Standard Test Method for Automated Measurement of Maturity, Fineness, Ribbon Width, and Micronaire of Cotton Fibers

Importancia y uso:

5.1 Cotton fiber that is on average finer and more mature is more desirable than coarse or immature fiber, although distinction between these qualities cannot be made quickly and accurately using current test methods. Immature fibers break more easily during processing and have a tendency to form into neps (small entanglements) during processing in the spinning mill. These consequences adversely affect yarn and fabric quality and appearance. Yarn and fabric produced from immature fiber is typically also less lustrous and does not take up dye consistently so yarn and fabric appearance may be different after dyeing.

5.2 Maturity has a high positive correlation with fiber length and strength but genetic differences and differences in fiber wall thickness caused by plant diseases, soil, and water conditions during the growing season interfere with this relationship.

5.2.1 Fine fibers are required for fine count yarn manufacture and fiber fineness affects yarn count, evenness and strength. Both fineness and ribbon width are strong genetic traits evident between species and affected by growing conditions within species.

5.2.2 Micronaire has traditionally been used as a measure of fiber fineness although the value actually measures fiber specific surface area or surface area per unit weight. As a result, micronaire varies concomitantly with both maturity and fineness (see Fig. 2). Maturity and fineness are related to micronaire via Lord’s equation.4

FIG. 2 Relationship Between Micronaire (X), Fineness (H), and Maturity (M)

5.3 Cottonscope values have been judged against fineness, maturity and ribbon width values produced by examination of thousands of individual, magnified fiber cross-sections. Relationships with equivalent values by these and other older test methods are highly significant5^,6 particularly if the number of cross-sections analyzed is high (>3000) and the cross-sections are carefully prepared and measured. Cottonscope measures approximately 20,000 fiber (snippets) per measurement and is a quick test in comparison to previous methods, for example, directly measuring cross-sections. The good relationship observed between ribbon width and the perimeter of fiber cross-sections makes ribbon width of interest to plant breeders and scientists observing fiber perimeter responses to plant and crop treatments.

5.4 The precision of Cottonscope has been measured. Measurement of consistent quality, machine picked cotton using a test regime of one in three bales (with two specimens tested per bale sample), provides a precision of between 6.8 and 7.5 % for fineness, between 1.2 and 1.5 % for maturity, between 4 and 5 % for micronaire and less than 1 % for ribbon width. These values incorporate sample and instrument variance but not inter-laboratory variance. Precision is improved by increasing the number of sub-samples measured per bale. The values for maturity and micronaire are similar to reported high volume instrument values.

5.4.1 The method has not yet been widely controlled for acceptance testing. Inter-laboratory trials have shown agreement and precision can be good if instrument calibrations and test procedures are properly coincided. Calibration material should be conditioned before testing as directed in Practice D1776.

5.4.2 Cottonscope algorithms are calibrated using known cotton and fiber standards, for example, USDA AMS prepared calibration cottons, measured on a manufacturer’s standard instrument with values and the calibration material passed to the next instrument. It is advised if there are differences of practical significance between reported test values for two or more laboratories, comparative tests should be performed to determine any statistical bias between them, using competent statistical analysis. Ideally, these tests are performed using the same homogenous material.

Subcomité:

D13.11

Volúmen:

07.02

Número ICS:

59.060.10 (Natural fibres)

Palabras clave:

cotton; Cottonscope; fineness; gravimetric fineness; linear density; maturity; micronaire; ribbon width;