Some Mechanical Properties of Wool Fibers in the "Hookean" Region from Zero to 100% Relative Humidity

Abstract

At 20°C and for all moisture contents, the mechanical behavior of wool fibers up to 1% extension in the Hookean region is linear viscoelastic. The equilibrium Young's modulus, based on the wet cross-sectional area of the wool fiber, is inde pendent of moisture content and is equal to 1.4X 10¹⁰ dynes-cm². The dynamic or transient behavior of a fiber at any moisture content at 20°C can be replaced by a spring contributing a fixed stiffness of 1.4X 10¹⁰ dynes/cm² to the dynamic Young's modulus together with a viscous dashpot in parallel and having moisture-dependent characteristics. The action of water, which in the original two-phase matrix-microfibril model, was proposed to weaken the matrix, must now be con sidered to increase the segmental mobility of the molecular structure of the matrix. Further, mechanical equilibrium between matrix and microfibril is taken to exist for the wet wool fiber, rather than the dry fiber.

Keywords

Corriedale wool fibers wool fibers. Moisture. Temperature RH Hookean region extension extension rate fiber length stress Stress relaxation affine strain stress dceay fiber structure linear viscoelasticity stress—strain curves Hookean slopes swelling segmental mobility water uptake length change mechanical equilibrium mechanical proper ties. Wool mechanical properties. Conditioning tensile testing.

References

Alfrey, T. and Doty, P. , Methods of Specifying the Properties of Visco-Elastic Materials, J. Appl. Phys. 16, 700-713 (1945).,

Feughelman. M. , Mechanical Properties of Wool Fibers. I. Creep in the "Hookean" Region of Wool Fibers in Water. J. Textile Inst. 49, T361-T378 (1958).

Feughetman, M. , A Two-Phase Structure of Keratin Fibers. Textile Res. J. 29, 223-227 (1959).

Feughetman. M. and Haly, A.R. , The Physical Properties of Wool Fibers at Various Regains. Part VI: Textile Res. J. 32, 227 (1962).

Feughetman, M. and Rohinson, M.S. , Stress Relaxation of Wool Fibers in Water at Extensions in the Hookean Region over the Temperature Range 0°-90°C , Textile Res. J. 39, 196-198 (1969).

Haly, A.R. and Feughetman, M. , Physical Properties of Wool Fibers at Various Regains. Part I: Textile Res. J. 31, 131-134 (1961).

Haly, A.R. and Swaneopot, O.A. The physical Properties of Wool Fibers at Various Regains, Textile Res. J. Part V: 31, 966-972 (1961).

Katz, S.M. and Tobolsky, A.V. , The Kelaxation of Stress in Wool Fibers. Textile Res. J. 20, 87 94 (1950).

Mason, P. The Viscoelasticity and Structure of Fibrous Protein. Part II, Kolloid-Z 218, 46-52 (1967).

10.

Menefee, E. , A Mechanical Model for Wool, Textile Res. J. 38, 1149-1163 (1968).

11.

Speakman, J.B. , The Plasticity of Wool, Proc. Roy. Soc. London, Ser. B103, 377-396 (1928).

12.

Tobaisky, A.V. , "Properties and Structure of Polymers," New York, Wiley, 1960 .

13.

Wood, G.C. , The Relaxation of Stretched Animal Fibers. II. The Relaxation of Human Hair , J. Textile Inst. 45, T462-T471 ( 1954).