Study Unit 5: Natural cellulose fibres: Flax

Question 1

History

Answer 1

Flax was probably the first textile fibre that human beings used. Linen is the name of fabrics produced from flax fibres. Fragments of linen fabrics dating back to about 10000 BC have been found in excavations in prehistoric lake regions of Switzerland. Very fine linen fabrics were used in Egypt for mummy wrappings between 3000 and 2500 BC. The use of flax also spread to the parts of Europe. Belgium became a very important flax growing centre. The water from the river Lys was found to be excellent for the retting of the flax, and a high quality fibre could be produced. Linen fabric was brought to Great Britain in about 1000 BC, but it was only by AD 500 that Ireland began to process flax into fine linen fabrics.
Today flax is grown for fibre in the Soviet Union, Poland, Belgium and Ireland. Linen has always been considered a prestige or luxury fibre. Production costs are high but this is compensated for linen’s cool, crisp and clean look. Linen accounts for about 2% of world’s fibre consumption.

Question 2

Fibre production

Answer 2

Flax is a bast fibre, obtained from the stalk or stem of the flax plant. The flax plant requires a temperature climate with generally cloudy skies and adequate moisture. Bright sunlight and high temperatures can be damaging. The flax plant needs a deep, rich, well-ploughed soil and only one crop in every five to seven years can be raised on a specific piece of land. This adds to the cost of linen. The flax seeds are sown by hand in April or May and the flax is harvested by the end of August (in the Northern Hemisphere). The flax plant is pulled out of the ground, usually by hand, and not cut, as this affects the quality of the fibre. The sap is lost when the plant is cut.

Question 3

Rippling

Answer 3

After drying, the plant is rippled. This means that it is pulled through special threshing machines that remove the seed balls or pods.

Question 4

Retting

Answer 4

The outer woody portion must be rotted away before the fibres can be obtained.

Question 5

Dew retting

Answer 5

The flax straw is spread out on the grass and exposed to the action of dew and sunlight for four to six weeks. This produces a strong fibre, but takes space and time, and is seldom used these days.

Question 6

Pool retting

Answer 6

The flax is packed in sheaves and immersed in pools of stagnant water. This takes two to four weeks.

Question 7

Tank retting

Answer 7

This is similar to pool retting, but the water is heated. Retting can be accomplished in a couple of days.

Question 8

Chemical retting

Answer 8

Chemicals such as sodium hydroxide (caustic soda) and diluted sulphuric acid are added to the water in the tanks. Retting is completed in a matter of hours, but the fibres can easily be damaged.

Question 9

Breaking and scotching

Answer 9

After retting the stalks are bundled together and passed between fluted rollers, which break the outer woody covering into small particles called shives. The scotching machine removes broken shives by beating or shaking the flax.

Question 10

Hackling

Answer 10

This is a simple combing process which separates the short fibres (tow) from the long fibres (line), leaving the latter in parallel formation. The process is similar to the carding and combing operation used for cotton and wool.

Question 11

Spinning

Answer 11

The fibres are now combed into a sliver, drawn out into rovings and wound onto bobbins, ready for spinning. Flax fibres are spun either dry or wet, but wet spinning gives the best quality yarn.

Question 12

Fibre properties

Answer 12

Flax has a high natural lustre. The irregular appearance of linen fabrics is a result of the fibre bundles. Linen fabrics are stiffer and harsher than cotton fabrics because the flax fibres have a higher degree of orientation and crystallinity. Crease-resistant finishes can be used to reduce wrinkling. Flax burns easily. It is a more expensive fibre compared to cotton.

Question 13

Physical structure

Answer 13

Flax fibres occur in fibre bundles. The individual fibres are about 25–40 mm in length, and a mixture of lignins, pectins and hemicelluloses cements them together. So, a process known as cottonisation breaks down the fibre bundles to the individual fibres. Flax fibres are smoother than cotton fibres. The fibres have crosswise markings called nodes or joints (Refer to figure 3.1 and 5.2). In cross-section, they are polygonal in shape (angular) and have a central canal (lumen). The diameter of the fibres is around 11–20 micrometres. The dew retted fibres are greyish in colour; the water retted fibre yellowish.

Question 14

Properties relating to durability

1. Abrasion resistance

Answer 14

The fibre has good abrasion resistance which is related to the fibre’s high orientation and crystallinity.

Question 15

2. Strength

Answer 15

Flax is very strong for a natural fibre with a tenacity of about 31–44 cN/tex, and 57 cN/ tex when wet.

Question 16

3. Flexibility

Answer 16

Flax is a stiff fibre, so flexibility is poor.

Question 17

4. Elongation

Answer 17

Flax has a low elongation (about 2–3% elongation at break).

Question 18

Properties relating to comfort

1. Moisture absorption

Answer 18

Flax fibres are more absorbent than cotton and have a moisture regain of 12%. It also has good wicking properties.

Question 19

2. Heat conductivity

Answer 19

Linen is a good conductor of heat and therefore is cool to wear.

Question 20

Properties relating to appearance retention

1. Resiliency

Answer 20

Resiliency is poor which means linen fabric will crease and wrinkle badly.

Question 21

2. Dimensional stability

Answer 21

Flax fibres do not stretch or shrink to any marked degree but, as with cotton, linen fabrics are subject to some relaxation shrinkage unless pre-shrunk during finishing.

Question 22

3. Elasticity

Answer 22

Elasticity is poor; when it is stretched by 3% its elastic recovery is only 65%.

Question 23

Properties relating to care

1. Effect of alkalis

Answer 23

Flax is not damaged by alkaline solutions.

Question 24

2. Effect of acids

Answer 24

Cool diluted acids do not damage flax. However, concentrated acids and hot diluted acids can damage it.

Question 25

3. Effect of sunlight

Answer 25

Linen is not greatly affected by sunlight which makes it a good choice for curtains.

Question 26

4. Biological properties

Answer 26

Mildew will attack damp linen fabrics. Linen is resistant to most insects. The serviceability of flax in apparel fabrics is summarised in table 5.2.

Question 27

Durability

Answer 27

Moderate

Question 28

Abrasion resistance

Answer 28

High

Question 29

Tenacity

Answer 29

Moderate to high

Question 30

Elongation

Answer 30

Low

Question 31

Comfort

Answer 31

High

Question 32

Absorbency

Answer 32

High

Question 33

Heat conductivity

Answer 33

High

Question 34

Appearance retention

Answer 34

Low

Question 35

Resiliency

Answer 35

Low

Question 36

Dimensional stability

Answer 36

Moderate

Question 37

Elastic recovery

Answer 37

Low

Question 38

Care

Answer 38

Generally, dry cleaning is recommended for drapery linens, upholstery linens and decorative linens
Washable household linen, handkerchiefs, and linen apparel can be washed easily, at the boil with alkali detergents
Linen fabrics may need frequent pressing, unless treated for crease resistance
More resistant to sunlight than cotton
Iron damp or with steam. Safe ironing temperature 232 oC Can be bleached with chlorine
Older linen fabrics may break along crease lines if folded continuously in the same place. Store linen cloths rolled up or flat

Question 39

End Uses

Answer 39

Low heat conductivity and good moisture absorption and wicking make flax ideal for warm weather clothing (eg shirts, trousers and suits).
 Flax is also used for linen (eg curtaining, upholstery, tablecloths and tea-towels). It is particularly suited for the latter as the fibres are longer than those of cotton and the fabric therefore produces less lint.