Structure of Cotton Linters

The microscopic structure of cotton linters fibers is similar in many respects to that of staple (lint) cotton. There are no pronounced differences between these two types, although in general linters fibers are darker, shorter, more nearly cylindrical, and have thicker walls and narrower central canals than the staple cotton. The thin primary wall, which covers the surface of the fibers, consists largely of waxy and pectic materials. The thick secondary wall is arranged in layers. In some linters fibers this layered pattern is due to the alternation of layers of cellulose which differ in porosity and density, and in others to the alternation of layers of cellulose with layers of noncellulosic material. The width of individual layers varies roughly between 0.1 and 0.4 micron in unswollen fibers. The cellulosic layers are further subdivided into fine threadlike fibrils which make an acute angle with respect to the long axis of the fiber. The orientation of the fibrils is not the same in all layers and may even reverse its direction of spiral in a single layer. These structural characteristics influence the manner of swelling.