How can I tell biodegradable plastic bags apart from non-biodegradable?

Question

I keep a lot of my stuff organized in normal disposable plastic bags I have left after shopping at various markets. And it works fine, except after a couple years I often find a bag in shreds, simply falling apart. Biodegradable - reaching their end of life, making a mess in my stuff and not serving their purposes. I'd be better off disposing of them or not getting them in the first place. Sometimes they are labeled, but sometimes there is nothing to signify whether they can last years or will fall apart.

Is there a reliable way to distinguish these from non-degradable plastic bags before they start falling apart?

Answer 1

Most non-biodegradable plastic bags are made of Polyethylene (PE) and often have a marking or logo like this:

There may also be a marking that say 'PE', 'PE-HD', 'LDPE' or 'PE-LD'

Bags that are biodegradable usually have a logo on it containing the words 'biodegradable' and/or 'compostable', e.g. something like this:

Note that there is 1 controversial type of plastic called 'Oxo-biodegradable'. Opponents say that oxo-biodegradable plastic just falls apart into microplastics that continue to pollute the environment. The manufacturer however refutes this and says it falls apart into biodegradable components.

If there is no logo or description on the plastic it's most likely PE, but you can't know for sure unless you get the bag tested in a lab.

BTW all types of plastic will degrade very slowly under normal circumstances. I don't think biodegradable plastics degrade much faster than non-biodegradable plastics. Most biodegradable plastic bags are made from Polythene film or corn-based materials like Polyactic Acid (PLA). For biodegradable plastics to degrade (in a reasonable timeframe) they need to be heated to very high temperatures for several days.

Answer 2

Amazon sold me several years' worth of allegedly compostable bags (so also biodegradeable, one would hope), my intent being to transfer compost from kitchen to garden pile every week or so. We dig the stuff in each time, of course. So I was not pleased to find an intact bag, still with the orange rinds from a couple of months ago, when our tree finished that fruiting session, still intact. I pulled it out and weighted it down with a rock nearby, in full sun and rain. It's perhaps too soon to tell whether it failed THAT test. But this discovery led me back to the stock I have on hand, which has a paper label that describes them as "starch based garbage bags," adding "PSM starch based." (Wouldn't that suggest they'd dissolve in, say, hot water?)

Anyway, I'm thinking that paper label is more than just a bad translation from Mandarin.

Oh, and as for logos: the paper label (only) has a plain-Jane "recycling" logo (triangle of three arrows). The bags themselves...nada.