Submitted to: Microscopy and Microanalysis
Publication Type: Proceedings
Publication Acceptance Date: June 1, 2003
Publication Date: August 3, 2003
Citation: Goynes Jr, W.R. 2003. Microscopic determination of cotton fiber maturity. In: Proceedings of Microscopy and Microanalysis 9, August 3-7, 2003, San Antonio, TX. p. 1294-1295. Interpretive Summary: Cotton fiber maturity determines physical properties and value. Completely developed, mature fibers have thicker secondary walls than do undeveloped, immature fibers. Thin-walled fibers create problems in dyeing and processing. They fail to accept dyes, and can produce other defects in textiles. If development of fibers on a seed is terminated when only the extremely thin outer layers have been produced, these fibers remain clustered together and do not blend with other fibers on processing. In yarns and fabrics, they form undyeable defects on fabric surfaces. There are several indirect methods for measuring fiber maturity, but direct determinations can be made only by microscopic processes. Historically, assessments of degree of maturity have been made using light microscopy. Immature fibers appear flat and ribbon-like, mature are rounded and tubular. Degree of maturity is difficult to access. A "differential dyeing" method developed by Goldthwait utilized a mixed dye bath and variations in structures of mature and immature fibers to distinguish wall thickness. Mature fibers dye red and immature fibers green. In addition, the scanning electron microscope permits direct observations of whole fibers at magnifications where gradations in fiber wall thickness can easily be seen. Maturity variations are even more evident in cut bundles of fibers. Recent progress in development of an image analysis measurement of fiber maturity offers promise of greater objectivity. Bundles of fibers are embedded and sectioned and parameters are analyzed using a CCD camera with a light microscope. Microscopic methods for determining maturity are compared in the paper to show how each is best used. An example of the problem caused in dyed fabrics is illustrated.
Technical Abstract: The textile cotton fiber is a natural product and its physical structure and properties depend on its complete development. The fiber develops from the outer primary wall inward. Completely developed, or mature, fibers have thicker secondary walls than do undeveloped or immature fibers. Since properties and value of harvested fibers are determined by degree of maturity, methods for determining this property are required. There are several indirect methods for measuring fiber maturity, but direct determinations can be made only by microscopic processes. Historically, assessments of degree of maturity have been made on individual samples using light microscopy. Immature and mature fibers can be distinguished by viewing the fibers longitudinally while mounted in oil on a glass slide. Immature fibers appear flat and ribbon-like, while those that are mature are rounded and tubular. Mature and immature fibers can be readily determined, however, degree of maturity is difficult to access. The method is subjective, being dependent on the judgment of the observer as to which fibers fall in each classification. A dyeing method developed by Goldthwait , referred to as "differential dyeing", utilizes variations in structures of mature and immature fibers to distinguish wall thickness. The mixed dye contains Diphenyl Fast Red 5BL Supra, and Chloratine Fast Green BLL. Mature fibers dye red and immature fibers green. The red dye molecule is more easily stripped from the immature fibers, leaving them predominantly green, while it remains in the structure of the mature fiber. Figure 1 shows cross sections of fibers dyed using this process.