Cotton impurities
Any foreign material other than fibres is
classified as impurities. Not only the quality and the price of fibres depend
upon the amount of impurities present in the fibres, also the subsequent
processes depend on it. Greater the impurities are-more-efforts have to put
into remove it. The removal of the impurities also results in the loss of
useful fibres. Impurities are also found in the 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 it. 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 impurity includes soil and sand particles
that may be added from the cotton fields due to mishandling of the fibres and
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
gets embedded around the natural wax of the cotton fibre
5. Abnormal Impurities
The abnormal impurities are very rate 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. poly propylene, 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 removes while the carding microdust.
Greater the impurities present in fibres more opening and cleaning is required.
However with more severe opening and cleaning, expensive fibres can be damaged
or they can be lost during the process
