What Makes Cotton Good?

by E. E. BERKLEY and H. D. BARKER

THE FARMER who has an indifferent local market will say that quality in cotton means a high yield and ease in picking. To the cotton broker, quality may mean above-average classer's grade and staple length. The technologist may define it as a strong, reasonably long, and fine cotton. The spinner's definition may include a smooth running, uniform cotton that produces a nep-free, strong yarn. The finisher looks for something that will bleach and dye uniformly. The consumer wants a product that will survive repeated washing and ironing.

All these are abstractions that are difficult to measure, but even so the cotton breeder has been able to perfect new, productive varieties that embody these diverse and poorly defined qualities.

The starting point is the development of rapid and reliable instruments and techniques to measure the properties of fiber and relate them to use value. Studies of the past decade have centered around cooperative regional plantings that would give us material for investigating the way in which fibers are formed, the period of fiber elongation, and how the cell wall develops. The investigations have aided greatly in interpreting influences of heredity and environment on the properties of fiber and how they affect the quality of the finished product.

At least four characteristics have a major bearing on quality of cotton: Length, strength, fineness, and structure of the fiber wall. The cotton breeder and the industry can now measure these factors quickly. Laboratory technicians can compile accurate data that will show the relation of specific qualities to the strength and appearance of yarn, and other manufacturing needs; evaluate the influence of heredity and place or condition of growth on the development of these properties; help the cotton breeder or the cotton grower make improvements in these qualities, and guide the manufacturers in choosing and using such properties to make goods of desired quality. The cotton breeder must study thousands of selections - to obtain the best combinations of agronomic and fiber quality factors. He can now get accurate information on the fiber properties of these selections; in the past he had to depend on "feel," judgment, and guess.

Fiber length is quickly measured by a photoelectric instrument known as the Fibrograph. Fiber strength is measured by the Pressley strength tester. Fiber fineness up to now has been measured tediously by weighing fibers of known lengths. A new instrument, the Arealometer, provides a rapid way to measure fineness, expressed as specific surface or cm'/Mgr. The cell-wall structure is measured by X-ray technique and expressed as X-ray angles : The greater the angle between the fibrils or cellulose strands and the long axis of the fiber, the lower the fiber strength, and vice versa.

Cotton fiber is made up of a multitude of fine, threadlike strands of crystalline cellulose glued together by other cellulose molecules that are not a part of the crystals, that is, amorphous cellulose. These threads are placed in the cell walls in a spiral like the strands of a rope. The cellulose strands reverse their spirals at intervals along the fiber, and the pitch at which they are deposited in the fiber can be determined by the X-ray. The angle between the long axis of the strands and that of the fiber is indicated by the size of the arc that is measured as the X-ray angle.

There are other properties, largely subdivisions of the four major ones listed. They cannot yet be measured so quickly, or they lack definite end points or precision of determination. Hence their exact importance in fiber quality is not so clearly established. For example, cell-wall thickness, one of the attributes of fineness, is hard to measure, and is reported unsatisfactorily as "percent of fiber with a given lumen-wall ratio." To some extent, the extremely thin-walled fibers and perhaps the oversized thick-walled fibers influence the processing, finishing, and wearability or utilization of the product. New and improved methods of measuring fiber wall thickness and fiber perimeter are needed before their effects can be accurately evaluated.