April 29, 2022
By Eman Abdallah Kamel
Eman is a writer and textile engineer. She received her bachelor’s degree in textile science from the Faculty of Applied Arts, Egypt.
Linen is very strong, highly absorbent, and comfortable to wear in hot climates. Throughout this article, flax is explained in terms of its history, fine structure, physical and chemical properties, manufacturing, use, and how linen is taken care of.
Linen
Flax fiber is a cellulose fiber derived from the stem of the flax plant. Linen yarn is woven from the long fibers behind the bark in a multi-layered stalk of the flax plant.
The woody stem and inner core (pectin), which bind the fibers together in a clump, must be removed to obtain the cellulose fibers from the plant. The cellulose fibers are then ready to be spun.
Flax is a natural fiber with high strength. It is also convenient and still widely used.
The largest exporters of flax yarns are China, Italy, Tunisia, and Lithuania, along with other high-quality linen fabric producers such as Ireland, Belgium, Poland, Austria, France, Germany, Sweden, Denmark, Belarus, Latvia, the Netherlands, Spain, Switzerland, and India.
Brief History of Flax Fibers
Archaeologists discovered the oldest flax fibers at an upper Paleolithic excavation site at Dzudzuana Cave in the eastern European country of Georgia. That fiber was kept in pollen chambers for 34,000 years.
Afterward, a 9,000-year-old linen cloth was found in Turkey. Samples of linen fabrics dating back to the ancient kingdoms of Mesopotamia were also found; they were mainly used by the rich at the time.
The ancient Egyptians loved linen fabrics and used them to wrap mummies. When the mummy of Pharaoh Tutankhamun was discovered in 1922, parts of the linen scrolls that covered his remains were almost completely preserved.
After the Romans invaded Egypt in the 4th century BC, they knew and nurtured linen. In the late Roman era in Egypt, the Egyptians were suppressed by the Romans. Then the Egyptians revolted against them—even the Islamic conquest of Egypt in 1641 AD by Arab leader Amr ibn al-Aas, whom the Egyptians called the savior because he saved them from the persecution of the Romans. At that time, the cultivation of flax trees and the manufacturing of linen fabrics flourished in Egypt.
The linen moved from the Nile Valley to Andalusia through the Islamic conquests of Spain. Linen fabrics were then spread in France and Italy. The industry developed to include tablecloths.
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Ireland became known for its fine linen fabrics during the 17th century. It maintains this reputation to this day. The Irish farmers harvest the flax before it reaches maturity; this produces fibers that produce a very fine thread. The plant never matures, so it does not produce seeds that can be used in later crops. To this day, the flax industry in Ireland is entirely reliant on the import of flax seeds.
Around 1626, linen was transported to the Netherlands by Irish settlers. Later, Linen knew his way to North America through the colonies as well. The industry of linen fabric was developed to include sailcloth, canvas, ropes, and finer linens.
In the 19th century, the invention of textile machinery led to the development of the linen industry, which increased production considerably. Linen cloth has also become accessible to all segments of society.
By the beginning of 1950, the production of linen fabrics had gradually decreased in both Europe and America due to the emergence of synthetic fibers and a lack of government support.
Micro-structure of Flax Plant Stem
Cuticle and Epidermis:
The cuticle is located at the outer part of the stem. This layer is composed of waxes, cutin, and aromatics. It is a protective barrier against water loss and the attack of microbial pathogens on the inner stem tissue. The cuticle can be easily observed by the oily red spot, which stains the wax in the cuticle with a light red color, thus providing a clear cuticle-specific mark.
A single layer of the thin-walled epidermis is bound to the epidermis in a single unit, starting as a single unit.
The cuticle is generally impervious to bacterial attack, but sometimes, some disorders and penetration of the cuticle can occur due to field-retting fungi.
Inner Core Cells:
The core central tissues are the primary xylem and other structural cells. That provides support and water delivery to the flax plant. Core cells are nearly 65%–75% of the stem material. The main sugars are glucose, a representative of cellulose, and xylose, a representative of hemicelluloses. Other carbohydrate components are present in lower quantities, such as pectin.
Lignin is chemically a phenolic polymer bound together. They are a class of complex organic polymers that form the primary structural materials in plant-supporting tissues.
Nearly all of the lignin in the linen stem is present in the core cells. Positive reactions with chlorine sulfite for syringyl lignin (dimethoxylated aromatic rings) and acid phloroglucinol for coniferyl lignin (monomethoxylated aromatic rings) indicated the presence of both types of lignin in the core cells. The lignin values for the core cells are about 25% to 30%.
Bast fibers:
The main function of bast fiber is to provide strength to the stem. Bast fibers are long, slim, and strong, specialized cells grouped in bundles in the cortex area. It is located between the cuticle and epidermis layers. These cellulose-rich cells are the source of flax fibers. These fibers are found in bundles, each with 10–30 fiber cells in the cross-section, giving about 600 fiber cells on the stem cross-section. Inside the bundle, individual fiber cells end at different points and are slightly twisted around each other, forming a kind of filament. The length of flax fiber cells ranges from 13 to 60 mm at a rate of 20 to 30 mm.
The value of cellulose in bast fibers ranges from 65% to 80%. Also, bast fibers include pectin, hemicellulose, and aromatic compounds in small amounts. Field-retted fibers showed an increase in glucose (by weight), indicating cellulose. While increases also occurred in galactose and mannose. These non-cellular sugars naturally appear to be part of the fiber. Research has proven that hemicelluloses such as galactoglucomannan and xylan are large components in flax fibers. The properties of flax, such as high moisture recovery, may be affected by the presence of these non-cellulosic carbohydrates within the cellulosic structure. Proteins and proteoglycans also bind to the secondary walls of linen fibers.
Pectin:
Pectin is a complex polysaccharide for many plant cell walls and plant tissues. Pectin is important in maintaining the structure of flax stems, and its degradation reduces the quality of flax fibers.
The percentage of pectin in flax fibers ranges from 20.5% to 34%. The levels of pectin in flax vary greatly and are affected by various factors.
Flax Properties
1. Physical Properties:
- Length: The average length of the flax fibers ranges from 15 to 30 inches. Due to the length of linen fibers, it can be gently woven to hold the ends in. Flax fibers are stronger than cotton because the highly crystallized polymer system in flax allows longer polymers to form more hydrogen bonds than cotton. Flax fibers gain strength when they are wet. Because of the alignment of the polymer in the amorphous areas of the polymer system in the wet state. The alignment increases the hydrogen bonds and thus increases the strength of the fibers.
- Color: Flax fiber color is yellowish to grey.
- Heat effect: Flax has good heat resistance due to the polymers along the fibers.
- Elastic-plastic recovery: Linen fibers are hard and inflexible due to the crystal structure of flax fibers. The crystalline structure that gives linen fibers their hardness is also the cause of the crease in flax fibers. When polymers break down, linen fibers easily wrinkle.
- Luster: Linen fiber is shiny.
- Absorption: Flax fibers are highly absorbent due to the presence of countless OH groups in the polymers. Because of the small internal polymer distances in crystalline regions, water molecules can only enter the polymer system in the amorphous regions.
- Sunlight effect: Flax fibers are not affected by sunlight.
2. Chemical Properties:
- Effect of Alkalis: Flax is not affected by alkalis, as there is no attraction between the linen polymers and alkali.
- Effect of Acids: Flax fibers are affected by acids because the acid analyzes the polymer at the glycosidic oxygen atom that binds the two glucose units to form the cellobiose (C12H22O11) unit. The linen polymer consists of a polymerization grade of about 18,000 units of cellulose.
- Effect of Bleaches: Sodium hypochlorite (NaClO) and sodium perborate (NaBO₃•nH₂O) don’t affect linen fibers as they are oxidizing bleaches.
- Pigment Ability: Flax fibers can be easily dyed. The most commonly used dyes for dyeing flax are direct, reactive, and vat dyes.
- The effect of fungi and bacteria: humidity and heat increase the susceptibility of linen to mold and damage as the fungi feed on the fibers. Flax fibers are treated with certain chemicals to protect them from mold, like copper naphthenate.
Manufacturing Process
- Cultivation,
- Retting,
- Crushing,
- Scutching,
- Spinning.
1. Cultivating
It takes about 100 days from sowing the seeds to harvesting the flax plant. Linen cannot withstand very hot weather. Therefore, in many countries, planting seeds is calculated based on the time of year when flax must be harvested due to the heat. Farmers also go back 100 days to decide when to plant. In some regions of the world, flax is grown in winter due to the heat of early spring.
When flax plants are a few inches high, weeds should be carefully removed from the area so as not to disturb sensitive sprouts. Within three months, the plants are straight, and slender stems may reach a height of 61–12 cm with small blue or white fibers.
When the stems and seeds turn brown, the plant is ready to be harvested after about 90 days. The plant should be withdrawn as soon as the brown color appears because any delay produces linen without a precious sheen.
It is imperative not to cut the stem in the harvesting process but to remove it from the ground intact. Flax quality is affected if the stem is cut because of the loss of sap. High-quality linens are harvested entirely by hand. Grasped directly below the seed heads and gently dragged. Stems are tied into bundles called beets and are ready to extract flax fibers from the stalk.
2. Retting
During the retting process, flax fibers are separated from the other parts of the stem to be spun. There are three methods of flax retting:
- The water-retting method produces the best linens. Flax fibers are soaked in water to dissolve pectin and separate the fibers. Swamps and ponds are excellent for this method.
- The dew dip method is another way to separate flax fibers. In this way, the morning dew helps to separate the flax fibers. And they are pulled as the day warms.
- Flax can also be retted by using a chemical process. But this process produces lower-quality linens.
Remember,
The retting process must be done carefully. If the flax is not completely retted, the plant stem cannot be separated from the fibers without injuring the sensitive fibers. Too much retting will weaken the flax fibers.
3. Crushing
After the retting process, flax plants are allowed to dry before they undergo a fracture process.
In the crushing process, decomposed stems are sent through grooved rollers that separate the outer fibers from the bark that will be used to make flax. This process divides the stem into small parts of the bark called shives.
4. Scutching
After that, the shives are scutched. The scutching machine removes broken shives with rotating paddles and finally separates flax fibers from the stem.
Next, the short fibers are separated to make stronger and coarser goods. Longer flax fibers, usually 12–20 cm in length, produce more luxurious fibers.
5. Spinning
Long fibers are placed through spreader machines to combine fibers of the same length and place them in parallel. The ends of the fibers overlap, creating a piece of silver. The silver passes through a group of rollers, making the roving (long and narrow bundle of flax fiber) ready for spinning.
Flax roving is placed on a spinning frame, drawn into thread, and eventually wound onto spools. On a spinning frame, many spools are filled at the same time. Fibers are formed into a continuous strip by pressing them between pulleys and combing them through fine pins.
The atmosphere inside the spinning factory should be humid and warm to make it easier for the fibers to work into yarn. Wet linen is spun, passing through a bath of hot water to bind the fibers together and thus produce fine threads. Dry yarn spins without moisture; it produces a coarse yarn used to make cheap threads.
The wet threads are transferred from the spinning frame rollers to the large drag rollers. They are then transferred to the dryers, and when the yarn is dry, it is wound onto bobbins for weaving or wound into yarn spools of different weights.
The measure of linen yarn is the cut. It is based on 453.59 g of linen weave to make 300 yards (274.2 m) of yarn equal to one cut.
Uses of Linen Fibers
Fabrics made from linen fibers include tablecloths, bath towels, dish towels, bedsheets, wall coverings, upholstery, and window treatments. Also, linen is used to make suits, dresses, skirts, shirts, luggage, canvases, and sewing thread.
Linen Fabric Care
- Linen fabrics are relatively easy to care for. It has no pilling tendency or lint. And it can be cleaned dry, steamed, or machine-washed.
- Separating linen fabrics from other fabrics of different fibers is recommended.
- Linen shrinks when washed at high temperatures; It is best to wash linen at a lukewarm temperature.
- Bleach may damage the fabric; use only a mild laundry detergent and ensure that you rinse thoroughly before drying.
- Keep the drying temperature low, and remove the clothes while they are still slightly wet.
- Linen fabrics are easier to iron when wet. Formal linen clothes often require ironing to maintain perfect smoothness.
- Place your linens in a cool, dry place. Insects like mites do not affect flax fibers.
Sources
- USDA
- https://orbit.dtu.dk/files/74573490/PhDThesis_MustafaAslan..PDF
- Linen Most Useful: Perspectives on Structure, Chemistry, and Enzymes for Retting Flax
©Eman Abdallah Kamel, 2022
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