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Physical properties
Structure
Cotton fibre is a cellulosic unicell that shows a base and tapering edges. It is a staple fibre ranging from ½ " to 2 ½ " in length. The diameter ranges from 12 to 20 micrometres. Cotton unicell shows outer cuticle, primary wall, secondary wall and a central canal called lumen. It is flat ribbon like with twist under microscope called ‘convulsions’. Matured fibres show narrow lumen and immature fibres show large lumen. The cross sectional shape of cotton fibre is similar to a kidney shape. Cotton fibre before ball opening exhibits round cylindrical shape but when exposed to outside atmosphere the cell sap dries up and makes it to flatten and loose its luster. About 65-70% of cotton fibre is crystalline and 35-30 % is amorphous.
Strength: The strength of cotton fibre is regarded as medium and the tenacity of cotton ranges from 3.0 to 5.0 grams per denier. One unique feature of cotton is its increase in strength when wet. When wet, it shows the strength equal to 110 to 120 % of its dry weight. The tenacity of cotton is increased when it is mercerized.
Elasticity : Cotton fibre has low elongation due to its crystalline structure. Around 3-7 % elongation is found. Around 75 % of elastic recovery is recorded at 2 % elongation. The elastic recovery reduces with increase in percent of elongation. At 5 % elongation, cotton recovers only 50%
Resiliency
The resiliency of cotton is low. Cotton fabrics wrinkle very easily and require ironing after washing. Appropriate finishing process improves wrinkle resistance of cotton.
Abrasion resistance: Cotton shows medium resistance to abrasion.
Moisture Regain: : Cotton is a hydrophilic fibre. The moisture regain of the fibre is 8.5 % under standard conditions. Cottons are highly comfortable as summer wear due to high absorbency and good heat conductivity.
Dimensional Stability: : Cotton fibres are stable and do not shrink or stretch as they are unicellular. Fabrics may show shrinkage due to tensions during fabric construction. However, it needs pre treatment to control shrinkage in use.
Thermal Properties: Cotton fabrics are good conductors of heat and thus regarded as cool fibre. Under dry conditions cotton can absorb the body sweat and keep the wearer comfortable. Light weight, open structured cotton fabrics are highly comfortable during humid weather. Cotton being cellulosic fibre does not melt but only scorches at high temperature of around 2500C as it withstands moderate temperatures, it can be ironed safely.
Cotton fibre burns slowly in flame and continues to burn after removal from flame as it supports combustion. It gives paper smell and leaves a small amount of fluffy ash as residue.
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