Hemp click here
Varieties of hemp click here
Chemical composition of hemp click here
Production and processing click here
Dyeing click here
Hemp in use click here
Hemp:
In many parts of Asia, the fiber hemp has been in use since
prehistoric times. Ancient records describe the use of hemp in China in
2800B.C. During the early Christian era, production of hemp spread to the
countries of Mediterranean Europe, and since then the fiber has come into
widespread use throughout the world.
Like flax, hemp is a bast fiber. It comes from the plant
Cannabis sativa, an annual of the family Moraceae, which grows to a height of
3m or more.
The hemp plant is now cultivated in almost every European
country, and in many parts of Asia.
Important producing country including the Soviet Union,
Yugoslavia, Romania and Hungary.
Varieties of hemp: there are broadly three groups of
cannabis varieties being cultivated:
Ø
Varieties primary cultivated for their fiber,
characterized by long stems and little branching, called industrial hemp.
Ø
Varieties grown for seed from which hemp oil is
extracted.
Ø
Varieties grown formedicinal or recreational
purposes.
A nominal if not legal distinction is often made between
hemp, with concentrations of psychoactive chemicals far too to be useful as a
drug, and cannabis used for medical, recreational, or spiritual purposes.
Chemical composition of hemp:
Cellulose ---------77.5%
Hemi cellulose ---10.1%
Lignin --------------6.8%
Pectin --------------2.9%
Water soluble ---1.8%
Fat and wax -----0.9%
Production and processing:
The hemp plant is harvested and processed in a manner
similar to that used for flax. Fiber is feed from woody matter by dew-retting
or water-retting, followed by breaking and scotching. The fiber is softened by
pounding it mechanically or by hand.
Hemp can be separated from the straw by a mechanical process
more easily than in the case of flax. ‘Green’ hemp is now produced commercially
in this way.
Dyeing:
Hemp is used very largely in its natural state. When dyeing
is necessary, direct color is often used. Basic dyestuffs provide bright
shades, the fiber being mordant with antimony and tannin.
Structure and properties:
Hemp is a coaser fiber than flax; it is dark in color and
different to bleach. The fiber is strong and durable, and is used very largely
for making string, cord and rope.
Some Italian hemps are produced with great care; they are
light in color and have an attractive luster similar to that of flax.
Strands of hemp fiber may be 2m in length. The individual
cells are, on average 13-26mm long. They are cylindrical in shape, with joints,
cracks, swellings and other irregularities on the surface.
Like flax, the cells of hemp fiber are thick-walled; they
are polygonal in cross-section, and the ends of the cells are blunt.
The hemp fiber is more lignified than flax, and is
consequently stiffer.
Hemp in use:
During its long history, hemp has been used for almost every
form of textile material. It has been made into fine fabrics by skilful
spinning and weave of carefully produced fiber, notably in Italy where a hemp
fabric similar to linen is made. Nowadays, hemp is used mainly for coarse
fabrics such as sacking and canvas, and for making rope and twines.
Hemp can be ‘cottonized’ by a process similar to that used
for flax, so that the individual fibers are feed. Cottonized hemp does not spin
easily alone, but it gives useful yarns when mixed with cotton(up to 50 percent
hemp).