Page 256 - Handbook of Properties of Textile and Technical Fibres

230 Handbook of Properties of Textile and Technical Fibres

In view of the above discussion, it follows that the tensile behavior of cotton fiber is
influenced by a complex combination of structural features including (1) the orienta-
tion of the fibrils within the walls of the fiber, which is complicated by the decrease in
the angle of inclination from the primary wall inward, (2) the presence of the reversal
points in the secondary walls that are thought to create weak areas and potential rupture
points, (3) the areas adjacent to the reversal zones are also potential points of fiber
fracture, (4) the deconvolution process in which fiber convolutions are removed,
particularly at low stress levels, (5) the differential surface effect due to the tapered
structure of cotton fiber and its possible effect on single-fiber strength, and (6) the
differential molecular orientation along the fiber axis from the tip to the root.
The structural effects on tensile behavior discussed above will become more sub-
stantial when a comparison is made between short- to medium-staple fibers and
long- to extralong-staple cotton fibers. In a study sponsored by the Supima Associa-
tion, Elmogahzy (Foullc and McAlister, 2002) tested several cotton varieties to
determine whether the molecular weight of the cotton fiber can be correlated to fiber
tensile strength. One of the measures used in this study was the polymer viscosity
(TAPPI T230 om-89), where the viscosity of 0.5% cellulose solutions, using 0.5M
cupriethylenediamine as a solvent is measured using a capillary viscometer. It was
clearly shown that viscosity values (centipoises) are positively correlated to fiber
strength values of different cotton types. As illustrated in Fig. 7.2, the extralong-
staple (ELS) cottons such as PIMA-S10, CHINESE-S9, and GIZA70-S8 have higher
viscosity values than the medium- or short-staple upland cottons. These high values
were translated to higher values of fiber tenacity. A simple correlation analysis
performed in this study revealed a correlation of 0.85 between viscosity and fiber
tenacity, and 0.40 between viscosity and fiber breaking elongation.

45
PIMA-S10
GIZA70-S8
40 Pima-S5 & S6 CHINESE-S9

Fiber strength (gf/tex) 35 Upland cottons ACALA-S7

30

25

20
50.0 100.0 150.0 200.0 250.0 300.0 350.0
Viscosity (centipoises)
Figure 7.2 Fiber tenacity for different cotton varieties characterized by their Polymer Viscosity
(http://www.supima.com/view-reports/wear-testing/).