Page 137 - Handbook of Properties of Textile and Technical Fibres

116 Handbook of Properties of Textile and Technical Fibres

4.2.2.2 Cortical cells

Cortical cells are “spindle shaped” and are aligned parallel to the fiber axis. Cortical
cells consist of several types: ortho and para, with slightly different physical and chem-
ical properties, and the less common intermediate mesocortical cells, which have a
structure that is intermediate between ortho and para. Satlow (1965) summarized
much of the morphological research carried out on cashmere prior to 1965. He
concluded from his own studies that Mongolian cashmere was bilateral and that on
average the amount of para material in cashmere was less than in wool while Roberts
(1973) found that cashmere had more para than wool (cashmere 50.4% ortho and
49.6% para compared with lambswool of similar fiber diameter 65.2% ortho and
34.8% para). Using nine samples of cashmere from China, Iran, Mongolia,
and Australia and six wool samples, Tester (1987) also reported that cashmere had
a bilateral structure like wool. Whereas his wool had a mean incidence of orthocortical
cells of 67.8% with the remainder being predominantly paracortical cells, cashmere
contained 59.8% orthocortical cells with the remainder predominantly mesocortical
cells. Tester concluded that the orthocortical proportions for the cashmere samples
were remarkably consistent given the geographical diversity of origin. Further, cash-
mere, with more mesocortical cells, had a higher microfibril packing density and order
than wool fibers of the same MFD, and this may be associated with the low crimp
exhibited by cashmere fiber.
Tucker et al. (1988) provide ortho/para cross-section stains for wool and most rare
animal fibers. Tucker et al. (1990a) studied the physical structure of a range of rare an-
imal fibers at low magnification. Cashmere and crossbred mohair samples from indi-
vidual goats, as well as a commercial cashmere sample, contained a range of structures
from classical bilateral to nonbilateral. Ortho and para-like cortical cells were present
in most of the fibers as well as cells that appeared “intermediate” between the two
types. Some fibers contained only ortho-type cells. One Angora goat/cashmere cross-
bred sample did not contain any bilateral fibers at all. Camel, Mongolian yak, guanaco,
and vicu~ na fibers all had a bilateral structure although it was less obvious with vicu~ na.
Neither mohair nor alpaca were bilateral and llama was difficult to classify.
Hudson (1992) completed a detailed study of Chinese and Australian cashmere and
Australia mohair and cashgora fibers. The incidence of ortho cells was generally lower
than reported by Roberts (1973) and Tester (1987), which may be related to different
staining techniques. All the cashmere samples displayed bilateral symmetry and
random arrangements not only between samples but also in fibers from the same fleece,
whereas Merino wool only exhibited bilateral symmetry. The cashmere and cashgora
cortex were composed of predominantly ortho and meso cells respectively: cashmere
41.5% and 36.4%; cashgora 49.3% and 31.1%; whereas wool was composed of pre-
dominantly ortho (67.4%) and para (22.6%) cells (Hudson, 1992). The two mohair
samples displayed random configurations similar to the results of earlier workers but
had a lower incidence of para cells (8.0%e10.7%) compared with cashmere (average
22.3%; range 7.0%e30.3%) and cashgora (average 19.5%; range 13.1%e25.5%).
The observations of Orwin et al. (1984) with Romney wool may be relevant to
alpaca and mohair given the similarity of diameter and extent of medullation. They