To create their
new plastic, known as polylimonene carbonate, the
scientists used molecules from two sources, carbon dioxide and limonene oxide,
which comes from the peel of citrus fruits and other plants.
"Limonene
has been around forever, carbon dioxide as well. What we've been able to do is
devise this catalyst for the first time that allows these two small molecules
to come together to make a plastic," said Cornell chemistry professor
Geoffrey Coates.
The catalyst
used in the chemical process is a compound that contains a small amount of
zinc. The zinc in the catalyst is the type found in the common sunscreen zinc
oxide.
The limonene
oxide liquid, the CO2 gas, and the catalyst are combined to make a white
powder. That powder can be melted into things typically made from plastic, such
as disposable cups.
This new
plastic has some properties similar to polystyrene, a petroleum-based plastic
that's in hundreds of household products.
The Cornell
research team, including Scott Allen and Chris Byrne, are testing to see how
sturdy it is and how it might hold up to heat and cold. They are also
evaluating its biodegradable properties.
Details of this
orange-based alternative are published in the Journal of the American Chemical
Society.
The research is
funded by the National Science Foundation.
Coates says the
discovery is stirring a lot of commercial inquiries.
"I'm
getting deluged by people wanting to know more," Coates said. "It's
fun to talk to people envisioning other uses for this."
Researchers in
"Basically
when an orange comes into a juice processing plant, 50 to 60 percent is juice,
the rest is waste," said Robin Bryant, research manager for the Florida
Department of Citrus.
Bryant says
sometimes orange peel is dried and added to cattle feed. Limonene already is an
ingredient in many cleaning products, she said, and scientists are researching
ways to create ethanol from citrus waste.
Polylimonene carbonate could possibly be used as a less
toxic ingredient in making cast iron and cast aluminum, or as an ingredient in
some herbicides or pesticides.
But even with
growing commercial possibilities for renewable resources, Coates cautions the
route from lab to store is long.
"In terms
of a timeline for discoveries being converted into commercial products, these
numbers can vary from months to years, or in some cases, never," he said.
And it is
unlikely that these green alternatives will ever completely replace the huge
quantities of oil-based plastics in the world.
"Last year
the world production (of limonene) was around 150 million pounds. This will
never replace polymers such as polyethylene. Last year just in
But nature
seems to have an abundance of other possible building blocks for new polymers,
from fruits to corn to pine trees.
"We're
really excited about not only using a byproduct from the orange juice industry
but also from the paper industry," said Coates. When timber is processed
into paper, one byproduct is a compound called pinene,
which gives pine cleaning products their smell.
The scientists
are also trying to find out if they can combine carbon dioxide with compounds
made from vegetable oil, which is abundant and very inexpensive.