Physical properties of wool
Length of wool
Finesse of wool
The fineness of wool fibre shows the same type of behavior
as that of the variations in the length. Fineness also varies within one
quality or grade of wool. The fineness ranges from 10 microns to 70 microns.
Merino wool is from 10 - 30 microns. Carpet wool is from 20 - 70 microns. Finer
fibers are suitable for a fine wool yarn.
CROSS-SECTION
The shape of fibre cross-section varies greatly from circular
to elliptical.
The crimp of wool fibre contributes to spinning quality. It
varies from 0 to 30 crimps/inch, fine wools 14 to 22, medium wools 8 to 14 and
coarse wools up to S crimps/inch.
Wool strength
The strength of wool fibre is poor compared to other textile
fibres due to low orientation in the fine structure. The breaking strength of a
fine fibre varies between 4.8 to 7.1 gm. The medium fibre has the strength of 10.0
to 16.0 gim and the coarse wool has 20 to 24 gm. The tensile strength varies
accordingly and has a range of 1600 to 2150 kg/cm2.
Elasticity of wool
The elasticity and elongation of wool are its most important
physical properties. The elasticity can be measured by determining the weight
required to stretch fiber to a given amount. The ability of wool to withstand
higher load is high compared to viscose and cotton. Also, the ability of wool to
recover its original length after stretching is very high compared to other
textile fibres.
Under normal test conditions, it will recover 90%. Wool fibre
can be elongated to 30% without permanent deformation or weakening if the
duration of the strain is short.
Hygroscopic properties of wool
Wool is more hygroscopic than any of the natural fibre. The
amount of water absorbed depends on temperature and humidity conditions.
Wool can absorb as much as 25% moisture. At normal conditions, wool will absorb
12-15% moisture. At 70-80% RH, the moisture will be 15-18%
The specific gravity of wool
1.30 gm/cc.
Lustre of wool
Wools vary considerably in luster. Certain wools are
lustrous. The rough surface is due to the atmospheric influences or mildew
where the scales are partly destroyed.
The natural color of wool
The color of the wool can be white to black or brown.
Wyoming and Australian wools are white. Texas wools are ivory. South American
wools are light ivory to dirty ivory shade. The colors are mainly due to the
cortical and medullary cells.
Electric properties of wool
Wool is a bad conductor of electricity.
Thermal properties of wool
The effect of heat on wool is not noticed much up to 130°C
unless it is exposed for a long time. When heated in dry air, it begins to feel
harsh and bristle at 115°C and scorch at about 200°C.
Burning test of wool
Wool is a protein fibre. So when it is brought near the fire,
it never catches fire, but burns emitting a peculiar smell of feather burning.
