Milling of wool

MILLING OF WOOL
By:
Prajwal Mohanta
Shreya Anand
Tanya Gupta

Wool
■ Wool is the textile fibre, which is irregular and roughly cylindrical, tapered at end and
multicellular protein hair fibre obtained from sheep and other animals. 1
■ Major varieties of wool come from Merino, Dorset, Blackface, Southdown Ewe,
Cheviot, and other breeds of sheep. 1
■ Wool is different from hair or fur because of the two distinct qualities:1
 Elasticity
 Ability to Felt
1 P. Corbman, Textiles: Fiber to Fabric, 4 ed., New York: McGraw- Hill Inc., 1967.

Characteristics of Wool
■ Readily absorb moisture.1
■ It absorbs sound. 1
■ It ignites at a higher temperature than cotton and some synthetic fibres.
■ Wool has natural affinity for the dyes. 1
■ Wool has excellent elasticity and memory and of all the natural fibres, it is the most
crease resistant fibre. 1
■ Additionally, wool is a natural resource: renewable and ecological. 1
1 American Wool, "Characteristics of Wool," Sheep Industry Association Inc., Centennial.

Structure of
Wool Fibre
■ The outer layer of the wool has a protective
layer of scales called the Cuticle cells that
overlap each other like the roof tiles. 1
■ The inner layer of the wool is called the
Cortex and this makes up about 90% of the
fibre. 1
■ Cortical cells have a complex internal
structure that includes:1
 Twisted Molecular Chain and Helical
Coil
 Microfibril
 Matrix
 Macrofibril
1 P. R. J. Lancashire, "Animal Fibers," August 2011. [Online]. Available: http://wwwchem.uwimona.edu.jm/courses/CHEM2402/Textiles/Animal_Fibres.html . [Accessed 10 March 2018].

Chemical
Structure of
Wool Fibre
■ Wool fibre is a protein known as Keratin.
Keratin is made up of amino acids joined
by peptide linkages. 1
■ In addition to carbon, hydrogen, oxygen
and nitrogen, it also contains sulphur.
These five elements are combined into 19
amino acids linked together in a ladder like
polypeptide chains.1
■ The amino acids present are mainly bulky,
due to which the wool is relatively
amorphous. 1
1 P. R. J. Lancashire, "Animal Fibers," August 2011. [Online]. Available: http://wwwchem.uwimona.edu.jm/courses/CHEM2402/Textiles/Animal_Fibres.html . [Accessed 10 March 2018]

Milling ■ This process is also known as Felting. 1
■ It is an essential process for woolen
material. 1
■ This property of wool is used in many kinds
of finishing process to alter the
appearance, body, elasticity, and the
strength of the woolen fabric.1
■ Different types of wool vary in their ability
to felt and this depends on length,
fineness, scaliness, waviness, etc. 1
1 H. K. Rouette, Encyclopedia of Textile Finishing, Aanchen: Springer Publications, 2000.

What is Milling?
■ Matting and condensing (increased shrinkage in length and width) of wool piece
goods (possibly also with a proportion of extraneous fibres) in a hot damp state,
preferably of more open carded yarns. Controlled Shrinkage. 1
■ It produces desired shrinkage and provides additional thickness to the fabric and
also give a firmer and fuller texture. 2
■ Milling is carried out in acid and/or in alkaline liquor. 1
■ Milling has two basic requirements:1
 Milling Auxiliaries
 Milling Calendar
2 P. Corbman, Textiles: Fiber to Fabric, 4 ed., New York: McGraw- Hill Inc., 1967.

Milling Auxiliaries
■ Milling auxiliaries (milling soaps) are used as the support for felt formation in the
milling of wool. 1
■ The action is based on an increase in wool suppleness and improvement of the
sliding action at the same time. 1
■ Suitable milling auxiliaries are milling soaps, triethanolamine soaps and further fatty
acids’ condensation products and alkyl naphthalene sulphonates, possibly with
inorganic and organic swelling compounds. 1

Milling Calendar
■ Special calendars for pressing the material and milling it to a smooth fabric. 1
■ Consists of a central cylinder (heated to 200°C) with several surface rollers (usually
8 in number which is either hot or cold). Temperatures and spacing are adjustable. 1

Theory of Milling
Arnold
• A process for the connection
of fibre materials and the
formation of a homogenous
top layer from loose fibre
materials by the use of friction
impact or pressure with the
assistance of heat and
moisture.1
Witt
• The reason of felting as the
flakey structure of wool in his
so called ‘mechanical sticking
theory’.1
Speakman
• Not able to find any great
difference in milling in the
presence of DFE so, from the
tests, he concluded that DFE
is not exclusively responsible
for milling. Depends upon
elasticity and regain structure
ability.1

Theory of Milling (Contd.)
Martin
•A clearly reduced felting
tendency of the wool was
observed by removing the
flakes from the fibre
roots.1
Felt Ability
•Speakman and Sun
experienced a better felt
ability in the shorter wool
fibres, while Sookne,
Bogaty and Harris
observed a better felt
ability in the longer fibres.1
Meichelbeck
•Showed that the
hydrophobic character of
the flakes has influence
on the milling process. 1

Objective of Milling
■ The object of milling is to make the fabric fuller and denser as a result of which the
woven pattern becomes more or less obscure. 1
■ Both dyed and undyed fabrics are milled.1
■ The milled cloth is suitable for producing a raised finish. 1
■ The process of Milling is generally done in stocks or on rotary machines. 1

Purpose of Milling
■ Inter fibre felting and fabric consolidation, example, preparation for raising. 1
■ Increase fabric strength. 1
■ Subduing or totally obscuring the weave structure. 1
■ Increase in fabric width and density. 1
■ Improvement in the handling of the fabric. 1

Requirements for Milling
Moisture •It helps in the extension and recovery of the
fibre.1
Heat •It helps to produce plasticity and elasticity in
the fibre which helps in milling.1
Pressure
•It causes wool fibers to move, helps to produce
contraction with subsequent extension. It
moves in the direction of root end, entangles
with other fibres and causes felting.1
1 J. T. Marsh, An Introduction to Textile Finishing, 2 ed., Great Britain: Jarrod and Sons, 1948.2018

More About Milling
■ Depending upon the intensity of the milling process, a ‘Pre-milled item’ is obtained,
whose fabric weave can be easily or perfectly recognized, or a ‘Felt’. 1
■ When Felt is obtained:1
 In a Core Felt, the fabric is evenly felted in the cross section.
 In a Surface Felt, the top of the fabric only exhibits a random layer.
■ Besides the compression of the fabric, a more or less strong matting is carried out in
milling. 1
■ Shrinkage test is conducted to know the amount of the shrinkage that happens after
process. It is conducted in small batches and relative steps are taken for the larger
rolls. 1

Process of Milling
■ The Milling process can be divided as:1
 Dirt Milling:
 Grease Milling
 Soap Milling
 Neutral Milling
 Acid Milling and Special Acid Milling processes.
 Milling of Pre- Washed Fabrics:
 Soap Milling
 Acid Milling
 Neutral Milling

Internal Parameters of Fabrics Affecting
Milling
 Flake Structure
 Hydrophobia of the Cuticle
 Longitudinal and Transverse Elasticity
 Swelling
 Fibre Length
 Fibre Fineness
 Grease Content
 Crimping
 Yarn Construction

External Parameters of Fabrics Affecting
Milling
 Moisture Content
 Weave Construction
 Mechanics
 Time
 pH
 Temperature
 Lubricants

Machines Used in Milling
Milling Washing Machines
• Developed for the reasons of efficiency in order to combine the processes of milling and washing as one
operation.1
• Fundamentally distinguished from the Cylinder Mills by the fact the tank of the machine can be filled by liquor.1
Cylinder Roller Milling Machines
• It involves the treatment in the Rotary Milling Machine, in which woolen piece goods are processed in rope form
and drawn through the machines between two rollers, where considerable pressure can be exerted by the top
roller.1
Hammer Milling
• Affects length and width.1
• The Width Milling -the pressure of the cylinders in the cylinder milling.1
• The Length Milling -compressing the fabric together in the compression channel under the effect of compression
valve.1
Quatro Stagioni
• Expresses the widest possible application of this milling for all the types of articles1

Milling Machines
Hammer
Milling
Open width
Milling
Traditional
Milling
Two Cylinder
Milling

Classification of Milling
Acid Milling
Alkaline Milling
Neutral milling (soap milling)
Milling in solvents

Alkaline Milling
■ This may be carried out with soap and soda ash or with alkali alone. For best results,
the following conditions may be used:1
 Sodium Carbonate- 6-7%
 pH- 9 to 11
 Temperature- 38°C
 Time – 2.5 hours
■ This is suitable for unscoured wool of low quality. It is not suitable for fine fabrics. 1

Process of Alkali Milling
Scouring
Warm Water
Washing
Transferring to
Milling machine
Wetted with
Sodium
Carbonate
Solution
Increasing
Temperature and
passing through
drafts
Analyzing Result
Removal of alkali
and reducing
Temperature
Final Scouring

Points for Alkaline Milling
■ Both scouring and milling can be carried out in one operation.. 1
■ There is a 30% saving of cost compared to soap milling. 1
■ No previous scouring is required.1
■ The handle of the fabric obtained after this type of milling is firm as compared to
that in the fabrics obtained after Soap Milling. 1

Soap Milling
■ It is a widely used method. For the process, the following conditions may be used:
 Soap solution- 8-10% strength
 2.5 gallons is sufficient for 100kg of cloth. (1 gallon=4.546 liters)
 Time – 3 hours
• After this type of milling, the material is given a short and warm wash to remove all
the traces of the soap. 1
• Generally used for stripped flannel, carded yarns fabric. 1

Soap Milling (Contd.)
■ Oliene types of soaps are generally preferred for maximum softness and handle but
for firmness, the Stearine soaps are used. 1
■ Temperature generally takes some time to rise so it is customary to close the
machine’s doors after first soaping. 1
■ It is better to start the process with clean clothes as dirty clothes mean more soap. 1
■ If the fabric becomes dry, small amount of the soap solution can be added and the
temperature of the lukewarm water must not exceed to avoid colour bleeding. 1

Process of Soap Milling
Scouring
Warm Water
Washing and
Hydroextraction
Transferring to
Milling machine
Adding soap and
Increasing
Temperature
Analyzing Result
Removal of soap
and reducing
Temperature
Final Scouring

Points for Soap Milling
■ Softer clothes are milled with less risk of damage. 1
■ No previous scouring is necessary.1
■ But it is slightly costly. 1

Acid Milling
■ Sulphuric acid is the best type of milling agent for this type of milling. For the
process, the following conditions may be used:
 Sulphuric acid- 0.2-0.5%
 pH- 2
 Time – 2.5 hours
But, the 0.2-0.5% Sulphuric acid is diluted with 2 pounds of dark oil, Vitriol for every
100 pounds of cloth. 1
■ After milling, the fabric should be washed thoroughly. 1

Process of Acid Milling
Scouring
Removal of Alkali
and checking
neutrality
Pretreatment with
acid water and
hydroextracting
Transferring to
Milling Machine
Addition of acid
Increase of
Temperature
Checking the
result
Removal of acid
and reducing
Temperature
NeutralizingFinal Wash

Points for Acid Milling
■ This method is used for stronger fabrics.1
■ Always employed for coloured woven goods due to less colour bleeding. 1
■ This method is useful to mill the cross breed wool which is difficult to mill with the
soap solution. 1
■ Suitable only for the animal fibres since it destroys the cellulosic fibres. 1
■ Produces unwanted harshness. 1

Solvent Milling
■ Finishing process is carried out in tetrachloroethane, in which knitted, hosiery or
woven textiles are milled with the addition of precisely metered quantities of
emulsified water, i.e. shrunk, condensed and changed in their surface structure. 1
■ The degree of milling can be precisely controlled by the quantity of water added and
treatment time. 1

Other Terms Related to Milling
■ The terms given below are the terms that are commonly used in the process of
milling. These points are briefly explained further. 1
 Beaver Cloth
 Combination Milling

Beaver Cloth
■ It is a heavy, firm- textured fabric, made from woolen yarns. 1
■ The lustrous nap of short fibres are produced by milling the cloth and raising the
fibres, which are cut, levelled and laid smoothly in one direction. 1
■ It is intended to have the appearance of natural beaver skin. 1
■ This type of cloth has a soft handle, with longer nap than that of a wool broadcloth. 1
■ It is generally used for over coating. 1

Combination Milling
■ It includes two types of milling, that is alkaline milling followed by acidic milling. 1
■ It helps in providing good felting and excellent handle. 1
■ Alkali and Acid resistant milling agents are required. 1

Bibliography
■ Corbman, B. (1967). Textiles: Fiber to Fabric (4th ed.). New York: McGraw-Hill Inc.
Retrieved March 10, 2018
■ American Wool. (n.d.). CHARACTERISTICS OF WOOL . Centennial: Division American
Sheep Industry Association, Inc. Retrieved March 10, 2018
■ Prof. Robert J. Lancashire. (2011, August).uwimona.edu. Retrieved March 10, 2018, from
Animal Fibers:
http://wwwchem.uwimona.edu.jm/courses/CHEM2402/Textiles/Animal_Fibres.html
■ Marsh, J. T. (1948). An Introduction To Textile Finishing (Vol. Second). Great Britain:
Jarrod and Sons. Retrieved March 10, 2018
■ Rouette, H. K. (2000). Encyclopedia of Textile Finishing. Aachen: Springer Publications.
Retrieved March 10, 2018

Milling of wool

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