Tuesday, 24 November, 2020

Fibre Crops and its Classification


Fibre plants were among the first cultivated plants in prehistoric times.

The number of commercially grown fibre crops is small and these are mostly of ancient origin in the tropics.

The tropics supply the bulk of the world’s fibre requirement.

In spite of the competition from the development of the synthetic fibre industry, plant fibre have retained their dominant role.

 

What is actually Fibre ?

The word has many meanings, depending on the particular sense in which it is used.

  • Botany
  • Contents

Botanically, fibres consist of very long narrow cells, many times longer than they are broad.

They are invariably quite thick walled having a corresponding small lumen.

Fibre cells are nonliving structures when mature and serve a purely mechanical function, that is, they impact strength and rigidity to the plant body.

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Chemically, vegetable fibre are mainly composed of cellulose (64-94%) which make up the structural framework of the cell wall.

The cell walls may also contain an appreciable proportion of lignin, hermicellulose, pectic substances, resin, mineral materials, fats and waxes.

 

Categories of Vegetable Fibre

Vegetable fibre can be classified into three types according to their botanical origin as follows

Surface Fibres which are associated with the fruits and seeds of plants, either carried on the seed coat itself or produced by the ovary wall as protection for the developing seeds.

The most important of the commercial fibres, cotton, belongs to this group.

Stem, Phloem, Soft, or Bast fibres which are found associated with the phloem, pericycle and cortex of stem of certain plants.

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The fibres arise either from the cambium or from the apical meristem, made up of elongated cells often with tapering ends, with cellulose walls which vary in the amount of lignification laid down on them.

Fibres of this category are derived mostly from dicotyledonous plants.

They are usually separated by retting- a process in which fibres are freed from other stem tissues through microbial activity.

The best known plants in this group are jute, kenaf, flax, hemp and roselle.

Leaf, structural or hard fibres which are strands of small, short, lignified cells ensheathing both xylem and phloem (fibro vascular bundle) and are primarily found scattered in the leaves of monocotyledonous plants.

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The fibres are highly lignified, coarser but weaker than the soft fibres in which cellulose is largely associated with peptic materials.

Retting, if done, would render the small cells practically useless. Such fibres are therefore usually separated by mechanical scraping.

The important fibres of this group are sisal, Manila hemp and new Zealand hemp.

The quantitatively dominant role of plant fibres is based partly on their low price compared to animal and some synthetic fibres, as well as on their technical characteristics.

Cotton provides 78% of world plant fibres while Jute and Kenaf provide about 2%.

The two fibres produced in the temperate zone, flax and hemp provide 3% and 1% respectively.