assignment 3 polymeric materials vu21218

8/15/2019 Assignment 3 Polymeric Materials VU21218

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A saturated polymeric molecule is as saturated as it can possibly be

under normal conditions. This means that the temperature of the

polymeric molecules& the force applied to it and any other variables are

neutral and within normal ranges. A saturated polymeric molecule isunable to dissolve or absorb any further solvent& and any solvent that

is added after this saturation point remains whole& usually 'oating to

the bottom of the polymeric molecule0s container.

Eamples of saturated !all bonds are single ones# hydrocarbon

molecules-

ouble and triple bonds can eist between C atoms !sharing of two or

three electron pairs#. These bonds are called unsaturated bonds./nsaturated molecules are more reactive.

Ethylene& C234upersaturated polymeric molecules are not possible under normal&

unmodi5ed circumstances. 6n order to supersaturate a polymeric

molecule& temperature can be raised& which allows more solvent to be

dissolved into the polymeric molecules. Alternatively& high

pressure can create a supersaturated polymeric molecule. The third

way to produce supersaturated polymeric molecules is to change

volume& such as by evaporation.


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Answer to the question no 7

Polymerisation is the process of binding a number of molecules which

contain a small number of Carbon atoms or monomer to form onemolecule of a large number of Carbon atoms. Polymerisation is a process

of reacting monomer molecules together in a chemical reaction to form

three%dimensional networ(s or polymer chains. There are types of

polymerisation which are-

• Addition polymerisation8

• Condensation polymerisation.

Addition polymerisation: )y binding great number from saturated small

molecules to give big molecules li(e poly%ethylene. This involves the

formation of the polymer 96T2:/T the elimination of any simple

compound.

Condensation polymerisation: )etween two dierent monomers by

losing water to give co%polymer li(e )a(elite. The polymer is formed from

the monomers by the elimination of some simple compounds.

Answer to the question no 3

Crystalline polymer: Crystalline polymers are solid polymers with a high

degree of structural order and rigidity. ;ost crystalline polymers are not

entirely crystalline. The chains or parts of chains& that aren


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which is followed by an overall drop in stress. The folded chains become

aligned. ;acroscopically because of the thinning down in cross section&

the stress rises locally and any deformation occurs preferentially there.

This helps the nec( propagate along the waist of the specimen under asteady load a process (nown as cold drawing. Any deformation produced

beyond the yield point is not recoverable.

,ig- +on%crystalline structure

6n a crystalline polymer the unfolding of chains begins in the amorphous

regions between the lamellae of the crystals. This is followed by brea(ing%

up and alignment of crystals.

Answer to the question no =

The normal state of most thermoses polymers is to be an amorphous solid

at room temperature. There are a lot of important dierences between theglass transition and melting. $i(e 6 said earlier& melting is something that

happens to a crystalline polymer& while the glass transition happens only

to polymers in the amorphous state. A given polymer will often have both

amorphous and crystalline domains within it& so the same sample can

often show a melting point and a Tg. )ut the chains that melt are not the

chains that undergo the glass transition.

There is another big dierence between melting and the glass transition.9hen we heat a crystalline polymer at a constant rate& the temperature


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will increase at a constant rate. The heat amount of heat required to raise

the temperature of one gram of the polymer one degree Celsius is called

the heat capacity.

+ow the temperature will continue to increase until the polymer reaches

its melting point. 9hen this happens& the temperature will hold steady for

awhile& even though you


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change in heat capacity& but it doesnPolymers are very large molecules that are made up of thousands % even

millions % of atoms that are bonded together in a repeating pattern. The

structure of a polymer is easily visuali*ed by imagining a chain. The chain

has many lin(s that are connected together. 6n the same way the atoms

within the polymer are bonded to each other to form lin(s in the polymer

chain. The molecular lin(s in the polymer chain are called repeat units

that are formed from one or more molecules called monomers.

Polymer Properties: The disordered tangling of the polymer chains

create what is (nown as an amorphous structure. Amorphous polymers

are typically transparent and much easier to melt to ma(e materials li(e

(itchen cling 5lm.

Properties of Polymers: The physical properties of a polymer& such as

its strength and 'eibility depend on-

• Chain length % in general& the longer the chains the stronger the

polymer8

• 4ide groups % polar side groups give stronger attraction between

polymer chains& ma(ing the polymer stronger8

• )ranching % straight& unbranched chains can pac( together more

closely than highly branched chains& giving polymers that are more

crystalline and therefore stronger8

• Cross%lin(ing % if polymer chains are lin(ed together etensively by

covalent bonds& the polymer is harder and more di?cult to melt.Applications of Polymers:

• Polymeric materials are used in and on soil to improve aeration&

provide mulch& and promote plant growth and health.

• ;any biomaterials& especially heart valve replacements and blood

vessels& are made of polymers li(e acron& Te'on and polyurethane.

• Consumer 4cience Plastic containers of all shapes and si*es are light

weight and economically less epensive than the more traditional

containers.


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• They are very commonly used in industry of automobile parts&

windshields for 5ghter planes& pipes& tan(s& pac(ing materials&

insulation& wood substitutes& adhesives& matri for composites& and

elastomers are all polymer applications used in the industrialmar(et.

• Polymers also demanding in sports playground equipment& various

balls& golf clubs& swimming pools& and protective helmets are often

produced from polymers.

• These are also used in clothing8 'oor coverings& garbage disposal

bags& and pac(aging are other polymer applications.

Answer to the question no @

"iscoelasticity is the property of materials that ehibit both viscous and

elastic characteristics when undergoing deformation. 4ynthetic polymers&

wood& and human tissue& as well as metals at high temperature& display

signi5cant viscoelastic eects. 6n some applications& even a small

viscoelastic response can be signi5cant. 6t represented by-

d

dt

ε

σ η =

ashpotdamper for viscous element.

• ,ollows +ewtonian 'uid constitutive law

σ µε =4pring for elastic element

• Assumed to linearly elastic

"iscoelastic behaviour- The dierence between elastic materials and

viscoelastic materials is that viscoelastic materials have a viscosity factor

and the elastic ones don0t. )ecause viscoelastic materials have the

viscosity factor& they have a strain rate dependent on time. Purely elastic

materials do not dissipate energy !heat# when a load is applied& then

removed8 however& a viscoelastic substance does.

9hen subBected to a step constant stress& viscoelastic materials

eperience a time%dependent increase in strain. This phenomenon is

(nown as viscoelastic creep.


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assignment 3 polymeric materials vu21218

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