Hemp is an annual plant that grows from seed. It grows in a range of soils, but tends to grow best on land that produces high yields of corn. The soil must be well drained, rich in nitrogen, and non-acidic. Hemp prefers a mild climate, humid atmosphere, and a rainfall of at least 25-30 in (64-76 cm) per year. Soil temperatures must reach a minimum of 42-46°F (5.5-7.7°C) before seeds can be planted.
- 1 The crop is ready for harvesting high
quality fiber when the plants begin to shed pollen, in mid-August for
North America. Harvesting for seed occurs four to six weeks later. Fiber
hemp is normally ready to harvest in 70-90 days after seeding. A special
machine with rows of independent teeth and a chopper is used. To harvest
hemp for textiles, specialized cutting equipment is required. Combines are
used for harvesting
An example
of hemp and hemp fibers.
grain,
which are modified to avoid machine parts being tangled up with bast fiber.
- 2 Once the crop is cut, the stalks are
allowed to rett (removal of the pectin [binder] by natural exposure to the
environment) in the field for four to six weeks—depending on the
weather—to loosen the fibers. While the stalks lay in the field, most of
the nutrients extracted by the plant are returned to the soil as the
leaves decompose. The stalks are turned several times using a special
machine for even retting and then baled with existing hay harvesting equipment.
Bales are stored in dry places, including sheds, barns, or other covered
storage. The moisture content of hemp stalks should not exceed 15%. When
planted for fiber, yields range from 2-6 short tons (1.8-5.4t) of dry
stalks per acre, or from 3-5 short tons (2.7-4.5 t) of baled hemp stalks
per acre in Canada.
Grain processing
- 3 Hemp seeds must be properly cleaned and
dried before storing. Extraction of oil usually takes place using a
mechanical expeller press under a nitrogen atmosphere, otherwise known as
mechanical cold pressing. Protection from oxygen, light, and heat is
critical for producing a tasty oil with an acceptable shelf-life. Solvent
extraction methods are also emerging for removing oil since they achieve
higher yields. Such methods use hexan, liquid carbon dioxide, or ethanol
as the solvent. Refining and deodorizing steps may be required for
cosmetics manufacturers.
- 4 A dehulling step, which removes the
crunchy skin from the seed using a crushing machine, may be required. Modifications
to existing equipment may be required to adequately clean the seeds of
hull residues.
Fiber processing
- 5 To separate the woody core from the bast
fiber, a sequence of rollers (breakers) or a hammermill are used. The bast
fiber is then cleaned and carded to the desired core content and fineness,
sometimes followed by cutting to size and baling. After cleaning and
carding, secondary steps are often required. These include matting for the
production of non-woven mats and fleeces, pulping (the breakdown of fiber
bundles by chemical and physical methods to produce fibers for paper
making), and steam explosion, a chemical removal of the natural binders to
produce a weavable fiber. Complete processing lines for fiber hemp have
outputs ranging from 2-8 short tons/hour (1.8-7.2 t/hr).
Packaging
- 6 The primary fiber is pressed into a
highly compressed bale, similar to other fibers like cotton, wool,
and polyester. Other products, such as horse bedding, are packaged in a
compressed bale.
Paper making
- 7 Bast fibers are usually used in paper,
which are put into a spherical tank called a digester with water and
chemicals. This mixture is heated for up to eight hours at elevated
temperature and pressure until all fibers are separated from each other. Washing
with excess water removes the chemicals and the extracted binding
components (pectin). The clean fibers are then fed into a machine called a
Hollander beater, which consists of a large tub equipped with a wheel
revolving around a horizontal axis. This beating step, which lasts for up
to 12 hours, cuts the fibers to the desired length and produces the
required surface roughness for proper bonding. Bleaching chemicals are
sometimes added during this step or to separate tanks with the fibers. The
bleached pulp is then pumped to the paper machine or pressed to a dryness
suitable for transportation to a paper mill at another location.
Quality Control
Hemp fibers are tested for
tensile strength, fineness (fiber diameter), and the color is recorded. Moisture
content is recorded during every stage of the growing and production process. The
THC content of the plant is also contiguously tested to make sure that the
level does not exceed the 0.3% mark. Research is still being conducted on the
effects that hemp would have on the industry. Set standards are constantly
being altered and changed.
Byproducts/Waste
The harvested hemp not used
is burned. During fiber processing, the core fiber is saved and usually used to
make paper, horse bedding, or construction materials. Most hemp producers
recycle the core fiber by removing dust, then baling and packaging. The dust
can be pressed into pellets used for fuel. The dirt and small chips of core are
also used as a high nutrient soil additive.
The Future
Where it is legal, the hemp
industry has been growing at an annual growth rate of 20%. Other potential uses
are being developed. For instance, hemp meal has demonstrated it can be used as
a food ingredient for aquiculture farms, specifically freshwater fish and
shrimp. Even hemp beer has entered the Canadian market, though it is expected
to remain a small part of beer sales. Composite materials for the building
industry are also being investigated. Using hemp as a source of food may become the largest application, since hemp seeds have much nutritional value. The seed contains essential fatty acids, protein, calcium, iron, zinc, and vitamins B, C, and E. Hemp seed can be made into oil or flour and can also be eaten whole, since it tastes similar to pine nuts or sunflower seeds.
The outlook for hemp in the United States is uncertain since it is still illegal to grow it. There are 10 states that passed legislation in 1998 to allow growing hemp for research purposes—Arkansas, California, Hawaii, Illinois, Minnesota, Montana, New Mexico, North Dakota, and Virginia—and a number of other states are considering it. However, federal law still prohibits growing industrial hemp. The Drug Enforcement Agency will have to change its mind before any market can be developed in the United States. Once that happens, hemp could become a billion dollar crop if there is enough investment and interest, prices are competitive, and high quality products can be made. Processing technology also needs to be upgraded for higher value-added products
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