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In the news today, Braskem Announces a Green Polypropylene Plant: the largest thermoplastic resin producer in the Americas will build the world's first manufacturing plant to produce "green propylene", a form of polypropylene made from renewable resources like sugar cane.  From their press-release: "The green polypropylene will have the same technical, processability and performance properties as polypropylene made using petroleum."

How is that?

One of the most well-known and often-discussed criticisms of bioplastics (for example, PLA) is that the properties of the final product do not quite match up with those of traditional plastics: it's not as strong, or not as heat-resistant, until you mix it in with other (usually non-green) chemicals and additives and binders.  At a fundamental level, the chemical structure of biopolymers is different from the chemical structure of artificial polymers... and so their resulting properties are different.

Here is the source of the success of "green polypropylene":

The chemical structure of "green polypropylene" is NOT different from the chemical structure of traditional, synthetic oil-based plastics.  There is not a single atom's worth of difference in the chemical structure.

The only difference is in how the polymer was created: in traditional plastics, the molecule is "built" from a process that starts with petroleum, in "green polypropylene" the molecule is "built" from a process that starts with sugar cane.  Once that molecule has been created, though, it is identical in every way to traditional plastics. 

To quote from the article in the most recent issue of bioplastics magazine: "Biobased polyethylene (and, once available, polypropylene) are NOT biodegradable. On the contrary, biobased PE and PP do not at all differ from petroleum based polyolefins. They have the same chemical structure and can be polymerized in the same way The same grades (film, injection, blow moulding, etc) can be created, and so on. The only difference is in the origin of the carbon.  Biobased polyolefins consist of renewable carbon."

Is that good or bad?

On the good side:

• It can be processed by existing plastics processing plants, so you don't have to build special new ones.
• It has the good properties of traditional plastics, like strength and heat and water resistence
• Creating it does not rely on oil, an unsafe and scarce non-renewable resource
• It can be safely recycled along with traditional plastics

On the bad side:

• Just like traditional plastic, it is not biodegradable

At first glance, of course, it seems like the good outweighs the bad.  When you look at the "two dimensions of green" -- renewability and degradability -- green polypropylene succeeds at one and fails at the other.  Isn't that a step in the right direction?  Isn't it a good thing, overall, to pursue every avenue for making plastics more environmentally friendly, even those that aren't environmentally "perfect"?  (We so often hear slogans these days like "pursue every option" or "don't let the perfect become the enemy of the good" and so on.)

I'm not saying I disagree. However, I think it is worthwhile to at least understand and think about the arguments from the other side.  Consider these questions:

What about the tonnes and tonnes of waste building up from discarded plastic?  Won't this simply continue to contribute to that problem?  Even though the carbon comes from renewable resources, once it's put into the "green propylene" it is trapped and will not be returned to the biosphere, because the product doesn't biodegrade.  Doesn't that do even more damage to the environment, by trapping what once was "free" carbon into these plastic products?

Some people will argue that green polypropylene is a "first step" technology, a way that we can be "more green right now" while we wait for the technology on biodegradable bioplastics to improve.  But if all of our industry starts getting geared up to this solution, will it simply delay our progress with plastics that are both based on renewable resources and biodegradable?

What do you think?