Sisal Fibres: Chemical Composition, Structure, Properties and Uses

What is Sisal Fibre?
Sisal fibre is a strong, coarse natural fibre that is extracted from the leaves of the sisal plant (Agave sisalana), which is native to Mexico and Central America. Sisal fibres are used in a variety of applications, including twine, rope, floor mats, and paper production. It is known for its strength and durability, making it a popular choice for many industrial and household applications.

Sisal comes from the leaves of an agave plant which takes approximately five years to mature before harvesting can begin; the best yields coming in the eighth through eleventh years, and by the twelfth year, only a minimal yield is given. Brazil is the main producing country, but it is also produced in East Africa, Mexico and Asia. Once the leaves are harvested, they go through the decortication process whereby leaves are crushed, beaten and then washed to remove the waste so that only the fibres remain. Once dried, the fibres are combed and graded according to length. Sisal is renewable but care must be taken with the waste water as it can cause pollution in water courses in the underdeveloped countries where it is produced.

We already know that sisal fibres are derived from the leaves of the sisal plant. It is usually obtained by machine decortications in which the leaf is crushed between rollers and then mechanically scraped. The fibre is then washed and dried by mechanical or natural means. The dried fibre represents only 4 % of the total weight of the leaf. Once it is dried the fibre is mechanically double brushed. The lustrous strands, usually creamy white, average from 80 to 120 cm in length and 0.2 to 0.4 mm in diameter. Sisal fibre is fairly coarse and inflexible. It is valued for cordage (ropes, baler, binder twines, etc.) use because of its strength and durability. The higher-grade fibre after treatment is converted into yarns and used by the carpet industry.

Chemical Composition of Sisal Fibre:
The chemical composition of sisal fibres can affect its properties, such as strength, durability, and resistance to moisture, as well as its suitability for various applications. Sisal fibre is composed primarily of cellulose and hemicelluloses. Percentage of different components are given below table.

Structure of Sisal Fibre:
Sisal fibres are used for textile processing are multicellular fibres. In cross section, the fibre bundles are built up of about 100–200 single cells which are bonded together by natural gums. Single cells consist of thick walls with a central lumen and shape of single cell is polygonic. The cross section of sisal fibres is neither circular nor fairly uniform in dimension. The lumen varies in size but is usually well defined. Longitudinally the fibre is straight and without crimp, and approximately cylindrical in appearance. There are many knots and stripes on the surface of the fibre, which confirms that the fibre bundle is composed of many single cells which are arranged in straight parallel lines.

Properties of Sisal Fibres:

1. Sisal fibres are exceptionally strong and durable with a low maintenance with minimal wear and tear.
2. It is recyclable.
3. Sisal fibre is resistant to many chemicals, which makes it suitable for use in harsh environments.
4. It is obtained from the outer leaf skin, removing the inner pulp.
5. It is available as plaid, herringbone and twill.
6. Sisal fibres are anti-static, do not attract or trap dust particles and do not absorb moisture or water easily.
7. Sisal fibre has a good degree of flexibility, which makes it suitable for applications that require the material to bend and flex without breaking.
8. The fine texture takes dyes easily and offers the largest range of dyed colours of all natural fibres.
9. Absorbent but releases air humidity which allows it to expand and contract
10. It exhibits good sound and impact absorbing properties.
11. Its leaves can be treated with natural borax for fire resistance properties.
12. Sisal fiber is highly resistant to abrasion, making it ideal for applications where the material will be subjected to repeated wear and tear.
13. Sisal fibre is biodegradable and environmentally friendly; no chemical fertilizers are used, and the waste materials can be used for biofuels.

Applications / Uses of Sisal Fibres:
From ancient times sisal has been the leading material for agricultural twine because of its strength, durability, ability to stretch, affinity for certain dyestuffs and resistance to deterioration in saltwater.

1. Sisal fibres are used commonly in the shipping industry for mooring small craft, lashing and handling cargo.
2. It is also surprisingly used as the fibre core of the steel wire cables of elevators, being used for lubrication and flexibility purposes. Traditionally sisal was the leading material for agricultural twine or baler twine. Although this has now been overtaken by PP.
3. Sisal fibres are used in automobile industry with fiberglass in composite materials.
4. Other products developed from sisal fibre include spa products, cat scratching posts, lumbar support belts, rugs, slippers, cloths and disc buffers.
5. Sisal is used in the production of various types of packaging, such as bags and containers, due to its strength and durability.
6. Sisal is used by itself in carpets or in blends with wool and acrylic for a softer hand.
7. It is used in agriculture for various applications, such as tying up crops, due to its strength and biodegradability.
8. Sisal fibres are used in the production of paper due to its low linting properties and ability to absorb water.

References:

1. Agro Textiles and Its Applications by Grace Annapoorani
2. Handbook of Properties of Textile and Technical Fibres, Second Edition Edited by Anthony R. Bunsell
3. Fibres to Fabrics by Bev Ashford
4. Textile Engineering – An Introduction Edited by Yasir Nawab
5. Bast and Other Plant Fibres Edited by Robert R Franck

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