Biodegradable Plant-Based Hydraulic Fluid
Plant estolide-based hydraulic fluid could replace conventional fluid in a wide
range of industrial and farm equipment. Here, a specialized machine built for
soil sampling uses hydraulics to raise or lower its height, adjust its width,
and drive the wheels.
A commercial-grade, biodegradable hydraulic fluid to power heavy equipment
is just around the corner, thanks to a new process that creates a key component
from vegetable oil.
Agricultural Research Service scientists at the National Center for
Agricultural Utilization Research in Peoria, Illinois, have made hydraulic
fluid that contains estolides from oilseeds such as meadowfoam and high-oleic
A class of long-chain esters, estolides are the basic ingredient in many
hydraulic fluids. These fluids, under pressure, transmit power to moving parts
of many machines, including cars, bulldozers, tractors, and most heavy
equipment used to build roads and structures.
The scientists began by making a plant-based estolide from meadowfoam seed,
an oilseed crop Agricultural Research
Service, discovered why. researchers helped breed and develop uses for.
Grown primarily in the Northwest, meadowfoam is an ingredient in cosmetics and
other facial-care products.
"We found that it also showed promise as a basestock in hydraulic
fluid," says Terry A. Isbell, an ARS chemist who helped develop
meadowfoam. But poor low-temperature properties and cost were prohibitive.
However, "We used the technology developed for meadowfoam estolides to
make estolides from other vegetable oils," Isbell says. "We found
that oils that are particularly high in oleic acid, such as sunflower,
safflower, and some soybean, would serve as a good source of starting material
for the formation of estolides."
Petroleum-based hydraulic fluids and lubricant basestocks do not degrade
well. Recently, construction equipment manufacturers began seeking a
biodegradable alternative, in response to tighter environmental regulations.
In tests, about 30 percent of a petroleum-based hydraulic fluid degraded in
28 days, compared to 80 percent for vegetable-based estolides.
The scientists' challenge: making estolides in large enough quantities to be
economically feasible for commercial manufacturers like Caterpillar, a heavy
equipment manufacturer with headquarters in Peoria. Caterpillar is testing the
new biodegradable hydraulic fluid in cooperation with ARS and Lambent
Technologies of Chicago, Illinois.
"The initial yield of estolides in our tests with vegetable oil was
very small because our process wasn't very efficient," says Isbell.
"Estolides have been made for a long time but never in large enough
quantities to be practical on a commercial scale."
Serendipity helped overcome this problem. "One day, Beth Stiner, a lab
technician formerly with ARS, conducted an experiment mixing vegetable oils
with sulfuric acid. The result was a very high yield of estolides. We've
adapted that reaction for our work," says Isbell.
Researchers made estolides by breaking vegetable oils into their two main
components: fatty acids and glycerin. In doing this, they discovered that
sulfuric acid acted as a catalyst to form the estolides.
Estolides form when two fatty acids the building blocks of vegetable oils
link together. ARS researchers used a blend of fatty acids that could be
obtained from high-oleic oils.
Oleic acid is commonly used in formulating food products that seem to show
potential for lowering blood cholesterol in humans. It also displays chemical
properties scientists want in formulating biodegradable hydraulic fluids.
A provisional patent has been filed on this new product. Lambent
Technologies, formerly Calgene, is seeking licensing rights to market the
"Right now we're waiting for Caterpillar to test the product and give
us their feedback," says Isbell. By Dawn Lyons-Johnson, Agricultural
Research Service Information Staff.
Terry A. Isbell, USDA-ARS
New Crops Research Unit,
National Center for Agricultural Utilization Research, 1815 N. University St.,
Peoria, IL 61604; phone (309) 681-6235, fax (309) 681-6524.
"Biodegradable Plant-Based Hydraulic Fluid" was published
in the November 1998 issue of Agricultural Research magazine. Click
here to see
this issue's table of contents.