Physical and Chemical Properties of Cotton

By Eman abdallah Kamel

Eman is a writer and an engineer. She received her Bachelor’s degree in Textile Science from the Faculty of Applied Arts in Egypt.

Cotton is one of the most popular fibers worldwide due to its unique properties. Here, you will learn about the physical and chemical properties of cotton.

Image source: istockphotos.com

Cotton

Cotton is a natural fiber derived from the seeds of the cotton plant, and it is classified under the Gossypium genus.

Cotton fibers are composed of

80-90% cellulose,
6-8% water,
0.5-1% waxes and fats,
4-6% hemicelluloses and pectins,
0-1.5% proteins,
and 1-1.8% ash.

Cotton fibers under a microscope show four main parts: the cuticle, the primary wall, the secondary wall, and the lumen. To learn more about cotton morphology, visit the Structure of Cotton Fiber.

Cotton has properties that make it suitable for manufacturing as well as a good choice for clothing. Let’s learn more about the properties of cotton fiber.

Properties

1. Physical Properties

Strength: Cotton fibers are medium-strength, ranging from 3 to 5 grams per denier. Fiber strength increases by 10% to 20% when wet.
Elasticity: Cotton fibers are slightly elastic. Their elasticity is increased by the twisting of the cotton fibers. The elastic recovery ratio from stress ranges between 0.70 and 0.74 at 2% elongation.
Resiliency: Cotton fibers have low elasticity. As a result, cotton products often wrinkle when worn.

Did you know?

Mercerized cotton is much stronger than natural cotton fibers.

Color: More than 99% of cultivated cotton fibers are ivory white or cream. Long-staple fibers, such as Pima and Egyptian cotton, tend to be creamy.
Color fastness: Cotton fibers have excellent color fastness.
Luster: Cotton is a fiber with a low luster due to its convolutions. Luster can be improved by permanently blowing the fibers through a mercerization process. More mature cotton fibers are stronger, finer, longer, lustrous, and more expensive.
Specific gravity: Gray cotton fibers have a specific gravity of 1.27, while bleached cotton fibers have a specific gravity of 1.54. 100% cellulose polymer has a specific gravity of 1.54.
Breaking strength: Cotton strength ranges from medium to high. Dry strength of cotton ranges from 27 to 44 grams per tex, while wet strength of cotton ranges from 28 to 57 grams per tex.
Breaking elongation: The breaking elongation of cotton fibers ranges from 3.0% to 9.5%.
Humidity: With increased humidity, cotton fabrics become moldy due to bacteria and fungi, causing a musty odor and stains. Therefore, when storing cotton fabrics, use mold-resistant products and avoid storing them in damp, dark areas. To learn more about cotton fabric care, visit Cotton Chemical Structure and Fabric Care.
Moisture absorption: The moisture regain of cotton under standard conditions ranges between 7% and 8.5%.
Dyeing: Cotton has a good affinity for dyes. To learn more about cotton dyes, visit Eight Main Dyes for Cotton.
Sunlight resistance: Cotton has excellent resistance to sunlight.

Did you know?

Cotton’s moisture-wicking ability makes it an excellent choice for comfortable wear in hot and humid climates. Due to its high moisture-wicking capacity and durability when wet, cotton is an ideal choice for drying.

2. Chemical Properties

Thermal: Cotton fibers burn and turn brown at 245°C and decompose above this temperature. Prolonged exposure to dry heat above 150°C causes the fibers to disintegrate gradually. The safe temperature for ironing cotton is 204°C.
Effect of alkali: Cotton is not adversely affected by alkali. Treatment with strong alkali solutions can have positive effects. For example,

Treatment with 25% sodium hydroxide causes swelling and a change in the cellulosic structure, a process called mercerization. Upon stretching, the cotton fibers have a high luster.
Treating cotton with strong ammonium hydroxide solutions also yields positive results. Under appropriate conditions, treating cotton with liquid ammonia, sunforest, improves its resistance to wrinkles and abrasion.

Effect of acids: Cotton fibers can be broken up by hot dilute acids or cold concentrated acids such as sulfuric acid, but they are not affected by cold weak acids.
Effect of organic solvents: Cotton is resistant to most common household and industrial solvents.

Waht are organic solvents?

Organic solvents are a large group of more than 200 chemical compounds capable of dissolving water-insoluble materials such as fats, oils, waxes, resins, rubber, asphalt, cellulose fibers, and plastics. Organic solvents contain at least one carbon molecule and one hydrogen molecule.

Bleaching: According to a study, bleaching with the enzyme pectinase can replace conventional bleaching with NaOH and H2O2. Higher degrees of whiteness can be achieved by slightly increasing the amount of hydrogen peroxide during enzymatic bleaching. The study demonstrated that enzymatic bleaching causes less damage to the yarns. The wastewater discharged after enzymatic bleaching also has lower pH values. Enzymatic bleaching with pectinase can be considered an environmentally friendly bleaching technology, as it can reduce the concentration of chemicals used and the concentration of wastewater pollutants through chemical substitution without affecting the quality of the bleached cotton.

Sources

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