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Colleen M. McMahan,
cmcmahan@pw.usda.gov1, Katrina Cornish,
kcornish@yulex.com2, and Maureen Whalen,
mwhalen@pw.usda.gov1. (1) Crop Improvement & Utilization
Research, USDA-Agricultural Research Service, Western Regional
Research Center, 800 Buchanan Street, Albany, CA 94710, (2) Yulex
Corporation, 1945 Camino Vida Roble, Suite C, Carlsbad, CA 92008
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| Natural rubber, biosynthesized cis-1,4-polyisoprene,
is the largest single volume elastomer in commerce, at ca. 9 million
tons sold globally per year. It is a strategic raw material used in
thousands of applications; critically in medical devices, personal
protective equipment, and specialty industrial uses, especially aircraft
tires. The US imports virtually all natural rubber used from Hevea
brasiliensis rubber trees grown in Asia and Africa. Primarily due to
its molecular structure, natural rubber displays outstanding performance
properties that, despite significant investment and innovation, have not
been duplicated by synthetically-produced polymers. Natural rubber latex
prices have increased over 80% since the beginning of 2005. A 3 million
ton shortage has been predicted over the next 10-15 years, driven by
Asian growth, influenced by petroleum supply and price, and expected to
worsen before it improves. Guayule (Parthenium argentatum), a
woody desert shrub indigenous to the southwestern US, produces high
molecular weight cis-1,4-polyisoprene with very low residual
protein content, and has entered the commercial arena as an alternative
material for the manufacture of medical devices safe for people
suffering from Type I IgE-mediated Hevea latex allergies.
Cultivation of guayule for latex production provides the favorable
economics to support commercialization; moreover, the agricultural
coproduct/bagasse produced with every ton of latex may prove key to its
long term sustainable competitive advantage. The resin-rich bagasse
shows significant promise as a feedstock for fuel production. Collection
of the entire plant is required to harvest the rubber, the material is
in the form of a finely divided dry solid after rubber extraction, and
energy content is very high, even in comparison to proposed energy
crops. The guayule biorefinery model ultimately describes production of
high value primary product, coproducts, and bioenergy. |