fibre structure and properties
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Fibre Structure and Properties
By:
Dr. Mumtaz Hasan Malik
Advanced Tetile Materials !T"#$%&'
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Lecture Outline
&. (ntroduction
). Polymerization
*. Fibre Formin+
,. (ntra#polymer Bondin+
$. (nter#polymer Forces o- Attraction
. /e0uirement o- Tetile Fibre#-ormin+ Polymers
%. Fibre Properties
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&. (ntroduction
• Nature and characteristics of matter
• Fibres are the units of matter characterized by flexibility
fineness and a high ratio of length to thickness
• Textile fibres can be defined as the units of matter
characterized by flexibility fineness, high ratio of length
to thickness, high thermal stability and a certainminimum strength and elongation.
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). Polymerization
• Polymerization is a chemical reaction in which monomers are
joined endtoend to form a !olymer.
• "egree of !olymerization #"P$ is the ratio of the a%erage
molecular weight of the !olymer to the molecular weight of the
monomer #re!eating unit$.
• &hen no by!roduct is liberated on !olymerization, the reaction is
called addition !olymerization #'crylic, modacrylic, !olyethylene, !oly!ro!ylene, !oly%inyl alcohol, !oly%inyl
chloride and !oly%inylidene chloride$.
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• &hen a by!roduct is also formed on !olymerization, the reaction
is called condensation !olymerization #!olyester, nylon,
elastomeric !olymers$.
• Polymers are of two ty!es, homo!olymers and co!olymers.
• &hen !olymers are !olymerized from only one kind of
monomers, the !olymers are called homo!olymers such as nylon
(, !olyethylene, !oly!ro!ylene, chloro fibres #!oly%inyl chloride
and !oly%inylidene chloride$.
• )o!olymers are formed from two or more different monomers
such as nylon (.(, !olyester, modacrylic.
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*. Fibre Formin+
• 'fter !olymerization, the !olymers are either melted or dissol%ed in a
sol%ent before the s!inning is done to manufacture the textile fibres.
• *n wet s!inning, !olymer is dissol%ed in a sol%ent and the s!inneret is
submerged in a chemical bath that causes the fibre to !reci!itate and
solidify when emerges #acrylic, %iscose, s!andex$
• *n dry s!inning, !olymers are dissol%ed in sol%ent and after extrusion
solidification of !olymer is achie%ed through e%a!oration #cellulose
acetate$
• *n melt s!inning, !olymers are melted and after extrusion, the
!olymer is solidified by cooling #!olyester, nylon (.($
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,. (ntra#polymer Bondin+
• +onds holding the atoms together to make u! the fibre !olymer is
called intra!olymer bonding.
• Textile fibre !olymers are mainly organic com!ounds, ex!ect
some natural mineral and manmade inorganic fibres.
• They are !redominantly com!osed of carbon and hydrogen atoms,
with some oxygen, nitrogen, chlorine andor fluorine atoms.
• *n general, single co%alent bonds join the atoms forming the
!olymer .
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• )o%alent bond between the atoms of carbon and carbon, carbon
and hydrogen, carbon and oxygen, carbon and chlorine, and
carbon and fluorine are %ery strong.
• -uch of the backbone of any !olymer consists of carbon
segments of %arying lengths.
• The bond strength of single co%alent bond joining the atoms of
fibre !olymers ranges from /01/ kilojoules.
• 2owe%er, segments of !olymer backbone, which consist of other
atoms, also influence the !ro!erties of the !olymer e.g. amide
grou! in nylon, !e!tide grou! in !rotein fibres, benzene ring
#)(2($ in !olyester, either linkage #3)343)3$ in cellulose ,
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$. (nter#polymer Forces o- Attraction
• The coherence of the !olymer system of a fibre is due to the
following inter!olymer forces of attraction6
3 7an der &aals8 Forces
3 2ydrogen +onds
3 9alt :inks
3 )ross :inks
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1an der 2aals3 Forces
• 7an der waals8 forces are weak electrostatic forces which attract neutral
molecules to each other in gases, li;uefied and solidified gases, organic
li;uids and organic solids such as textile fibres.
• *f two or more atoms andor molecules are close enough together, then
%an der waals8 forces will exist between them.
• *f fibre !olymers are about /.1 nm a!art, %an der waals forces will occur
between them. This is the case in the crystalline regions of any fibre.
• 7an der waals forces are influenced by the size of the atoms, larger the
size stronger the force. #fig
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• 7an der waals8 forces are also formed between fibre !olymers and
dye molecules, when they come close enough together.
• +ond energy of %an der waals8 forces is >.0 kilojoules.Hydro+en Bonds
• 2ydrogen bonds are weak electrostatic bonds which occur
between the co%alently bonded slightly !ositi%e charged hydrogenatoms and strongly electronegati%e atoms.
• The distance between the two o!!ositely charged atoms is less
than /.? nm.
• +ond energy 1/.@ kilojoules #fig $
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S i
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Salt 4inka+es
• &hen ionic or electro co%alent bonds are formed between the ions
or radicals of the chemical com!ounds the bonds are called salt
linkages.
• The charged radicals are %ery close to each other #/.< nm$
• They occur between the !olymers of !rotein fibres and at the
terminals of nylon fibres
• They are strong force of attraction with bond energy of ?0.0
kilojoules.
5 4i k
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5ross 4inks
• )ross links are single co%alent bonds and occur between the
!olymers of elastomeric and !rotein fibres, exce!t silk.
• The number of crosslinks in a !olymer system is called degree of
crosslinking.
• Areater the degree of crosslinking more rigid the fibre.
• The bond energy of the cross links is 10?. kilojoules.
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. /e0uirement o- Tetile Fibre#-ormin+
Polymers
• Polymers for textile fibres may be6 3 2ydro!hilic
3 :inear
3 :ong
3 4rientable
3 )hemical Besistant
3 Thermal Besistant
• Hydrop6ilic !ro!erties of !olymers enhance the comfort
!ro!erties of fibres.
4i l ll d l li b i i ff ffi i
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• 4inear !olymers allow ade;uate !olymer alignment to bring into effect sufficient
inter!olymer forces of attraction to gi%e a cohesi%e !olymer system, thus a useful
textile fibre.
• 2owe%er, threedimensional arrangements of side grou!s gi%e three ty!es of linear !olymer configurations generally referred as stereo!olymers i.e. atactic, syndiotatic
and isotactic !olymers.
Atactic Polymer !Stereo#irre+ular'
• 9ide grou!s are arranged at random abo%e and below the !lane of the !olymer
backbone.
• Csually not found in !olymer system of fibre.
• They do not allow close enough alignment of !olymers to gi%e effecti%e inter
!olymer forces of attraction.
S di t ti P l !St l '
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Syndiotactic Polymer !Stereo#re+ular'
• 9ide grou!s are arranged in a regular alternation abo%e and below the !lane of
the !olymer backbone.
• Begular !olymer structure !ro%ides close enough alignment of !olymer system
to form effecti%e !olymer forces of attraction suitable for a textile fibre.
(soactic Polymer !Stereo#re+ular'
• 9ide grou! are arranged on the same !lane of the !olymer backbone.
• *sotactic !olymers orient themsel%es readily and %ery closely.
• 5ffecti%e inter!olymer forces of attraction gi%e a cohesi%e !olymer system
suitable for textile fibre.
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• 4en+t6 of the fibre !olymers should be long #D
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%. Fibre Properties
• Fibre !ro!erties are as underE
3 :ength
3 Fineness
3 "ensity
3 -oisture 'bsor!tion
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4en+t6:
• Fibre length %aries greatly within any one sam!le of natural textile
raw materials #)7 0/ G for cotton, ?/(/G for wool,
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i
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Fineness:
• The trans%erse fibre dimensions are of the utmost im!ortance in
many contexts.
• *n homogenous and isotro!ic cylindrical materials resistance to
bending %aries as the s;uare of the crosssectional area.
• Besistance to bending diminishes as the fineness of the fibre
increases.
• Fibre fineness affects the softness and dra!e of fabric.
• Torgional rigidity increases as the fibre becomes coarse.
• Finer the fibre higher the luster of the fabric.
2i h h ifi f h h i i h d
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• 2igher the s!ecific surface shorter the time re;uire to exhaust a dye
bath and higher rate of absor!tion of water %a!or.
• Finer the fibre, lesser the amount of twist to !re%ent fibre sli!!age.
• Finer the fibre, more uniform the yarn and higher the s!inning
limit.
Density:
• Fibre density !lays a direct !art in affecting the weight of fabrics,
higher the density hea%ier the fabric.
• "ensity also hel!s to indentify fibre ty!e.
Th b l f d i b i d i h di l f
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• The best %alues of density are obtained with dis!lacement of
organic li;uids such as nitrobenzene, oli%e oil, toluene, benzene
and carbon tetrachloride.
• Flotation method is also used to determine fibre density.
• "ensity gradient tube is also used for this !ur!ose which contains
a hea%y li;uid e.g. !entachloroethane #
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