| Media
Contacts:
Dr. George W.
Roberts, 919/515-7328
Dr. Saad A. Khan, 919/515-4519
Linda E. Rudd,
919/515-3848
April
10, 2003
NC
State Researchers Develop New Plastic Recycling Process
FOR
IMMEDIATE RELEASE
|
Plastics
are everywhere these days, but current recycling
techniques allow only a very limited portion to
be reclaimed after initial use. Researchers in
the Department of Chemical Engineering at North
Carolina State University, working to change that,
have developed a unique recycling process for
some of the most common kinds of polymers.
The
familiar soda bottle is made of a plastic called
polyethylene terephthalate (PET). These bottles
are ubiquitous, yet recycling them poses challenges,
primarily because of contaminants or impurities.
Dr. George W. Roberts, professor of chemical engineering,
Dr. Saad A. Khan, professor of chemical engineering
and director of the chemical engineering graduate
program, and Joan Patterson, doctoral student
in chemical engineering, are working on a project
designed to address this problem. |
Joan
Patterson, doctoral student in chemical engineering
at North Carolina State University, demonstrates
the twin-screw extruder that will be used to
recycle PET plastic bottles into plastic pellets,
in bag at left.
|
“We’re trying to develop
a process where we can take waste polymer and convert
it back into the material from which it was made. In
the process, all the impurities are removed from the
polymer,” said Roberts. “Ideally, this should
be done in a single step because the economics have
to make sense for the process to have widespread applicability.”
The process, according to Roberts, has
two unique elements. “First we run the process
in a machine called a twin-screw extruder, which has
high throughput. A lot of polymer can be processed in
a very short time,” he said. “The extruder
melts the PET and creates very thin films so we can
interface the high molecular weight polymer with another
material, either ethylene
glycol or methanol, that will reduce the molecular weight
of the polymer substantially.”
Second, supercritical carbon dioxide
(CO2) is combined with the ethylene glycol or methanol,
which reduces the viscosity, or stickiness, of the polymer,
making it easier to process and allowing better contact
between the materials. At the end of the process, the
CO2 is vented from the extruder and run through a condenser,
where dissolved impurities can be removed. The CO2 is
then recycled.
The process has several advantages.
The conversion is done under efficient processing conditions
and is a one-step, environmentally benign procedure.
In addition, the process can be tailor-made for materials
of different molecular weights.
A single-screw extruder has been used
successfully in the research laboratory at NC State
for this procedure. Now Roberts and his team are looking
for ways to make this process economically feasible
for an industrial-scale operation. “The basic
reaction of ethylene glycol with the polymer is known,
but our preliminary data say that this enhanced reaction
is several orders of magnitude faster when done in the
extruder with supercritical CO2 than if it is run conventionally,”
said Roberts.“That translates into lower cost.”
According to Khan, twin-screw extruders
are common in the workplace, so these machines can be
reconfigured to use supercritical CO2. First, the research
team must determine how variables – including
rate of flow of polymer; the amounts of CO2, ethylene
glycol or methanol; temperature; pressure of CO2; and
machine configuration – affect the processing.
“To our knowledge, the machines
in the marketplace have never been used for this purpose,
but they can be modified for this process,” said
Roberts. “Part of our research involves configuring
the existing machines so they can give optimal performance.”
-rudd-
|
Raleigh,
NC 27695
