Can Plants Produce Polymers for Plastic Cheaply?
Metabolix and other companies are exploring whether plants can be genetically engineered to make polymers for producing bioplastics in a way that’s cheaper than oil-based plastics, the Christian Science Monitor reports.
Scientists believe the answer to cheaper bioplastics lies in plants, which can theoretically be engineered to function like mini-factories that produce the polymers. Cambridge, Mass.-based Metabolix is part of a fledgling bioplastics industry that has been trying to develop an eco-friendly product that is also cheaper than traditional plastics.
CSM reports that in 2001, the company bought 10 years worth of research from seed giant Monsanto on making plastics from plants. It then began experimenting with the genome of switchgrass for this purpose, since it is a perennial crop that can withstand erratic weather.
Switchgrass has a high content of biomass and if it were to be mass farmed for the purpose of making bioplastics, it would not affect food supply — unlike corn, which has often been used for the same purpose. And, adds CSM, corn-based bioplastics come with environmental issues as well because of the chemicals required to grow corn.
Tapping plants to produce polymers instead of sugars requires high-tech genetic engineering. But this is simpler in theory than in practice. The switchgrass cells have to be first be modified to carry three genes taken from soil-based bacteria that can produce a compound called polyhydroxybutyrate, or PHB. Metabolix researchers grow these cells in a petri dish and they eventually mature into a new plant that is bagged and transferred to pots in the greenhouse.
CSM says that while this process does produce PHB, it does not generate enough of it for mass production of bioplastics. Metabolix’s modified switchgrass produces 2 percent of its body weight in PHB; to reach profitability it will need to produce 10 percent of its body weight. The company’s scientists are hoping that photosynthesis will help bridge this gap and increase the amount of PHB produced in the switchgrass, but this remains to be seen.
Metabolix has proved this concept in tobacco plants, but while using a cash crop like tobacco to produce plastics is not viable, the company says this demonstrates that its method works.
Other researchers are exploring different plant sources as a base for plastics. A new process can convert a wide variety of vegetable and animal fats and oils — ranging from lard to waste cooking oil — into a key ingredient for making plastics that currently comes from petroleum, according to a report published last month in the journal ACS Sustainable Chemistry & Engineering.
In June, University of Massachusetts Amherst researchers discovered a new chemical process to make p-xylene, an important ingredient of common plastics, at 90 percent yield from lignocellulosic biomass, the highest yield achieved to date. Xylene chemicals are used to produce PET (polyethylene terephthalate), which is used in many products including soda bottles, food packaging, synthetic fibers for clothing and automotive parts.
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