Saturday, 24 May 2008
The botanical name of cotton is Gossypium. It has four varieties
a. G. Arboreum, G. Herbaccum- Old world cotton, native of Asia and India- Low yield - fibers are also short and coarse.
b. G. Hirsutum, G. Barbadense- America and Carribeans- High yield- fibres long and fine
Classification of Cottons
1. Primary Parmaters- Fibre length, length uniformity, fineness, maturity and bundle strength at 0 guage and 3.2 mm guage length.
2. secondary- Trash content, honey dew content and color
1.1 Fibre length and uniformity- Most important quality parameter that decides the price of cotton-Long staple cottons are used to spin finer counts and hence fetch higher prices
Uniformity ratio= (50% span length x 100)/ 2.5% span length
1.2 Fibre fineness: Indian cotton particularly long and extra long staple varities and hybrids show low micronaire values as compared to cottons of similar staple length grown in USA, Egypt and Sudan.This is due to lower maturity levels of Indian cottons.
1.3 Fibre Maturity
Maturity Coefficient = (Mature+0.6xHalf Mature+0.4xImmature)/100
Poor fibre maturity results in nappiness of the yarn and also leads to problems in even dyeing of fabric. Generally, lack of moisture and nutrients and incidence of insects and pests during cotton boll developments results in low fibre maturity
1.4 Fiber Strength
In the OE rotor system, it is fibre bundle strength, that is assigned the highest importance. Fibre bundle strength is determined by using the stelometer at zero guage. and 1/8 inch (3.2mm) guage length. It is well known that fibre strength decreases when guage length is increased. Also it is observed that yarn strength is correlated well with fibre tenacity at 3.2 mm guage length. Hence the ratio of strength at zero to that of 3.2mm is known as strength uniformity ratio.
2.1 Trash including other contaminants
Cut Seeds- during ginning
Trash and other extraneous matter. General carelessness in picking, sorting, handling and transportation of Kapas at all stages upto and including ginning.
2.2 Honey dew and Color of cotton.
Honey dew consists of sugar secreted by sucking insects that harbour on the cotton plants. Presence leads to roller lapping.
Color is more important in USA, where cotton is picked by machines and doing so gets rubbed against plant parts and thus gets contaminated.
Assessment of Spinning Performance
Where L= 50% span length
S= Bundle strength at 3.2 mm guage
M= maturity coefficient
F= Micronaire Value
FQI can be used to arrive at yarn CSP for a given count by using empirical equations.