Page 145 - Handbook of Properties of Textile and Technical Fibres

Physical, chemical, and tensile properties of cashmere, mohair, alpaca 123

tops (which are ready for spinning) are relevant to yarn and fabric processing and
properties, it is necessary to measure breaking strength on raw fibers to understand
how fibers will process during dehairing, carding, and topmaking. Evaluating fibers
after scouring and dehairing would provide different values compared with evalu-
ating raw fiber. There is limited extent of knowledge regarding the stress-strain
properties, failure properties, and breaking stress (strength)ofrareanimal fibers
and much of what is known is in older references. Many reports attempt to compare
fibers, such as mohair or alpaca, by testing only one or two samples, usually of pro-
cessed fiber.
Watson and Martins (1966) provide stress/strain curves and tensile properties of
one sample each of (MFD in brackets) scoured mohair (36 mm), scoured alpaca
(30 mm), dehaired cashmere (17.5 mm), dehaired Bactrian camel (21 mm), and
dehaired vicu~ na (14 mm). The results were similar to 22 mm wool with the exception
that the vicu~ na was very brittle with one-third of fibers having elongations at break of
2%e10%, which is not surprising given the likelihood of greater weathering from
extreme UV exposure. Kondo et al. (1971) showed a sharper peak in the stress-
strain curve of mohair relative to wool. They attributed this to a stronger bond between
the scales and the cortex in mohair. Similarly, Roberts (1973) found that Mongolian
cashmere and lambswool, of similar MFD, had similar stress-strain characteristics,
extension at break, and tensile strength. Patni et al. (1984) provide tenacity and exten-
sion measurements for dry and wet Angora, cashmere, mohair, and wool. The stress-
strain curves for these fibers were similar. For 100% Angora yarns the tenacity was
5.4 g/tex and elongation 12.8%, and increasing the blend of cotton increased yarn
tenacity and reduced elongation, while increasing the blend of wool reduced both
tenacity and elongation. Kim et al. (1995) provide breaking strain data for Angora fiber
and yarns. Harizi et al. (2007) report tensile properties and stress/strain curves for
20 mm 18 mm long Dromedary camel undercoat.
Couchman (1984) provides single fiber strength for four samples of Australian
cashmere (MFD range 15.1e17.9 mm), two samples of Chinese cashmere (MFD
13.6e13.9 mm), and an Iranian sample (MFD 17.4 mm). Tenacities for the Australian
samples were 7.0, 7.9, 12.1, and 15.5 cN/tex, for Chinese cashmere 8.2 and 11.2 cN/
tex, and the Iranian sample 16.2 cN/tex. There was a large range in single fiber tenacity
within cashmere samples.
Single fiber strength values of mohair and camel hair were comparable with those of
better wools (Meredith, 1945). King (1967) examined some tensile properties of
mohair and kemp. Kemp fibers were included in a report of Smuts and Hunter
(1974). Smuts et al. (1981) showed that mohair had higher tenacity, initial modulus,
and extension than wool of the same diameter and that mohair tensile characteristics
were fairly constant over the range of diameters tested. Hunter and Smuts (1985) per-
formed both bundle and single-fiber tests on mohair, showing tenacity to be indepen-
dent of fiber diameter. Hunter (1993) summarizes many other reports relating to the
tensile properties of mohair.
Villarroel (1959) found Peruvian Huacaya alpaca fibers were more extensible than
Suri alpaca fibers in both wet and dry conditions (Table 4.3). The maximum stress at
break for Huacaya fibers was also greater than that for Suri fibers when compared at