Secondary properties of textile fibres:
- Physical shape
- Elastic recovery and elongation
- Resiliency
- Flammability and other thermal reactions
- Density
- Lusture
- Colour
- Moisture regain
The fibre shapes i.e. the surface structure is important for the fibre behaviour in a yarn and
in a fabric. A rough scaly surface of wool fibres, for example, influences the felting,and
shrinkage properties of wool fabrics. The scales enable fibres to grip one another when a
yarn is spun.
The smooth, glassy surface of a fibre such as the nylon fibre, affects the lustre of the fibre. A
smooth surface will not cling to dirt so readily. The cross-sectional shape of a fibre
influences the behaviour of the fabric. A circular or near-circular cross-section (wool} gives
an attractive or comfortable feel as compared to a flat, ribbon-like cross-section {totton).
Circular fibres often have a poorer covering-power than the flatter or triangular ones~ A flat
or triangular cross-section gives more lustre. Serrated or indented cross-sections (viscose)
give better colour absorption as a result of the larger area. More colour is also needed in
the case of fine filaments. The latter also give a softer handle or feel.
Elastic recovery and elongation:
Afibre, which is subjected to a force, will stretch to a certain degree. This stretching can also beexpressed as a percentage of the original fibre length, which is the elongation. The elongation of a fibre may be measured at any specified load or as the elongation reached when the fibre
breaks.
When a fibre is subjected to a small force (or stretched to a small degree), it may exhibit
almost perfect elasticity. Elasticity is the property of a fibre to recover its original length
after stretching caused by a load.
The term breaking elongation refers to the amount of stretch that occurs to the point
where the fibre breaks. Elastic Recovery designates the percentage of return from
elongation or stretch toward the original length or measurement. If a fibre returns to its
original length from a specified amount of attenuation, it is said to have 100% elastic
recovery at X% elongation.
Resiliency:
It is the ability of a fibre to return to shape following compression, bending or similar
deformation. It is important in determining the crease recovery of a fibre or fabric, and it
plays a significant role in the rapidity with which flattened carpet pile will regain its shape
and restore its appearance.
deformation. It is important in determining the crease recovery of a fibre or fabric, and it
plays a significant role in the rapidity with which flattened carpet pile will regain its shape
and restore its appearance.
Resilience is the property of a fibre which enables it to recover from a certain load or
stretched position and flexibility is that property to resist repeated bending and folding. A
supple fibre has a low resilience and is easily compressible. A stiff fibre has a high resilience
and cannot be easily compressed.
serve as helpful guidelines in the fibre identification. Federal legislation on textile
inflammability is an important consumer issue and a variety of types of textile end-use
products must meet a specified resistance to flames.
All fibres are affected in one-way or another as they are heated. Some, like wool, begin to
decompose before melting; others, like polyethylene or acetate will soften and melt before
decomposition sets in. The behaviour of fibres on heating and their ignition properties are
of great practical importance. Indeed, fabrics should withstand the temperatures used in
ironing, laundering (with water or solvent) etc. Since synthetic fibres are thermoplastic
substances (i.e. they will soften as they are heated), this softening will largely determine
their practical usefulness.
In the presence of air, most fibres will burn. In this context, the term LOI is used. It stands for
Limiting Oxygen Index. The higher the value of LOI, the more difficult a substance will ignite
since LOI is a measure of the amount of oxygen which has to be present in the air to let a substance (continue to) burn. On average, most substances have an LOI of about 20. Efforts are made to reduce the flammability of textile materials in order to limit accidents. These efforts are The staple length of natural fibres is not an easy property to define because the fibre length can vary over a great area. A statistical interpretation of the data obtained on fibre length in a laboratory, makes it possible to determine the staple length {an average length). In order for a fibre to be spinnable, i.e. to be twistable, and therefore offer sufficient cohesion to the whole, a fibre must at least have a length of 5 to 15 millimetres. Fibres which are longer than 150 millimetres require specialized spinning machines which make the spinning process more expensive.
The most common natural fibres have a ratio length I thickness which equals one thousand
or several thousands (cotton: 1500; wool: 3000; flax: 1200). Coarser fibres such as jute and
sisal have ratios between 100 and 1000. When filaments of man-made fibres are chopped
into shorter fibres, an effort is made to bring the ratios close to those of natural fibres, i.e.
between 1000 and 4000.
Tenacity:Second necessary property for a product to qualify for textile fibre is adequate strength,
termed as tenacity. Tenacity is defined as the tensile stress expressed as force per unit
linear density of the unstrained specimen.
The strength of a fibre is generally dependent on the length of the polymer chain, the
degree of orientation of these polymer chains, the strength and types of the forces of
attraction between the polymer chains (interpolymer forces). The longer a polymer chain is,
the higher the degrees of orientation and crystallization and, hence, the stronger the
interpolymer forces. Crystalline systems feel stiff and present less resistance to repeated
bending or folding. Stronger fibres will lead to stronger yarns under the appropriate
conditions of twist.
The tensile strength or breaking load is commonly described as the force required to reach break.
In the case of a fibre, the strength is described as tenacity (specific stress at break)
mass per unit length
or several thousands (cotton: 1500; wool: 3000; flax: 1200). Coarser fibres such as jute and
sisal have ratios between 100 and 1000. When filaments of man-made fibres are chopped
into shorter fibres, an effort is made to bring the ratios close to those of natural fibres, i.e.
between 1000 and 4000.
Tenacity:Second necessary property for a product to qualify for textile fibre is adequate strength,
termed as tenacity. Tenacity is defined as the tensile stress expressed as force per unit
linear density of the unstrained specimen.
The strength of a fibre is generally dependent on the length of the polymer chain, the
degree of orientation of these polymer chains, the strength and types of the forces of
attraction between the polymer chains (interpolymer forces). The longer a polymer chain is,
the higher the degrees of orientation and crystallization and, hence, the stronger the
interpolymer forces. Crystalline systems feel stiff and present less resistance to repeated
bending or folding. Stronger fibres will lead to stronger yarns under the appropriate
conditions of twist.
The tensile strength or breaking load is commonly described as the force required to reach break.
In the case of a fibre, the strength is described as tenacity (specific stress at break)
breaking load
Tenacity = -----------------------------mass per unit length
Tenacity is expressed in terms of {centi)newtons per tex {cN/tex or N/tex).
It is important to note that the fibre strength does not always indicate comparable yarn orfabric strength. Fibres with high strength are useful in seer and lightweight fabrics. Fabrics
used in work cloths and various industrial applications are better from high tenacity fibres.
Fibre tenacity does not always reflect the actual strength of textile yarn. It is possible for
yarns to be made so that fibre slippage occurs; this does not make optimum use of the
actual fibre tenacity made both in the field of synthesis of fibres (chemical modification) and, afterwards, byusing substances which slow down or resist burning.
cellulose, which is a combination of carbon, hydrogen and oxygen. They all burn as paper or
wood, ignite readily, leave little or no ashes and release a distinctive fire smell of burnt
paper.
Fibres of animal origin also have a similar chemical composition; they all contain nitrogen
and will therefore not easily burn through. They shrivel and form charred ashes. They leave
a fire smell of burnt feathers.
Exceptions are weighted natural silk (leaves ashes which keep the form of the yarn) and
acetate where introducing acetate groups in the polymer chains makes the fibre melt
before it can ignite.
Man-made fibres based on protein burn as fibres of animal origin. Fully synthetic fibres melt
without ignition.
is the ability to cover a surface. Fabrics made with fibres of different densities will have
difference in fabric appearance, flexibility, air permeability and cover.
The density, also called volumic mass or mass density, is the mass per unit volume and has p
as its symbol. It is usually expressed in grams per cubic centimeter. Another term is specific
gravity, which is the ratio of the mass of a fibre material and the mass of an equal volume of
water (density lg/cm3). The specific gravity of a substance vis-a-vis water equals the
numerical value of the (absolute) density of this substance if it is expressed in g/cm3• Every
fibre is characterized by its density, which can be measured in various ways.
Measurement of density can be carried out with a gradient column, where the liquid in the
tube has a density which varies in height. If a fibre is dropped in the tube, it will sink to the
point at which the fibre density equals the liquid density, and remain suspended there.᷿
This experiment is based on the fact that a fibre which is submerged in a liquid with the
same density will sink nor drift but float, and that the density of a liquid can easily be
measured. Treatments for finishing fibres, can influence the results. Foreign substances on
or in the fibres must be removed before doing the experiment.
The list below gives an overview of the most important fibres and their densities.
| Textile Fibres | Fibre densities in g/cm3 | Commercial name |
| Cotton | 1.55 | Raw |
| Cotton | 1.54 | Mercerized |
| Flax | 1.5 | |
| Jute | 1.5 | |
| Wool | 1.3 | No brand |
| Silk | 1.33 | Natural |
| Silk | 1.6 | Weighted |
| Silk | 1.32 | Tussah |
| Polyester | 1.22 | Kadel, vestan |
| Polyester | 1.38 | Teryleen, Dacron |
| Viscose | 1.53 | |
| Cuprammonium | 1.53 | |
| Polyurethane | 1.15 | Lycra |
| Polypropylene | 0.9 | Meraklon |
| Polyethylene | 0.92 | Courlene |
| Polyethylene | 0.95 | Courlene X3 |
| Nylon 6 | 1.13 | Perlon |
| Nylon 66 | 1.14 | Tri-nylon |
| Acryl | 1.14-1.17 | Orion (staple/filament) |
| Polyvinyl alcohol | 1.3 | Kuralon, vinal |
Lusture:It refers to the gloss, sheen or shine that a fibre has. It is the result of the amount of light
reflected by a fibre, and it determines the fibre's natural brightness or dullness.
reflected by a fibre, and it determines the fibre's natural brightness or dullness.
Colour:Natural colour of fibres vary from pure white to deep gray, tan or black. Man-made fibres
are usually white or off-white as they are produced.
are usually white or off-white as they are produced.
absorbed depends on the relative humidity of the air.
For absorption of moisture of a fibre, the term regain is used. This is the amount of
moisture present in a textile material expres~ed as the percentage of the oven-dry weight
(dry weight) of the textile. This dry mass is the constant weight of textile obtained after
drying at a temperature of 105°C to 110°C. If B is the dry weight and A is the conditioned
weight (the weight after being in a normalized atmosphere of 20°C and 65% relative
humidity), the regain expressed in percentage will be.
A - B
Moisture Regain = ----------- X 100
B
Another relevant term is moisture content and, expressed in percentage, is:
A - B
Moisture content= ------------ X 100
B
The moisture content is the mass of moisture in a fibre and is expressed as a percentage of
the total weight. It is a measure of the amount of water held under any particular set of
circumstances. The moisture content is always lower than the regain.
the total weight. It is a measure of the amount of water held under any particular set of
circumstances. The moisture content is always lower than the regain.
Fibres can present great variations in the amount of moisture they will absorb. Wool has a
regain of 16%, cotton of 8.5%, acetate only of 6%. Fibres, which can absorb sufficient moisture,
are most suitable for processing into clothing because they will absorb perspiration from the
body and will hold considerable amounts of moisture without feeling clammy. The ability of a
fibre to a bsorb moisture will also affect the processing and finishing of fibres. Fibres which easily
absorb moisture, will therefore let dyestuffs penetrate more easily during the dyeing process.
Synthetic fibres, which often absorb little moisture, are easily washed and dried by comparison
with fibres, which absorb a lot of moisture. On the other hand, this entails the phenomenon of
electrostatic charging.
The strength of a fibre is affected significantly by the water it absorbs. Fibres, which easily
absorb moistu re, will usually be less strong when wet (except for flax an cotton) and will present
increased elongation at break. One should also realize that absorption of moisture can also
make the fibre swell to a considerable degree, which is important for fixating dyestuffs.
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