Fiber properties
Physical properties

Raw cotton is creamy white in colour. The cotton fiber is a single cell, which grows out of the seed as a hollow cylindrical tube over one thousand times as long as it is thick.

The quality of cotton depends on its length, strength, fineness, and maturity. Other factors affecting cotton quality are leaf residue, and ginning preparation.

Length : Staple length is very important because it affects how the cotton fiber is handled during spinning and it relates to fiber fineness and fiber tensile strength. Longer cotton fibers are finer and make stronger yarns. Cotton fibers range in length from ½ inch to 2 inches, depending on the variety. There are three groups of cotton that are commercially important:

1. Uplands cottons, which are 7/8 – 11/4 inches in length and were developed from cottons native to Mexico and Central America.
2. Long staple cottons, which are 1 5/16 – 1 ½ inches in length and were developed from Egyption and South American cottons. Different varieties include American Pima, Egyption, American Egyption, and Sea Islands cottons.
3. Short staple cottons, which are less than ¾ inch in length and are produced primarily in India and Eastern Asia.

Long staple cotton fibers are considered to be finer quality because they can be made into softer, smoother, stronger, and more lustrous fabrics. Because they command a higher price and less is produced than the medium and short staple lengths, they are sometimes identified on a label or tag as Pima or Supima. Or may be referred to as long-staple cotton or extra long staple cotton.

Convolutions

Convolutions, or ribbon-like twists, characterize the cotton fibers. When the cotton fibers mature, the boll opens, the cotton fibers dry out, and the central canal collapses; reverse spirals cause the cotton fibers to twist. The twist forms a natural crimp that enables the cotton fibers to cohere to one another, so that despite its short length, cotton is one of the most spinnable fibers. The convolutions can be a disadvantage, since dirt collects in the twists and must be removed by vigorous washing. Long staple cotton has about 300 convolutions per inch; short staple cotton has less than 200.

Fineness

Cotton fibers vary from 16-20 micrometers in diameter. The cross-sectional shape varies with the maturity of the cotton fiber. Immature cotton fibers tend to be u-shaped and the cell wall is thinner; mature cotton fibers are more nearly circular, with a very small central canal. In every cotton boll there are immature fibers. The proportion of immature to mature cotton fibers cause problems in processing, especially in spinning and dyeing.

Colour

Cotton is naturally creamy white. As it ages, it becomes more beige. If it rained on just before harvest, the cotton fiber is grayer. White cotton fiber is preferred.

Picking and ginning affect the appearance of cotton fibers. Carefully picked cotton is cleaner. Well-ginned cotton is uniform in appearance and white in colour. Poorly ginned cotton will have brown flecks in it, called trash, such as bits of leaf or stem or dirt. These brown flecks decrease the quality of the cotton fiber. Cotton canvsas made from such cotton fibers are suitable for utility cloths and occasionally are fashionable when a “natural” look is popular.

Grading and classing of cotton is done by hand by machine. Visual inspection of staple length and colour compare the cotton from the bale being graded with standards prepared by the United States Department of Agriculture.

Luster

The luster of cotton canvas is low, unless it has been given special treatments or finishes. This is, in part, a consequence of the natural twist of cotton and its resultant uneven surface that breaks up and scatters light rays reflected from the cotton fiber surface.

Specific gravity

Cotton has a specific gravity of 1.54. (compare with that of polyester at 1.38 or nylon at 1.14) This means that cotton canvas feel heavier in weight than comparable fabrics made from polyester or nylon.

Mechanical properties
Strength

Strength of cotton canvas on a scale of high, medium, and low would rank as medium (tenacity is 3.0 to 4.9g/d). It has a fairly high degree of crystallinity but somewhat lower orientation. The strength is increased by the length of the polymer chains. In comparison with other cellulose fibers, cotton is weaker than flak and stronger than rayon.

Cotton is 10 to 20 percent stronger when wet than when dry. Its strength can be increased by a process called mercerization in which yarns or fabrics held under tension are treated with controlled solutions of sodium hydroxide. The alkali causes the fiber to swell and straighten out to become stronger and more lustrous.

Modulus

Cotton fibers have a moderately high modulus , similar to that of polyester. This helps the two fibers to blend well.

Elongation and Recovery

Like most other cellulosic fibers, cotton has low elongation and elastic recovery. Knitted cotton cuffs and bands may stretch during wear and tear and may not recover fully.

Resilience

Cotton canvas wrinkle easily and do not recover well from wrinkling. In stretching or wrinkling, hydrogen bonds between chains are broken and then reformed in the new position, holding in the wrinkle or other deformation. Through the application of durable press finishes, however, resilience can be improved. Unfinished cotton canvas generally must be ironed after laundering.

Flexibility

Compared to many other fibers cotton is fairly flexible. However, when fineness is take into account, its bending resistance on a relative scale is high, affecting the drapability of cotton canvas.

Chemical properties
Absorbency and moisture regain

Due to its many hydroxyl groups, which attract water, cotton canvas is an absorbent fabric. Its good absorbency makes cotton comfortable in hot weather and suitable for materials where absorbency is important (such as diapers and towels). Cotton canvas is relatively slow to dry because the absorbed moisture must be evaporated from the fiber. For the same reason, cotton canvas take waterborne dyes readily. The percentage moisture regain of cotton canvas is 7 to 8 percent at standard temperature and humidity.

Heat and electrical conductivity

Cotton canvas conducts electricity and thus does not build up static electrical charges. It has moderately high heat conductivity, which makes the canvas fabric comfortable in hot weather.

Effect of heat; combustibility

Cotton canvas is not thermoplastic and not melt. Exposure to dry heat at temperatures about 300 degrees ferentheit, however, does cause gradual decomposition and deterioration of the canvas fabric. Excessively high ironing temperatures cause cotton canvas to scorch or turn yellow.

Cotton canvas is combustible . It burns upon exposure to a flame and continues to burn when the flame has been removed. Burning cotton canvas smells like burning paper, and a fluffy, gray ash residue remains. It is not possible to distinguish cotton from other cellulose fibers by burning.

Chemical reactivity

Cotton canvas that has been cleaned and bleached is about 99percent cellulose. Its chemical reactions are typical cellulosic materials. Dyestuff that are too acidic in reaction cannot be applied to cotton canvas fabrics.

Environmental properties
Resistance to microorganisms and insects

Mildew grows in cotton canvas fibers, especially if they are stored under conditions of dampness, warmth, and darkness. This fungus stains the cotton canvas fiber and eventually rots and degrades it. Other bacteria and fungi that grow in soiled, moist areas will also deteriorate or rot cotton canvas fabrics.

Moths and carpet beetles do not attack cotton canvas, but silverfish may eat the cotton canvas fiber. Heavily starched cotton canvas fabrics are liable to be damaged by silverfish.

Resistance to environmental conditions

Although cotton canvas fiber shows better resistance to sunlight than do many fibers, extended exposure to sun will cause weakening and deterioration of cotton fabrics. Cotton draperies will last longer if lined with another layer of fabric.

Age does not seriously affect cotton canvas fabrics; however, it is important that the fabrics be stored in clean condition and in dry areas to prevent mildew. Special acid-free tissue paper can be used to store antique cotton garments, cotton quilts, and spreads. Ordinary tissue paper should not be used for wrapping fabrics for long term storage because the paper contains an acid residue that may damage the cloth.

Other properties
Dimensional stability

Cotton canvas fibers swell considerably in the transverse direction when wet. Unfinished woven or knitted cotton fabrics will shrink in the first few launderings because the laundering releases tensions created during weaving or finishing. The relaxation of these tensions may cause changes in the fabric dimensions. Cotton canvas fabrics can be given special finishes to prevent this relaxation shrinkage.

Abrasion resistance

Fabrics made from cotton generally have low abrasion resistance. Garments will show wear at hem, cuffs, and collars; all cotton sheets will not be as durable as those that are blends with more abrasion resistant fibers such as polyester. Cotton fabrics will not, however, pill badly.

More on production of cotton canvas

More on qualities and classification of cotton canvas

More on artist unprimed cotton canvas

Back to cotton canvas main page