Different Types of Impurities in Cotton

Last Updated on 26/10/2021

Different Types of Impurities in Cotton Fiber

Ramandeep Singh
B.Tech, Dept. of Textile Engineering
Giani Zail Singh Punjab Technical University Campus,
Bathinda, Punjab, India
Email: rmnsandhu3335@gmail.com


Fiber Impurities:
At any stage during textile manufacturing, from loose fiber to grey fabric, fibers may contain a variety of hydrophobic chemicals that interfere with uniform wetting. These impurities may be of natural origin, such as fats and waxes, or synthetic chemicals deliberately applied to the fibers to facilitate processes such as carding, spinning or knitting.

impurities in cotton

The term impurity is used to describe material other than fiber which is found in raw or processed stock. Generally, impurities must be removed during the spinning process, so the type and amount of impurity is also of importance to the yarn manufacturer.

Impurities are also found in man made fibers but the levels are much lower than those found in the natural fibers.

Different Types of Impurities in Cotton:
There are two types of impurities in cotton, they are

  1. Impurities in raw cotton
  2. Impurities in processed cotton

Now discussed overall impurities in cotton.

1. Impurities in Raw Cotton:
The types of impurity found in raw cotton can be classified as follows :

The largest type of impurity found in raw cotton. It may consist of unginned seeds, with fibers still attached, ginned seeds or under-developed seeds and part of seed.

seeds in raw cotton
Fig: Seeds in raw cotton

A collection of vegetable fragments, most of them consisting of leaf, bract, and stalk. Bract is a form of small leaf growing beneath the cotton ball.

Sand and soil which originates from the cotton field.

Dirt and Micro dust:
The finest of impurities consisting of very fine particles of chaff, dirt, small fiber fragments and mildew spores.

The term trash is often applied to the combination of all the above impurities.

Impurities in Processed Cotton:
The types of impurity found in processed cotton can be described as follows:

The main impurities in processed cotton are Neps, Seed-Coat Fragments, and Non-Seed Impurities in Cotton. The production of high-quality fiber and textiles that meet the highest standards of the cotton industry has been a central and ongoing challenge in cotton research. Neps and white specks are imperfections that severely decrease textile quality at the consumer level and, therefore, have immense economic consequences. Neps are entanglements or clumps of immature fibers that produce imperfections when woven into fabric. Frequently, neps take up dye poorly and appear as light spots or white specks scattered randomly throughout dyed fabrics Seed-coat fragments are pieces of seed or mote (underdeveloped or aborted ovules) coats with fibers (mostly immature) attached that were broken or crushed during cotton processing. Motes are the main source of immature fibers, fiber clusters, and/or seed-coat fragments.

Major impurities in processed cotton are,

  1. Trash
  2. Neps
  3. Stickiness
  4. Contamination

Trash particles or visible foreign matter (VFM) in cotton are typically plant parts that are incorporated into the seed-cotton during harvest and then broken down into smaller pieces during mechanical ginning. Chief components are pieces of stem, bract, bark, seed-coat fragments, motes (whole immature seeds) and leaf. Trash accounts for 1–5% by weight of baled cotton with the amount and type of trash reflected in the leaf and color classing grade of particular cotton. Trash content in a particular cotton is still largely determined by subjective assessment against physical and descriptive grades.

trash in cotton
Fig: Trash in cotton

Neps occur in all ginned cotton but hardly at all in unpicked seed-cotton. Neps are fiber entanglements that have a hard central knot that is detectable. Harvesting, ginning (particularly lint cleaning), opening, cleaning, carding and combing in the mill are mechanical processes that affect the amount of nep found in cotton. The propensity for cotton to nep is dependent upon its fiber properties, particularly its fineness and maturity, and the level of biological contamination, e.g. seed coat fragments, bark and stickness.

neps in cotton
Fig: Neps in cotton

The formation of a nep usually centers around some sort of catching device around which fibers collect and become entangled. Three types of nep are defined throughout the literature; mechanical neps, biological or shiny neps and seed-coat fragment neps.

Sticky cotton is a major concern for spinning mills. Physiological plant sugars in immature fibers, contaminants from crushed seed and seed coat fragments, grease, oil and pesticide residues are all potential sources of stickiness. However, these are insignificant compared with contamination of cotton from the exudates of the silverleaf whitefly (Bemisia tabaci) and the cotton aphid (Aphis gossypii).

Contamination, even from a single foreign fiber, can lead to the downgrading of yarn, fabric or garments or even the total rejection of an entire batch. In 2002 the ITMF reported85 that claims due to contamination amounted to between 1.4 and 3.2% of total sales of cotton and blended yarns. Most contamination arises from impurities being incorporated into the bale as a result of human interaction during harvesting, ginning and baling.

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