Heat Induced Chemical Changes in Cotton Fiber

Abstract

SINCE the introduction of artificial drying in ginning, cotton mills have complained about overdried cotton and its effect on cotton spinning. Studies on gin-dried cotton indicate there are more ends down and in some cases weaker yam [2,3]. Some preliminary work by the authors on overdried cotton also indicated structural changes in the fiber as measured by decreased moisture regain.Since it is difficult to know the history of cotton fiber and conditions under which it was ginned, laboratory studies were made on cotton of known history, physical condition, and characteristics to deter-, mine how heat drying damages cotton fiber during ginning and mill processing. Materials and MethodsThe cottons used in the laboratory tests were experimental upland cottons from the Texas Agricultural Experiment Station at Lubbock, Texas. An effort was made to obtain cottons with a minimum of field weathering. Micronaire readings on the fibers ranged from 2.6 to 5.4, representing cottons of three stages of maturity with a good range for test drying (Table I). An early and a late harvested cotton from a producer in the Lubbock area was ginned with no heat, at 175° F., and at 350° F. (80° C. and 175° C.) respectively. Tests were made on these samples along with the laboratory heated cotton to obtain additional information on overdrying.Prior to heat treatment in the laboratory, the cottons were allowed to come to a moisture equilibrium of al)out 4%. Heating in the laboratory was conducted in a forced draft oven at 70°, 80*. 90°, 110°, 1 SO°, and 200° C. The duration of heat--ing was 10, 20, and 30 min. An unheated sample of the three different degrees of development was used for comparison. After heating, samples again reached a moisture level of about 4% before chemical tests were made.Tests used to determine changes in cotton due to drying were as follows.

Heat Treatment of Cotton: Effect on Endotoxin Content, Fiber and Yarn Properties, and Processability

“…Complete thermal degradation and significant changes in the supramolecular structure of cellulose do not occur at the conditions used for depyrogenation of glassware [24,44,46], but mechanical stress of ginning severely reduces fiber strength and length of over-heated cotton, and reduces the processability of fibers into yarn [ 12,13,22,26 ] . Detrimental effects on color, strength, elongation, and length occur when cotton is heated at 200°C for 20 minutes [ 3 ] .…”

Heat-induced changes in cellulose nanocrystal/amino-aldehyde biocomposite systems

“…A significant increase in reducing sugars was observed by heating of cotton above 140 °C [34], and reducing sugars, especially hexoses show a yellowing similar to the aldehyde-containing celluloses [35]. Thermal treatment at 140 °C for 20 min decreased the degree of polymerization of cotton cellulose by about 13% [36], resulting in terminal aldehyde groups. It was proved that the contribution to yellowing of these aldehydes at C1 position is higher by 70% than that of the aldehyde groups at other positions of the cellulose chain [35].…”

Cellulose derivatives containing carboxylic acid groups

“…Various types of degradation such as mechanical (Nissan et al, 1965), heat (Nissan et al, 1965;Kangle and Nabar, 1968;Hessler and Workman, 1959), ultrasonic waves (Nissan et al, 1965), visible and ultraviolet light (Nissan et al, 1965, Guthrie, 1971, and ionizing radiation (Nissan et al, 1965;Demint and Arthur, 1959) also produce carboxylic acid groups on cellulose but their number is usually small and little if any work has been done on their subsequent reaction.…”