What is Micronaire Value? | Relationships Between Micronaire, Fineness, and Maturity

Micronaire is one of the two most important fiber characteristics for international cotton classers and spinners. Micronaire is an indicator of air permeability. It is regarded as an indication of both fineness (linear density) and maturity (degree of cell-wall development). For a given type of cotton, a relatively low micronaire has been used as a predictor of problems in processing, but a low micronaire may also indicate fine fibers with adequate maturity. Similarly, growers may be discounted for high micronaire when, in fact, the fibers have adequate fineness and good maturity, because high micronaire fibers are normally coarse, which is undesirable from the point of view of spinning and yarn evenness.

Micronaire value
Fig: Micronaire value graph
Fineness is generally expressed as gravimetric fineness or linear density (wall area times a constant), and maturity is generally expressed as maturity ratio (wall area divided by perimeter squared). One of the first practical tools to measure fineness and maturity was the determination of linear density and maturity ratio on the Shirley Developments Limited Fineness and Maturity Tester (FMT).

Although linear density, maturity ratio, and micronaire are useful to spinners, all three properties can be viewed for any given cotton in terms of wall thickness and perimeter. Wall area is a function of wall thickness and perimeter . Wall thickness and perimeter are fundamental cross-sectional characteristics of the fiber with respect to wall area, because the function cannot be decomposed further into other geometric measures. If one examines the fiber cross section, the wall thickness is not constant but varies around the fiber, so that points must be sampled to get an averaged value. As a consequence, an averaged wall thickness and perimeter are fundamental with respect to an averaged wall area. Exploring the relationships on a fundamental level can be beneficial by demonstrating how a unique wall thickness and perimeter value together give an equivalent micronaire- fineness-maturity combination.

Cottons with a much greater genetic diversity are being developed, and a greater range of both fiber perimeter and wall thickness, and their combinations, is probable. Consequently, the relationships between micronaire, fineness, and maturity are being modified . This is because the original set of U.S. cottons that were used to calibrate the micronaire instrument had perimeters with a smaller range compared to current cultivars. The original relationships apply best to those cottons having perimeters similar to the calibration samples. For other cottons, these relationships do not apply as well, which results in modified expressions.

Even though micronaire is of great practical value for trade and industry, a literature review indicated no theoretical or experimental studies have been reported that model the three fiber characteristics in terms of the fundamental measures of thickness and perimeter. The specific objectives of this research were to use fineness and maturity components – wall thickness and perimeter to develop models for fineness, maturity, and micronaire; to simulate the interaction of fineness and maturity and the resultant micronaire; to quantify the relative sensitivity of the models to changes in thickness and perimeter; and to demonstrate variability in the coefficients of determination between micronaire and the other variables. 

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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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