Tuesday, October 29, 2019

HEMP FIBRE, CHEMICAL COMPOSITION OF HEMP FIBRE, PROPERTIES OF HEMP FIBRE, USES OF HEMP FIBRE


HEMP FIBRE:

Hemp is a bast fibre. Botanical name of hemp fibre is “Cannabis sativa L”.  The bast fibres come  from outer layer. The primary bast fibre is attached to core fibre with the help of the pectin. Primary bast fibres make up approximately 70 percent of the fibres and are long, high in cellulose and low in lignin. Primary bast fibres are the most valuable part of the stalk, and are generally considered to be among the strongest plant fibres known.

HISTORY OF HEMP FIBRE:



CHEMICAL COMPOSITION OF HEMP FIBRE:



Chemical composition chart of hemp fibre:



CULTIVATION OF HEMP FIBRE:

Soil and climate:

Hemp is an annual plant that grows from seed. It may be grown in a range of soils, but it grows best on land that produces high yields of corn. The soil must be well drained. Soil should be rich in nitrogenand non-acidic in nature. Hemp prefers a mild climate and humid atmosphere.hemp plant requires a rainfall of at least 25 inches-30 inches (64 cm.-76 cm.) per year. Soil temperatures must reach a minimum of 42-46°F (5.5-7.7°C) before seeds can be planted.

Harvesting:

The crop is ready for harvesting high quality fibre when the plants begin to shed pollen, in middle of August for North America. Harvesting for seed occurs four to six weeks later. “Fibre hemp is normally ready to harvest in 70-90 days after sowing of seeds”. 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 grain, which are modified to avoid machine parts being tangled up with bast fibre.

Retting of hemp fibre:

Once the crop is harvested, the stalks are allowed to rett (removal of the pectin by natural exposure to the environment) in the field for four to six weeks depending on the weather to loosen the fibres. 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 fibre, 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.

Fibre processing:

To separate the woody core from the bast fibre, a sequence of rollers (breakers) or a hammermill are used. The bast fibre 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 fibre bundles by chemical and physical methods to produce fibres for paper making), and steam explosion, a chemical removal of the natural binders to produce a weavable fibre. Complete processing lines for fibre hemp have outputs ranging from 2-8 short tons/hour (1.8-7.2 t/hr).

Packaging:

The primary fibre is pressed into a highly compressed bale, similar to other fibres like cotton, wool, and polyester. Other products, such as horse bedding, are packaged in a compressed bale.

Seed processing:

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.

Dehulling: 

“Dehulling is a process of removal of the crunchy skin from the seeds with the help of  a crushing machine”. Modifications to existing equipment may be required to adequately clean the seeds of hull residues.

CHARACTERISTICS OF HEMP FIBRE:



USES OF HEMP FIBRE
The main uses of the hemp fibres are given below:

PAPER MAKING:

Hemp as Clothing and Textiles

Building Materials

Insulation

Filters

Geotextile

Able to use fewer finishing such as no plaster, painting or wallpaper.

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