on these products. Please note that all compostable products are not equal – some are only suitable for industrial/commercial composting (which is limited in NZ) and won’t break down adequately in your backyard compost. So make sure you always look for home composting certifications.