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Important Characteristics of Cotton

Cotton, a Miracle of Nature

Cotton is considered one of the most widely used agricultural products. It is used in the production of various fabrics, towels, tents, and more. Cotton is still recognized today as one of nature’s wonders, from which thousands of useful products are produced, providing employment for millions of people worldwide. Humans have been using cotton as a plant for clothing production for over 7,000 years.

Natural Fibers

Natural fibers are divided into two main categories:

  1. **Protein Fibers:** Obtained from animals.
  2. **Plant Fibers:** Obtained from plants.

The primary component of all plant fibers is cellulose, a carbohydrate found in all plants. Cotton is also considered one of the most important plant fibers.

Characteristics of Cotton

Cotton fibers have several characteristics, including:

– Softness

– High absorbency

– Dyes well

– Printable

– Washable in a washing machine

– Can be dry cleaned

Structure and Characteristics of Cotton Fibers

Each cotton fiber consists of multiple concentric layers. The outer layer of the fiber is separable and contains oily substances and pectin (plant gelatin). The outer wall of the fiber consists of small cellulose strands. Raw cotton is composed of the following materials:

– **Cellulose:** 80 to 90%

– **Water:** 6 to 8%

– **Fat and Oil:** 0.5 to 1%

– **Protein:** 0 to 1.5%

– **Hemicellulose and Pectin:** 4 to 6%

– **Pollen:** 1 to 1.8%

Parameters Affecting the Classification of Cotton Types

In this article, we will discuss cotton from three general perspectives:

  1. Quantitative parameters (such as fiber length, micronaire, etc.)
  2. The color of cotton fibers
  3. The amount of trash and foreign materials present among cotton fibers

Fiber Length

Fiber length is typically defined as the “upper half mean length.” The length of the fibers has a direct relationship with the cotton variety; however, exposure to inappropriate temperatures, water shortages, or nutrient deficiencies can also lead to shorter fibers. Fiber length affects the strength, uniformity of the yarn, and spinning efficiency.

According to U.S. standards, the classification for cotton fiber length is as follows:

– Less than 0.99 inches (25 mm): Short

– 0.99 to 1.10 inches (25 to 27 mm): Medium

– 1.11 to 1.26 inches (28 to 32 mm): Long

– More than 1.26 inches (32 mm): Very long

Length Uniformity

Length uniformity, or uniformity ratio, is defined as “the ratio between the overall mean length and the upper half mean length of the fibers, expressed as a percentage.” If all fibers in a bale were of the same length, the overall mean length and the upper half mean length would be equal, resulting in a length uniformity of 100%. However, due to natural variations in fiber lengths, length uniformity is always less than 100%. Length uniformity affects yarn consistency, strength, and spinning efficiency. This parameter has an inverse relationship with the number of short fibers (fibers shorter than half an inch). Samples with a low length uniformity index contain a high percentage of short fibers, making spinning more difficult and potentially producing low-quality yarn.

In U.S. standards, this parameter is categorized as follows:

– Below 77%: Very low

– 77 to 79%: Low

– 80 to 82%: Medium

– 83 to 85%: High

– Above 85%: Very high

Fiber Strength

Fiber strength is measured in grams per tex. One tex is equivalent to the weight of 1,000 meters of fiber in grams. Therefore, the strength parameter indicates the force required to break a bundle of cotton fibers measuring one tex. Strength is measured on the same bundle of fibers used to measure fiber length. Fiber strength is highly dependent on the cotton variety, although nutritional deficiencies and climatic conditions can also influence this parameter. Additionally, cotton with stronger fibers tends to break less during manufacturing processes.

In U.S. standards, the following values are considered for this parameter:

– 23 and below: Very weak

– 24 to 25: Weak

– 26 to 28: Medium

– 29 to 30: Strong

– 31 and above: Very strong

Micronaire

Micronaire indicates the fineness and maturity of the fibers. Micronaire can be influenced during the growth of the cotton plant by factors such as humidity, temperature, sunlight, nutrients, and adverse conditions affecting the plant or the bolls. The fineness of the fibers impacts production efficiency and the quality of the final product. During opening, cleaning, and carding processes, fibers with low micronaire or fine fibers require slower machine speeds to prevent damage. Yarns produced from fine fibers contain more fibers of a given diameter, resulting in stronger yarn. The dyeability and color retention are related to fiber maturity; the more mature the fiber, the greater the dye absorption and retention.

The micronaire parameter is classified as follows:

– Below 3: Very fine

– 3.1 to 3.9: Fine

– 4 to 4.9: Medium

– 5 to 5.9: Coarse

– Above 6: Very coarse

In U.S. standards, fiber maturity is categorized as follows:

– Below 0.7: Unusual

– 0.7 to 0.8: Immature

– 0.8 to 1: Mature

– Above 1: Very mature

Fiber Elongation

Elongation, expressed as a percentage, indicates the extent to which fibers can stretch before breaking. The higher this percentage, the better the quality of the cotton.

Here are the values used in U.S. standards:

– Below 5%: Very low

– 5 to 5.8%: Low

– 5.9 to 6.7%: Medium

– 6.8 to 7.6%: High

– Above 7.6%: Very high

Color Grade

The color of cotton samples is determined by two indices: brightness (Rd) and yellowness (+b). Brightness indicates how light or dark the sample is, while yellowness represents the degree of pigmentation. The color of the fibers is affected by climatic factors, pests, fungi, soil type, storage conditions, and more. The color can change due to excessive moisture and temperature conditions during storage, both before and after cleaning the cotton. Environmental color changes affect the dye absorption and retention of the fibers, thereby reducing production efficiency.

In this diagram, the intersection of the +b and Rd values indicates the color group of cotton based on U.S. standards. As the diagram moves upward, brightness (whiteness) increases, and as it moves from left to right, yellowness increases. Thus, the best color for cotton is found in the area of the diagram that moves upward and closer to the left, where cotton classified as GM has the brightest color.