Flax
The flax fiber from the annual plant Linum usitatissimum (flax
family, Linaceae) has been used since ancient times as the fiber for linen. The
plant grows in temperate, moderately moist climates, for example, in Belgium,
France, Ireland, Italy, and Russia. The plant is also cultivated for its seed,
from which linseed oil is produced. A by-product of the seed plant is the tow
fiber used in papermaking.
The bast fibers are dew or water retted with dew retting generally yielding a gray fiber. High quality flax fiber is produced by water (stream) retting
in the river Lys in Belgium. The boiled,
bleached fiber contains almost 100% cellulose. The flax fiber is the strongest of
the vegetable fibers, even stronger than cotton. The fiber is highly absorbent,
an important property for clothing, but is particularly inextensible. The most
important application is in linen for clothing, fabrics, lace, and sheeting. Flax
fiber is also used in canvas, threads and twines, and certain industrial applications such as fire hoses. Chemical pulping of flax provides the raw material for
production of high quality currency and writing paper. Flax fiber is also commonly used in cigarette papers. Flax fibers are graded for fineness, softness,
stretch, density, color, uniformity, luster, length, handle, and cleanliness.
Hemp
The source of hemp fiber is the plant Cannabis sativa (mulberry
family, Moraceae) originating in central China. It is grown in central Asia and
eastern Europe. The stem is used for fiber, the seeds for oil, and leaves and
fiowers for drugs, among them marijuana. The stalks grow 5–7 m tall and 6–
16 mm thick. The hollow stems, smooth until the rough foliage at the top, are
hand cut and spread on the ground for dew retting for the highest quality
product. Water retting is used on sun-dried bundles from which the seeds and
leaves have been removed. Strands of hemp fiber can be 2 m in length. The
fibers are graded for color, luster, spinning quality, density, cleanliness, and
strength.
It has a Z
twist in contrast to the S twist of flax. Hemp is regarded as a substitute for
flax in yarn and twine. Its earlier use in ropes has been replaced by leaf and synthetic fibers. Hemp fiber is used in Japan, China, Hungry, and Italy to make
specialty papers, including cigarette paper, but bleaching is difficult. The fiber
is coarser and has less fiexibility than flax. There is currently interest in reintroducing hemp into the United States and Canada as an alternate fiber crop
for farmers. However, this is wrought with political and legal problems due to
the inability to distinguish industrial hemp from hemp plants with high narcotic
content.
Jute
Jute fiber is obtained from two herbaceous annual plants, Corchorus
capsularis (linden family, Tiliaceae) originating from Asia, and C. olitorius originating from Africa. The former has a round seed pod, and the latter a long pod.
Jute is grown mainly in India, Bangladesh, Thailand, and Nepal.
The plants are harvested by hand, dried in the field for defoliation, and
water (pool) retted for periods up to a month. The depth of the retting pools is
dependent on the volume of rainfall during the monsoon season in Southeast
Asia. Thus a year with less rainfall results in low water levels in the retting
pools and a lower grade jute product due to contamination with sand and silt.
The fibers for export are graded for color, length, fineness, strength, cleanliness,
luster, softness, and uniformity. The color ranges from cream white to reddish
brown, but usually the fiber has a golden luster. The fibers are polygonal in cross-section with a
wide lumen. Jute has traditionally been an important textile fiber, second only
to cotton; however, jute has been steadily replaced by synthetics in the traditional high volume uses such as carpet backings and burlap (hessian) fabrics
and sacks. The strands are also used for twine, while kraft pulping of
jute gives ultimate fibers for cigarette papers. The Indian government in cooperation with the United Nations Development Program has been involved in a significant jute diversification program to find new uses for jute in finer yarns and
textiles, composites and boards, and paper products. A particularly promising
outlet for jute is in molded composites with thermoplastic materials for interior
automobile head, door and trunk liners.
Kenaf and Roselle
These closely related bast fibers are derived from
Hibiscus cannabinus and H. sabdariffa (mallow family, Malvaceae), respectively.
The fibers have other local names. Kenaf is grown for production in China,
Egypt, and regions of the former Soviet Union; roselle is produced in India and
Thailand. Plantation-grown kenaf is capable of growing from seedlings to 5 m at
maturity in five months. It is reported to yield ~6–10 tons of dry matter per acre,
nine times the yield of wood.
The plants are hand-cut, mowed, or pulled in developing countries while
mechanized harvesting methods are under investigation in the United States.
Ribboning machines are sometimes used to separate the fiber-containing bark
before retting for recovery of the kenaf strands. For pulping, the kenaf is shredded or hammermilled to 5-cm pieces, washed, and screened.
The ultimate cells
are nearly cylindrical with thick cell walls. Kenaf fibers are shorter and coarser
than those of jute. Both chemical (kraft) and mechanical pulps have been
produced from kenaf, and successful demonstration runs of newsprint have
been made for the Dallas Morning News, the St. Petersburg Times, and the
Bakersfield Californian with a furnish of 82% kenaf chemithermomechanical
pulp and 18% softwood kraft pulp. Kenaf fiber is also considered a substitute
for jute and used in sacking, rope, twine, bags, and as papermaking pulp in
India, Thailand, and the Balkan countries. Roselle bleached pulp is marketed
in Thailand.
Ramie
The ramie fiber is located in the bark of Boehmeria nivea, a member of the nettle family (Urticaceae). The plant is a native of China (hence, its
name China grass), where it has been used for fabrics and fishing nets for
hundreds of years. It is also grown in the Philippines, Japan, Brazil, and Europe.
The ramie plant grows 1–2.5 m high with stems 8–16 mm thick. The roots send
up shoots on harvesting, and two to four cuttings are possible annually, depending on soil and climate.
The plant is harvested by hand sickle and, after defoliation, is stripped
and scraped by hand or machine decorticated. Because of the high gum (xylan
and araban) content of up to 35%, retting is not possible. The fibers are separated
chemically by boiling in an alkaline solution in open vats or under pressure, then
washed, bleached with hypochlorite, neutralized, oiled to facilitate spinning, and
dried.
The degummed, bleached fiber contains 96–98% cellulose. The ramie fibers are oval-like in cross-section with
thick cell walls and a fine lumen. The cell wall constituents in the ramie fiber,
like other bast fibers except flax, have a counterclockwise twist. Ramie is the
longest of the vegetable fibers and has excellent luster and exceptional strength;
however, it tends to be stiff and brittle. Wet strength is high and the fiber dries
rapidly, an advantage in fish nets.
Traditional uses for ramie have been for heavy industrial-type fabrics such
as canvas, packaging material, and upholstery. Increased production of the fiber
in Asia, particularly China, has promoted the use in blended fabrics with silk,
linen, and cotton which can now be found on the market.
Sunn Hemp
The stems of the herbaceous plant Crotalaria juncea (legume
family, Fabaceae), called sunn or sunn hemp, provide a bast fiber. The plant is
native to India, the chief fiber producer, and it is also grown in Bangladesh, Brazil,
and Pakistan. It has a long tap root and grows to a height of up to 5 m. Harvesting
is done manually by pulling or cutting. The plant is defoliated in the field, water
retted, and processed similarly to jute. The white fiber is graded by color, firmness,
length, strength, uniformity, and extraneous matter content. Sunn is used for
canvas, paper, fishing nets, twine, and other cordage.
Urena and Abutilon
These are less important vegetable fibers of a
jutelike nature. Urena lobata (Cadillo) of the mallow family (Malvaceae) is a perennial that grows in Zaire and Brazil to a height of 4–5 m with stems 10–18 mm
in diameter. Because of a lignified base, the stems are cut 20 cm above the
ground. The plants are defoliated in the field and retted similarly to jute
and kenaf. The retted material is stripped and washed and, in some
cases, rubbed by hand. The soft, near-white fiber is graded for luster, color,
uniformity, strength, and cleanliness. It is used for sacking, cordage, and coarse
textiles.
Abutilon theophrasti
Abutilon theophrasti is a herbaceous annual plant producing a jute-like
fiber. The plant is native to China and is commercially grown in China and
the former Soviet Union. Because of its association with jute in mixtures and
export, it is also called China jute. The plant grows to a height of 3–6 in with
a stem diameter of 6–16 mm. After harvesting by hand and defoliation, bundles
of the stems are water retted and the fiber is extracted by methods similar to
those for jute. The fiber is used for twine and ropes.