M. Feughelman

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

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 Youngs 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 Youngs 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.

An Electron Spin Resonance Study of the Copper (II) Interaction with Wool-Keratin Part I : An Interpretation and the Properties of a Copper (II)/Wool ESR Spectrum

The esr spectrum observed from a wool sample treated in a copper (II) solution in the pH range of 1.5 to 5.0 was inter preted by assuming two paramagnetic species each with an effective spin S=1/2. The interaction giving rise to this esr spectrum was ascribed to the complex formation between Cu(II) and the free carboxyl groups in the wool.

Finite Element Analysis of the Composite Fiber, Alpha Keratin

The individual mechanical properties of each of the phases, microfibrils, and matrix in α-keratin fibers were analyzed in terms of a two-phase composite of microfibrils and matrix. The authors applied finite element techniques appropriate for composite micromechanics to the data available on the mechanical properties of various α- keratins with varying moisture contents. Despite some simplifying assumptions the result of the analysis was in general agreement with our present understanding of keratin structure. The results indicated the following: Absorption of water by the keratin structure has a pronounced weakening effect confined mainly to the matrix. Differences existing between different keratins were in the main due to variation of matrix properties produced by the presence of high glycine-tyrosine and high sulphur proteins, both of which increase the mechanical stiffness of the matrix. Data obtained for porcupine quill show that whereas the microfibrils can be considered as isotropic at all moisture contents of the keratin structure, the matrix must become highly anisotropic at saturated moisture contents.

An Electron Spin Resonance Study of the Copper (II) Interaction with Wool-Keratin Part II: The Nature of the Copper (II) Interaction with Wool-Keratin

An examination of the Cu (II)/wool esr signal intensity variations, together with other relevant copper (II) uptake data, have shown that two types of products are formed during the Cu (II)/wool interaction. One of these gives rise to the observed esr signal, while the other is a diamagnetic sulfide of copper. The latter product arises as a result of a reaction of the metal ion and the products of a water/wool interaction. A reaction scheme consistent with the experi mental observations is suggested.

The Internal Dynamic Mechanical Loss in α-Keratin Fibers during Moisture Sorption

The dynamic mechanical loss in α-keratin fibers such as wool and horse hair can be measured by the phase difference “φ” between the oscillating extension applied to the fiber and the resultant oscillatory force. When the environment of a fiber is changed from dry to more moist conditions, the value of φ has a maximum at the point in time when the swelling of the fiber reaches a maximum. This phenomenon parallels others already observed and confirms the general picture that during sorption the molecular structure of a keratin fiber has a maximum mobility. It follows that any applied deformation at this stage will reach structural equilibrium in the shortest time.

An Electron Spin Resonance Study of the Copper (II) Interaction with Wool-Keratin Part III: A Kinetic Model for the Cu(II)/Wool Interaction

The uptakes of Cu(II) by wool are interpreted with the help of a kinetic model developed on the basis of a previously suggested reaction scheme. The kinetic model may be used to obtain information about the Cu(II)/wool interaction.

Cohesive Set in Torsion of Wool Fibers

When a wool fiber is held extended in water, the stress in the fiber drops with time due to the breakdown of strained bonds in the fiber. If the fiber, still extended, is dried, the stress in the fiber rises due to the formation of strained bonds [1]. If the fiber is then released, it tends to return to its native length. However, the Youngs modulus of a dry fiber (0% RH) is greater by a factor of 2.7 than for a wet fiber. This means that the stress in the fiber only partially returns the fiber to its native length. The difference between the native length of the fiber and the length attained on release is called cohesive set. When a wool fiber immersed in water is held at a fixed twist, the torque opposing the twist also drops with time due to bond breakdown [4] to a steady value T wOn drying, however, in contrast to the situation with the fiber in extension, the torque on the fiber drops to T D, and in the case of cystine-reduced fibers can even be negative (Table I). On drying, the torsional modulus of the fiber increases by a larger factor than the Youngs modulus (by a factor of at least about 10 from wet to 0% RH [4]. This results, on release of a normal wool fiber, in a cohesive set of over 95%, and in the case of cystine-reduced fibers, it may be over 100% (Le., the fiber twists further in the direction of the original twist).

A Note on Some Molecular Interactions Involved in the Aging of Keratin Fibers

keratin fibers.’ When the wool fibers are allowed to retract to their native configuration the reformation of the hydrogen bonds associated with the main chains of the a-helices will proceed rapidly as a sequential action with the reformation of the helical turns. The ionised carboxylic acid and amino groups associated with the side chains of the a&dquo;-helices and, which provide the Coulombic interactions, are also associated with bulky structures. These groups are not as sterically directed towards reformation, when the fiber retracts ~and the helices reform. Consequently, they take time to regroup and to interact in the lowest free-energy state of the unextended fiber. The aging of wool fibers at any specific moisture content is an equilibration of the molecular structure for the keratin to its lowest free-energy state and at-

A Note on the Significance of Hygrostress in Wool Fibers

than normal and this is because of the structural differences already discussed. Doubtless, the relatively large number of folded fibers plays a significant part, and it has been demonstrated by Lord ~3~ that, within limits, a larger rotor can reduce the number of folded fibers and improve the yarn quality. Unfortunately, power costs escalate rapidly with size, and a choice has to be made between cost and quality. There are also some data which suggest that an oversize rotor can cause a deterioration in quality, although the reasons for this are not yet understood. As labor costs rise and machine costs fall relative to power costs, there may be a move towards larger rotors, but the movement is likely to be slow. Because not all bridging fibers become folded, there may be a possibility of improving the yarn by reducing the cohesion of the fibers on the collecting surface to a minimum so that fewer of the bridging fibers get caught by the outgoing yarn. While the &dquo;optimum&dquo; twist multiple to give the best strength seems to be higher than normal, it remains to be seen whether this is the same as far as fabric strength is concerned. Since even the lower yarn strengths seem to be more than adequate for processing -indeed the yarn is usually superior to ring yarn in practice-perhaps it is necessary that different criteria should be used. Certainly, many of the criteria now used seem to be inapplicable and this emphasizes the point that these yarns are not necessarily better nor worse than ring yarns, they are merely different.