Pectic Substance in Cotton and Its Relation to the Properties of the Fibre

Pectic substance has long been known to be present in naturally-occurring cotton fibres. There exist, how ever, at least two divergent viewpoints regarding the lo cation of this substance in the fibre. The difference in these viewpoints has led to very different conclusions re garding the influence of pectic substance on such important properties of cotton as tensile strength, moisture and dye absorption, and viscosity in cuprammonium hydroxide solu tions. The chief difficulty, heretofore encountered in attempts to evaluate more precisely the role of the pectic substance, has been the lack of a reliable method for its quantitative estimation in the presence of other carbohydrate material. Recently, however, a new method, which permits the accu rate determination of small amounts of uronic acids in the presence of large proportions of cellulose, was developed in this laboratory. This development has made possible the present investigation, which concerns itself with the state of the pectic szcbstance in native cotton fibres, its ease of removal by various reagents, its behavior in cuprammonium hydroxide solutions and its influence on the tensile strength and on the viscosity of cuprammonium dispersions of the cotton. The results indicate that a pectin-cellulose complex does not exist in cotton fibres and that the pectic sub stance is present as an insoluble salt. The replacement of these ions, under non-hydrolytic conditions, by the mono valent cations, sodium or ammonium, renders the pectic substance soluble. Cotton freed of pectic substance with alkali showed no change in tensile strength or in viscosity, whereas treatment of the fibre with acids, which removed only a small proportion of the pectic substance, produced an appreciable lowering of these two properties. When dewaxed fibres were dispersed in cuprammonium solutions, it was found that a small portion remained in soluble and was readily removed in a centrifuge. Analysis of the material showed it to consist practically entirely of pectic substance. Similar results were obtained on fibres which had been pretreated with concentrated hydro chloric acid. Consideration of these results led to the con clusion that the pectic substance does not contribute to the viscosity of cuprammonium dispersions of cotton. Deter minations of the viscosities of cuprammonium solutions to which had been added several samples of pectic material from different sources substantiate this conclusion.