Stress-strain properties of individual Merino wool fibres are minor contributors to variations in staple strength induced by genetic selection and nutritional manipulation

Abstract

This paper investigates the contribution of single fibre stress-strain properties to variations in staple strength induced by both selective breeding for staple strength and nutritional manipulation. Merino weaners (n = 40), selected from ‘sound’ and ‘tender’ lines of staple strength selection flocks, were allocated to feeding regimes designed to induce liveweight changes simulating typical Mediterranean seasonal changes. Average staple strength differed by 5 N/ktex between ‘sound’ and ‘tender’ selection flocks and 18 N/ktex between extreme nutritional treatments. The force-extension properties of individual wool fibres (n = 100 per sheep) were measured using a single fibre strength meter. After normalising for differences in fibre cross-sectional area at the point of break, the key parameters used to describe the stress-strain curve for each fibre were: Young’s modulus (GPa), yield stress (MPa), stress at 15% strain (MPa), stress at break (MPa), strain at break (%) and work to break (MPa). The average stress-strain properties of single fibres differed widely between individual sheep. Stress at break ranged from 163 to 235 MPa (44% range), strain at break ranged from 21 to 44% (103% range) and work to break from 43 to 71 MPa (65% range). There were no significant differences in any of the single fibre properties between the staple strength selection flocks, nor was there any significant interaction (P > 0.05) between staple strength selection flock and nutritional regimes. Nutritional regime had a significant effect on stress at break, strain at break and work to break, but none of the single fibre stress-strain properties removed any appreciable variance in staple strength over and above that accounted for by differences in along- and between-fibre diameter variation. There appears to be little scope for improvement of single fibre stress-strain properties as a means of increasing staple strength in normal production environments. Selection directly for staple strength or indirectly using the fibre diameter variability traits is an effective method to improve staple strength.

Dietary Selenium Changes and Its Relation With Adaptability in Small Ruminants

“…This increment in staple strength might be attributed to the treatments (G2 and G3) and related with increase in fiber diameter. These findings agree with previous studies by Thompson (1998) and Thompson and Hynd (2009) who found that an increase of 1 µm in minimum fiber diameter was associated with an increase in staple strength of about 5 N/ktex.…”

Fibers Mechanically Similar to Sheep Wool Obtained by Wet Spinning of Gelatin and Optional Plasticizers

“…Due to its mechanical qualities, fully oriented gelatin fibers ( λ = 4) as produced in the present work are an eligible alternative to other protein fibers, such as sheep wool: single fibers of commercial sheep wool (measured with the same set‐up and test parameters) had an elastic modulus of 2.7 GPa and a tensile strength of 116 MPa. According to the literature, merino wool has higher stiffness (3.9 GPa) and tensile strength (212 MPa) . In Figure , the mechanical properties of the produced gelatin fibers are compared with major commodity fibers; the relevant properties were measured in‐house or taken from literature .…”

Effect of Staple Strength on Spinning Performance and Yarn Quality of Superfine Wools

“…Because we were unable to undertake OFDA4000 measurements, it can only be speculated that the along fiber diameter profiles of the 24 and 43 N/ktex differed. Lamb [11] has observed that staple strength is influenced by factors other than individual fiber strength, and so may not relate as well to breakage in processing. As well as along fiber diameter profile variation, Lamb has observed that staple strength is also influenced by the extent to which fibers share the load in the ATLAS staple strength measurement, with one of the influences being variation in within staple fiber length.…”

“…In an extensive review of staple strength literature, Lamb [11] noted that staple strength is found to have almost no relationship to the average strength of bundles of fibers in the resulting tops or with subsequent yarn strength and spinning performance, apart from its effect via the length of the top. Lamb commented that "any variation in thickness along the fibre reduces the total load that can be supported and variation of fibres in thickness and length means that they can extend at different times and rates and so not share the load equally or not break at the same time, which reduces the peak force.…”