COTTON USA IS SOFT, SENSUAL AND NATURAL

U.S. COTTON FACTS

U.S. harvesting and ginning practices

The ginning process

In 2007-08, approximately 70% of the total crop was machine picked. The remaining was machine stripped, primarily in Texas, Oklahoma and Kansas. After harvesting, cotton is taken to the gin by truck or trailer or stored in modules to be transported later to the gin.

This season, 2% of seed cotton was ginned from trailers and 98% was ginned from modules. Gins are widely distributed throughout the production areas resulting in seed cotton being transported only relatively short distances. There were 807 active gins in the U.S. in 2007 with a total volume of 18,713,150 running bales ginned. During the ginning process, the cottonseed is removed and the lint is cleaned and pressed into bales. American Upland cotton is saw ginned, which is a different process from the roller ginning used for American Pima Cotton.

Several types of gin presses are available for producing bales of similar sizes and densities. In order to ensure the textile mills receive uniform cotton bales, the U.S. ginning industry has adopted the gin universal density bale which has a nominal density of 28 pounds per cubic foot (450 kilograms per cubic meter). It is estimated that 99.9% of the U.S. cotton crop is in universal density bales. This allows the shipper and customer to know a very close approximation of how many kilograms of cotton there are in the number of bales shipped.

Classification of U.S. cotton

High Volume Instrument (HVI) classing has been available on an optional basis to all growers since 1981. In 1990, the National Advisory Committee on Cotton Marketing, an industry-wide committee representing U.S. growers, exporters, manufacturers, ginners and warehousemen, recommended that HVI measurements be required for any Upland cotton which might be placed in the government’s price support program, effective with the 1991 crop. As a result, virtually all of the U.S. Upland cotton crop is now HVI classed. HVI Measures: For each bale classed in 2008, the following quality information was provided:

Length

Measure of the average length of the longer one half of the fibres (upper half mean length), reported in 100ths and 32nds of an inch.

Length uniformity

Determined by dividing the mean length of the fibres by the upper mean length and reported as a percentage. The higher the percentage, the greater the uniformity. If all the fibres in the sample were of the same length, the mean length and the upper half mean length would be the same, and the uniformity index would be 100. However, cotton fibres within a sample vary considerably, so length uniformity would be less than 100.

Micronaire

A measure of fibre fineness represented by the air permeability of a mass of cotton fibres compressed to a fixed volume. Measurement is performed on an instrument known as a micronometer, and the measurement is commonly referred to as “micronaire” or “mic”. The information is used to determine the relative size or fineness of fibres. The micronaire reading can also provide a relative indication of fibre maturity, or cell wall thickness, for varieties of cotton with similar fiber parameters. This has an effect on how well the fibre accepts dye and the overall appearance of the fabric. Variation in colour within one piece of fabric could indicate poor blending or extreme micronaire limits.

Strength

Strength is reported in grams per tex. A tex unit is equal to the weight in grams of 1,000 meters of fibre. Therefore, the strength reported is force in grams required to break a bundle of fibres one tex unit in size.

Colour

The colour of cotton is measured by the degree of reflectance (Rd) and yellowness (+b). Reflectance indicates how bright or dull a sample is, and yellowness indicates the degree of colour pigment. A three-digit colour code is used to indicate the colour grade. This colour grade is determined by locating the quadrant of the colour chart in which the Rd and +b values intersect. For example, a sample with an Rd value of 72 and a+b value of 9.0 would have a colour code of 41-3.

Colour Grades: There are 25 colour grades and five categories of below grade colour divided into five key colour grades divided into various sub grades. The five main colour grades are: White, Light Spotted, Spotted, Tinged and Yellow Stained. In addition there are seven leaf grades, as well as one below grade leaf grade category.

Trash (or leaf)

Trash in raw cotton is measured by a video scanner, commonly referred to as a trashmeter. It is a measure of both leaf and other elements such as grass and bark. The surface of the cotton sample is scanned by the camera and the percentage of the surface area occupied by trash particles is calculated.

HVI Classification of Pima Cotton

Fibre properties are also measured for American Pima cotton. While the basic testing procedures for American Pima cotton are the same as for American Upland cotton, different grade standards are used because of the genetic differences in Upland and Pima and the different ginning methods used. As American Pima cotton is ginned on roller gins, rather than saw gins, its appearance is not as smooth as that of Upland. Also, the colour of American Pima is creamier than that of Upland.