POLYMERPOLYMER(2)(2)

Polymer crystallinityPolymer crystallinity

Deff Deff Packing of molecular chains to Packing of molecular chains to produce an ordered atomic arrayproduce an ordered atomic array

Complexity of molecular structure Complexity of molecular structure large large variety from well ordered crystalline-variety from well ordered crystalline-amorphousamorphous

Density of crystalline polymer Density of crystalline polymer >amorphous one of the same material & >amorphous one of the same material & MWMWin cryatalline the chain is more in cryatalline the chain is more closely packedclosely packed

Degree of cryatallinity Degree of cryatallinity by weight:by weight:

s, s, c, c, a a density density of speciment to of speciment to determine the % determine the % crystallineity, of crystallineity, of perfectly crystalline perfectly crystalline polymer, of totally polymer, of totally amorphous polymeramorphous polymer

DensityDensity

n = number of mersn = number of mers

A= MW of mersA= MW of mers

Vc = unit cell Vc = unit cell volumevolume

Na= 6.023x10Na= 6.023x1023 23

mers/molmers/mol

Degree of crytallinity depends on rate of Degree of crytallinity depends on rate of cooling during solidification, chain cooling during solidification, chain configuration, molecular chemistryconfiguration, molecular chemistry

Crystallization is not favored in polymers with Crystallization is not favored in polymers with chemically complex repeat unit but easily chemically complex repeat unit but easily accomplished for linear polymer, even for very accomplished for linear polymer, even for very rapid cooling ratesrapid cooling rates

Branches polymer Branches polymer rarely to be crystalline; rarely to be crystalline; any side branches interfere crystalizationany side branches interfere crystalization

Crosslink polymer Crosslink polymer almost totally almost totally amorphous; the crosslink prevent the chain amorphous; the crosslink prevent the chain from rearranging & aligning to crystalline from rearranging & aligning to crystalline structurestructure

Bulkier side bond groups of atom Bulkier side bond groups of atom less less tendency for crystallizationtendency for crystallization

General rule for cryatalllization “the more General rule for cryatalllization “the more irregular & random the repeat unit irregular & random the repeat unit arrangement, the greater is the tendency for the arrangement, the greater is the tendency for the development of noncrytallinity”development of noncrytallinity”

Random & graft copolymer Random & graft copolymer amorphous amorphous

Degree of crystallinity affects physical Degree of crystallinity affects physical propertiesproperties

Crystalline polymers are usually stronger & Crystalline polymers are usually stronger & more resistant to dissolution & softening by heatmore resistant to dissolution & softening by heat

MeltingMelting

Tm Tm Transformation of solid Transformation of solid material (ordered structure) to material (ordered structure) to viscous liquid (random structure)viscous liquid (random structure)

Occurs upon heating at TmOccurs upon heating at Tm Melting takes place over a range of Melting takes place over a range of

TT Thicker the layer, higher TmThicker the layer, higher Tm Impurities decrease TmImpurities decrease Tm

Glass transitionGlass transition Tg Tg Temperature at Temperature at

which polymer transforms which polymer transforms from rubbery to rigid from rubbery to rigid upon coolingupon cooling

Affect on stiffness, heat Affect on stiffness, heat capacity & coeff. of capacity & coeff. of thermal expansionthermal expansion

Occurs in amorphous & Occurs in amorphous & semi crytallinesemi crytalline

Lower T limit for Lower T limit for applicationapplication

Due to a reduction in Due to a reduction in motion of large segment motion of large segment of molecule chain with of molecule chain with changing Tchanging T

Crystalline Crystalline discontinue discontinue change in specific change in specific vol. at Tmvol. at Tm

Polymer synthesis & Polymer synthesis & processingprocessing

Polymer synthesis: 1)polymerisation Polymer synthesis: 1)polymerisation 2)additive materials 3)finishing pieces2)additive materials 3)finishing pieces

POLYMERISATIONPOLYMERISATION

monomers are linked together to monomers are linked together to generate long chains composed of generate long chains composed of repeat units repeat units

raw material: derived from coal, raw material: derived from coal, natural gas, petroleumnatural gas, petroleum

1) Addition/chain 1) Addition/chain reaction polymerizationreaction polymerizationmonomer units are monomer units are attached one at a time attached one at a time in chainlike fashion to in chainlike fashion to form a linear form a linear macromoleculesmacromolecules synthesis of synthesis of polyethylene, polyethylene, polypropylene, PVCpolypropylene, PVC3 stages: initiation, 3 stages: initiation, propagation & propagation & termination termination affect affect MWMW

i) Initiation i) Initiation active centre active centre capable of propagation is capable of propagation is formed by reaction formed by reaction between an initiator between an initiator (catalyst) species & (catalyst) species & monomer unitmonomer unit

ii) Propagation ii) Propagation linear linear growth of polymer chain growth of polymer chain by sequential addition of by sequential addition of monomer unit to the monomer unit to the active growing chain active growing chain moleculemolecule

1000 repeat units in 101000 repeat units in 10-2-2 - -1010-3-3 s s

iii) Terminationiii) Termination

a) active end of 2 propagation chain may a) active end of 2 propagation chain may link together form 1 moleculelink together form 1 molecule

b) two growing molecule that react to b) two growing molecule that react to form two “dead chains”form two “dead chains”

2) Condensation (step reaction) polymerisation2) Condensation (step reaction) polymerisation Stepwise intermolecular chemical reaction that Stepwise intermolecular chemical reaction that

may involve more than 1 monomer speciesmay involve more than 1 monomer species By product: small MW (water)By product: small MW (water) No reactant species has chemical formula in the No reactant species has chemical formula in the

repeat unit; intermolecular reaction occurs repeat unit; intermolecular reaction occurs everytime a repeat unit is formedeverytime a repeat unit is formed

Reaction times for condensation are generally Reaction times for condensation are generally longer than for addition polymerisationlonger than for addition polymerisation

POLYMER ADDITIVESPOLYMER ADDITIVES

Additives introduce to enhance/modify Additives introduce to enhance/modify properties, thus more serviceable: properties, thus more serviceable: plasticizers, stabilizers, colorants, flame plasticizers, stabilizers, colorants, flame retardants, fillersretardants, fillers

* Stabilizers* Stabilizers- Additive to counteract deterioration in Additive to counteract deterioration in

some polymers under normal environment some polymers under normal environment expose to light-UV & oxidation expose to light-UV & oxidation

- UV radiation UV radiation interact with & cause interact with & cause severe in covalent bond & molecular chainsevere in covalent bond & molecular chain

Approaches to UV stabilization:Approaches to UV stabilization:

1)Add UV absorbent material 1)Add UV absorbent material layer at surface; layer at surface; to block out the radiation before penetrating to block out the radiation before penetrating into & damage the polymerinto & damage the polymer

2)Add materials that react with bond broken by 2)Add materials that react with bond broken by radiation before they participate in other radiation before they participate in other reactions reactions lead more damage lead more damage

- Oxidation Oxidation chemical interaction between chemical interaction between oxygen (O2 or O3) with polymer; Stabilizer oxygen (O2 or O3) with polymer; Stabilizer consume oxygen before it reaches polymer &/ consume oxygen before it reaches polymer &/ prevent the oxidation reaction that would prevent the oxidation reaction that would further damagefurther damage

- Prevent photochemical degradation Prevent photochemical degradation C black C black

* Colorants* Colorants- give color to - give color to polymerpolymer- added as dyes- added as dyes molecules dyes molecules dyes dissolve in polymerdissolve in polymer- added as pigment - added as pigment remain separate remain separate phasephase

* Plasticizers* Plasticizers- Improve flexibility, Improve flexibility,

toughness; reduce toughness; reduce hardness & stiffnesshardness & stiffness

- Used in brittle Used in brittle materials (Tr): PVC, materials (Tr): PVC,

-small plasticizer -small plasticizer molecules occupy molecules occupy position between position between large polymer chainlarge polymer chain

* Flame retardants* Flame retardants-Used in textile & toys-Used in textile & toys-interfere the -interfere the

combustion combustion process/initiating process/initiating different combustion different combustion reactionreaction generate generate less heat, reduce Tless heat, reduce T slowing burningslowing burning

Polymer typePolymer type

Classification is based on end-use: plastics, elastomers, Classification is based on end-use: plastics, elastomers, fibers, coating, adhesive, foams & films. Particular fibers, coating, adhesive, foams & films. Particular polymers may be used in more than 1 applications.polymers may be used in more than 1 applications.

PLASTICSPLASTICS materials that have structural rigidity under load & use materials that have structural rigidity under load & use

for general purpose applicationfor general purpose application Polyethylene, polypropylene, PVC, polystyrene, epoxiesPolyethylene, polypropylene, PVC, polystyrene, epoxies Some are very rigid, other are flexible, exhibite elastic Some are very rigid, other are flexible, exhibite elastic

& plastic deformation when stress, sometimes & plastic deformation when stress, sometimes experiencing deformation before fractureexperiencing deformation before fracture

Linear/branched must be used below glass transition T Linear/branched must be used below glass transition T (if amorphous) or below melting T (semicryatalline)(if amorphous) or below melting T (semicryatalline)

ELASTOMERS (rubber)ELASTOMERS (rubber)

To increase tensile To increase tensile strength, abrasion, strength, abrasion, tear resistance & tear resistance & stiffness stiffness additives (C black)additives (C black)

Silicone material Silicone material backbone chain backbone chain Si & OSi & O

R, R’= side bonded R, R’= side bonded atomatom

Crosslink structureCrosslink structure

Silicon elastomers:Silicon elastomers: have a high degree have a high degree

of flexibility at low of flexibility at low T (to -90 C); T (to -90 C);

stable at T as high stable at T as high as 250 Cas 250 C

Resistant to Resistant to weathering & weathering & lubricant oil (used lubricant oil (used in automobile in automobile engine engine compartement)compartement)

Biocompatiility Biocompatiility (blood tubing)(blood tubing)

FIBERSFIBERSlong filament at least long filament at least

100:1 length to 100:1 length to diameter ratiodiameter ratio

high tensile range over high tensile range over wide T rangewide T range

high modulus elastisityhigh modulus elastisityabrasion resistanceabrasion resistancehigh MW to be a strong high MW to be a strong

material; will not break material; will not break during drawingduring drawing

high crystalline high crystalline polymer; high tensile polymer; high tensile strength strength linear linear structure with regular structure with regular order order

*convenience in *convenience in washing:washing:

fiber properties fiber properties (melting & glass T)(melting & glass T)

stable in various stable in various environments: acids, environments: acids, base, bleaches, dry base, bleaches, dry cleaning solvent & cleaning solvent & sunlightsunlight

COATINGCOATING

Function:Function:

1)1) Protect from corrosive/deteriorative reactionProtect from corrosive/deteriorative reaction

2)2) Improve appearanceImprove appearance

3)3) Provide electrical insulationProvide electrical insulation paint, varnish, enamelpaint, varnish, enamel Many coating are latex (stable suspension of Many coating are latex (stable suspension of

small insoluble polymer particle disperse in small insoluble polymer particle disperse in water); less organic solvent, less VOC water); less organic solvent, less VOC emission emission smog smog

ADHESIVESADHESIVESused to bond 2 surface of used to bond 2 surface of

solid material togethersolid material together2 type: mechanical & 2 type: mechanical &

chemicalchemical*Mechanical: there is *Mechanical: there is

actual penetration of actual penetration of adhhesive into surface adhhesive into surface pores & crevicespores & crevices

*Chemical involves *Chemical involves intermolecular forcesintermolecular forces

polyurethanes, polyurethanes, polysiloxanes, epoxies polysiloxanes, epoxies acrylicacrylic

Factors to choose Factors to choose adhesive:adhesive:

1.1. Materials & Materials & porosities to be bondporosities to be bond

2.2. Requires adhesive Requires adhesive propertiesproperties

3.3. Exposure Exposure environmentenvironment

4.4. Processing conditionsProcessing conditions

Adhesive advantage over other joining Adhesive advantage over other joining technologies: technologies:

1. join dissimilar materials & thin components1. join dissimilar materials & thin components

2. lighter weight2. lighter weight

3. better fatigue resistance3. better fatigue resistance

4. lower manufacturing cost4. lower manufacturing cost DrawbacksDrawbacksT limitation; maintain mechanical T limitation; maintain mechanical

integrity only at low T, strength decreases with integrity only at low T, strength decreases with TT

Used in aerospace, automotive, construction etcUsed in aerospace, automotive, construction etc

FilmsFilms

0.025-0.125 mm 0.025-0.125 mm thicknessthickness

-low density, high -low density, high flexibility, high tensile flexibility, high tensile & tear strength, & tear strength, resistance to moisture resistance to moisture & chemical, low -& chemical, low -permeability to some permeability to some gases (water vapor)gases (water vapor)

-polytethylene, -polytethylene, polypropylene, polypropylene, cellulose acetatecellulose acetate

FoamsFoams

-plastic material with -plastic material with high vol of small pores high vol of small pores & trapped gas bubble& trapped gas bubble

-polyurethane, rubber, -polyurethane, rubber, polystyrenepolystyrene

-generated by -generated by dissolving an inert into dissolving an inert into molten polymer (high molten polymer (high P); when P reduce P); when P reduce rapidly, the gas comes rapidly, the gas comes out of solution & forms out of solution & forms bubbles & pores that bubbles & pores that remain in the solid as it remain in the solid as it coolscools