Creep Creep

Relaxation

Relaxation

Creep of cellulose acetate

Creep of cellulose acetate

Relaxation in PMMA Relaxation in PMMA

10

9

8

7

0.001 0.01 0.1 1 10 100 1000

Stress relaxationof PMMA

Time (hours)

400C

Log E

(t),

(dynes/

cm2)

600C

800C920C

1000C

1100C

1120C

1150C1200C

1250C

1350C

Creep & recovery Creep & recovery

Some specific polymers Some specific polymers Polyvinyl chloride (PVC) {-C-C-}n Polyvinyl chloride (PVC) {-C-C-}n

Cl HCl H

H HH H

–– ––––––

Very rigid and strong, Tg = 60-80 Csiding, pipe, conduit, usw.

Very rigid and strong, Tg = 60-80 Csiding, pipe, conduit, usw.

Presence of Cl gives rise to solubility in various organic solvents - allows "solvent welding"

Presence of Cl gives rise to solubility in various organic solvents - allows "solvent welding"

Some specific polymers Some specific polymers Polyvinyl chloride (PVC) {-C-C-}n Polyvinyl chloride (PVC) {-C-C-}n

Cl HCl H

H HH H

–– ––––––

Presence of Cl gives rise to solubility in various organic solvents

Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer"

Presence of Cl gives rise to solubility in various organic solvents

Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer"

PVC sheet then roll-formed onto fabric backing and - voilá - "vinyl"!PVC sheet then roll-formed onto fabric backing and - voilá - "vinyl"!

Some specific polymers Some specific polymers Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer"

Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer"

PVC sheet then roll-formed onto fabric backing and - voilá - "vinyl"!PVC sheet then roll-formed onto fabric backing and - voilá - "vinyl"!

Problem: solvent slowly evaporates, esp. when (auto) vinyl seats & fascia heated by sun

Problem: solvent slowly evaporates, esp. when (auto) vinyl seats & fascia heated by sun

Armorall to the rescue! Periodically put solvent back into polymerArmorall to the rescue! Periodically put solvent back into polymer

Oils - Low MW……liquids lubricants, hydraulic fluids, water

repellants, usw.

Oils - Low MW……liquids lubricants, hydraulic fluids, water

repellants, usw. Elastomers - intermediate MW, crosslinked

waterproofing, caulk, prostheses, usw. Elastomers - intermediate MW, crosslinked

waterproofing, caulk, prostheses, usw.

Molding compds - high MW, crosslinkednon-structural parts, insulation, usw.

Molding compds - high MW, crosslinkednon-structural parts, insulation, usw.

Crosslinking – moisture reacts w/parts of chain to

crosslink……acetic acid is byproduct of rxn

Crosslinking – moisture reacts w/parts of chain to

crosslink……acetic acid is byproduct of rxn

silicones silicones

Some specific polymers Some specific polymers

High TM – form at elevated tempsHigh TM – form at elevated temps

Non-crystalline, nearly as strong as highly crystalline nylon, but tougher (stiff chain, pendant groups, H bonding betwn chains)

Non-crystalline, nearly as strong as highly crystalline nylon, but tougher (stiff chain, pendant groups, H bonding betwn chains)

{-O-C-O- -C- -}n{-O-C-O- -C- -}n

O H-C-HH

H-C-HH

polycarbonate

Some specific polymers Some specific polymers

Nylon cousin, but far stronger (very stiff chain)Nylon cousin, but far stronger (very stiff chain)

{-C- -C-N- -N-}n{-C- -C-N- -N-}n

OO HH

aramidaramid

OO HH

Non-burning, very high TM, solvent resistantNon-burning, very high TM, solvent resistant

When made into fibers ––> KevlarWhen made into fibers ––> Kevlar

Some specific polymers Some specific polymers

H2C-C-C{-O- -C- -O-}nC-C-CH2 H2C-C-C{-O- -C- -O-}nC-C-CH2

H-C-HH

H-C-HH

epoxy

H

H OO

H

H

hardenerH2N-R-NH2

PrepregsPrepregs

Some specific polymers

Some specific polymers

Composites - overview Composites - overview

Example - carbide tools (previously discussed) Example - carbide tools (previously discussed)

Co matrix phaseCo matrix phase

angular WC fragmentsangular WC fragments

Composites - overview Composites - overview

Artificial combination of matrix phase & dispersed phase Artificial combination of matrix phase & dispersed phase

Matrix:metal, alloyceramic mat'lpolymer

Matrix:metal, alloyceramic mat'lpolymer

Dispersed phase:particulatefiber

Dispersed phase:particulatefiber

Composites - metal matrix composites (MMCs) Composites - metal matrix composites (MMCs)

Particulates:ThO2-dispersed Ni (TD Ni)sintered Al powder (SAP)

Particulates:ThO2-dispersed Ni (TD Ni)sintered Al powder (SAP)

- except strengthening maintained at hi T- except strengthening maintained at hi T

Improves:strengthcreep resistancehi T corrosion resistance

Improves:strengthcreep resistancehi T corrosion resistance

Works like precipitation hardeningWorks like precipitation hardening

Composites - metal matrix composites (MMCs) Composites - metal matrix composites (MMCs)

Fibers:Conts - C, SiC, B, Al2O3

Disconts - C, Al2O3 , SiC whiskers

Fibers:Conts - C, SiC, B, Al2O3

Disconts - C, Al2O3 , SiC whiskers

May get rxn betwn phases at hi TMay get rxn betwn phases at hi T

Matrix mat'lsMatrix mat'ls

Composites - ceramic matrix composites (CMCs) Composites - ceramic matrix composites (CMCs)

Particulates, fibers:SiC, B, Al2O3 , C, SiC & Si3N4

whiskers

Particulates, fibers:SiC, B, Al2O3 , C, SiC & Si3N4

whiskers

Improve fracture toughness:Improve fracture toughness:

slow crack growthdeflect crack tipsredistribute stresses around crack

tipsbridge crack tips

slow crack growthdeflect crack tipsredistribute stresses around crack

tipsbridge crack tips

MatrixMatrix

Composites - polymer matrix composites (PMCs) Composites - polymer matrix composites (PMCs)

Fibers:mainly - glass (GFRPs), carbon (CFRPs),

aramid,others - B, SiC, Al2O3

Fibers:mainly - glass (GFRPs), carbon (CFRPs),

aramid,others - B, SiC, Al2O3

Composites - polymer matrix composites (PMCs) Composites - polymer matrix composites (PMCs) MatrixMatrix

Composites - polymer matrix composites (PMCs) Composites - polymer matrix composites (PMCs)

Very common - polyesters, vinyl estersVery common - polyesters, vinyl esters

CompositesComposites

Role of matrix in FR composites:a. transfer stresses betwn fibersb. provide barrier to environmentc. protect fibers

Role of matrix in FR composites:a. transfer stresses betwn fibersb. provide barrier to environmentc. protect fibers

Matrix/fiber bond:matrix must wet fiber physical & chemical bond desirablemechanical interlocking

Matrix/fiber bond:matrix must wet fiber physical & chemical bond desirablemechanical interlocking

Fibers frequently coated w/ coupling agentFibers frequently coated w/ coupling agent

non-couplednon-coupled

CompositesComposites

coupledcoupled

CompositesComposites

Fibers - variablesamountfiber lengthdistributionorientation

Fibers - variablesamountfiber lengthdistributionorientation

Fiber orientation can berandom aligned intermediate

Fiber orientation can berandom aligned intermediate