Saturday, March 1, 2014

Cellulosic Fibers (Natural) – Linen[1-3]
Art Resource

Marie-Therese Wisniowski

Preamble
This is the twenty-fifth post in the "Art Resource" series, specifically aimed to construct an appropriate knowledge base in order to develop an artistic voice in ArtCloth.

Other posts in this series are:
Glossary of Terms
Units Used in Dyeing and Printing of Fabrics
Occupational, Health & Safety
A Brief History of Color
The Nature of Color
Psychology of Color
Color Schemes
The Naming of Colors
The Munsell Color Classification System
Methuen Color Index and Classification System
The CIE System
Pantone - A Modern Color Classification System
Optical Properties of Fiber Materials
General Properties of Fiber Polymers and Fibers - Part I
General Properties of Fiber Polymers and Fibers - Part II
General Properties of Fiber Polymers and Fibers - Part III
General Properties of Fiber Polymers and Fibers - Part IV
General Properties of Fiber Polymers and Fibers - Part V
Protein Fibers - Wool
Protein Fibers - Speciality Hair Fibers
Protein Fibers - Silk
Protein Fibers - Wool versus Silk
Timelines of Fabrics, Dyes and Other Stuff
Cellulosic Fibers (Natural) - Cotton
Cellulosic Fibers (Natural) - Linen
Other Natural Cellulosic Fibers
General Overview of Man-Made Fibers
Man-Made Cellulosic Fibers - Viscose
Man-Made Cellulosic Fibers - Esters
Man-Made Synthetic Fibers - Nylon
Man-Made Synthetic Fibers - Polyester
Man-Made Synthetic Fibers - Acrylic and Modacrylic
Man-Made Synthetic Fibers - Olefins
Man-Made Synthetic Fibers - Elastomers
Man-Made Synthetic Fibers - Mineral Fibers
Man Made Fibers - Other Textile Fibers
Fiber Blends
From Fiber to Yarn: Overview - Part I
From Fiber to Yarn: Overview - Part II
Melt-Spun Fibers
Characteristics of Filament Yarn
Yarn Classification
Direct Spun Yarns
Textured Filament Yarns
Fabric Construction - Felt
Fabric Construction - Nonwoven fabrics
A Fashion Data Base
Fabric Construction - Leather
Fabric Construction - Films
Glossary of Colors, Dyes, Inks, Pigments and Resins
Fabric Construction – Foams and Poromeric Material
Knitting
Hosiery
Glossary of Fabrics, Fibers, Finishes, Garments and Yarns
Weaving and the Loom
Similarities and Differences in Woven Fabrics
The Three Basic Weaves - Plain Weave (Part I)
The Three Basic Weaves - Plain Weave (Part II)
The Three Basic Weaves - Twill Weave
The Three Basic Weaves - Satin Weave
Figured Weaves - Leno Weave
Figured Weaves – Piqué Weave
Figured Fabrics
Glossary of Art, Artists, Art Motifs and Art Movements
Crêpe Fabrics
Crêpe Effect Fabrics
Pile Fabrics - General
Woven Pile Fabrics
Chenille Yarn and Tufted Pile Fabrics

The Glossary of Terms, Timelines of Fabrics, Dyes and Other Stuff, A Fashion Data Base, Glossary of Colors, Dyes, Inks, Pigments and Resins, Glossary of Fabrics, Fibers, Finishes, Garments and Yarns and Glossary of Art, Artists, Art Motifs and Art Movements have been updated in order to better inform your art practice.

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Introduction
Now that you have read about cotton, you will discover that linen, another cellulose fiber, has many similar characteristics. However, it is not used as widely as cotton for wearing apparel, since it is more expensive to produce and moreover, it cannot be used in a great variety of fabrics.

European Linen Duvet & Shams for Bedding.


History of Linen and How It Is Processed
Traces of treated flax (from which linen is made) have been found in pre-historic Stone Age ruins. The ancient Egyptians were the first to extract the long, tough fibers from the outer stem of the flax plant and to weave it into a fine cloth. Egyptian mummies wrapped in linen fabrics can be seen in museums today.

Ancient Egyptian mummy wrapped in linen in a coffin.

The word flax is derived from the Old English, fleax. The Teutons referred to it as flakso, coming from the teutonic root fleh, to plait. Linen is the term applied to yarn spun from flax fibers, and to the cloth or fabric woven from this yarn.

In the early days in the USA some linen was produced. The fabric, linsey-woolsey, was a combination of linen and wool, which was spun and woven by early colonists.

Three year olds in the Mill Farm Girl's Gown made of striped linsey-woolsey at left and mixed wool flannel at right.

Today the flax plant is grown for fiber in Belgium, Ireland, USSR, Poland, Lithuania, Germany and elsewhere. In the USA it is grown for its seed, the source of linseed oil. Much of the linen grown in the Western world is finished into fabric in Ireland, which is often called the linen capital of the world.

When flax is grown for fiber use, the seeds are planted close together so the plant has no room to branch out and so must grow tall to produce the long fiber, which makes the linen smooth. Fibers lie in bundles in the stem of the plant just under the bark. These must be loosened from the stalk before they can be combed to make ready for spinning. Most of the fibers are between 12” (30 cm) to 20“ (50 cm) long. Very short fibers, called tow, are used for less expensive fabrics.

Harvesting bundles of flax for fiber production.

The preparation of linen for spinning and weaving is a long and tedious process. In harvesting, the flax is pulled, never cut, as the fibers extend below the ground into the roots. The flax fibers must be separated from the stem by a process called retting. The plant is soaked in a special type of soft water to loosen the outer stalk. The stems are then dried and, by a process called scutching, rollers break and discard the useless woody portions of the stalks, leaving exposed the long, smooth fibers.

The fibers are next hackled, a careful combing process, and finally arranged into continuous broad ribbons - called sliver - for spinning. Once the purified fiber is obtained, the process of making yarn is much like that used for other fibers, except that it must be kept damp constantly.

The remains of hackling will be strands of fine floss, which are now ready to be spun into linen thread.

Because the natural color of linen is tan, it is usually bleached.


Fiber Morphology
The flax fiber is classified as a natural, cellulose, bast, multi-cellular fiber. It has a fiber density of 1.50 g cm-3 and so is considered a heavy fiber. It is for this reason that most linen textile materials are of light construction. Thick linen textile materials would be too heavy to wear (see below).

The Macrostructure of Flax
The flax fiber is a thick, regular fiber with a subdued luster. It ranges in length from about 10 cm to 100 cm, averaging about 50 cm in length. As the flax fiber is a strand of cells, its thickness depends on the number of these cells in any one fiber cross-section. The flax cells are about 25 mm long and 10 – 20 microns thick. This would give an average fiber thickness ranging from about 40 to 80 micron.

A cross-section of bleached flax or linen fibers magnified 200 times. Note the polygonal cross-section of the fibers.

The monetary value of flax is directly proportional to its fiber length. Its fiber length-to-breadth ratio is therefore of considerable significance. For the longest and “best” flax this tends to be about 15000:1. Short flax fibers may have a fiber length-to-breadth ratio of 1500:1 – or less.

The color of flax varies from light blond to grey blond, the particular shade resulting from the agricultural and climatic conditions under which it was grown and the quality of retting.

The subdued luster of flax is due to its long regular fiber surface, which is coated with a film of wax. This enables a significant amount of incident light to be reflected, resulting in a subdued luster. However, when compared with that of lusterous man-made fibers the subdued luster of flax is insignificant.

The cross markings, known as nodes, on flax fibers give them their characteristic microscopic appearance. There may be up to 800 nodes in a single flax fiber cell. The length of the node indicates the width or thickness of the fiber cell. The nodes are thought to be fissures in the cell walls. Wherever a node occurs it indicates a change in spiral direction of the fibrils, which constitute the cell walls. As with the cotton fibers, such spiraling imparts strength to the cell and hence to the flax fiber.

A longitudinal section of bleached flax or linen fiber, magnified 200 times. Note the cross-markings or nodes.

The Micro-Structure of Flax
Although the flax fiber cell is covered with a wax film, this does not constitute a distinct cuticle as in the case of cotton. The cell walls of flax are constructed of spiraling fibrils composed of cellulose polymers. On the whole, the flax cell is more sturdily constructed than the cotton cell, as indicated by the former’s thicker cell walls. This explains in part the greater tenacity of flax compared with cotton.


The Polymer System
Chemically the flax polymer system is the same as the cotton polymer system – both are cellulose polymers.

Physically the flax polymer differs from the cotton polymer, in that its degree of polymerization is ca. 18,000. This means the flax polymer is made up of about 18,000 cellobiose units. The flax polymer is about 18,000 nm long and about 0.8 nm thick. This makes it the longest known, linear textile polymer. The polymer system of flax is more crystalline than that of cotton, because it is a longer polymer. These spiral about each other at approximately 6o to the fiber axis, thereby contributing to the tenacity and durability of the fiber (see below).


Properties of Flax
Flax consists of bundles of crystalline fibrils held together by an amorphous, absorbent, cellulose-like, complex matrix. As in cotton, the fibrils in each fiber are in a spiral arrangement, with the spirals changing direction at intervals.

The strength and stiffness of the highly crystalline fibrils, the extreme length of the cellulose polymers, and the moisture affinity of the matrix, combine to give flax a unique set of properties.

Cross-section of flax fibers (electron micrograph). Individual fibers are held in bundles by a gummy cellulosic matrix. Although flax can be separated into these individual fibers, in practice this is not done.

The crystalline fibrils give strength, a stiff drape (the fabric is not very pliable) and a fairly high specific gravity (the fabric is heavy for its thickness). Since flax is often spun into tight, compact yarns, linen fabrics usually are quite crisp and have a heavy drape for this reason as well (see below). A linen tea-towel feels quite different from a cotton one, and even the finest linen handkerchief has a stiff body.

Due to its crystallinity, polymer length, and effective holding power of the matrix complex, linen is strong and so can withstand repeated laundering with minimum shedding of fluff and lint. This explains its popularity for table, bed and tea-towel linen.

As in cotton, the spiralling of the fibrils in the fibers means that when flax expands with moisture, it becomes stronger. The increased wet strength of flax, as well as the ease with which it can be spun into yarn, made it an ideal fabric for sails.

Linen sails on a Schooner.


Micro and Physical Properties
Elasticity and Resiliency
Linen is less elastic than cotton and so wrinkles easily. A crease-resistant finish is desirable.

The very inelastic nature of linen is due to its very crystalline polymer system. It tends to lock its polymers into position with the aid of countless hydrogen bonds, which form between the polymers. Hence, the polymers cannot yield, and they resist being displaced from their positions in the polymer system.

The unyielding nature of the very crystalline polymer system gives flax fiber its stiff handle (see above). Flax will resist being flexed or bent. As with cotton, the crispness of its handle is due to its ability to absorb moisture rapidly.

The ready wrinkling and creasing, which occurs with linen textile materials is also due to the very crystalline polymer system of the flax fibers. When these are bent or flexed, their polymers are liable to break leading to fractures in the polymer system. These fractures become weak areas on the fiber structure, leading to wrinkling and creasing the linen textile material.

Fiber Strength
Stronger than cotton it is not affected by water. It is not elastic, so it may wear along folded lines.

Microscopic Appearance
Flax fibers appear like bamboo under the microscope. They have crosswise markings that appear like joints or nodes (see above).

Moisture Absorption
Absorbs moisture even more readily than cotton. A good summer fiber because it feels cool.

Natural Body
Good linen is crisp and leathery in feel and cool to touch. Starching is seldom needed.

Tenacity
Flax is a very strong fiber because it is a very crystalline polymer system which permits its extremely long polymers to form more hydrogen bonds than cotton polymers.

Thermal Properties
Flax has the best heat resistance and conductivity of all commonly used textile fibers. The most satisfactory explanation lies in the long polymer chains, which have the ability to absorb thermal agitation via their 3N-6 vibrational channels (where N is the number of atoms in the polymer system).

Washability
Washes like cotton except that it is best ironed quite damp with a hot iron.


Chemical Properties
Owing to the similar chemical constitution of cotton and flax, the explanation offered for the chemical properties of cotton equally apply to flax (see post on Cotton).

Nevertheless, it needs to be remembered that linen textile materials are not mercerized. Normal laundering will result in alkaline hydrolysis of the waxes and gums that bond the cells forming the flax fiber together. This results in cell ends projecting above the surface of the linen material and is referred to as cottonizing of linen. Severe cottonizing will cause a noticeable weakening of the linen textile material.


Finishes
Beetling is a common finish for linen. The surface of the fabric is beaten with great wooden blocks, which flatten the yarns so more light is reflected. The linen fabric therefore has greater luster. Ironing on the right side maintains this luster.

Wrinkle-Resistant
These treatments are common. Resin finishes cut down on moisture absorption and make the fabric warmer. However, most people prefer this to the usual wrinkling.

Shrinkage Control
Treatments of several types are often applied to linen fabrics for clothing use.

Bleaching
It is necessary if white linens are desired. Bleaching always weakens a fabric somewhat, but linen is so strong that correct bleaching tends not to be too injurious.


References:
[1] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).
[2] A Fritz and J. Cant, Consumer Textiles, Oxford University Press, Melbourne (1986).
[3] E.J. Gawne, Fabrics for Clothing, Chas. A. Bennett Co., Inc., Peoria, Illinois (1973).

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