Biodegradable additives give microbes the chemical leverage they need to body slam plastics into oblivion. Additives, which are also called degradation initiators, involve seriously complex chemical engineering that must balance the usefulness of the product, consumer safety and the ultimate end us of the plastic, be it recycling or decomposition.
These additives are proprietary (i.e. top-secret) blends of organic compounds. Specific recipes of additives manipulate microbes in different ways, and companies tout their formulas as superior to others.
When blended into regular plastics, they make up only about 0.5 to 2 percent of the product's total composition, and crucially, they don't change the polymer's performance. That is, you won't go on vacation and come home two weeks later to an orange juice jug that's crumbled to messy pieces. They also don't affect a container's content in any way, and they don't have adverse effects on traditional plastics recycling.
In fact, you'd never know anything was different about the plastic until it hits the landfill, which is really the only place that has the right combination of moisture and various microbes that can exploit the additive in the plastic. The additives will do their job outside of a landfill, too, but the process will take significantly longer.
The process doesn't happen right away. At first, just a few microbes are attracted to the additive; those first microbes create a small chink the plastic armor. More species of microbes arrive, their combinations of acids and enzymes, along with water, eventually allows them to break down huge polymers into smaller and smaller bits.
But what about compostable plastics? Well, there are no additives used with these so-called bioplastics (often made of polylactic acid or PLA). They're made from natural materials such as corn or pea starch or types of vegetable fats and oils. What's more, not all bioplastics are intended to decompose. Rather, they are made from renewable substances (like corn) for sustainability purposes. Some kinds won't degrade much at all in a landfill setting.
Bioplastics and plastics with additives often compete with each other for a share of the polymer market. Sometimes that competition erupts into an extremely public slugfest. Keep reading and you'll see how the waters of the biodegradable plastics conversation are anything but placid.