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STUCK ON STARCH:
A New Wood Adhesive
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Wood.
(K8849-1) |
Environmentally conscious shoppers
may soon be able to furnish family rooms and offices with items made from a
surplus farm product—starch.
Each year, the plywood paneling and furniture made from particle board and sold
in the United States contain more than a billion pounds of adhesives.
"Industrial wood adhesives are now made solely from petroleum and natural
gas," says ARS chemist Syed H. Imam,
"but we've found a way to make them from a combination of other
ingredients, including starch."
Imam works in the Biopolymer Research Unit of the National Center for
Agricultural Utilization Research, Peoria, Illinois. He and his colleagues came
upon the idea of making wood adhesives from starch while researching totally
biodegradable, starch-based films. Their goal is to find ways to make
alternatives to plastic agricultural mulch films now used to curb weed growth
in high-value agricultural crops.
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Chemist Syed Imam examines pellets
of the sticky extruded material that led
to the development of starch adhesive.
(K8848-1) |
The scientists made biodegradable
films from a slurry of starch and dissolved polyvinyl alcohol, which they
processed through a machine called an extruder. Noting the hot film was quite
sticky while coming out of the extruder, the researchers considered the
chemistry. "We reckoned the material could be made into an excellent
adhesive to bind layers of veneer," Imam said. "What we needed to do
was make the material more flowable so it could be easily brushed onto
wood."
Breathe With Ease
Imam and his colleagues weren't just thinking of farmers who would like to see
increased demand for commodities such as corn. People working in wood
industries and consumers might also benefit.
The researchers developed a process to make a flowable, strong, and
moisture-resistant adhesive from a combination of cornstarch, polyvinyl
alcohol, latex, and citric acid. The main safety benefit: The process required
no volatile formaldehydes or phenols found in conventional wood adhesives. That
could be a major selling point for wood products companies—indoor air
quality that poses less health risk to workers. |
Starch being applied to a plywood veneer.
(K8850-1) |
Residents of new and recently furnished homes and offices might also breathe a
sigh of relief knowing the products surrounding them contain fewer toxic
chemicals. Pressed wood products, especially those made with urea formaldehyde
resins and having edges not fully covered by a water-repellent finish, may emit
unacceptably high levels of toxic compounds into humid indoor environments that
are poorly ventilated.
A fire retardant could be added to composite wood products made with starch
adhesive. This could be useful for kitchen counter tops where many destructive
fires begin. But should the new-style wood composites burn anyway, they would
not produce fumes as toxic as those from products containing formaldehyde and
phenols.
Because of environmental interests, several U.S. companies as well as the
United Nations Industrial Development Organization and the International Center
for Science and High Technology, Trieste, Italy, have expressed interest in the
new adhesive.
How expensive is it to make this safer glue? Given present prices for
ingredients, the cost of making it may be 25 to 30 cents per kilogram more than
the cost to make conventional adhesives, according to Lijun Mao, a senior
scientist for Planet Polymer Technologies, Inc., San Diego, California.
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Pellets of sticky extruded material.
(K8848-20) |
Binding Strength
Owens Corning has been evaluating Imam's adhesive under a materials transfer
agreement. "We're conducting further research because the starch adhesive
provided excellent bonding strength," said chemist Liang Cheng, a senior
scientist who is involved in the company's project to possibly modify current
phenolic binder systems.
In his research, Imam and his coworkers used partially melted starch. To a
slurry of the starch and dissolved polyvinyl alcohol powder they added the
chemical hexamethoxymethylmelamine which, with the help of the catalyst citric
acid, firmly bound the starch to the alcohol. Then they added latex to the mix
before brushing it on wood. Hot plates pressed the adhesive-covered veneer
layers together for 15 minutes.
The latex helped increase the strength of the adhesive bonding and also
provided resistance to weakening by moisture. Research still in progress will
show whether adding wax to the formulation will further improve water
resistance.
Considerable improvement in moisture resistance might be needed to help the
plywood stand up in outdoor settings, Imam says. But for conditions harsher
than most indoor settings, his birch veneer plywoods measured up to commercial
ones. In these tests, he first stored the plywood samples at normal or high
humidities for a month or soaked them in water for 2 hours. Then he measured
the force needed to pull the layers apart. In 98 percent of samples from each
of the storage environments, the adhesive proved stronger than the wood.
More research is needed to determine the commercial potential of the new
adhesive. Accordingly, ARS is seeking cooperators to speed the technology for
defined uses. A cooperative research and development agreement (CRADA), for
example, might entail temporary use of a company's scaled-up research equipment
in a recently renovated NCAUR pilot plant.—By
Ben Hardin, Agricultural
Research Service Information Staff.
This research is part of New Uses, Quality, and Marketability of Plant and
Animal Products, an ARS National Program (#306) described on the World Wide Web
at http://www.nps.ars.usda.gov/programs/cppvs.htm.
Syed H. Imam is at the
USDA-ARS National Center for
Agricultural Utilization Research, 1815 N. University St., Peoria, IL
61604; phone (309) 681-6335, fax (309) 681-6689. |
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"STUCK ON STARCH: A New Wood Adhesive" was
published in the April 2000 issue
of Agricultural Research magazine.
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