MaterialsGuru

The New York Times reported on this interesting technology on April 9, 2007:

Scientists worldwide are struggling to make motor fuel from waste, but Richard Gross has taken an unusual approach: making a “fuel-latent plastic,” designed for conversion. It can be used like ordinary plastic, for packaging or other purposes, but when it is waste, can easily be turned into a substitute diesel fuel.

Following the original story, several prominent blogs also reported on this interesting technology (See posts on Green Options, Wired Blog Network, Green Brooklyn, FutureSheet). However, it was only recently that I came across this news on the Plastics and Resins blog on CR4’s Chemical and Material Science section, which I must admit, was a fascinating find!

What I find most interesting is that the packaging material made out of this bioplastic can be converted into fuel after it has been already used and rejected. In this way, it provides value multiple times during its life cycle. Not to mention that the original biopolymer is synthesized using a bioprocess from natural raw materials using enzymes or chemical catalysts.

Prof. Richard Gross, who holds the prestigious Herman F. Mark Chair at the Brooklyn Polytechnic University, has been active in this field for many years. As I read his bio on his website, I was delighted to learn that he had worked with Prof. Robert Lenz at UMass, Amherst (I obtained my PhD from UMass in 1998!). Prof. Lenz, of course, is very well known for his pioneering work with bacterial synthesis of PHA’s. In 2003, Prof. Gross received the Presidential Green Chemistry Award for his work on lipase-catalyzed polyester synthesis (see cover story in Chemical & Engineering News, June 30, 2003) via condensation or ring-opening polymerization reactions.

Over the years, Prof. Gross have developed an expertise in enzyme catalyzed reactions such as step condensation and ring opening polymerizations for preparation of aliphatic polyesters. Used extensively in his research is a class of lipase B enzyme called Candida Antarctica (CALB) which is physically immobilized on a macroporous polymer material. Commercially, this enzyme is available as Novozym 435 from a Denmark-based biotech company Novozymes.

Starting materials for such synthesis are hydroxyl fatty acids, which can be derived from plant or animal sources (oils/fats). According to the research summary on Prof. Gross’s website, polyesters prepared by lipase-catalysis from long chain hydroxylfattyacids are strong-tough plastics that offer properties that are intermediate between poly(ε-caprolactone) and polyethylene. Although, not quite in the class of engineering plastics, these materials can still be expected to have moderately good physical properties for packaging applications. If unsaturated fatty acids are used, it is possible to introduce crosslinking in the resulting polyester, which can further improve the physical properties of these materials.

In packaging applications, these materials can be converted into a film or rigid containers depending on their physical properties. Typically, the packaging material is discarded right after the first use. Therefore, a lot of waste is generated from packaging materials. I was surprised to learn from the New York Times story that a soldier generates on average more than 7 lbs of packaging waste per day. That’s quite a lot!

This is where I am impressed by the value of Prof. Gross’s idea. If the packaging material is made from his biopolyester, the trash can be collected and converted into biodiesel using Cutinases, a class of enzymes that catalyze the hydrolysis of the ester bonds in cutin, a waxy lipid-polyester found in the plant cuticle. In this way, the long-chain biopolyester gradually breaks down into smaller alkyl-ester fragments, which at a certain point, separate out of the water mixture as biodiesel! Now it can be used to run diesel generators, for example, to make electricity.

What an excellent idea!