A detailed guide to Cotton testing
Cotton, being a natural fibre, each bale of cotton exhibits unique fiber properties. The properties of cotton are influenced by environmental as well as geographic factors. The adoption of new spinning methods, the advances in the traditional spinning process and the higher consumer demands call for extensive research and improvement of the cotton quality. To make high-quality yarn and ultimately superior garments, high-quality cotton fibre is essential. An important consideration prior to any effort of improving quality, is to obtain reliable information on the properties of cotton using a combination of instrument evaluations. In this blog we shall discuss in detail the need for cotton testing as well as the significance of different cotton testing parameters.
Significance of Cotton Testing:
Quality Consistency: Different end-use requirements, such as yarn strength and yarn and fabric appearance, require different fiber qualities. The ability of a fabric to hold dyes, as well as its performance in further finishing processes largely depend on fiber qualities.
For a given product requirements or spinning characteristics, a textile producer may not be able to obtain all the raw fiber qualities needed when buying a particular genetic as quality of a cotton variety not only varies from region to region but also varies tremendously from year to year. In such instances, quality measures become the basis for blends and mixes of various types of cotton to obtain specific properties of cotton with requisite quality measures. Efficient automated production processes with high processing speeds which are prevalent in the textiles industry also requires well-defined quality of input of raw materials.
Types of Cotton Testing:
1. Fiber Analysis:
Fibre analysis includes evaluation of following parameters:
- Staple length
- Length uniformity index
- Strength
- Micronaire
- Color and color grade
- HVI trash
Staple Length:
Staple length is reported as the average length of the longer half of the fibers (normally called “upper-half-mean” length), measured by clamping a fiber sample, then combing and brushing to make the fibers straight and parallel. Historically, the staple length was estimated manually, using the “hand stapling” process performed by a cotton classer. Today, thanks to technological advances, the staple length is now calculated from the length fibrogram sensed by the High-Volume Instrument (HVI). The fibrogram is an arrangement of fibers from the shortest to the longest in terms of span lengths (the distances fibers extend from a random catching point).
Staple Length is a critical property because the staple length of cotton affects yarn strength, evenness, and efficiency of the spinning process.
Extreme temperatures, water stress, insect pressure, nutrient deficiencies, and excessive cleaning or drying can all shorten the staple length of cotton.
Length uniformity index
The ratio between the “mean length” of fibers and the “upper-half-mean length” of fibers is referred to as the “length uniformity index.” Both the mean length and upper-half-mean length measurements are taken when the fiber beard described above is passed through the length sensor of the HVI system. There is a natural distribution in the length of cotton fibers but the lower the variation in this length distribution, the higher the length uniformity index.
Like staple length, length uniformity affects yarn strength and evenness. It also affects the efficiency of the spinning process. Cotton with a low length uniformity index has a high variance in fiber length which can make processing difficult and ultimately result in lower-quality yarn.
Interpretation of Length Uniformity
| Degree of Uniformity | HVI Length Uniformity Index (%) |
| Very High | Above 85 |
| High | 83-85 |
| Intermediate | 80-82 |
| Low | 77-79 |
| Very Low | Below 77 |
Strength:
Fiber strength, as measured on the HVI is the force in grams required to break a bundle of fibers in one tex unit in mass—a tex unit being the weight in grams of 1000 meters of fiber length. Strength measurements are conducted on the same beard of cotton used by the HVI to measure staple length and uniformity.
Fiber strength largely depend on genetics. Therefore, cotton variety plays an important role in fiber quality. Growth environment and crop management also play a huge role in determining fiber strength. It is key to understand exactly which combination of factors contributes to the highest quality crop and replicate that combination season after season.
Interpretation of Fibre strength
| Degree of Strength | Strength (Grams/Tex) |
| Very Strong | 31 and above |
| Strong | 29-30 |
| Average | 26-28 |
| Intermediate | 24-25 |
| Weak | Below 23 |
Micronaire:
The micronaire is a measurement of fiber fineness and maturity. It is determined by measuring the air permeability of a constant mass of cotton fibers compressed to a fixed volume. Fine or immature fibers that are easily compressed have a lower air permeability and therefore low micronaire. Coarse or mature fibers that resist compression have a high micronaire measurement.
Cotton fiber fineness affects processing performance and end-product quality in several ways. While micronaire is not a direct measurement of fiber fineness, it does provide some feedback on fineness. Micronaire is most influenced by the environmental conditions during the growing season. Various combinations of moisture, temperature, sunlight and length of season all contribute to the micronaire level.
So why is the micronaire measurement so important? Micronaire provides important information about the dyeing characteristics of the cotton products produced from the fiber. Uneven distribution of micronaire within a fabric can result in poor color uniformity of that fabric and problems such as barre or streaks. Micronaire uniformity makes it more valuable because it offers a greater product quality.
Color & Color Grade
Several factors impact the color of cotton fiber. Environmental variables that impact the color of cotton fiber include rainfall, freezes, insects, and microorganisms, as well as contact with the soil, grass, and the leafy portions of the cotton plant (on the field and during harvest) can all have an effect. While in storage after ginning, high levels of moisture and temperature can also impact the shade of the cotton fiber.
The color of cotton is measured using a cotton colorimeter and is expressed by the degrees of reflectance (Rd). It typically ranges between 50-85 units and indicates how white or gray a sample is as well as yellowness (+b). The higher the Rd value, the whiter the cotton. In color measurement science, positive b (+b) values indicate intensity of yellow shades, so cotton with a higher +b measurement is more yellow. The most typical range of +b in upland cotton is from 6 to 12.
There are 25 official color grades for American upland cotton (plus five categories of below grade color) and, traditionally, cotton classers determined the color grade of cotton by comparing a sample to physical color standards.
HVI Trash
Trash particles in cotton fiber come from parts of the cotton plant such as leaf and bark that are removed along with the fiber during harvesting. The HVI trash measurement is not part of the official USDA cotton classification but is provided as additional information.
When cotton fiber is tested using HVI instruments, the surface of the sample is scanned by a video camera. The percentage of the surface area occupied by trash particles is then determined by image processing software.
Conclusion:
In the textile industry, the quality of cotton fiber plays a critical role in determining the performance and aesthetics of the final product. Comprehensive cotton testing, encompassing staple length, length uniformity, fiber strength, micronaire, color grade, and HVI trash content, provides essential insights into the fiber’s properties. By understanding these parameters, manufacturers can optimize spinning processes, achieve consistent quality, and meet the high demands of consumers for superior textiles. As advancements in technology continue to enhance testing methods, the precision and reliability of cotton quality assessments will only improve, ensuring that the industry can adapt to evolving market needs while maintaining the highest standards of production.
ATIRA’s extensive infrastructure and experienced team ensure accurate, reliable results that help you achieve the highest quality in your textile products. Contact ATIRA today to learn more about our comprehensive cotton testing services.
