We showed DARPA that we could make a new plastic from plant oils that has remarkable properties, which includes being tougher and more durable than typical polyethylenes. Additionally, the bioplastic can be placed in a simple container where it is safely broken down to liquid fuel.

—Prof. Gross

The Defense Advanced Research Projects Agency’s (DARPA) Mobile Integrated Sustainable Energy Recovery (MISER) program has awarded the researchers $2.34 million to advance this technology and transfer it to industry.

MISER’s goal is to improve the logistics of land-based military operations by reducing the quantities of solid waste from packaging materials that require personnel, fuel, and critical transport equipment for removal. Plastic packaging has energy content that approaches that of diesel fuel. The DARPA work is designed specifically to achieve nearly complete plastic packaging waste reduction while harnessing 90% of the packaging energy content for use in electricity generation.

DARPA had provided the original seed grant to Prof. Gross as well as a $1.1 million Phase 1 grant follow-up to the researchers in 2004.

Military units generate substantial quantities of packaging waste when engaging in stationary field operations. If we can turn this waste into fuel, we will see a double benefit—we will reduce the amount of waste that we have to remove, and we will reduce the amount of new fuel that we must deliver to the units.

—Khine Latt, program manager for DARPA’s Mobile Integrated Sustainable Energy Recovery program

Professor Gross was responsible for the design and testing of the polymer, while DNA 2.0 designed and developed the enzymes used for the biological route to production. The polymer has properties similar to polyethylene and will be prepared from renewable resources with a cost comparable to current commercially manufactured plastics. Unlike polyethylene, the new bioplastics have a special structure that allows them to be converted to liquid fuel.

Development of a biological route to synthesis of these polymers required engineering of several enzymes. DNA 2.0’s DeNovo Genes protein engineering technology uses protein sequence mining methods and machine learning algorithms to design small numbers of variants that are tested directly for commercially relevant protein properties. By quantifying the contributions of individual amino acids to the desired activity, further improved variants are then designed.

The next phase of the research will entail developing a more efficient low-cost process for both manufacturing the bioplastic and converting it into fuel.

Professor Green received a Presidential Green Chemistry Award in 2003 for his development of lipase-catalyzed polymer synthesis. The use of enzymes reduces the activation energy of polymerizations and thus decreases process energy consumption. Further, the regioselectivity of lipases can be used to polymerize polyols directly.

Resources:

• “In-vitro Enzyme Catalyzed Polymer Synthesis”; R. A. Gross, A Kumar, B Kalra; Chemical Reviews, 101(7), 2097-2124 (2001)

• “Biodegradable Polymers for the Environment”; R. A. Gross, B. Kalra; Science, 297, 803-806 (2002)

• Mobile Integrated Sustainable Energy Recovery (DARPA)

• Could there ever be a petroleum-free military? (DARPA DSO)

• Environmental Programs at the US Army Natick Soldier Center Using Biodegradable and Biobased Materials