I know biodegradables (e.g. plastic bags) cost more to make, and I heard they’re weaker so they have to be made thicker than normal plastic bags, which probably costs more to ship. Is there any point in using biodegradables when they’re going to be incinerated anyway?
Actually, I thought landfills are designed NOT to let things decompose. If that were true, what’s the point of biodegradables at all, other than composting bags?
Essentially, if it’s going to be landfilled or incinerated, it’s not going to do much. If it’s going to be incinerated, there MIGHT be small differences in air pollution and/or energy recoverability (when trash is burned to generate power), but I haven’t done the math so I don’t know.
In those situations, which are probably the most common, it’s essentially greenwashing. Wikipedia also talks about how certain degradable bags break down into smaller pieces without ever being fully broken down, and when this gets into the environment (such as in trash gyres), wildlife can and do consume the pieces. Regular plastic bags photodegrade from sunlight, too, so I’m not sure which is worse for animals.
So what’s the point of it all? Marketing, mainly. Green sells. Greenwashing sells too and costs less to do.
Perhaps, in some cities, biodegradable bags can hold household compost and/or green waste and then be subsequently biodegraded in an industrial-grade composting facility that has the temperature and microbial activity necessary to properly digest it. But really, if you have that kind of system already, why not just use metal cans and skip the wasteful bag liner altogether? It’s the same deal as biodegradable utensils – more of a stop-gap band-aid for people who don’t want to deal with reusables.
TL;DR: Biodegradable plastics are more expensive, occasionally a little less wasteful, and much more capable of making people feel better about consumption, which in turn makes businesses more money.
They’ll break down if left out in the open. The gotcha to the greenwashing is that nobody wants to leave plastic bags exposed to the elements long enough to break down - eventually they get picked up and discarded.
Once they hit landfill, the degradation stops. Pretty much nothing breaks down appreciably in a modern landfill - even things you’d expect to disintegrate like newspapers can survive intact for years.
About the only exception to this is bags that get blown around and snagged in dangerous or difficult places to clean like barbed-wire fences or powerlines - they’ll eventually break into pieces small enough to get loose, but then you just have more pieces of garbage. It’s not like the bags are made of ice that will cleanly evaporate away.
What about digestibility? They say a lot of sea turtles are killed by floating plastic bags, which look like jellyfish to them and cause intestinal blockages if consumed. Do these help that issue?
Wikipedia noted that some of the degradable/biodegradable bags have an increased tendency to fragment, which might contribute to more of it being eaten by wildlife than whole/more complete bags. But, again, regular plastic degrades in the sun, too, so in the end it I’m guessing that it might not be much of a difference either way.