Cotton impurities

Any foreign material other than fibres is classified as impurities. Not only do the quality and the price of fibres depend upon the amount of impurities present in the fibres, also the subsequent processes depend on it. The greater the impurities are-more-efforts have to be put in to remove them. The removal of the impurities also results in the loss of useful fibres. Impurities are also found in manmade fibres however the level is significantly low as compared to impurities in natural fibres

The impurities in cotton fibres can be classified into:

1. Seed

Seed impurity is the largest type of impurity present in raw cotton and it includes un-ginned seeds with fibres attached to them. ginned seeds and parts of seeds.

2. Chaff

The chaff is the vegetable fragments consisting of leaf particles, bract, shale and stalk of the cotton plant Bract is a small type of a leaf that grows beneath the cotton boll and shale is the silvery interior lining of the cotton boll.

3. Dirt

The dirt impurities include soil and sand particles that may be added from the cotton fields due to mishandling of the fibres also the cotton fibres pick up dust and sand if they are transported by open trucks

4. Micro-dust

The micro-dust includes very fine particles of chaff, dirt, small fibre fragments and spores of mildew. These particles are extremely small and are often a fraction of the fibre diameter They generally get embedded around the natural wax of the cotton fibre

5. Abnormal Impurities

The abnormal impurities are very rare however when found in the cotton fibres. They can cause serious problems. These impurities include pieces of stones, pieces of iron. cloth fragments. foreign fibres such as jute. polypropylene, etc. (that may be included due to the bagging of cotton fibres made up of these fibres). grease and oil (from machine harvesting or ginning), tar and coal (from the air while the cotton fibres are transported openly).small pieces of wood, etc

Term trash is applied to all of these impurities present in the raw cotton. The total trash content of cotton fibres ranges from 1 % to 10 % of the total weight of the cotton fibres. The amount of trash content directly determines the amount of cleaning required

Removal of impurities

The removal of impurities is associated with the opening of the fibres and is carried out in stages during the spinning process. Initially, the impurities are removed in the blow room with the very basic opening of the larger tufts of fibres into smaller tufts. Then further at the carding machine, due to fibre separation more impurities are removed. The blow room mostly removes the seed and chaff while the carding microdust. The greater the impurities present in fibres more opening and cleaning are required. However, with more severe opening and cleaning, expensive fibres can be damaged or they can be lost during the process