Properties of Cotton Fibre (Physical, Chemical and Technical Properties)

Cotton fibre properties


This article is written by Agniv Chatterjee.

When we think of natural fibres, cotton comes first in our minds. Cotton is a plant-based natural fibre, and it is grown in many countries.

Cotton is a cellulosic staple fibre. The length of cotton fibre determines the quality of fibre. The longer the length of the fibre the better the quality of fibre is.

It requires adequate temperature and moisture to produce high-quality yarn. Hence it is mostly grown in hot and humid places. It has a density of 1.52 g/cm^3 making it one of the heavy fibres. In this article, Agniv has explained properties of cotton fibre in the following four categories.

  1. Technical properties of cotton fibre
  2. Physical properties of cotton fibre
  3. Chemical properties of cotton
  4. Miscellaneous properties of cotton

1. Technical properties of cotton

a. Fibre density – 1.52 g/cm^3
b. Fibre Diameter
        Micronaire – 2.0-7.0
        Approximate denier – 0.7-2.5
c. Elasticity recovery
        At 2 % Extension – 74%
        At 5 % Extension – 45%

d. Breaking elongation (dry) – 3-9.5
e. Tensile Strength (g per tex/g per denier)

        Dry: 27 – 44 / 3.0 – 4.9
        Wet: 28 – 57 / 3.3 – 6.4

f. Moisture Regain at Standard Conditions - 7%
g. Water Absorbing Capacity (USP method)
        Less than 24 grams of water per gram of fiber

h. Density (g/cm3) – 1.54
i. Degree of Polymerization- 9000-15000
j. Crystallinity by X-ray Diffraction -73%(average)
k. Color (Whiteness Index) - 90-100

2. Physical properties of cotton

2.1 Tenacity

The strength of cotton is increased by its long polymers, the countless, regular, hydrogen bond formation between adjacent polymers and the spiraling fibrils in the primary and secondary cell walls. It is one of the few fibres which gains strength on wetting which occurs due to improved arrangement in the amorphous region of the fibre.

2.2 Elastic-plastic nature

Cotton fibre is inelastic in nature because of its crystalline polymer system and hence for this reason cotton fibres wrinkle and crease easily. The polymer molecules can slide past each other only under considerable strain as they are prevented from doing so by their long lengths and countless hydrogen bond between them to hold the polymer molecules in position. Strong strain forces cause polymer fracture as the crystallinity of the polymers makes it difficult to bend and crush. These polymer fracture forms weak points on the polymer system and hence forming weak areas in the fibre structure. Therefore, cotton fibres get creased and wrinkled on the application of force.

2.3 Hygroscopic nature

The cotton molecule is very moisture absorbent due to its abundant polar –OH group which attracts water molecules towards it. But the OH molecule can only enter the cotton molecule through the amorphous region as the intermolecular spaces in the crystalline region are very small. The swelling up of cotton fibre in presence of water is mainly due to the separation of polymers by water molecules in the amorphous region. Cotton fibres usually feel crisp on touching as it absorbs moisture from the skin of the finger. The hygroscopic nature of the fibre prevents cotton materials to develop static electricity. The polarity of the water molecule is attracted by the hydroxyl group of the polymer and hence static charges are dissipated.

2.4 Thermal Properties

Cotton fibre has the ability to conduct heat energy, minimizing any destructive heat accumulation. Hence cotton fibres can withstand hot ironing temperatures. But excessive heating on cotton fibre chars and burns them indicates that cotton fibre is not thermoplastic. This prevents the fibre from assuming the new position of the polymers when heat is applied. The polymers begin to vibrate on heating and gradually disintegrate.


Related post: Use of cotton fibre

3. Chemical properties of cotton

3.1 Effect of Acid

Cotton fibres are weakened and destroyed by acid as acidic conditions hydrolyse the cotton polymer at the glucoside oxygen atom of the cellobiose unit. Cotton polymers are more rapidly hydrolysed by mineral acid than organic acid.

3.2 Effect of Alkali

Cotton fibres are unaffected by alkalis due to the lack of attraction between the polymer and the alkalis. Mercerization without tensioning or slack mercerization results in swelling of cotton fibres. The main reason of this swelling is due to alkali and radicles entering the amorphous region of the fibre polymer system thus forcing the polymers wide apart causing swelling. This allows them poorly oriented polymers to arrange themselves more orderly and hence increases the fibre strength. When mercerization is done under tension then little swelling or fibre contraction occurs. The fibre hence produced has less tenacity and distinct, subdued lustre. The increase in tenacity on mercerization under tension can be explained as the alkaline liquor helps to align the polymer molecules and form hydrogen bonds. It also causes the fibre to become smooth and more regular enabling it to reflect light more evenly and hence causing it to subdued lustre. Also, mercerization of cotton increases its dye uptake. Thus, mercerized cotton dye and print a deeper hue than any other mercerized fibre.

3.3 Effect of Bleach

Sodium Hypochlorite and Sodium Perborate are the most common bleaching agents used on cotton textile. Sodium Perborate a white powder bleaches cotton fibres at room temperature. Bleaching with sodium perborate is more effective at temperatures more than 50 degrees C. The bleach is effectively in an alkaline medium when cotton materials are resistant. Oxidising bleaches liberates oxygen and hence the interaction between the oxygen liberated by bleach and the molecules of fibre surface causes the discolouration of cotton. It is found that oxygen forms water-soluble molecules with the fibre which is rinsed off when the fibre is washed. Carefully bleaching the fabric can protect the fabric from chemical attacks of the bleach.

3.4 Effect of Sunlight and Environment

The ultraviolet rays of sunlight provide photochemical while heat energy is provided by infrared rays to degrade cotton fibres in presence of atmospheric air, oxygen, moisture and pollutant. Atmospheric moisture is the main cause of the breakdown of cotton fibre by various hydrolytic reactions. First, the fibre starts to discolouration. Gradually the reactive nature of the hydrolytic compound increases the rate of degradation of cotton. The weakening and breakdown of polymer is a clear indication of the degradation of cotton fibre. Air pollutants are generally acidic in nature and hence readily accelerate the breakdown of cotton fibre through acid hydrolysis.

3.5 Colour Fastness

Cotton fibre can be dyed by azoic dye, direct dye, reactive dye, sulphur dye and vat dye. It is one of the easiest fibres to dye and print. This is due to the polarity of the polymer molecules of the cotton fibre. Hence this attracts any polar dye molecules in the polymer system. Also, dye molecules that can be evenly dispersed in water can also be efficiently absorbed by this polymer system. The dye molecules enter the polymer through its amorphous region as the smaller spaces of the crystalline region prevent the entry of any dye molecules in it.

4. Miscellaneous properties of cotton

4.1 Versatility

Cotton fibres can be dyed with any colour and they retain dye well. Hence it is a versatile fibre and can be used for various purposes. It can be woven in three different ways namely plain weave such as chambray and gingham, twill weaves such as denim and khaki, and satin weave such as satin.

4.2 Wrinkling

Cotton fabric wrinkles easily and needs to be ironed regularly to improve its appearance. Also, many cotton fabrics are finished in a way that will help them resists wrinkles.

4.3 Absorbency

Cotton has the property to absorb liquid in large quantities. It has a capacity to absorb liquid up to 27 times its weight. This makes cotton comfortable to wear as it absorbs sweat well. For this reason, it can be used to manufacture towels and washcloths.

4.4 Shrinkage

Cotton fabric has the tendency to shrink after the first wash. Hence to avoid this some cotton fabrics comes to the shopkeeper pre-shrunk for sale. Thus, they do not have to get worried about getting small after the first wash.

4.5 Breathability

Cotton fabric allows air to pass through freely. It absorbs sweat and releases it on its surface. Hence making it a comfortable fabric to be worn in hot and humid countries.

Reference

About the Author: Agniv Chatterjee is pursuing his graduate degree from the Department of Textile Technology, Government College of Engineering and Textile Technology, Serampore.