The Processing of
Woolskins to Make Ugg Boots
Courtesy of the following CSIRO web site: http://www.tft.csiro.au/leather/ughboots.html
Woolskins are usually preserved with salt
prior to being processed by tanneries. At the tannery the skins are processed in
large vessels called paddles which vary in capacity from 3000 to 15000 litres.
In contrast to hide processing, in woolskin processing mechanical action is kept
to a minimum in order to minimise felting of the wool. Rotating blades on the
paddles move the skins slowly and gently, and processing is performed at much
higher float ratios (typically 20-35 litres of water per skin) than are used in
hide processing.
Typically it takes about 10 working days for
the skins to be tanned and finished ready to be cut into panels for ugg boots.
1.
Tanning/ Processing
Soaking
(16 hours)
The skins are rinsed in cold water to remove excess salt and dirt from the wool
and pelt. Rehydration (soaking) of the pelt takes place in a fresh cold water
float overnight.
Fleshing
The skins are fleshed using a fleshing machine which removes excess fat and
muscle tissue from the back of the skins. This allows for more rapid and
complete penetration of chemicals in the later stages of processing,
particularly during pickling and tanning.
Scouring
(30-45 minutes)
Surfactants are used at 38oC to remove dirt and grease (lanolin) from the wool.
Pickling
(16 hours)
Prior to tanning, the skins are pickled in a solution containing acid and salt.
The salt is added to prevent swelling of the skins by the acid. The internal pH
of the skins is lowered to approximately 2.8-3.0, thereby preparing the skins
for penetration by the tanning agent.
Tanning
(16 hours)
Tanning is generally achieved by using chromium salts which form cross-links
with the collagen, stabilising the skin structure and preventing putrefaction.
The tanning step is conducted at about 25oC and pH 2.5-3.0 to allow for
penetration of the chrome. Once penetrated, the chrome is fixed to the collagen
by raising the pH to about 3.6 using sodium bicarbonate, and heating to about
35-40oC. This step raises the shrinkage temperature of the skin from about 60oC
to around 100oC.
Wool
Dyeing / Fatliquoring (3-4 hours)
After tanning, the wool may be dyed a variety of colours. Wool dyeing is
performed at about pH 4.5-6 and at 60-65oC, "Pelt reserve agents"
being added to prevent the wool dye staining the pelt. After the dye is
exhausted, the pH is lowered to about 4.0 to fix the dyes to the wool, and
fatliquor is added to the bath. Fatliquors are emulsified oils which are used in
leather manufacture to lubricate the collagen fibres, allowing them to move
freely when the skin is dried, thereby imparting softness to the skin.
Drying
(4-24 hours)
Once tanned and wool dyed, the skins are then dried in heated forced-air dryers
by "toggling" the skins to a frame. Drying is conducted at
temperatures of 50-80oC.
Drycleaning
(4-24 hours)
The dried skins are "drycleaned" in either white spirit (a
high-boiling petroleum fraction) or perchloroethylene. The drycleaning removes
the natural fat and grease present within the skins.
Pelt
Dyeing / Syntanning
Once the pelt grease is removed, the skins are returned to the paddle for pelt
dyeing. This step is performed at low temperature (less than 30oC) in order to
minimise staining of the wool by the pelt dye. After pelt dyeing, the skins are
"syntanned" using synthetic tanning agents in order to give the pelts
added fullness and firmness. The skins are then redried.
2.
Finishing
Once all the tanning and processing steps
have been completed, the skins are ready for final finishing prior to being used
in ugg boot manufacture.
Staking
After "conditioning" the skins to approximately 20% moisture content,
the skins are staked in a staking machine. This softens and stretches the skin
pelt, and puts a "nap" on the pelt surface.
Combing
/ Ironing / Clipping
The wool is combed in a combing machine to remove tangles and any burrs or grass
seeds present in the wool. An iron (a hot, 150oC revolving cylinder) straightens
the wool, removing the natural wool crimp.Finally, a cylinder clipping machine
is used to clip the wool pile to the desired length, usually about 12-15 mm.
3.
Manufacturing
Panels are cut from the skins using a
"clicking press". Once cut, the panels are sewn together using
industrial sewing machines, then the sole is glued to the boot. Once this is
done, the boots are ready for sale!
..............................................................................................................................................
These
are the major stages in Wool Production:-
1.
Shearing
2.
Washing
3.
Blending
4.
Carding
5.
Spinning
6.
Weaving
7.
Fulling & finishing
8.
Chemical Finishes
Grease
wool is processed into its finished products by either the worsted or woollen
system.
·
Worsted
system
In the worst system, the wool is combed after drying.
This is method is only used on longer wools, and as a result the fibres
are laid parallel to one another.
Worsted materials normally have a smooth finish, and are extremely
durable.
Some examples of worsted products include suits, dresses, and gabardines.
·
Woollen
System
Wools
of short length are often used in the woollen system.
In this system the wool is not combed, but rather carded.
As a result, the materials are thicker, and garments look bulky in
appearance. Some examples of the woollen
products include, sweaters, and carpets.
The End Product
The many uses of wool
After the wool has been processed it is then turned into a
number of fine products. Wool is a versatile fibre that is fire resistant,
elastic , durable, and serves as a source of insulation. Wool can absorb
up to 30% of its weight in moisture which allows it to have insulating
properties.
Wool is used in such products as coats and blankets, but did
you know that wool can be used to make boots and even toys.
With so many uses, wool is considered the Michael Jordan of fibres. Fibres
are continually compared to wool because of its many strengths, such as the fact
that it is fire resistant as well as stronger than steel.
Source: The above information has been
taken from the following website: http://ag.ansc.purdue.edu/sheep/ansc442/Semprojs/wool/index.htm
