Properties of Polymer

8/13/2019 Properties of Polymer

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Properties of polymers

Md. Hedayatullah.M.Tech I (G.E.T) 2ndSem.

Reg. No.12307003

GETY524 Waste to energy conversion

E-mail

[email protected].


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What is a polymer?

A long molecule

made up from lots

of small molecules

calledmonomers.


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Physical properties of polymers

Thermal Behavior: Melting point.

Glass Transition Temperature (Tg)

Crystalline melting temperature. (Tm) Co-efficient of thermal expansion

Solubility.

Surface and interface properties Surface dynamics

Surface energies


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Material properties.

1.Density:- The ratio of mass to volume of amaterial. Generally Polymers are Low density molecules. (in

compare to metals and ceramics)

It depends upon the Degree of Polymerisation., Crosslinkage between the chains of polymer and

Crytallinity in the Polymer.

Density Crystallinity , Cross linkage, DP

2. Electrical conductivity:-

Polymers are generly non-conducting electrically

except Polyacetylene.


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Mechanical Properties.

1.Elasticity:- Low modulus of elasticity (stiffness)

Eis two or three orders of magnitude

lower than metals and ceramics

2. Tensile strength:- Low tensile strengthTSis about 10% of the metal

3. Much lower hardness than metals or ceramics

4. Greater ductility on average

Tremendous range of values, from 1%

elongation for polystyrene to 500% or

more for polypropylene


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Figure 8.11 - Relationship of mechanicalproperties, portrayed as deformation resistance,as a function of temperature for an amorphousthermoplastic, a 100% crystalline (theoretical)thermoplastic, and a partially crystallized

thermoplastic


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Thermal behaviour.1. Free volume of polymers

varries with temperatue.

2. Much higher coefficient of

thermal expansion

Roughly five times the value

for metals and 10 times the

value for ceramics

3. Much lower melting

temperatures

Specific heats two to four times those of metals and

ceramicsThermal conductivities about three orders of

magnitude lower than those of metals

Insulating electrical properties


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Glass Transition Temperature (Tg)

The temperature at which amorphouspolymers undergo a transition from arubbery, viscous amorphous liquid, to abrittle, glassy amorphous solid is called

the Glass Transition temperature of thatpolymer.

It is denoted by Tg.

The glass transition temperature may beengineered by altering the degree ofbranching or crosslinking in the polymeror by the addition of plasticizer.


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Chemical properties of

polymers. 1. Molecular weight

2.Degree of polymerisation.

3.Polydispersity Index.

4.Conformation of chain in space.

5.Configuration of the chain

(Microstructure)


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MOLECULAR WEIGHT

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Molecular weight, M: Mass of a mole of chains.

high M

Polymers can have various lengths depending on the number of repeat

units. During the polymerization process not all chains in a polymer grow to the

same length, so there is a distribution of molecular weights. There are

several ways of defining an average molecular weight.

The molecular weight distribution in a polymer describes the relationship

between the number of molesof each polymer species and the molar

massof that species.

LOW M


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MOLECULAR WEIGHT DISTRIBUTION

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xi = number fraction of chains in size range i

iiw

iin

MwM

MxM

wi = weight fraction of chains in size range i

Mn= the number averagemolecular weight (mass)

Mi = mean (middle)

molecular weight of size

range i


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Degree of Polymerization, DP

DP= average number of repeat units per chain

m

MDP

n

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weightmolecularunitrepeatwhere m

Ex. problem 4.1b,

for PVC: m = 2(carbon) + 3(hydrogen) + 1(Clorine)

(from front of book) = 2(12.011) + 3(1.008) + 1(35.45)

= 62.496 g/mol

DP = 21,150 / 62.496 = 338.42


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Polymer Chain Lengths

Many polymer properties are affected by the length of thepolymer chains. For example, the melting temperature

increases with increasing molecular weight. At room temp, polymers with very short chains (roughly 100

g/mol) will exist as liquids.

Those with weights of 1000 g/molare typically waxy solidsand soft resins.

Solidpolymers range between 10,000and several milliong/mol.

The molecular weight affects the polymers properties(examples: elastic modulus & strength).

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Chain End-to-End Distance, r Representation of a

single polymer chain

molecule that has

numerous random kinks

and coils produced bychain bond rotations; it is

very similar to a heavily

tangled fishing line.

r is the end to enddistance of the polymer

chain which is much

smaller than the total

chain length. 19


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Molecular Structures-

Branched

Where side-branch chains have connected to main

chains, these are termed branched polymers. Linearstructures may have side-branching.

HDPEhigh density polyethylene is primarily a

linear polymer with minor branching, while LDPE

low density polyethylene contains numerous shortchain branches.

Greater chain linearity and chain length tend to

increase the melting point and improve the physical

and mechanical properties of the polymer due togreater crystallinity. 21

Branched Cross-Linked NetworkLinear


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Molecular StructuresCross-linked,

Network

In cross-linked polymers, adjacent linearchains are joined to one another at various

positions by covalent bonding of atoms.

Examples are the rubber elastic materials.

Small molecules that form 3 or more active

covalent bonds create structures called

network polymers. Examples are the epoxies

and polyurethanes. 22

Branched Cross-Linked NetworkLinear

secondarybonding


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Thermoplastics and

Thermosets The response of a polymer to mechanical forces at

elevated temperature is related to its dominant

molecular structure.

One classification of polymers is according to its

behavior and rising temperature. Thermoplastics andThermosets are the 2 categories.

A thermoplastic is a polymer that turns to a liquid when

heated and freezes to a very glassy state when cooled

sufficiently. Most thermoplastics are high-molecular-weight

polymers whose chains associate through weak Van

der Waals forces (polyethylene); stronger dipole-dipole

interactions and hydrogen bonding (nylon).23

Th l ti d


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Thermoplastics and

Thermosets Thermoplastic polymers differ from

thermosetting polymers (Bakelite,vulcanized rubber) since thermoplasticscan be remelted and remolded.

Thermosetting plastics when heated, will

chemically decompose, so they can not berecycled. Yet, once a thermoset is cured ittends to be stronger than a thermoplastic.

Typically, linear polymers with minor

branched structures (and flexible chains)are thermoplastics. The networkedstructures are thermosets.

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Examples of Thermoplastics


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More Examples of Thermoplastics

PTFE

Polymer
http://www2.dupont.com/Teflon/en_US/index.html


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Specific Thermoplastic Properties


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Thermoset data


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Thermoset Properties


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Specific Elastomeric Properties

Elastomers, often referred to as rubber, can be a thermoplastic or a

thermoset depending on the structure. They are excellent for parts

requiring flexiblity, strength and durability: such as automotive andindustrial seals, gaskets and molded goods, roofing and belting, aircraft

and chemical processing seals, food, pharmaceutical and semiconductor

seals, and wire and cable coatings.


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3

Thermoplastics:

--little cross linking

--ductile

--soften with heating

--polyethylene

polypropylene

polycarbonatepolystyrene

Thermosets:

--large cross linking(10 to 50% of mers)

--hard and brittle

--do NOT soften with heating

--vulcanized rubber, epoxies,

polyester resin, phenolic resin

Callister,Fig. 16.9

T

Molecular weight

Tg

Tmmobileliquid

viscous

liquid

rubber

tough

plastic

partiallycrystalline

solidcrystalline

solid

Thermoplastic vs Thermoset


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Crystallinity in Polymers The crystalline state

may exist in polymericmaterials.

However, since itinvolves moleculesinstead of just atoms or

ions, as with metals orceramics, the atomicarrangement will bemore complex forpolymers.

There are orderedatomic arrangementsinvolving molecularchains.

Example shown is a

polyethylene unit cell 32


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Crystal Structures

Fe3Ciron carbide

orthorhombic crystal

structure


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The effect of temperature on the structure andbehavior of thermoplastics.


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Polymer CrystallinityPolymers are rarely 100%

crystalline

Difficult for all regions of all

chains to become aligned

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Degree of crystallinity

expressed as % crystallinity.-- Some physical properties

depend on % crystallinity.

-- Heat treating causes

crystalline regions to grow

and % crystallinity toincrease.

crystallineregion

amorphous

region


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Thank you..

Properties of Polymer

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