Compressive Stress Relaxation Properties of Polyester and Cupra Fiber Assemblies under High Humidity Conditions

In this study, a compression stress relaxation phenomena of three-dimensional fiber assembly for futon wadding use is investigated under high humidity condition, which simulates actual sleeping environmental condition. KES-G5 compression tester is used for the compression stress relaxation measurement, and humid air is supplied to the tester with high humidity air generator. Samples used are polyester (PET) staple fiber with round section and with w-shaped section, and cupra-ammonium (cupra) staple fiber. Results are obtained asfollows. (1)Stress relaxation rate of cupra staple fiber assembly in high humidity condition is large compared to that of standard condition. Change in stress relaxation rate of PET staple fiber assembly between high humidity and standard conditions is not so large. (2)Stress relaxation function, Y(t) of cupra staple fiber assembly in high humidity condition is expressed as two stage exponential function. Y(t)=A_1exp(-t/τ_1)+A_2exp(-t/τ_2). where, A_1, A_2(n.d.) and τ_1,τ_2(s) are constants obtained from experimental curve. (3)Stress relaxation function of PET staple fiber assembly in high humidity condition is expressed as power function of time. σ=βt^-α where, σ: stress(Pa), α and β: constants obtained from experimental curve. (4)The effect of high humidity condition on compression stress relaxation phenomena of cupra fiber assembly is discussed based on viscoelastic theory, and compared to that of PET fiber assembly