Changes in Fine Structure and Mechanical Properties Induced by Cyanoethylation of Cotton Yarns

Abstract

Cotton yarns were impregnated with 6% sodium hydroxide and reacted in the relaxed state with acrylonitrile at 60° ('. and different periods of time up to 60 min. to give prod ucts with degrees of suhstitution up to 2.6 cyanoethyl groups per anhydroglucose unit. As substitution increases, the x-ray diffraction pattern shows only slight alteration until substitution has exceeded 1.1, after which the crystalline structure rapidly gives way to ' an amorphous structure, complete at about DS = 2.0. At the same time density decreases nearly linearly with substitution. At the stage where the product becomes essentially amorphous, it can be annealed at temperatures of about 175° C. into a new pattern char acteristic of cyanoethyl cellulose. This annealing is accompanied by a substantial density increase. Stress relaxation of the cyanoethylated yarns at a substitution of 1.1 suggests a glass-rubber transition point about 140° C. which becomes more distinct and moves to lower temperatures as substitution increases. At a substitution of about 2.0 the stress relaxation reaches its lowest value (about 4% of the value at 20° C.) at the highest tem peratures tested (220° C.). With further substitution a minimum relaxation at an inter mediate temperature is followed by increasing stress as the temperature is raised. This effect is associated with crystallization. Breaking strength increases slightly at low substitutions but decreases then to less than 50% for the highest substitutions. Elonga tion at break increases gradually, exceeding 100% above the control at DS = 2 and above. Tensile stiffness decreases to about 3% of its initial value. Work of rupture and recovery show considerable decreases below DS = 2, but sharp rises between 2.0 and 2.6. Im mediate elastic recovery is little affected below DS = 2, but rises above this. Delayed elastic recovery shows continuous improvement as substitution increases, eventually ex ceeding the control by nearly 50%.