polymers and composite materials - wordpress.com · polymers and composite materials ......
TRANSCRIPT
Contents
• Classification of Polymers
• Types of polymerization
• Elastomers/ Rubber
• Advanced Polymeric Material
• Biopolymers
• Composite Materials
POLYMERS (the whole train) are made out of MONOMERS
(individual cars of the train) joined together.
• Polymer: High molecular weight moleculemade up of a small repeat unit (monomer).
– A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-
• Monomer: Low molecular weight compoundthat can be connected together to give apolymer
• Oligomer: Short polymer chain (unit 6-12)
Polymers: Introduction
Classification of Polymers
I. On the basis of SOURCE or ORIGIN(Conventional Classification)
(a) Natural/Biopolymers (found in nature)examples: cellulose, rubber, RNA, DNA, protein
(b) Semi-synthetic polymers (main source is naturebut with some modification as per our need)examples: cellulose-nitrate,-acetate, vulcanizedrubber etc.
(c) Synthetic Polymers (which are prepared in thelab/industries) examples: polyethene, PVC,nylon, polyester etc.
II. Depending upon the mode of synthesis
a) Addition Polymer
b) Condensation polymer
• ADDITION POLYMER
When the monomer units are repeatedly addedto form long chains without the elimination ofany by-product molecules, the product formedis called addition polymers
Examples: polyethene, PVC, Teflon,polyurethane, SBR etc.
• CONDENSATION POLYMER
When the monomer units are react together,with the elimination of by-product moleculessuch as water, carbon dioxide, HCl, ammoniaalcohol etc., the product formed is calledcondensation polymers
Examples: nylon-6, nylon-6,6, epoxy resins, UFresins, Kevlar (polyamide) etc.
III. Depending upon the nature of the repeatingstructural units
a) Homo-polymer
b) Co-polymer
• HOMO-POLYMER
The polymer formed from one kind ofmonomers, called homo-polymer.
Examples: Polyethene, PVC, Teflon, etc.
Types of Homo-polymer
a) Linear b) Branched c) Cross-linked
Linear polymers
• These polymers consist of long and straight chains.
• Examples are high density polythene, PVC, etc.
Branched Polymers
• These polymers contain linear chains having some branches, e.g.,
• Examples are low density polythene, amylopectine etc.
Cross-linked Polymers
• Monomeric units are linked together to constitute a 3-dimensional network structure
• Hard and rigid
• Example: vulcanized rubber etc.
• CO-POLYMER
The polymer formed from more than one kindof monomers, called co-polymer.
Examples: Terylene, Nylon-6,6, SBR, Saran,Kevlar etc.
Types of Co-polymer
IV. Based on molecular forces/applications• polymer applications in different fields depend
on their unique mechanical properties liketensile strength, elasticity, toughness, etc.
• These mechanical properties are governed byintermolecular forces, e.g., van der Waalsforces and hydrogen bonds, present in thepolymer.
• the polymers are classified on the basis ofmagnitude of intermolecular forces present inthem.
a) Elastomers (b) Fibers (c) Plastic
Elastomers
• These are rubber – like solids with elasticproperties.
• the polymer chains are held together by the weakest intermolecular forces.
• These weak binding forces permit the polymer to be stretched.
• A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber.
• The examples are buna-S, buna-N, neoprene
Fibers
• Fibres are the thread forming solids whichpossess high tensile
• These characteristics can be attributed to thestrong intermolecular forces like hydrogenbonding.
• These strong forces also lead to close packing ofchains and thus impart crystalline nature.
• Examples are polyamides (nylon 6, 6),polyesters (terylene)
Thermoplastic Polymers
• These are the linear or slightly branched longchain molecules capable of repeatedly softeningon heating and hardening on cooling.
• These polymers possess intermolecular forcesof attraction intermediate between elastomersand fibres.
• Some common thermoplastics are polythene,polystyrene, polyvinyls, etc
Thermosetting Polymers
• These polymers are cross linked or heavilybranched molecules, which on heating undergoextensive cross linking.
• chain motion is greatly restricted by a highdegree of crosslinking.
• These cannot be reused.
• Some common
• examples are bakelite, urea-formaldelyderesins, epoxy resins etc.
Types of Polymerization
I. Addition Polymerization
II. Condensation Polymerization
Addition polymerization• the molecules of the same monomer or
different monomers add together on a largescale to form a polymer.
• The monomers used are unsaturatedcompounds, e.g., alkenes, alkadienes and theirderivatives.
• This mode of polymerisation leading to anincrease in chain length or chain growth cantake place through the formation of either freeradicals or ionic species.
• However, the free radical governed addition orchain growth polymerisation is the mostcommon mode.
Examples of Addition polymerization
Condensation polymerization• Polymerization generally involves a repetitive
condensation reaction between two bi-functionalmonomers.
• These poly-condensation reactions may result in theloss of some simple molecules as water, alcohol, etc.,and lead to the formation of high molecular masspolymers.
• In these reactions, the product of each step is again abi-functional species and the sequence ofcondensation goes on.
• Since, each step produces a distinct functionalisedspecies and is independent of each other,
• this process is also called as step growthpolymerisation
Examples of condensation polymerization
Examples of condensation polymerization
Rubber
TacticityTacticity – stereoregularity or spatial arrangement of R units
along chain
C C
H
H
H
R R
H
H
H
CC
R
H
H
H
CC
R
H
H
H
CC
isotactic – all R groups on same side
of chain
C C
H
H
H
R
C C
H
H
H
R
C C
H
H
H
R R
H
H
H
CC
syndiotactic – R groups alternate
sides
Tacticity (cont.)atactic – R groups randomly
positioned
C C
H
H
H
R R
H
H
H
CC
R
H
H
H
CC
R
H
H
H
CC
Biopolymer
I. Starch
II. Cellulose
GlucoseStructural formula.
Straight chain glucose
H-C=O
|
H-C-OH
|
HO-C-H
|
H-C-OH
|
H-C-OH
|
CH2OH
Glucoseglucose bending
GlucoseTwo ring-shape
versions
alpha-glucose
beta-glucose
Glucose bends itself into 4 different shapes millions of times
a second
1
4
6
2
3
5
Used in making
cellulose
Used in making starch
flips either waybends
(a) and glucose ring structures
Glucose Glucose
4 1 4 1
(b) Starch: 1–4 linkage of glucose monomers
(c) Cellulose: 1–4 linkage of glucose monomers
41
41