Contributed by Reuben Hudson, Chemistry Postdoctoral Fellow, and Jeff Katz, Associate Professor of Chemistry, Colby College
Beyond solving an obvious energy dilemma, curbing our societal need for petroleum will also require finding alternative materials for a sustainable future. When filling up at the gas pump or heating our homes with oil we often consider how we’re tapping into a dwindling supply of fossil fuels. We often forget, however, that many of the advanced materials in use today are sourced from the same feedstock. Manufactured items not made from metal, glass, wood, ceramics, wool or cotton most likely come from petroleum: plastic bottles, bags, panels, casings, countertops, fabrics and much, much more.
If feedstock sourcing were the only concern, economic drivers would steer the market toward biorenewable alternatives once their price dropped below that of extracting and processing crude oil. Unfortunately, the fate of our petroleum materials and fuels represents an equally daunting concern. The net increase in atmospheric CO2 as a result of burning fossil fuels contributes to global climate change, and the environmental persistence of many petroleum derived materials leads to widespread and long-lasting pollution. We could be faced with a future where even after we've stopped pumping oil, evidence of these practices remain in the form of an irreparably altered climate and undegraded plastic trash still circulating in the oceans or clogging landfills.
In an attempt at more sustainable products, researchers more and more turn to materials sourced from renewable feedstocks and that persist in the environment on a time scale no longer than their useful lifespan. Toward these goals biodegradable plastics from petroleum have been made, as have non-biodegradable, exceptionally durable plastics from biomass. As both a biodegradable and biomass-sourced polymer, the bioplastic polylactic acid (PLA) is gaining mainstream acceptance as a sustainable material. Significant synthetic effort still goes into PLA production: lactic acid must be generated and isolated from corn or potatoes before its derivatives can be polymerized to form PLA. Circumventing the need for such involved processing techniques, some useful polymers can be derived directly from biomass. By feeding sugars to the right microorganisms, we can encourage them to produce polyhydroxybutyrate (PHB), which we can then extract and use directly. Rather than having engineered microorganisms build polymers for us, we can source them from organisms that would have otherwise built the polymers anyway.
The biopolymer chitin, the structural component of marine crustacean shells, insect cuticle, and found in many other biological organisms, offers an excellent strength profile from a materials standpoint. A recent report from the Weiss Institute at Harvard demonstrated the generation of large-scale functional objects such as cups, clips, chess pieces, and egg cartons from chitosan, a derivative of chitin, by dissolving the polymer in 1% acetic acid/water and carefully controlling the evaporation of liquid. Adapting their laboratory procedure for use in K-12 outreach sessions, in collaboration with Beyond Benign we similarly dissolved both chitosan and chitin in vinegar, poured the solution into silicone ice cube trays (molds) and let the liquid evaporate by placing the molds on a seedling heating mat.
By engaging young students in sustainability-focused outreach, we hope to inspire the next generation of scientists to develop materials that are both sourced from biomass and fully biodegradable.
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