Biomedical Engineering Reference
In-Depth Information
12.2.2 Corn stover
Published calculations indicate that the potential for corn stover in the United States could
be 75 million dry tons (US) per year (Perlack et al ., 2005). Corn stover consists of stalks,
leaves, and cobs after the corn kernels are harvested. More than 90% of the stover is left in
the fields, less than 1% is collected for industrial processing, and about 5% is baled for
animal feed and bedding. Much of the remaining 90% or so must be plowed. The plowing
operation can cause organic carbon and nitrogen losses due to oxidation, and increases the
amount of fertilizer and chemicals that need to be applied. The decay of the stover increases
the release of carbon dioxide, a greenhouse gas. Although some residue (
30%) is required
to protect the soil from erosion, most residues (
60%) can be safely taken out of the fields
for valuable utilization, which has the potential to be a win-win situation for the producer,
the processor, and the consumer. The farmer wins from the stover sales, reduced cultivation
costs and possible carbon credits for the greenhouse gas offset. The processors make value-
added industrial products that are previously produced from petroleum. The consumer
benefits from productive agricultural practices and an improved environment.
12.2.3 Bast fiber crops
Bast fiber crops are a group of plants that can produce natural cellulose fibers from plant
stem skin. In history, cultivation of bast fiber crops is the oldest method to produce natural
fibers for meeting clothing needs and other daily necessaries. The most important bast fiber
crops are ramie, flax, hemp, jute, and kenaf, based on their production capacity and
consumption quantity. To date, the production of bast fiber crops still primarily aims at the
textile market. Facing fierce competition from synthetic fibers that have increased
productivity and a steadily expanded end-use market, the world capacity of bast fiber
production continues to decline. Currently, the production volume of the major bast fibers
in the world is about 4.8 million metric tons, equivalent to 14% of the global production of
manufactured fibers (Fibersource, 2002 ).
Bast fiber crops are also a group of lignocellulosic biomass that can be used for bioenergy
production. A basic fact is that the bast fiber extraction rate from the bast fiber biomass is
only about 10-30%. The remaining material after the fiber extraction process is a large
portion of residues (woody core and short fiber). While the traditional textile application of
bast fibers is well established, the potential of using bast fiber residues for biofuel production
is still undervalued. Furthermore, some subtropical fiber crops, like sunn hemp, can grow in
summer with a short cultivation period and large amount of biomass yield (IFAS, 2009). The
production of these fiber crops requires no use of extra land, no use of pesticide and nitrogen
fertilizer, has no competition with food crops, and no conflict with the current infrastructure
for industrial crops. Therefore, the bast fiber crops can be developed as a type of sustainable
feedstock viable for bioenergy and bio-based product diversification, rural economic
development, and efficient use of land resources.
Bast fiber crops have a similar biological stem structure. They are typically composed of
a bark layer, a bast layer and a stem core. The bark layer is called cuticle, a thin skin to form
a protective stem surface and to hold bast fiber bundles. The bast layer includes a primary
fiber layer where bast fibers can be extracted. The stem core usually consists of woody
tissue called xylem and pith. Figure 12.2 shows the cross-sectional view of sunn hemp stem.
The height of bast fiber crops varies depending on crop species. Overall, it is in the range of
60 to 600 cm (Krishnan et al ., 2000 ; Salmon-Minotte and Franck, 2000 ; Sponner et al .,
2000 ; Kozlowski et al ., 2000 ).
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