Description about Flax

1. FLAX FIBER AND
MANUFACTURING
OF LINEN YARN
Dr. Hosne Ara Begum
Associate professor and Head
Department of Yarn Manufacturing Engineering

2. The word flax is derived from the old English fleax. The
other common names of flax are- lin, llion, liner, linum,
linen, lein and lan. The other common names of flax are-
lin, llion, liner, linum, linen, lein and lan. Flax (Botanical
name: Linum usitatissimum) is a member of Linaceae
family. Amongst all natural fibers Flax is the oldest fiber
crops in the world. It is long and strong bast fiber that
comes form the outer portions of the flax stem. The flax
fiber is classified as natural, cellulosic, bast, multi cellular
fiber. Flax is also known as linen. Linen is the term
applied to the yarn spun from the flax fibers.

3. Flax is likely the oldest textile fiber known, with the
evidence of production dating 7000 years or more. In
Egyptian graves mummies have been found wrapped
in linen clothes. Flax fiber is composed of about 70%
of cellulose, it cannot provoke allergies, absorbs
humidity and allows skin to breath; therefore it is very
indicated in the manufacturing of summer articles and
many other applications.

4. History of flax:
During the seventeenth century, Linen manufacture
became established as a domestic industry in many
countries of Western Europe. Linen has been known in
civilized societies for thousands of years. Flax was
already being cultivated systematically by ancient
Egyptians, Babylonians, Phoenicians, and other
civilizations between 5000 and 4000 BC. Mummies from
the pyramids of Egypt are wrapped by linen. Cotton was
unknown in ancient Egypt until about 400 BC. The
Romans laid down precise procedures for processing flax
fibers which were hardly different, in principle, from
those used today. Linen was especially popular in the
Madder Ages. It remains to this day a highly valued
natural product.

5. Flax fibers are extracted from the stalks of the flax plant, which
may be grown either for its fibers or for its seed. For fiber
extraction, tall varieties with white to light blue flowers and a
height of 80 to 120 cm are grown. The shorter types are grown
for linseed oil. The stems are composed of 70 percent
cellulose.
Chemical composition
The chemical composition of flax fiber is as
following:
Cellulose: 75%,
Hemicelluloses, pectin, aromatics: 5%,
Lignin: 4%,
Fat/Wax: 3%,
Ash: 0.5% and
Water: 12.5%.

6. Harvesting and Fiber Extraction:
There are two ways to harvest flax, one is cutting
method other is pulling method.
Cutting method:-The mature plant is cut from the
ground with mowing mechanized equipment, and
raked with bundle.
Pulling method:- The mature plant is pull out from the
ground including the roots for targeted towards
maximizing the fiber length. It is manual and
traditional method. Nowadays, machine harvesting
methods are also used. It will then be stored by
farmers before extraction of fibers.
Roughing out: The seeds and other extraneous
material from the stems are removed by this process.

7. Retting
Tank retting
Pond retting
Field retting/Dew retting
Chemical retting
Enzyme retting

8. Dressing the flax: Dressing the flax is the term given to removing
the straw from the fibers.
Dressing consists of three steps: Breaking, Scutching, and
Hackling.
Breaking: After loosening the fibers from the wood by retting, the
process of breaks up the straw into short segments is called
breaking.
Scutching: In order to remove some of the straw from the fiber, it
helps to swing a wooden scutching knife down the fibers while
they hang vertically, thus scraping the edge of the knife along the
fibers and pull away pieces of the stalk.
Hackling: Hackling is the process of combing the scutching fibers
into spin able fiber bundles, the products are line fiber, with a
length of 45 to 90 cm. After combing the remaining other
particles and short fibers are removed, which is called hackle tow.
The line flax and also hackled tow are being spun into yarns by
using the linen spinning process.

9. Polymer system
The polymer system of flax is same as cotton
because both of fiber are constituent from
cellulose, but Flax has a long chain polymer than
cotton and its molecular weight is higher than
cotton. Degree of polymerization of flax has
18000(average) but cotton has 5000(average).
This means that every polymer chain of flax is
made up of about 18000 Cellubiose units, which is
approximately 18000μm long and 0.8 nm thick.

11. Cottonization of flax fiber: Cottonization of flax is when the
fiber bundles are broken down to their ultimate by
mechanical or chemical means. These broken flaxes are
called cottonization of flax. The length of broken ultimate
cells or individual fibers of about 25 to 40 mm in length and
these are cottonized flax.
Cottonising of flax fibre involves reducing the length of the
fibres to that suitable for cotton machinery. This is normally
done by cutting. It can be done on long-line sliver but it
appears to be more common to use the waste tow from the
hackling process as this fibre is of lower value and may be
more individualised. Cottonised flax fibre is also available by
the mechanical processing equipment developed by Laroche,
Temafa and Rieter.

12. Cottonisation by Chemical Means
Removal of the non-cellulosic components of flax involves two processes:
degumming to
remove pectic substances, and scouring for removal of residual plant material,
waxes, pectins and colouring matter. Degumming is achieved by immersion of
fibre in a hot alkali (NaOH) solution with or without the aid of other auxiliaries
such as sequestrants and surfactants. The addition of other auxiliary compounds
can aid the efficiency of the process, for example sodium pyrophosphate is used
as a chelator for metal ions and also conveys scouring properties. However it is
very costly for use in the degumming process. A less expensive option is sodium
metasilicate which acts as both a cleaning agent and emulsifier. Sodium sulphite
can be added and has a bleaching action on the fibre. A combination of all three
additives can be added to the caustic solution in order to improve degumming
and reduce cost. Sharma [16] has investigated the use of chelating agents alone
for the chemical retting of flax stems. The natural colour of flax is grey brown
caused by particles of plant tissue, gums and pectins adhering to the fibre.
Scouring is effected by boiling in a solution of sodium carbonate and surfactant,
thereby
improving the colour. Further bleaching can be achieved using hypochlorite,
peroxide or chlorite depending on the degree of whiteness desired.

13. Cottonisation using Enzymatic Methods
Water retting is deemed environmentally unfriendly due to the
polluted effluent; dew retting suffers from climatic variability
affecting quality and uniformity. Enzymes have the potential to
offer a controlled and environmentally acceptable means of
retting fibres by simulating the natural microbial retting process
in a controlled manner.
Natural retting involves degradation of the pectic substances in
the middle lamellae of the flax stem and research work has
focused on the use of commercial pectolytic enzymes. Not
having been produced specifically for the treatment of flax
fibre, the products are often complex mixtueres of enzymes
and there is usually some cellulase activity present which may
cause fibre damage. However the work of Sharma [16] and Van
Sumere [4] suggests that the presence of some hemicellulase
and cellulose activity is required in addition to the pectolytic
activity.

14. A commercial enzyme mixture, Flaxzyme, was developed by
Novo Nordisk and evaluated by Van Sumere and Sharma [5].
The mixture comprises pectinases, hemicellulases and
cellulases and produced fibre properties comparable to those
obtained for the best water retted fibre. Sharma [18] also
reported increased fibre yield and enhanced fibre quality when
using
enzymatic methods compared to conventional water and dew
retting. However due to the cost of the enzymes a commercial
enzyme retting process has yet to be developed. Akin et al [10]
has reported on pilot scale studies of enzyme retting of
commercially cleaned and cottonised flax.
Variations of enzyme application have been attempted
including crimping or pressure [10, 19]; spray techniques [9];
use of chelators [14, 15]; use of a water pre-soak [11] and
sealed storage in sulphur dioxide prior to enzyme retting [12].

15. Cottonisation using Ultrasound
The use of ultrasound in the textile industry has been of interest for many
years and is commonly used in wet textile processes and finishing to
enhance reaction rates. Ultrasound induces molecular vibration on passing
through a liquid and it is thought the resultant impact wave and cavitation
can cause cottonisation of flax fibre in water. The high energy released
weakens the bonds between elementary fibres in the technical fibre.
Sirghie et al [6] have developed a method for cottonising bast fibres using a
combination of enzymes and ultrasound, with or without an emulsifying
agent. The action of the enzymes removes the non-cellulosic compounds
from the technical fibres, the process is accelerated by the ultrasound,
thereby saving both time and energy. The emulsifying agents are used to
protect
the fibres from the mechanical damage caused during processing on cotton
spinning equipment. The process reportedly produces fibres possessing
homogeneous properties very similar to cotton fibres. Samples of flax
treated by this process have been tested and found to have a very high
degree of cottonisation. A yarn of 27Nm count has been spun comprising
60:40 flax:cotton.

16. Steam Explosion
The steam explosion technique (STEX) is based upon high temperature
chemical degumming using alkali and reducing agents. For flax ‘retting’
was developed from a patent published in the 1930s for the extraction of
fibres from agricultural wastes [7]. Kessler et al [22] have shown that STEX
treatment of dew retted flax can be controlled to give a well defined level
of treatment leading to good short fibre quality with minimum loss in
fibre yield. Technical fiber is saturated with a solution of sodium
hydroxide, surfactants and a reducing agent and treated with steam in an
autoclave at high temperature (typically up to 200 oC) and pressure (1.5
MP) for about 20 minutes to hydrolyse the pectins and other cementing
materials. Pressure may then be reduced somewhat and then suddenly
released, causing explosive decompression which bursts the fibre bundles
apart as the pressure forces the flax out of the autoclave. The cottonised
flax is rinsed and dried. The process can be adjusted to produce highly
separated, cottonised, fibres with outstanding properties but has not
found favour with commercial users.

17. Physical properties:
Length: Normally the length of flax fiber is varying from
30 to 60 cm. Commercial flax is in the form of
cemented bundles of individual fiber cell. Scutching
and hackling helps to breaks the coarse bundle of fiber
but can not separate the fiber strand into their
individual fiber cell. The length of individual fiber is
varying 6-65 mm
Strength: Flax is a very strong fiber because for its long
chain crystalline polymer system. It is stronger fiber
than cotton. It has an average tenacity about 57.4
cN/tex. It is 20% stronger in wet condition than dry.
Extensibility: The extensibility of flax, about 2%, is the
lowest of all apparel fibers.

18. Electrostatic charge: This is practically nil, since the fiber always
contains moisture.
Surface, Luster: Because of its smooth surface, linen fabric has a
subdued luster, does not soil easily, and does not shed lint.
Thermal insulation: Flax has the best heat resistance and
conductivity of all the commonly used textile fibers. Yarns and
fabrics made from the smooth flax fibers do not enclose much air
and have relatively poor insulation properties. Linen fabrics feel
fresh and cool, a distinct advantage for summer clothing.
Micro-organism: Compare to cotton flax has a high resistance to
rotting. Under severe conditions of warmth, damp and
contamination, mildews may attack the cellulose of flax, but this
resistance is high if the yarn or fabric is dry.

19. The long strands of fibre up to 1m in length, made up of strings of
ultimate fibres, are then overlapped to form a sliver. The sliver
undergoes several drafting stages using pinned gills to control the fibres
and then a final stage of drafting on a flyer rover which inserts a small
amount of twist into the strand. All this uses specialised machinery set
up to handle very long fibres. The scutched tow passes through a
breaker card followed by a finisher card. The sliver is then processed by
intersecting gills and may be combed before being drawn into a roving.
In both cases the roving packages will normally be treated chemically to
remove the gum and bleach the fibres but may go straight to the
spinning frame. The roving is then passed through a bath of cold water
with additives before being immediately drafted and spun. The bath
must be close to boiling if the flax has not been chemically treated. This
wet spinning is unique to bast fibres but is essential for the production
of fine yarns by allowing drafting of the component fibres of the original
long strands.
Yarn Manufacturing