Stress Relaxation of Ramie Fiber during Acid Hydrolysis

Abstract

Stress relaxation measurements for ramie fiber were carried out during hydrolysis with sulfuric acid. The mechanism of stress decay was discussed, and an attempt was made to separate physical and chemical relaxation mechanisms. The results obtained were as follows: (1) The relative stress f(t)/f(1) for ramie fiber during hydrolysis could be represented by the following equation: f(t)/f(1)=A_1 exp (-t/τ_1)+A_2 exp (-t/τ_2) where A_i is a constant and TI is the relaxation time (τ_1<τ_2). It was considered that the first term in the above equation represents the stress decay behavior due to scission of hydrogen bonds in the amorphous region of cellulose, while the second term represents the che mical relaxation due to the scission of glucosidic bonds. (2) The apparent activation energies for the two relaxation processes were 16 kcal/mole (physical relaxation process) and 12 kcal/mole (chemical relaxation process). The activation energy of chemical relaxation was close to that obtained from diffusion controlled reaction. (3) It may be concluded that the value of AI in the above equation represents the fraction of bonds such as hydrogen bonds which contribute to the physical relaxation process. (4) The relaxation time T2 of chemical relaxation was nearly equal to the inverse of the rate constant, 1/k, obtained from measurements of the degree of polymerization.