A Microscopical Study of the Effects of Some Typical Chemical Environments on the Primary Wall of the Cotton Fiber

Abstract

The topography and structure of the primary wall of the cotton lint fiber are described and illustrated by electron micrographs. The changes in this thin membrane brought about by alkali boil (kiering), hypochlorite and peroxide bleaching, mercerization, acid hydrolysis, and dry heat are shown by means of microscopical examination of isolated pieces of the primary wall after exposure to these environments. The noncellulosic constituents of the wall, which account for a large part of its chemical composition, are progressively removed during alkaline kiering. Excessive conditions of kiering appear to damage the cellulose framework of the wall. Peroxide bleaching is apparently effective in removing the encrusting noncellulosic material, but hypo chlorite alone does not have this effect. Mercerization of the isolated wall induces shrinkage in both longitudinal and transverse directions; the shrinkage increases when the noncellulosic materials are removed from the membrane prior to mercerization. The morphology and struc ture of the wall account for the observed behavior on mercerization, and electron micrographs of the mercerized wall show a shrunken network of cellulose fibrils. The primary wall shows resistance to disintegration by acid hydrolysis, and its fibrillar pattern is preserved intact, after long periods of contact with hot mineral acid. Long periods of heating in air "set" the primary wall in a configuration similar to that which it had on the corrugated surface of the cotton fiber. The contribution of the primary wall to certain gross properties of the fiber and its behavior during finishing treatments is discussed.