Physical properties of wool


Physical properties of wool 


Physical properties of wool

    Length of wool

  The length of wool fibres vary greatly from 3.6 cm to 35 cm. The length varies not only on different breeds but also on the same animal. The various wool fibers can be divided into three varieties ie., fine, medium and coarse. As discussed previously, fine wool varies from 3.2 cm to 10 cm. medium wool from 5 cm to 20 cm and that of coarse wool 15 cm and more. The short fibres are used for heavily felted cloths.

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.



    Crimp of wool
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. 

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