Liquid-Ammonia and Caustic Mercerization of Cotton Fibers: Changes in Fine Structure and Mechanical Properties

Cotton fibers blended to give three levels of fiber maturity were mercerized in anhydrous liquid ammonia and in sodium hydroxide solution, slack and under tension. Both reagents produced similar changes in the cottons, but to differing degrees. Both ammonia and caustic treatments produced changes in morphology (swollen fibers, decrease in convolutions) and in fine structure of the cellulose (increased accessibility as measured by increased moisture regain, iodine sorption, accessibility to deuterium exchange, and decreased density). X-ray diffraction showed increased amorphous fraction and partial recrystallization into cellulose III and cellulose II lattice after treatment with ammonia and caustic, respectively; the x-ray orientation angle was decreased by treatments under tension. Both reagents produced increased fiber elongation-at-break with slack treatment and increased fiber tenacity with tension treatment; caustic mercerization produced a slight increase in fiber tenacity after slack treatment.