Introduction to Textile Fiber.pdf

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3
General introduction of textile fiber
Classification, Properties and Product
Uses of Textile Fibers
Texitle fibres
Spinnability: It is the comprehensive effect of
various properties of textile fibers, mainly including
the surface morphological characteristics such as fiber
length, linear density and curl degree. Physical and
mechanical properties such as strength and elongation,
modulus, electrostatic characteristics and friction;
Chemical stability and dyeing resistance.
 Usage: beautiful, comfortable, safe and
durable.
Fiber: a thin strip of material with a certain length and flexibility, the ratio of
length to diameter is generally greater than 1000 (except that the ratio of
length to diameter of Indian cotton is 850:1) 。
1. Characteristics of textile fibers

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fibre
Texitle
fibres
Nonwoven
fiber
Natural
fiber
chemical
fibre
Plant fiber: cotton and hemp
Animal fiber: silk, wool, etc
Mineral: asbestos, etc.
Inorganic fiber: such as glass fiber and metal fiber.
Regener-
ated fiber
Regenerated protein fiber: soybean protein fiber, etc
Regenerated cellulose fiber: viscose fiber, cuprammonia
fiber, etc.
Cellulose ester fiber: diacetate fiber, etc.
synthetic
fibre
Heterochain
class
Polyester fiber (polyester)
Polyamide fiber (nylon)
Polyurethane elastic fiber (spandex)
Others: polyurea, polyoxymethylene, polyimide,
polybenzimidazole, etc.
Carbon
chain
Polyacrylonitrile fiber (acrylic fiber)
Polyvinyl acetal fiber (vinylon)
Polyvinyl chloride fiber (PVC)
Polyolefin fiber (such as polypropylene fiber, etc.)
Others: fluorine-containing fibers, etc.
2. Classification of textile fibers

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The use performance of textile fibers has different requirements according to
the different uses of textile products, such as clothing textiles, decorative
textiles and industrial textiles.

2023/12/17
Textile fiber Properties
Common cloth
Elasticity, elasticity, dimensional stability, hygroscopicity, water
repellency, air permeability, warmth retention and insulation of common
clothing materials. thermal, antistatic, flame retardant, antibacterial,
insect-proof, fire safety
Special fabrics
light-resistant, weather-resistant, heat-resistant, wear-resistant,
waterproof, fireproof, high-strength, and fireproof，radiation, high
modulus
Decorative
articles
flame retardancy, heat insulation, sound insulation, antistatic property,
mildew resistance, antibacterial property and wear resistance.
Industrial
products
high strength, high modulus, high temperature resistance, corrosion
resistance, impact resistance, super water absorption and high heat
insulation, properties, high separation, light weight, aging resistance and
fatigue resistance
Biological
products
biological hygroscopicity or decomposition, permeability and selectivity
of medical supplies
Military supplies
Heat resistance, fire resistance, wear resistance, permeability, light
weight, radiation resistance, weather resistance and chemical stability
Requirements for fiber properties of textiles with different uses

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There is a very close relationship between fiber and the service performance,
aesthetic characteristics and economy of textile products.
Relationship between fiber quality and product performance
fiber quality Performance of textile products
fineness
Thickness, rigidity, flexibility, elasticity, wrinkle resistance, air
permeability, fuzzing and pilling
Section shape Gloss, coverage, warmth retention, fuzzing and pilling, hand feel
length Thickness, fuzzing and pilling, etc
Curliness Quality, luster, elasticity, warmth retention and air permeability
relative density Quality and coverage
strength Strength, fuzzing and pilling, durability
Initial modulus Elasticity, dimensional stability, etc
Hygroscopicity Moisture absorption and permeability, dimensional stability
Electrical performance Wear resistance, dirt absorption and pilling
Thermal performance Warmth retention, dimensional stability and flammability
Dyeability Possibility of color and composition pattern

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1.The length of the fiber
 Silk is the longest, so called filament, can be used directly for weaving without
spinning.
 Cotton, hemp, wool, etc. are called short fibers
 Wool is longer, generally over 50 mm in length and up to 300 mm in length.
 Cotton fiber length is short, fine velvet cotton is generally less than 33 mm, long
velvet cotton is generally less than 50 mm, length of more than 50 mm for extra-
long wool cotton.
Straightening length: length in a fully straightened state
Natural length: projection length
Straightness: The ratio of natural length to straightening length
Concept
The length of cotton fibers varies by origin:
Indian cotton 12.7 to 15.9 mm, Egyptian cotton 27.0 to 34.9 mm, island cotton 38.l to
44.5 mm.
The physical properties of textile fibers

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1.The length of the fiber
The cut-off length of a chemical fiber is determined by the machine desktop and the
length of the fiber mixed with it:
The length of chemical fibers mixed with cotton is 35 to 38 mm and is called cotton chemical
fiber.
The length of chemical fibers processed on the wool spinning machine is similar to the length
of wool, the rough comb wool spinning is 64 to 76 mm, and the combing wool spinning is 76 to
114 mm, known as wool chemical fiber.
Using existing cotton spinning machine or chemical fiber special textile equipment processing
51 to 76 mm length of various chemical fibers pure or blended, called medium-length fiber
spinning.
Expressed in body length or average length. Uneven fiber
length can be expressed in neatness. There is a relationship
between the length and fineness of natural fibers.
The relationship between fiber length and yarn quality is large.
Within a certain range, the length increases and the yarn
increases strongly. Long fibers can be spinning into thinner
yarns.
Charac-
teristics
influence

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2.The fineness of the fiber
Fineness: Expressed (fibre) by mass-line density per unit
length. The statutory unit is special (Tex), chemical fiber, silk
use, but not the statutory unit. Foreign trade is sometimes use.
 Special (tex) popular title number, refers to the fiber in the fixed return rate,
1000 meters length has the quality (g).
 1 tex = 1 mg/m 。
 Denier/Dan (Denier, D): Refers to the mass (g) of fiber at a fixed return rate of
9000 m in length.1tex = 9denier ； 1 dtex =0.9 denier 。
 The units of the branch number are imperial branch number and metric branch
number, imperial branch number is eliminated, the metric branch number is the
length of 1 gram of heavy fiber, the countdown to the line density.
Measurement method: weighing method, airflow instrument method, projection diameter
method, etc. (self-study).
Concept

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3.Fiber cross-section and longitudinal morphological structure
Structures, fine gaps and holes that
can be seen with an electron
microscope.
Microscopic morphological structure
Structures, longitudinal surface
features, longitudinal shapes, cross-
sectional patterns that can be seen
with optical microscopes.
Macro-morphological structure
Many fibers have a special portrait appearance (Lengthways Appearance) and Cross
Section View, and understanding these shape characteristics is important for analyzing
fiber properties and identifying fibers.

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4.Fiber curling performance
Curl (crimp) can make short fiber spinning to increase the friction
between fibers and holding force, so that yarn has a certain strength.
It also improves the elasticity of fibers and textiles, making the feel
soft and accentuates the fabric's style. It has an effect on the fabric's
wrinkle resistance, warmth and surface gloss improvement.
 The curling properties of fibers can be characterized by
curlyness, curly number, etc.
 Cotton in natural fibers has natural curls, wool has natural
curls.
 General synthetic fiber surface smooth, fiber friction is
small, poor binding force, spinning processing difficulties,
so in the post-processing to use mechanical, chemical or
physical methods, so that the fiber has a certain curl.
concept

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4.Fiber curling performance
 The curlyness index that characterizes short fibers:
0
L
2
1
/cm


弯折点个数
）
卷曲数（个
Medium: L0 - the length of the fiber
at a pre-added tension of 1.26 × 10-
3 dN/tex.
%
100
L
L
L
0
0
1



卷曲率
Medium: L1 - Load 8.8× 10-2 dN/tex
and maintain the fiber length measured
after 1min.
Curling elastic recovery rate
Medium: L2 - Remove the load to relax the fiber by 2 min and then add the fiber length
measured by pretension.
Curl recovery rate %
100
L
L
L
1
2
1



卷曲回复率
%
100
L
L
L
L
0
1
2
1




卷曲弹性回复率

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1、the air humidity of the representation method
Moisture absorption of fiber materials (Hygroscopicity)
 Textile fibers placed in the atmosphere with the absorption and release of
moisture performance called textile fiber moisture absorption.
 The return rate of fiber and textile has a great influence on strength, and causes
the phenomenon of "shrinkage", which affects electrical performance and
wearing comfort.
(1) Water vapor pressure E: wet air is seen; A mixture of rational gas and water vapor,
in which the pressure of water vapor indicates the humidity of the wet gas
(2) Absolute humidity H (absolute humidity): the mass of water contained in the air
per unit volume.
(3) Relative humidity RH: Absolute humidity H vs. absolute humidity Hs at
saturation at the same temperature.
Moisture absorption of textile fibers

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2. Standard atmosphere
The standard atmosphere, also known as the standard state of the atmosphere, has
three basic parameters: temperature (20 degrees C), relative humidity (65%) and
atmospheric pressure (101.3 kPa).
3、The phenomenon of moisture absorption of
fibers and its characterization
① Moisture rate R: The percentage of moisture weight contained in
textile materials to dry weight of textile materials.
② Moisture content M: Percentage of moisture weight in textile
materials to wet weight of textile materials.
%
100
0



G
G
G
R
0
0
100%
G G
M
G

 
Type middle: G0 —— Wet and heavy textile materials; G —— The textile material is dry and heavy.
(1) The method of representing the
amount of moisture absorption

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③ Criteria Moisture Regain: The equilibrium return rate measured by textile
materials from the time of moisture absorption to equilibrium under standard
atmospheric conditions.
④ Actual Moisture Reflux Rate: The return rate of fiber products under the actual
environmental conditions. The actual return rate only indicates the actual
moisture content of the material.
⑤ Public return rate: in order to weigh and nuclear price needs, the state uniform
provisions of the return rate of various textile materials.
 For trade, pricing, inspection and other needs to determine the rate of return, purely for
the convenience of work.
 It represents the percentage of water added to the drying mass to the drying mass when
converting the fair (commercial) quality.
 Usually the rate of fair return is higher than the standard rate of return or the upper limit.
The rules on the rate of public reflux are not consistent.
Standard weight: Is the weight of textile materials at a fixed return rate.
3.The phenomenon of moisture absorption of
(1) The method of representing the
amount of moisture absorption

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(2) The moisture absorption
process of the fiber
① The type of water molecule absorbed
Depending on how water molecules exist in fibers, they can be divided into:
 Combined with water: Water absorbed due to the polarization of polar groups in
fibers is directly adsorption water, single-molecule adsorption layer. Absorption
of water is the main cause of fiber moisture absorption. Water molecules
adsorbed due to the action of hydrophilical groups in fibers. They combine
strongly, mainly hydrogen bonds, and emit more heat.
 Indirect adsorption of water: When the fiber monomolecular layer adsorption
reaches saturation, the water molecule continues to enter the cell gap of the
fiber, because the water molecule of the single molecular layer continues to
indirectly adsorption water molecules, so that the water molecular layer
thickens, forming a multi-molecular layer.
 Capillary water: Fiber has many fine holes, because of the role of capillary pipe
to absorb water called capillary pipe water.

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② Moisture absorption process
It is generally believed that when the fiber absorbs moisture, the water
molecules first absorb to the surface of the fiber, and then the water vapor spreads
to the inside of the fiber, binding with hydrophilic groups on the macromolecules
in the fiber, and then the water molecules enter the gap holes in the fibers, forming
capillary water.

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③ Damp heat absorption
Fibers absorb moisture along with the release of heat, which is
called hygroscopic heat.
 Absolutely dry fibers in the hygroscopic process, initially release the maximum
amount of heat, and then gradually reduce, and finally equal to zero.
 The heat emitted when 1g fiber is completely wet is called Integral Sorption
Heat.
 The thermal effect of 1g of water removed from a large amount of dry or wet
fibers is called differential adsorption heat.
concept

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④ Moisture absorption isotherm
The fiber with a certain return rate is
placed under a new atmospheric condition,
it will immediately wet or absorb moisture,
after a certain period of time, its return rate
gradually tends to a stable value, called the
Balanced moisture regain. Under certain
atmospheric pressure and temperature
conditions, the relationship curve between
the Balanced moisture regain of fiber
material due to moisture absorption
(wetting) and the relative humidity of the
atmosphere.
concept

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The same fiber in a certain
temperature and humidity
conditions, from wet to
balance and from moisture
absorption to balance, the
two balance return rate is
not equal, the former is
greater than the latter, this
phenomenon is called
moisture absorption lag.
(3) Hygroscopic lag
concept

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 Moisturizing and pre-humidifying:
Humidification: textile materials have a certain degree of moisture absorption, so
before the experiment, it is necessary to put the specimen unified in the standard
state for a certain period of time, so as to achieve a balanced return rate.
Pre-humidification: In order to avoid the error caused by the hygroscopic hysteria of
the fiber, the material should be dried at a lower temperature (generally 40 to 50
degrees C down to wet 0.5 to l h), so that the return rate of the fiber is much lower
than the return rate required by the test. Then in the standard state, the equilibrium
return rate is reached.
 Workshop temperature and humidity regulation:
For example: when the fiber is wet, the RH% of the workshop air (the specified
value, and when the fiber is in the hygroscopic, the RH% of the workshop air)the
specified value.
Reason
Applica-
tion
The hygroscopic process forms a new hydrogen bond, which frees less hydroxyl.
Desorption process, amorphated area fiber molecules have the tendency to form
crosslink points, by internal resistance resistance, fiber molecular distance can not
be fully restored to the pre-absorption state.
(3) Hygroscopic lag

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3.The phenomenon of moisture absorption
of fibers and its characterization
(4) Factors affecting the
hygroscopicity of fibers
 Time: exponential process;
 Temperature: two factors;
 Air velocity: high velocity, less moisture absorption;
 Fiber structure:
Hydrophilic group; Crystallinity; Fiber internal void; Surface adsorption;
Companions and impurities:
a. There are nitrogen-containing substances, cotton wax, pectin, fat, etc. in cotton fiber, among which
nitrogen-containing substances and pectin can absorb water more than their main components, while wax
and fat are not easy to absorb water. Therefore, the higher the degrease degree of cotton fiber, the better its
moisture absorption ability;
b. The grease on the wool surface is a water-repellent substance, and its existence weakens the moisture
absorption ability;
c. pectin of hemp fiber and sericin in silk are beneficial to moisture absorption;
d. The properties of oil on the surface of chemical fiber will cause the change of moisture absorption
capacity. When the hydrophilic groups of oil surfactant are oriented towards the air, the moisture
absorption of fiber will increase.

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4.Fiber swelling (1) The anisotropy of fiber swelling
Fibers are absorbed and accompanied by an increase
in volume, a phenomenon called swelling. The
phenomenon of a much larger increase in fiber
diameter than a length increase is called anisotropy of
swelling.
Diameter swelling: d
d
S
d


Length swelling: l
l
S
l


Section swelling: A
A
S
A


Volume swelling: V
V
S
V


concept

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4.Fiber swelling (2) Changes in the properties of
fibers after swelling
 Impact on weight: increase;
 Effect on length and cross-sectional area: the volume expands after the fiber
absorbs moisture, the lateral expansion is large and the vertical expansion is
small, showing obvious anisotropy. The expansion of fiber is caused by the
weakening of the interrelation between the molecules of the amorphous region
after the fiber absorbs moisture, and the increase of the range of motion of the
macromolecular chain segment of the amorphous region. The crystallization
part limits the swelling of the fiber, so the fiber in the water only limited
swelling. The same fiber can judge the orientation of macromolecules
according to the size of the anisotropy after the hygroscopic expansion.
 Effect on density: W increase, fiber density increase; Most fibers have the
highest density at W - 4 % to 6 % . W increases again, and the fiber density
gradually becomes smaller, because the fiber volume expands significantly, and
the water weight is smaller than the fiber.

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 Effect on mechanical properties: After the fiber absorbs moisture, its mechanical
properties such as strength, elongation, elasticity, stiffness and so on change.
• The general rule is that W increases and its strength decreases: this is because water molecules enter the
amorphous zone inside the fiber, weakening the binding force between macromolecules, making it easy
for molecules to slip under external forces. The degree of force degradation depends on the internal
structure of the fiber and how much moisture is absorbed. Because the polymerization of large
molecules is low, the crystallization is also low, fiber fracture is mainly manifested in the slip of large
molecules, and the weakening of macromolecular binding force after water molecules enter is also
significant, so the strong drop after moisture absorption is very significant.
• Poor absorbent ability of fiber, W increase, strong change is not significant, synthetic fiber because of
the ability to absorb moisture is weak, so the reduction of strength after moisture absorption is not
obvious.
4.Fiber swelling
(2) Changes in the properties of

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 Effect on mechanical properties: After the fiber absorbs moisture, its mechanical
properties such as strength, elongation, elasticity, stiffness and so on change.
• Cotton, hemp fiber, moisture absorption strength increased: this is due to cotton and hemp fiber
polymerization is very high, crystallization is also very high, fiber fracture is mainly manifested in the
large molecule itself, and water molecules into the large molecule binding force is not significant, and
mainly shows that water molecules can enter some large molecular chain entanglement is removed,
molecular chain stretch and force molecular chain increase, the average burden of fiber on the external
force, so that the fiber is strong.
• Influence on fiber elongation: With the increase of W, the elongation increases. This is because after
water molecules enter the fiber, the binding force between macromolecules is weakened, which makes
it easy to straighten out and produce relative slippage when subjected to external force. Brittleness and
rigidity of fiber are reduced, plastic deformation is increased, and friction coefficient is increased.
4.Fiber swelling
(2) Changes in the properties of

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After moisture absorption, the interrelation between amorphous region
molecules was weakened, which was caused by the increase of the
movement range of macromolecular segments in amorphous region.
However, the crystallization part limits the swelling of the fiber, so the
fiber only swells in water in a limited way, not in an infinite way.
4. Swelling of fiber (3) Causes and functions of swelling
Cause
Funct-
ion
 Thicken and harden the fabric.
 Causing fabric shrinkage, wet
shrinkage is called shrinkage.
 In dyeing and finishing, after the
fiber swells, the micro-gap
increases, and dye molecules or
auxiliary molecules can diffuse
into the fiber.

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1. Related terms
The mechanic properties of fibers refer to various behaviors under
the effects of stretching, compression, bending, shearing and twisting.
Microscopically, it can be regarded as the performance of molecular
motion in the force field.
 Tensile stress: the direction of stress is perpendicular to the
stressed surface;
 Shear stress: the direction of stress is perpendicular to the
stressed surface;
 Deformation: the change of the present situation or size of an
object under the action of the balance force;
 Strain: The deformation per unit length is relative deformation.
F
F
θ
F
F
The mechanics of textile fibers

Y
B
C
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3
2.The stretching properties of fibers
Study fiber stretching performance with stress-strain experiments to
determine its strength, hard and soft, brittle.
(1) Typical stress-strain curve of fiber
 Y point used to be an elastic area, which can be restored to its
original state.
 After y point, it is plastic, which can not be restored to its original
state, permanent deformation occurs, and the material yields.
 Y point is the yield point, and the corresponding stress and strain
are yield stress and yield strain.
 YB segment is called strain softening.
 BC necking stage.
 Ct segment orientation sclerosis.
 T fracture occurs, and the stress is tensile strength.

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2.The stretching properties of fibers (1) Typical stress-strain curve of fiber
Y
B
C
When the stress exceeds the tensile strength of the t, the fiber is
pulled and destroyed. There are two ways to destroy:
 Brittle Rapture: The fiber has little
deformation before breaking, and breaks
before the yield point, with a smooth
fracture surface.
 Plastic Fracture: the fiber is deformed
greatly before failure, and there are
obvious yield points and Necking
phenomena in the stretching process, and
the fracture surface is rough.。

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• How to distinguish between fracture forms？
------ The key is to yield：
The pre-yield fracture is brittle fracture.
Post-yield fracture is ductile fracture.
brittle
fracture
Pre-yield
fracture
Plastic-
free flow
smooth
surface
Tensile stress
component
Ductile
fracture
Post-yield
fracture
Plastic
flow
Surface
asperities
Shear stress
component

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3
Brittle fracture Ductile fracture

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A
A
E








Breaking point B
point: Breaking
point
A :Elastic limit strain A:Elastic limit stress
B :Elongation at break B:Breaking strength Y :Yield stress
Yield limit Y point:
Yielding point
Elastic limit point
A point: Point of elastic limit

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3
(1) Hard and brittle
(polystyrene, PMMA, etc.)
(2) Hard and tough
(nylon etc.)
(3) Hard and strong
(blend of PVC and PS)
(4) Soft and tough
(rubber)
(5) Soft and weak
(random PP)

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Mechanical type
of polymer
Soft and
weak
Soft and
tough
Hard and
brittle
Hard and
strong
Hard and
tough
Polymer stress
—— Strain curve
Modulus
(Rigid)
Low Low High High High
Yield stress
(strength)
Low Low High High High
ultimate strength
(strength)
Low Medium High High
breaking
elongation
(ductility)
Medium
According to
yield stress
Low Medium High
Area under
stress-strain
curve (toughness)
Low Medium Low Medium High
Charact-
eristics
of
stress-
strain
curve

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3
(1) Typical stress-strain curve of fiber
Microinterpretation of stress-strain curves:
 ab: the bond angle and bond length of macromolecule
change, and the ratio of strain to stress is called initial
modulus;
 bc: yielding does not change the relative displacement
of molecular chain centroid, and with the increase of
stress, the fiber relaxation time decreases
correspondingly;
 cd: With the orientation of stretching direction, the
center of mass changes its relative displacement and
tends to be arranged in parallel, which mainly occurs in
amorphous region, and the deformation ability
decreases and the stress increases sharply.
 de: There is enough energy to overcome the
intermolecular force in the crystallization region and
perform secondary shaping until the fiber breaks.

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(2) The strength of the fiber
Strength refers
to the ability of
matter to resist
destruction
Tensile
stress
Tensile-
strength
Bending
moment
Bending
strength
Compress
-ive stress
Compressiv
e strength
Tensile
modulus
Flexural
modulus
Hardness

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3
 Generally, the strength of fiber material refers to the maximum external force that it can
bear to resist damage. Macroscopically, it is irreversible and irreversible. From the
microscopic point of view, it is the large-scale destruction of one or several kinds of
bonds.
 For fibers, the most important bond types include intermolecular forces, namely Van der
Waals forces, hydrogen bonds and covalent bonds. The bond energies of the three
compounds are 4 ~ 21 kj/mol, 8 ~ 42 kj/mol and 290 ~ 420 kj/mol, respectively.
 Theoretically, the maximum stress that a polyethylene molecular chain can bear is
2.5×106 N/cm2 (25 MPa). This value is 15 ~ 20 times of the actual strength of the best
sample at present.
① Theoretical strength
The ability of fibers to resist fractures is called the strength of fibers.
concept

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3
② Fiber fracture mechanism
The possible mechanism of polymer fracture under stress is as follows:
 Firstly, the hydrogen bond or van der Waals force in the non-oriented part is destroyed,
 Subsequently, the stress concentrates on the oriented main chain, causing the covalent bond to
be destroyed.
 With the constant destruction of Van der Waals force and covalent bond, the tensile object is
finally destroyed. The reason for that great difference between actual strength and theoretical
strength of polymer.
Chemical bond
destruction
Intermolecular slippage Van der Waals force or hydrogen
bond destruction

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3
③ The main factors affecting the actual strength
 Fiber structure (chemical structure, relative molecular weight,
crystallization and orientation, fiber structure defects)
 Test conditions (ambient temperature, humidity, strain rate, sample length,
number of samples, etc.)
All the factors that are conducive to improving the elastic modulus of
the material, increasing the surface function of the fracture process and
increasing the molecular stability all make the strength of the material
increase.
All factors that make the material form weakness and increase the
unevenness of stress distribution reduce the strength of the material.

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3
 Chemical constitution
• The strength of the material depends on the primary and secondary keys, so the chemical
structure is the fundamental factor affecting its strength.
• The main chain contains high polymer of aromatic rings, which is higher in strength and
modulus than the main chain of fat family.
• Increasing the replacement of the base polarity or producing hydrogen bonds increases the
strength, and the denser the polar group or hydrogen bond, the higher the intensity.
 Molecular weight
• Molecular weight is a structural parameter that plays a decisive role
in the mechanics of polymer materials (including strength, elasticity,
toughness);
• Different polymers require different minimum polymerization;
• Exceeding the minimum polymerization, as the molecular weight
increases, the strength of the material gradually increases. But when
the molecular weight is quite large, the strength of the material
mainly depends on the size of the chemical bond energy, no longer
rely on the molecular weight and change.

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3
 Crystal
• The main influencing factors are crystallization, grain size and crystal structure.
• The crystallization increased, and the yield strength, fracture strength, hardness and elastic modulus
of the material were all increased, but the rupture elongation and toughness decreased.
• Uniform small ball crystals can improve the strength, elongation, modulus and toughness of the
material, while large spherical crystals will reduce the ruptured elongation and toughness;
• The straightening chain crystal has the greatest tensile strength, the second-highest string crystal, and
the smallest ball crystal.
 Cross-linked
• Crosslinking can improve the anti-creep ability of materials and
improve the fracture strength.
• Moderate cross-linking strength increases, and excessive crosslinking
can make the material fragile.
0 100 200 300 400 500
 /%
大球晶
均匀小球晶

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3
 Trend
• The orientation makes the mechanical properties anisotropic and enhanced in the
orientation direction;
• For brittle materials, the strength, modulus and elongation parallel to the orientation
direction increase, while the strength and elongation perpendicular to the orientation
direction decrease.
• For plastic and easily crystallized materials, the strength and modulus parallel to the
orientation direction increase, while the strength perpendicular to the orientation direction
decreases and the elongation increases.
 The effect of temperature and deformation rate
• With the increase of temperature, the yield strength of the
material decreases obviously, which has little influence on the
fracture strength.
• The yield strength increases with the increase of tensile rate.

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3
④ The tensile strength of common fibers
Fiber variety
Fracture strength
（N/tex） Fiber variety
Fracture strength
（N/tex）
Dry Wet state Dry Wet state
dacron
High strength
and low
elongation type
0.53-0.62 0.53-0.62 Fuxian 0.31-0.40 0.25-0.29
conventional
type
0.42-0.52 0.42-0.52 Vinegar fiber 0.11-0.14 0.07-0.09
Nylon 6 0.38-0.62 0.33-0.53 cotton 0.18-0.31 0.22-0.40
acrylic fibres 0.25-0.40 0.22-0.35 Sheep wool 0.09-0.15 0.07-0.14
polyvinyl alcohol fibre 0.44-0.51 0.35-0.43 Silk 0.26-0.35 0.19-0.25
polypropylene fibre 0.40-0.62 0.40-0.62 ramee 0.49-0.57 0.51-0.68
polyvinyl chloride fibre 0.22-0.35 0.22-0.35 spandex 0.04-0.09 0.03-0.09
Viscose 0.18-0.26 0.11-0.16

Chart
3
3.Fiber elongation
(2) elongation at break (elongation at break)
The fiber elongates under the action of tensile force, and increases continuously
with the increase of tensile force and the extension of action time until it breaks. The
difference between the length of the fiber at break and the original length is called
break elongation. The percentage of the ratio of elongation at break to the original
length of the fiber is called elongation at break or extension at break, which is
expressed by Y.
(1) Fracture length
One end of the fiber is fixed, and the other end hangs downward and keeps
extending. The length when the fiber breaks due to its own weight is called the
breaking length, which is expressed by LR, that is, the length of the fiber when its own
weight is equal to its absolute strength, and the unit is km. Actually, it is converted by
measuring absolute strength.
0
0
100%
L L
Y
L

 
1
1000 1000
m
R
PN
P
L
G
  
--
--
P
G
绝对强力
纤维单位长度的质量，g/ m
0
--
--
L
L
纤维伸长至断裂时的长度
纤维的原长

Chart
3 The mechanics of textile fibers
4.Fiber stretch elasticity
The Initial modulus, also known as elastic modulus or Young's
modulus, refers to the stress required when the fiber is stretched
to 1% of the original length. Unit: same as the stress unit.
It reflects the elasticity or
rigidity of fibers under small stress
conditions.
The initial modulus of textile materials
is large, and the products are more
inclusive, such as polyester, acrylic; On the
other hand, the initial modulus is small, the
product is relatively soft, easy to wrinkle,
such as: nylon.
(1) Initial modulus
concept

Chart
① One load back elastic energy
（2）纤维的弹性回复
The ability of fibers to return to their
original condition from deformation
is called elasticity. Measured by
stretch load experiment.
 Primary load rebound performance
 Multiple cyclic load resilience
concept
Charac-
teristics

Chart
① One load back elastic energy
(2) Elastic response of fiber
Method of rebound rate determination:
A certain load (or a certain elongation is
generated) is applied first, and then the load is
removed, and the remaining elongation is determined
after a certain amount of time (30s or 60s, depending
on the instrument and method of measurement). The
rebound rate can be expressed as follows:
-
% 100%= 100%
  
 
  
弹总余
总总
回弹率（）

Chart
② Cycle the load back to elasticity multiple times
(2) Elastic response of fiber
The residual deformation
value produced by the fiber
：OR1~ORn
A measure of the nature
of rebound after multiple
metamorphosis of fibers
True reflection of the
elasticity of the actual

Chart
5.Fiber fatigue and fabric durability
Closely related to lag is the fatigue resistance (or multiple
deformation resistance) of fibers.
Fatigue refers to the attenuation or damage of a material's
mechanics after repeated stress and strain. Fatigue can be
expressed in fatigue life. That is, the number of cycle stresses
and strains that the specimen was subjected to before it was
damaged under a given condition.
"The ability of a fabric to maintain its function due to
factors such as an integrated external force and the
environment is called the "durability" of the fabric.
The fiber lag ring area with better elasticity is small, and its
fatigue resistance is higher.
concept
concept

Chart
6.Fiber fracture function and wear resistance
Fibers stretch from stretch to break, and the total work done by
external forces on fibers is called Work at Break.
concept

Chart
3
6.Fiber fracture function and wear resistance
• Practice has proved that wear resistance is a comprehensive performance
of fiber strength, elongation and elasticity, in which the effect of elongation
and elasticity is more important.
e.g:
 Although the strength of hemp fiber is high, its elongation is low and its elasticity
is poor, so its wear resistance is also poor.
 Although the strength of wool fiber is low, it has high elongation and good
elasticity, and the work of breaking after repeated stretching is not much reduced,
so it has good wear resistance.
 Nylon has excellent wear resistance because of its high strength, elongation and
elasticity.
Wear resistance (Abrasion Performance) is a key indicator of
fiber durability. Wear resistance is generally expressed by the
fiber after several stretches of the fracture.
concept

Chart
3 The thermal, electrical and optical properties of
textile fibers
1.Commonly used thermal indicators
The thermal capacity of the fiber material (C)：The fiber of unit mass
absorbs or releases heat at a temperature change of 1 degree C. The heat
ratio of fibers varies with environmental conditions, not a constant.
 The influence of temperature and moisture; Effects of holes in fibers
and gaps between fibers.
Thermal conductivity of fiber materials:In the direction of heat transfer
fiber material thickness of 1 meter, area of 1 meter 2, the temperature
difference between the two parallel surfaces is 1 degree C, within 1
second through the material conducted by the number of heat joules, also
known as thermal conductivity, its countdown is called thermal resistance,
it represents the material in a certain temperature gradient conditions, the
speed of heat diffusion through the material itself.
The smaller the thermal conductivity, the lower the thermal conductivity of the material, the
better its thermal insulation or warmth. The thermal conductivity of the fiber itself is not a
constant, and anisotropy is present due to the fiber structure.
concept
concept

Chart
3
2.Thermodynamic properties
 The internal structure of most fiber materials is two-phase structure, that is,
crystalline phase (crystalline region) and liquid phase (amorphous region). For
crystalline phase, there are two thermodynamic states under the action of heat.
For liquid phase amorphous region, there are about three thermodynamic states
under the action of heat.
 Fiber, crystal is formed by polymer, and its melting process has a wide
temperature range-melting range. Because of the wide melting range, the
temperature at the beginning of melting is usually called the melting point, and
the temperature when the crystal area is completely melted is called the melting
point (the definition and value of melting point are slightly different due to
different measurement methods).
 If the crystallinity of the fiber material is high and the crystal is regular, the
melting range will be narrowed and the melting point will also increase. Under
the same crystallinity condition, the grain size will be large and the melting point
will increase.
The thermal, electrical and optical properties of
textile fibers

Chart
3 The thermal, electrical and optical properties of
textile fibers
3. Heat setting
Morphing refers to the process of making fibers (including yarns, fabrics)
reach a certain (required) macro-form (shape), then cutting off the
connections between macromolecules as much as possible, relaxing the
macromolecules, and then re-establishing as many junctions between
molecules as possible in the new equilibrium position. Thermal shape
refers to the formation under the influence of heat (by heating, cooling
means to cut off and recombine the connection between macromolecules).
Life's clothing ironing, steaming in production, and other finishing processes are all
in the use of thermal shape.
concept

Chart
3
3.Heat setting
Temporary setting refers to short stabilization time and poor anti-
interference ability. Temporary setting does not fully eliminate the
internal stress of the fiber, but only uses the "freezing" of the glass
segment to maintain the appearance shape;
Permanent setting not only fully eliminates the internal stress, but
also forms a new stable intermolecular bond inside the fiber, so the
permanent setting fiber material has strong appearance maintenance
ability.
Effect
 Temperature;
 Time;
 Tension (load);
 Setting medium.
Affect
textile fibers

Chart
3
4.Heat resistance and thermal stability
The thermal stability of fiber materials is generally expressed as a
strong reduction. Tests show that in textile fibers, polyester heat
resistance and thermal stability are the best, nylon, acrylic, viscose fiber
heat resistance is also good, but the thermal stability is poor; The heat
resistance and thermal stability of wool and silk protein fibers are poor.
Cotton, linen cellulose fiber heat resistance and thermal stability in
general; Veylon's resistance to hot water is poor.
The heat resistance of fiber material refers to the resistance to heat
break-through ring, under the high temperature of the fiber inside the
macromolecules will break down, fiber strength decline, color and other
properties will also change. Can be expressed by damaging the
temperature or deteriorating performance when heated. The heat
resistance of the material when the heat temperature exceeds 500
degrees C is generally called high temperature resistance.
textile fibers
Concept
Concept

Chart
3
5. Thermal shrinkage
The thermal shrinkage of fiber refers to the reduction of the force
between macromolecules in the fiber when the temperature increases, so
that the macromolecular retracts under the action of internal stress, or
because of the weakening of the force between straightening
macromolecules, the macromolecules overcome the bondage between
molecules through thermal motion and automatically bend to obtain curly
conformation, resulting in fiber contraction.
textile fibers
Concept

Chart
3
1.Fhe extreme oxygen index LOI
The greater the extreme oxygen index, the better the fire resistance of
the material, i.e. the more flame retardant.
Extreme oxygen index LOI: The fiber material maintains the
minimum oxygen volume percentage required to burn after
igniting in the oxygen-nitrogen atmosphere.
LOI = Volume of oxygen /(The volume of oxygen+the volume
of nitrogen) *100%
LOI and fiber classification:
 Or flammable fiber: fiber with LOI < 21%.
 Flame retardant or flame retardant fiber: fiber with LOI > 21%.
 Flame retardant fiber: fiber with LOI > 26%.
textile fibers
Concept

Chart
3
1.The extreme oxygen index LOI
classify combustion
characteristics
Limiting
oxygen index
Fiber type
fire
resist
ant
fibre
Non-
combustibl
e fiber
Open flame
cannot be ignited.
>35 Glass fiber, metal fiber,
asbestos fiber, carbon fiber,
etc.
flame-
retardant
fibre
When it can burn
or carbonize, it
will go out from
the fire.
26-34 Chloroprene, vinylidene
chloride, aramid fiber,
modified acrylic fiber,
phenolic fiber, etc.
Non-
flame
retar
dant
fiber
Combustib
le fiber
21-26 Polyester, nylon, vinylon,
silk, wool, etc.
Flammable
fiber
<21 Cotton, hemp, viscose fiber,
polypropylene fiber, acrylic
fiber, etc.
textile fibers

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3
2.Improve the flame retardant way of fiber materials
 One is flame-retardant finishing of fiber products.
 The other is to make flame retardant fiber. There are also two
kinds of production of flame retardant fibers. One is to use
nanotechnology to add fire retardant into spinning solution to
spin flame retardant fibers, such as modified flame retardant
fibers of viscose, acrylic and polyester, and the other is to spin
flame retardant polymers (Nomex).
textile fibers

Chart
3
1.Conductive property
Fiber ratio resistance
and its expression
 Specific volume
resistance ρv
 Specific surface
resistance ρs
 Specific mass
resistance ρm
(1) Fiber ratio resistance and its expression
textile fibers

Chart
3
1. Conductive property
 Influence of temperature on specific resistance
of fiber: The specific resistance of fiber material
decreases with the increase of temperature, and
the electrical conductivity increases. For most
fiber materials, whenever the temperature rises
by 10℃, its specific resistance decreases by
about 5 times.
 Influence of structure on fiber resistance:
crystallinity and orientation.
 Influence of impurities on fiber resistance.
(2) The main factors affecting fiber
ratio resistance
 Effect of moisture absorption on fiber-to-resistance: Moisture absorption has a
great effect on the ratio resistance of fiber material, and the absorption of dry
fiber material is decreased rapidly than resistance.
textile fibers

Chart
3
2. Electrostatic phenomena
When two objects with different electricality are separated by contact or
friction, a stationary charge (one with a positive charge and the other with
a negative charge) occurs on the surface of contact between the two
objects, a phenomenon known as static electricity.
The experimental results show that the surface material is acidic, the negative charge is often
accumulated, and the surface substance is alkaline, the positive charge is often accumulated.
Charge accumulation will have escape, resistivity of small fibers its charge escape speed is
fast, even if the generation of charge, people are not easy to detect.
The quality of the strip is worse, the yarn head increases, the strip drys and
the feathers deteriorate, the short fibers easily become flying flowers or
adhesive parts, the long fibers are easy to tangle the machine parts, the
clothes are easy to absorb dust, fire, wrapped around the human body,
serious will cause fire accidents. But static electricity phenomenon will
also bring people a lot of benefits, static dust removal and so on.
Harm
(-) Acet acrylic acrylic acrylic polyester Villun vinegar fiber hemp fiber silk cotton fiber viscose fiber
nylon wool (static potential sequence table is just an expression of a law, and the actual situation will
(1) Static electricity
phenomenon and hazards
textile fibers
Concept

Chart
3
 Humidification: It is the most common and cheap method to increase the relative
humidity of the workshop, reduce the generation of static electricity of fiber
materials and accelerate the dissipation of static electricity.
 Adding surfactants: The surfactants used have the ability to improve lubrication,
reduce friction, increase moisture absorption, and even have antistatic ability.
Therefore, such surfactants are also called antistatic agents. This method is
especially suitable for static elimination of chemical fiber and wool, and it is also
one of the most commonly used methods at present. However, like humidification,
it only ensures the smooth processing and makes little contribution to the use of
products.
 Improve the friction and conductivity of parts: By improving the material and
structure of parts, less static electricity is generated and the conduction of static
electricity is accelerated.
(2) Eliminate static electricity method
textile fibers

Chart
3
 Reasonable collocation of different raw materials: static electricity generated by
neutralizing products with each other in use by selecting suitable raw materials,
blending or interweaving. For example, the friction between nylon 66 and leather
will produce a static voltage of +3800V, while the friction between polyester and
leather will produce a static voltage of-1400 V. The static voltage after the mixture
of nylon 66 and leather (nylon/polyester 40/60) is very low and hard to detect. The
chemical fiber carpet produced by this combination has achieved good antistatic
effect.
 Using antistatic fiber: it is difficult to process permanent antistatic fiber. Now, the
common method is to mix or weave metal fiber. With the increase of metal fiber
usage, although the antistatic property is improved and even the electromagnetic
shielding effect is greatly improved, the cost of fabric is increased, the hand feel is
decreased and the warmth retention ability is weakened.
(2) Eliminate static electricity method
textile fibers

Chart
3
The optical properties of fibers refer to the properties of fibers'
absorption, reflection, scattering, refraction and transmission of light,
including fiber's excitation spectrum and luminescence.
2. Refraction and birefringence
The size of birefringence can reflect the orientation degree of fiber
macromolecules. The larger the birefringence, the more orderly the arrangement of
macromolecules and the more parallel to the fiber axis. On the contrary, when the
arrangement of macromolecules is disordered, the birefringence will be zero.
1. Color
Color is color and luster. Color is dependent on the selective
absorption and reflection of light by fibers at different
wavelengths. Gloss depends on how light reflects on the fiber
surface. Color is not only the appearance quality of fiber
material, but also reflects the intrinsic quality of fiber material.
textile fibers

Chart
3
3.Light resistance and light protection
The internal structure of fibers exposed to sunlight will change to varying degrees, the large molecules
will have different degrees of cracking, polymerization decline, intermolecular force reduction, the greater
the degree, the fiber's fracture strength, fracture elongation and durability will be reduced, and will cause
discoloration and other appearance changes.
Ultraviolet Infrared rays
The order of light resistance is acrylic fiber > wool > hemp > cotton > viscose >
polyester > nylon > silk.
wave band Wavelength (nm) Effect on skin
UV—A 320—400 Produces melanin and brown spots that age, dry and increase
wrinkles
UV—B 290—320 Produces erythema and pigmentation, often exposed to, and is at
risk of cancer
UV—C 180—290 Strong penetration, can affect white blood cells, but most of the
ozone layer, cloud absorption
Ultraviolet Protection Factor：The ratio of the minimum irradiance of ultraviolet light required to produce
erythema when the skin is free of fabric protection to the degree of Irradiance of ultraviolet light required to
produce erythema and the minimum irradiance of ultraviolet radiation that produces erythema through the
fabric.
Titanium dioxide, zinc oxide, talcum powder, clay, calcium carbonate etc. have a high refractive
index, which allows UV rays to scatter and thus prevent UV rays from invading the skin.
textile fibers

Chart
3 Identification of textile fibers
1.Feel visual inspection method
To judge natural or chemical fibers by looking at (length, color, etc.), pinching
(elasticity, hardness, cold and warmth, etc.), listening to (singling, etc.). Features: It
is one of the simple methods to identify natural fibers and individual chemical fiber
varieties, but its accuracy is poor, especially difficult to identify specific varieties in
chemical fibers. Applied to raw materials in the state of dispersed fibers.
Almost white, even, some
with metallic luster.
But it is soft and
not uniform.
colour and lustre
few
With various
impurities.
Miscellaneous
The same variety is
relatively uniform.
Very different
Length and fineness
chemical fibre
natural fiber
Fiber category
Observation
content

Chart
3
1.Feel visual inspection method
Identification of textile fibers

Chart
3
2.Microscopic method
 Principle: According to the vertical and horizontal morphological characteristics
of various fibers to identify fibers. is one of the most widely used methods. As
There is a natural twist of cotton; Scales are hairs;
It is hemp that has transverse joints and longitudinal cracks;
Synthetic fibers are generally smooth and rod-shaped in the longitudinal direction, and
some of them can also see titanium dioxide matting agents randomly distributed in granules.
Pros and cons: Can be used for pure spinning (composed of one fiber), blending
(consisting of two or more fibers) and interwoven (different raw materials for
longitude and latitude yarn) product identification, can correctly distinguish between
natural fibers and chemical fibers. Can't determine the specific variety of synthetic
fiber.
 Note: Consider the special-shaped fibers (such as triangular section) in chemical
fiber. After preliminary identification by microscope, further verification is
required.
 Application: preliminarily identify the fiber, and determine whether it is pure
fabric or blended fabric, as well as the type or category of fiber in blended fabric.

Chart
3
2. Microscopic method

Chart
3
3. Combustion method
 Principle: Different chemical compositions of fibers have different combustion
characteristics.
 Steps: ① approaching the flame, ② burning characteristics in the flame, ③
leaving the flame, ④ distinguishing the smell and residue after burning.
Commonly used fibers are divided into three categories, namely cellulose fiber,
protein fiber and synthetic fiber.
 Scope of application:
• Suitable for single-component
fibers, yarns and fabrics;
• It is not suitable for fibers,
yarns and fabrics with mixed
ingredients, or fibers and
textiles that have undergone
fire prevention, flame
prevention and other finishing.

Chart
3
4.Chemical dissolution method
 Principle: Different fibers have different solubility properties in different
reagents
 Application: Identification of a variety of textile materials, including dyeing
fibers or mixed ingredients of fibers, yarns and fabrics. Analysis of the
content of various fibers in blended products.
 Method:
• Pure textile identification steps:
The extraction yarn and fiber → placed in the test tube→ injected with a certain
concentration of solvent → observe the dissolution (dissolved, partially dissolved,
slightly soluble, insoluble), record the dissolved temperature (normal temperature
dissolve, heating dissolve, boiling dissolve) → control the dissolving performance table,
determine the variety.
• Mixed textile identification:
The fabric is broken down into fibers→ placed in concave slides→ observe the
dissolution of various fibers under a microscope→ determine the composition of the
fibers.
 Note: Strict control of concentration, temperature, time of action, etc.

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3
4.Chemical dissolution method
Common fiber solubility performance tables
S--dissolution; SS--slightly soluble; P-- partial dissolution; I--insoluble.

Chart
3
5.Drug coloring method
 S in the table-dissolution; Ss-slightly soluble; P—— partial dissolution; I-
insoluble.
 Matters needing attention:
The identified materials are undyed single-component fibers, yarns and fabrics;
The identified material has not been treated with finishing agent.
 Method
The colorants commonly used are iodine-potassium iodide solution and No.
1 colorant. Specific identification can be put into the sample micro-boiling
coloring solution, boiling dye 0.5-1min, the time from the injection of the
specimen after the dyeing fluid micro-boiling began to calculate. After
dyeing, pour out the dyeing liquid, cold water cleaning, drying. For wool, silk
and nylon can be used boiling dyeing 3s method to expand the color
difference. After dyeing with the standard sample, according to the hue to
determine the fiber category.

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3
5.Drug coloring method
The coloring reaction of several textile fibers

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3
6.System identification method
7. Fluorescence method;
8. Melting point method;
9. Density gradient method;
10. Infrared spectroscopy;
……

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