Effects of Gamma,High-Energy Electron,and Thermal Neutron Radiations on the Fibrillar Structure of Cotton Fibers

Abstract

Changes in the structure of cotton fibers after expesure to gamma, high-energy electron, and thermal neutron radiations, in various ambient atmospheres, were evaluated by the techniques of optical and electron microscopy. Radiation exposures evaluated were: gamma rays, 10⁵ to 4 × 10⁸ r.; 2-Mev electrons, 5 × 10⁴ to 10⁸ rep; integrated thermal neutron fluxes, 5 × 10¹⁴ to 10¹⁷ nvt. Changes in the physical and chemical properties of similarly irradiated fibers have been, or are to be, reported in other pub lications. All irradiated, unmodified cottons could be differentiated from unexposed cottons by optical microscopical observations of samples stained in Nile Blue Sulfate. Gamma ray and electron exposed samples differed from unexposed fibers. in swelling behavior in 0.2 M ( in Cu) cupriethylenediamine hydroxide, but thermal-neutron-irradiated cotton differed from the control only after exposure to an integrated flux of 10¹⁷ nvt. Electron micrographs of the fibrillation patterns exhibited by fibers exposed to gamma and electron radiation doses of 5 X 10⁶ to 10⁸ r. or rep on beating in water in a Waring Blender showed the formation of increasingly smaller fragments of samples. Some shortening of fibrils and an increase in number of broken ends of microfibrils were seen in neutron-irradiated cotton exposed to 10" nvt; at lower integrated neutron fluxes, fibrillation was unchanged. No distinct differences were found in microscopical tests between gamma and electron irradiated fibers or between gamma-exposed fibers irradiated in oxygen and nitrogen. At doses of 4 × 10" r. of gamma rays, the trend toward smaller fragments reversed and short chunks of material were observed.

Varying amounts of degradation were observed in modified cottons after irradiation. Smaller fragments were observed in cottons modified to change and reduce the total crystalline cellulose; the fibrillation of acrylonitrile-treated cotton appeared unchanged, but irradiation produced a decrease in the size of fragments of dichloropropanol- and dimethylol cyclic ethyleneurea-modified samples.