Petroleum-based plastic may be fantastic, but due to the durability that makes the material so popular it may take hundreds of years to break down. Plastic made from renewable biomass, known as bioplastic, is a biodegradable alternative to fossil fuel versions. A company called Metabolix, based in Cambridge (MA), has been working on a technology to genetically engineer plants such as switchgrass to create a biodegradable polymer that can be extracted directly from the plant.
The research is focused on a polymer called polyhydroxybutyrate (PHB), which is part of the polyhydroxyalkanoate polymer (PHA) family of biopolymers that Metabolix already supplies to plastics manufacturers. The new plant-based process is potentially cheaper and requires less equipment, Metabolix says.
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"Our challenge is to increase the flow of carbon to PHB which we are doing from two different approaches. In the first we are adding genes to accomplish the process of metabolic engineering such that more of the fixed carbon flows to PHB and in the second we are working to enhance the photosynthetic system in the plant such that the plant fixes more carbon which we then target to PHB," Metabolix co-founder and chief scientific officer Olly Peoples told Gizmag.
According to Peoples, Metabolix so far has managed to convert around six percent of leaf tissue into PHB, but less than that with the rest of the plant, which is supposed to be fully harvested.
PHB would be suitable for plastic used in injection molding and to make industrial chemicals such as butanol and propylene, which the company is researching with funding from the US Department of Energy.
According to Peoples, besides offering another option to fossil fuel plastic, PHB from switchgrass is potentially carbon neutral and even negative. "Crop PHB will be based on CO2 fixed from the air and the co-product from the switchgrass program is basically a source of solid biofuel to replace coal so the carbon footprint is going to be negative. Petroleum requires energy and releases CO2 and PHB switchgrass will generate renewable energy and fix CO2," he said.
Calculation methods for petroleum plastic are based on reports from more than a decade ago, Peoples says. Since then, supply has changed, especially in the US, with the expansion of tar sands and hydraulic fracturing further increasing the environmental impact of fossil fuels. "My simple way of looking at this is that in general oil and gas are getting harder and dirtier to extract in ways that are not going to improve their carbon footprint, whereas biobased products are still early in their development and will continue to improve from what is already a positive starting point."