[Biology Class Notes] on Plant Fibres Pdf for Exam

Plant fibres are derived from plants. Plant fibres, also called fibre crops, are elongated thick-walled cells with pointed ends which consist of cellulose and may or may not contain lignin.  Fibre Crops are grown for their fibres, which are used for making paper, rope, and cloth. In medical practice, they are used as a surgical dressing made up of natural or artificial materials. Fibres may be modified chemically like in viscose. There are different types of plant fibres like jute, flax, cotton, etc. Commercially, fibres are used in the textile industry for weaving the cloth, as a filtering medium, and also for insulation purposes.

Types of Fibre 

Fibres obtained from various sources can be categorised as follows:

• Plants fibres (Example: Jute, flax, cotton, hemp)

• Animals fibres (Example: Silk, wool) 

• Regenerated and Synthetic fibres 

i) Fibres generated from carbohydrate materials (Example: rayon). 

ii) Fibres generated from protein materials (Example: Aridil from milk casein).

Examples of Fibre Crops

Cotton consists of the epidermal trichomes or hairs of the seeds of cultivated species of the Gossypium (Gossypium herbaceum, Gossypium barbadense ), belonging to the family Malvaceae. 

Preparation of Absorbent Cotton

After flowering, the plant bears fruits which are known as capsules. The fruits are 3 to 5 cells. Each capsule contains numerous seeds. The hairs from which seeds are covered are known as bolls. Then these balls are collected and dried and taken to the ginning press. Various devices separate the hairs. Linters are the hairs with a short length which are used for the manufacture of absorbent cotton. While long hairs are utilised for the cloth preparation. After mixing with a soda ash solution, it is put under pressure for about 10-15 hours. It is then treated with a suitable bleaching agent after washing it with water. Then it is dried and carded into flat sheets.   Finally, it is packed in wrappers. Afterward, it is sterilised by means of Gamma radiation. 

Description 

• Colour – White (due to bleaching)

• Odour – Odourless 

• Taste – Tasteless 

• Size Cotton fibres are 2.5 – 4.5 cm, in length, and 25 – 35 diameters.  

Chemical Constituents 

Raw cotton contains about 90% of cellulose, 7 to 8% of moisture, wax, fat, and remains of protoplasm.  Purified cotton or absorbent cotton comes with 6 – 7 % of moisture and is entirely cellulose.

Chemical Tests

1. First, Cotton fibres are soaked in iodine water and then dried.  Then the addition of few ml.  of 80% sulfuric acid trichomes which assume the purplish-blue or bluish-green colour 

2. Ammoniacal copper oxide solution dissolves raw cotton fibres with the formation of balloons. While absorbent cotton dissolves completely with uniform swelling.

3. Cotton is insoluble in dilute sodium hydroxide solution and hydrochloric acid.  It is soluble in 66 % of sulfuric acid.

Uses 

Cotton is used as a filtering medium in surgical dressings and also as an insulating material.  Cotton absorbs blood, mucus, pus and it prevents wounds from infections. 

 

Storage

Absorbent cotton should be stored in a cool place. Cotton is made friable and brittle by the bacterial contamination.  The absorbent cotton should be wrapped in wrappers to avoid dust and microbial contamination. Heat and long storage make absorbent cotton non-absorbent. 

Jute 

Biological Source

It consists of phloem fibres of the stem of various species of the Corchorus (Corchorus olitorius and Corchorus capsularis Linn.) and Family Tiliaceae. 

Chemical Constituents 

The fibres are yellowish-brown in colour and contain cellulose (53%), hemicellulose (20%), and lignin (10 %). 

Chemical Test 

The middle lamella is highly lignified and gives a red colour with phloroglucinol and hydrochloric acid.

Uses

It is used in the manufacture of tows, padding splints, filtering, and straining mediums. Jute fibres are used for the preparation of coarse bags (Gunny bags).  

Flax 

Biological Source 

These are pericyclic fibres obtained from the stem of the plant Linum usitatissimum belonging to family Linaceae.

Uses 

The fibres were earlier used in the manufacture of lint, but at present cotton has replaced these fibres.  It is used in the preparation of rugs, lace, lawn, and filtering medium.

Difference between Natural and Synthetic Fibre

Fibres are used as a raw material to make garments, clothes or any other applicational types of equipment. There are two types of fibres based upon the source of production. Natural fibres that are obtained from plants, animals or minerals and synthetic fibres that are obtained through chemical processes with the help of machines. Some of the examples of natural fibre include cotton, jute, silk, etc. And synthetic fibre includes polyester, Nylon, rayon, etc. However, there are a lot of differences between natural and synthetic fibres which are as follows:

Difference between Natural and Synthetic Fibre

Sample Questions

1. What are natural fibres?

2.  What are plant fibres? give example

3. Differentiate between natural fibre and man-made fibre

4. What are the advantages of using natural fibre over man-made fibre?

5. Explain the type of fibre and give examples of each.

6. How is cotton prepared and what are its uses?

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