fibre structure and properties

8/16/2019 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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fibre structure and properties

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