These days, an interesting trend in product offerings is on the rise. Many products, particularly those traditionally tied to the petrochemical industry, are now offering "green" alternatives. One such green trend is the increased offering of biodegradable products, which can be decomposed with varying levels of bacterial treatment into biomass and carbon dioxide, thus returning the materials to the carbon cycle. On paper, it's great - at the end of a product's lifecycle, it will return to the earth.
But reality has some bad news for biodegradable products. The truth is that biodegradability is neither as good as it sounds nor is it a sufficient condition for marketing green products. I'll try to explain why.
First, do no harm
The greenness of the biodegradable idea is that you will not harm the environment with excess waste. However, there are two problems with this presumption. The first is that biodegradable products mostly can't meet the conventional definition of biodegradable, and the second is that the greenness of your product might be compromised by the biodegradation.
There exists an inherent trade-off between the shelf-life of a product and the circumstances in which it can biodegrade. You would prefer to not have your furniture growing fungus after a few months, and don't like it when bacteria eat holes in your biodegradable plastic cup before you use it. Consequently, most "biodegradable" products are designed to simply not meet the layman's standard. For most of these products, if you toss it in your backyard compost heap, a year later, it'll still be there, staring at you. As it turns out, the vast majority of biodegradable products are designed so that they can biodegrade only in very specific circumstances - for example, European standards specify a heated, activated sludge. Your average junkyard is not going to have this readily available. In fact, the place where such an environment is going to be readily available is a biogas-generating treatment reactor for sewage or food waste. There just aren't many of these places available, particularly in the US.
A biogas reactor is the best case scenario. In most biogas reactors, the gases emitted are burned and used to generate power or heat. The reality is that most of these products will continue to accumulate in dumps and biodegrade slowly - much faster than conventional plastics, on the order of 20-50 years, but still slowly. And when they do, they will emit greenhouse gases. And therein lies the other problem with presuming biodegradables ultimately do no harm to the environment.
While eliminating plastic waste is a good thing, no doubt, the life cycle benefits of these plastics make things a lot more dubious. If you are not willing to sort and biodegrade all of this waste separately from non-biodegradable waste, then the plastic will slowly release carbon dioxide and, more significantly, methane, as it is digested.
Many biodegradable products are bio-based - that is, they are derived from biological feedstocks. In that sense, at the very least the carbon balance works out: the net amount of carbon released as a result of your product coming into being will, at worst, be slightly positive due to carbon emitted from energy used in manufacturing. Some other products, however, like BASF's Ecoflex plastic, are not actually bio-based, but made from petrochemicals. For these products, the carbon balance over their life cycle is already very positive because their feedstocks did not sequester any.
But there's more - what matters in the end for the environment is not the net amount of carbon released into the atmosphere, it is the Global Warming Potential, or GWP. While carbon dioxide is a greenhouse gas emitted in quantity, as GHGs go it isn't so bad. It doesn't really interact with other chemicals and just kinda floats around. It's defined as having a GWP of 1. Other gases, on the other hand, trap heat even better by absorbing more wavelengths of radiation, or interact with water droplets in the air to promote the formation of water vapor, a greenhouse gas in its own right. And one of the worst culprits out there in terms of impact is methane, which has a huge GWP (20 yr GWP: 72; 100 yr GWP: 25; 500 yr GWP: 7.6).
Suddenly the picture isn't so hot for these biodegradable products, of which I know none that don't require methanogens to fully decompose.
Biodegradable isn't enough
Suddenly, it looks like these biodegradables don't have as much going for them in terms of greenness. I hate to say it, but there's more. And yes, it involves markets.
Turns out that the biodegradable label is relatively easy to obtain. What really ends up being the rub is that biodegradable products don't command the premium that people expect them to. Biodegradable products have to compete in a market full of high-performance petrochemical products, but cost far more - in some cases, between 30%-100% more than their petrochemical-based alternatives- and often have problems with water resistance and performance.
The overwhelming market response has been, aside from a few conscience-guided or greenwashing initiatives, that biodegradable is nice, but cost is more important. The example of Cargill's Natureworks is the most relevant: you've probably heard of corn plastic (corn PLA), but where, besides the hippiest supermarkets, have you seen it?
The few biodegradable products that have overcome their cost hurdle have been able to command a premium not because of the biodegradability but because of other unique and innovative features, with biodegradable as a bonus. I could give some examples, but then I'd be violating multiple confidentiality agreements =\ Either way, the outcome is precisely what I would have expected for new entrants with weakly differentiated, sometimes inferior products competing with what are largely commoditized markets, like those for polyethylene or polyproplyene homopolymer.
In conclusion, I congratulate you for reading this extraordinarily long post. Oh, and if you haven't figured it out, I don't think biodegradable products are going to go mainstream until we have the infrastructure and technology to deal with them sensibly and make them cheaply. This is one trend that's going to stay under the radar for the foreseeable future.