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ELASTOMERS (Filler & Reinforcements (Examples (Calcium carbonite Wet…
ELASTOMERS
Filler & Reinforcements
Concepts
Definitions
Black or non-black fillers
Reinforcing fillers
: increase prop. (strength), strong bonds filler/polymer
Non-reinforcement fillers
: weak to no bonds, weak interface, functionality, deterioration of prop. > Lower the cost
Reinforcing parameters
: particle size/shape, relative surface area, particle size distribution, surface chemistry/activity, surface morphology
Structure and shape
Particle size
:
Reinforcing: 10-50 nm + high pol/filler adhesion
Semi-reinf.: 50-1000 nm
Non-reinf. : > 1000 nm
:warning: Length scale matching: smallest size not always the better
Filler structure
: Agregate > Smaller part (same structure, higher surface area) or lower structure (same size, same surface area)
Surface area
:
N2-abs [m2/g]: small part. cover the complete surface including small cavities
CTAB-abs [m2/g]: larger mol., trapped in larger cavities, decrease surface acc. for pol.
DBP-abs [cm3/100g]: oily subst., fills empty space
Interface/Specific surface area
: to decrease abs. of polat ingredient > target: BET-N2 surface=CTAB surface
Mixing process
Aim: homogenization
Steps: Plastization > Incorporation > Dispersion > Distribution
Effect on properties
Affect the curing process
: absorb curing agents (silanol), accelerator like, faster curing (high T cond.), pH value of filler, surface treatment
Affect the processability*
: dep. on the filler type and amount
Effect on crack propagation
: slow crack growth
Effect on tensile prop.
Examples
Calcium carbonite
Wet or dry, diameter 0,7-5 um, prepared by grounded natural calcium carbonates
+
: low cost, used at high loadings
-
: poor pol.-filler interaction, tear res.
-> Precipitate: higher surface area, diff. cryst. forms and shapes, >100 nm
Clays
Platy aluminosilicate with cont. sheet structure of overlapping flakes
Challenge
: exfoliation into indiv. clay plates
Uses
: fiber adhesive compound, non-tire rubber goods
+
: moderate cost, good processability
Aluminium-trihydrate (ATH)
+
: Flame retardant
-
: High loading needed (=no elasticity)
Talc and micro-talc
Mg-, Al-silicates
+
: inert, heat res., use as release agent
TiO2
White, coloring agent, semi-reinforcing
Layered silicates, organoclays
Layers in clay: bond by Van der Waals
High interlayer spacing: nanofiller can go inside
Increase ILS: NA+, K+, Ca2+, NH4+
Surface becomes more compatible with hyfrophobic pol.
Nanofillers
1D < 100 nm ->Large surface area
High reinforcing potential
Challenge
: mixing > no compatible is not enough dispersion
Carbon Black
Structure
: Primary part (20-200 nm) > Aggregates (200-600 nm) > Agglomerate (1-6 mm)
If particle size increases:
Increase of: elongation, resilience, dispersion, extrusion
Decrease of: tensile, hardness, tear/abrasion res., mixing T, viscosity, green strength
If structure decreases:
Increase of: elongation, tear res., elongation
Decrease of: hardness, compression, abrasion res., mixing T, dispersion, viscosity, extrusion
Silica
Uses
: tyre, silicone rubbers
Granulate
or
micropearls
forms
Granulate (um)/Micropearls (100 um)/Grinded particle (1-100 umm) >
Agglomerate
(1-5 um) : break under high shear pressure >
Aggregate
(50-400 um) : mech. unbreakable, reinforcing > *Elementary part. (5-4 nm)
Compromise between aggregate size and specific area
Surface chemistry
> surface prop. management
Ex: silanols groups at silica surface to manage rubber interface
-
Absorption of ingredients, use of interfacial agent with hydrophobic meda
Coupling agent
Problems
:
High surface energy (agglomeration)
Acidic surface (influence of curing)
Hydrophilic surface (absorption of moisture)
Strongly polar/hydrophilic nature
-> Addition of coupling agent
Bifunctional
:
Outer funct.: react with silanol-groups of silica
Inner sulfur-bridge with rubber during vulc.
Silane
: mixing T>130°C
:warning: Production of ethanol > high T + long time to remove, silanisation start at 140°C, max dump T=165°C
New silane coupling agent
Long chain alcohol stops the volatile alcohol
Low rank sulfur: no contribution to S donation
Small amount of water/OH required for hydrolysis of NXT silane to couple with S
Characteristics
+
: Smaller size, range of size primary particles, higher structure (increase reinforcing, elasticity, decrease filler content)
-
: cost ++, high surface energy, acidic surface, polar/hydrophilic
Silica vs CB
CB
:
+
: Higher reinforcement (without CA), lower structure, chemistry
Chemistry
: graphine crystalline area, funct. groupe at cryst. edges, phenol/carboxyl/lactone...
Silica
:
+
: More stable at higher strain ratio, lower surface area
Chemistry
: functional groups on the surface (siloxanes, silanols)
At 1-to1 replacement: silica much more reinforcing
Filler migration
Affinity of CB: BR>SBR>CR>NBR>NR>EPDM>IIR
Affinity of silica: NBR>SBR>NR>BR>EPR>IIR
*In tire¨: silica > lower rolling res. without inf. wet grip/abrasion
Dual phase filler
: prop. silica decrease at high T
Reinforcing mechanism
log(shear mod) vs strain amplitude: accumulation of different effects
Hydrodynamic effect
: η=η0(1+2,5Φ), G'=G0'(1+2,5Φ+14,1Φ^2...)
Filler-filler inter.
: Payne effect
Filler-pol. int.
: rev. adhesion/abs. and release from black surface, occuled rubber + Mullin effet
Pol. network contribution
: strain-indep. to modulus, formed during vulc. reaction, G=NkT
Hydrodynamical amplification
Dilute suspension of spherical inclusion:
Es=Ec/Em=1+2,5Φ+αΦ
Ec: final mod., Em: pure matrix, Φ: vol. faction (filler), α: 2nd order term
Einstein-Smallwood
: f=1+2,5Φ
Guth-Gold
: f=1+2,5Φ+14,1Φ^2
Padé
: f=1+2,5Φ+5Φ^2
For short fibers (Halpin-Tsai): Es=(1+2ηΦ)/(1-ηΦ)
Filler-Polymer Interaction
Ex: Velcro= rev. adhesion/abs., release from black surface > slipping of pol. chains + dissipation of energy
Occluded rubber: pol. chains are trapped in void of the agglomerates and aggregates
Bound rubber
Tendency of a part of rubber pol. mol. to chem./phys. adhere to the CB surface (insoluble)
Around CB primary part.: thin shell of pol. formed with restricted mobility (
glassy layer
)
Factors
:
Filler: concentration, aggregate size (stricture), surface area/activity, chem. compo.
Elastomer: chem. compo., unsaturation, polarity, structure
Mixing variables: mixing energy, time, temperature
Chemical additives
Filler-pol. interaction
Mullin effect: instant. + irr. softening of the stress-strain curve
2nd and higher def. cycles > lower tenile prop. (damage of CB network an rearrangement of the pol. mol. during 1st cycle)
Strain
: shortest chains between filler are slipping along surface
Relaxation
: diff. from the starting configuration
Filler-filler interaction
Ex: Soap bubbles
Payne effect
: damage of the CB network at strain >1% from CB, result in decreasing mod.
Electrical conductivity
: increase rapidly then decrease
Low percolation does not always signify higher reinforcing character
Explain Payne effect
: Kraus model (breakage + reforming), Huber-Vilgis (breakage + reformation, fractal nature), Maier-Goeritz (filler-rubber int., abs.-desorption)
Rubber Elasticity & Characterization
Statistical theory of rubber elasticity
General expression for rubber deformation
Owing to statistical treatment of the probable end-to-end distance of a single molecule
Kinetic theory
= analogy with theory of gases
Assumptions
Network contains N chains/unit vol.
Mean-square end-to-end distance for the whole assembly of chains in the unstrained state is the same as for a corresponding st of free chains:
r^2=n.l^2
No change of volume on deformation
Junction points between chains move on def. as if they were embedded in an elastic continuum. Compo. of each length of each chain change in the same ratio as the corr. dimension of the bulk rubber
Entropy of the network is th sum of indiv. S:
S=C-kb^2r^2
Entropy
Case of pure, homo. strain of any type
Unit cube > rectangular parall. with 3 unequal edges λ1, λ2, λ3
Extension ratio, >1=stretch, <1=compression
x=λ1x0, y=λ2y0, z=λ3z0
Original state
: S0=c-kb^2(x0^2+y0^2+z0^2)
Strain state
: S=c-kb^2((λ1x0)^2+(λ2y0)^2+(λ3z0)^2)
Total entropy of the network
: DS=S-S0
Assumption
: chain contour length/MW is the same: b=ct + r0 random + r0^2=3/2b:
DS=-1/2.Nk(λ1^2+λ2^2+λ3^2-3)
Work of deformation
: W=-T.DS
W=1/2G(λ1^2+λ2^2+λ3^2-3)
with
G=NkT
G: shear modulus
, G=density.RT/Mc
Modification
: not all cross-links will be effective, defects: loose loops and loose ends
G=NekT=density.RT/Mc-2.Mc/M
Experimental exmination
Simple elongation
λ1=λ, λ2=λ3=λ^(-1/2)
W=G/2.λ^2+2/λ
σ=dW/dλ=G(λ-λ^-2)
Rem: σ/E0=1/3.(λ-λ^-2)
Simple shear
λ1=λ, λ2=1, λ3=1/λ, and λ=stretched/unstretched length
Shear strain
: γ=λ-1/λ=tanφ
W=-G/2.(λ^2+λ^(-2)-2)=G/2.tanφ
Shear stress
: τ=dW/dγ=Gγ
Rem
: validity of Hook's law in shear but NOT in elongation or compression
G=τ/A.U/H=f/A.tanφ
Moduli
:
E=2G(1=v)=3K(1-2v)
Elastomers: v=0,5, E=3G
Pure shear
Extensions in 3D without rotation
λ1=λ, λ2=1, λ3=1/λ
Principal stresses
: t1/t2 (t3=0):
t1=G(λ1^2-1/λ2^2) and t2=G(1-1/λ2^2)
Force/unit area
: f1=G(λ1-1/λ1^3) and f2=G(1-1/λ1^2)
-> t1=f1/(λ2λ3)=λ1.f1
Phenomenological theory of rubber elasticity - Mooney-Rivlin theory
Mooney
Assumptions
: rubber incompressible and isotropic in unstrained state + Hooke's law OK for simple shear
W=C1(λ1^2+λ2^2+λ3^2-3)+C2(1/λ1^2+1/λ2^2+1/λ3^2-3)
Simple shear
W=(C1+C2)(λ1^2+1/λ^2-2)=(C1+C2)γ^2
σ=dW/dγ=2(C1+C2)γ
Mod. of rigidity
: 2(C1+C2)
Simple extension/comp.
:
f=dW/dλ=2(λ1-1/λ1^2)(C1+C2/λ1)
Ravlin
Assumptions
: incompressible/isotropic in unstrained state + isotropy requires that W shall be sym. wrt λ1, λ2, λ3 + stain energy=f(λi) one
Invariants
:
I1=λ1^2+λ2^2+λ3^2
I2=λ1^2.λ2^2+λ2^2.λ3^2+λ1^2.λ3^2
I3=λ1^2.λ2^2.λ3^2=(V/V0)^2=1 for incompressible
W=(sum i,j) Cij(I1-3)^i.(I2-3)^i
Rem: at 0 strain I1=I2=3
Other form
: W=C1(I1-3)+C2(I2-3)
+
restricted to squares of extension ratios
Strain energy function
: (useless)
U=(sum, n)un/αn.(λ1^αn+λ2^αn+λ3^αn-3)
Furukawa
σ=2(λ-1/λ)(C1+C2/λ)
Limiting chain extensibility + strain-induced crystallization
σ=2(C1+C2/λ).F(λ)
where F(λ)=λ+1/λ^2+λm*/3.(λ/λmax)^3+...
Characterization of rubbers
Mooney viscosity
Needed information
: method of sample preparation, Mooney viscosity number, rotor size, preheat time, time interval to viscosity reading, T of the test
Results: 50ML(I+4)100C
with 50M: viscosity, L: rotor, I: preheat time,4: time after starting the rotor, 100C: T
Measurement of curing time
Essential balance between rubber processing safety and faster curing rate
Induction/scorch > Curing > overcure
Prevulcanization inhibitors: salicylic acid, phtalic anhydride, acetyl salicylic (0,3-10 phr), CTP (0,1-0,2 phr)
Stress-strain experiment
Measurable quantities
: E, Modulus at diff. elongation, tensile strength, elongation at break, creeping of elongation, stress relaxation, hysterisis, crosslinking density
Measurement of crosslinking density
Mooney-Rivlin
: σ/(λ-1/λ)=2(C1+C2/λ)
Slope
: 2C1=vkt with v:crosslinking density
N'=v/2
with v: nb of effective network chains
Other
Rebound resilience
Permanent set/Compression set
DIN abrasion test
Dynamic mechanical analysis
Damping
: tanδ=E''/E'
with E'': loss modulus, E': stored modulus
δ=0* > elastic, δ=90° > viscous
E
=E'+iE'', E
=σ/ε=σ0/ε0.exp(iδ)
E*=σ0/ε0.cos(δ) (stored) + iσ0/ε0.sin(δ) (loss
Factors influencing Tg
Free volume
Presence of low MW compound (plasticizers) (decrease Tg)
Crosslinking (increase Tg)
Backbone flexibility
Intermolecular force
Viscoelasticity
General
Ideal solid
> Elastic
Hooke: σ=Eε, τ=Gγ
An elastic mat. obeying HL > perfect spring
Valid at very small strain
Ideal fluid
> Viscous
Newton: τ=η.dγ/dt
Model > Dashpot (piston)
Maxwell
Comb. of Newton and Hooke's law on series
Final strain=stain(elast)+stain(visc)
dγ/dt=1/G.dσ/dt+σ/η
If constant shear: dγ/dt=0
BC: t=t0, σ=σ0 :
σ=σ0.exp(-tG/η)
Voigh-Kelvin
Stress shared btw element and each is subjected to the same deformation
Final stress=stress(elast)+stress(visc)
σ(t)=γ(t).G+η.dγ(t)/dt
or σe(t)=ε(t)E+ηe.dε(t)/dt (eq.)
Simplification
: γ(t)/σ0=J(t)=5(1-exp(-t/τ))
J=I/G: creep compliance in shear
Viscoelastic regions
**Glassy modulus > Cohesive energy density prop. δ^2
δ: solubility parameter
δ^2= δd (dispersion) + δp (dipole) + δh (H bonding)
Rubbery modulus: E=3,RT
Creep and recovery
Slope (when strain) prop. ηe
Retardation time: τ
Irrecoverable creep increases with time
Creep and recovery tests = cycled
Stress relaxation = reverse of creep
Rubber compounding
Rubber components
Elastomer
: basic prop. of the compound
Peptizing agents
: aid during mastication
Filler
: mod. the mecha. prop., processability, price
Softeners
: increase filler dispersion and processability
Vulcanization chemicals
: vulcanizing agents, activators, accelerators, inhibitors...
Protective agents
: antiozonants, antioxidants, UV-stabilizers, flame retardants
*Unit: phr (per hundred rubbber)
Mixing processes
: incorporation, dispersive mixing, distributive mixing
Vulcanization of rubber
Definition
Polymer chains > crosslinked by reaction with the vulcanization agent, 3D network
Soft, wear mat. -> strong elastic product
Increase thermal, UV, ageing and chemical res.
*Types¨:
:<3: Sulphur vulc. (140-180°C) : NR, IR, BR, SBR, IIR, NBR, EPDM, CR
:<3: Peroxide vulc. (160-180°C): EPM, EPDM, CM, CSM, silicone, NBR
Electron beam (room T- high T)
Metal oxide (for hologenated rubber): CR, CSM
Acetoxysilane (for silicone rubber)
Triazine curing (for diene rubber)
Resine curing (for diene rubber)
Ingredients
Accelerators
Organic compound containing sulphur, nitrogen, and phosphorous
Increase: crosslink density, ageing res.
Decrease: vulc. time, vulc. T, sulphur content in rubber, possibility of prevulcanization and reversion
Reactions
with ZnO > Zn-salt
ZN-salt with Sulphur
React with RH
Formation of active complex with ZnO
Activators
Organic acids and alcohols
Ex
: Zinc oxide (electronegativity), stearic acid (comb. of ZnO: increas crosslink density, egeing, tensile strength, reduce energy of curing), other fatty acids
Sulphur
Sulphur donors
Organic compound containing sulphur
No elemental S in rubber
Good addinf prop. dur to lack of free S
Sulphur curing
If S is soluble : easy blooming into surface, prone to reversion
If S insoluble: remaining inside the rubber
Crosslink structure in a sulphur-vulcanized rubber shaped by changin the ratio of sulfur/acc. 3 systems:
S/Acc>1: conventional, mainly polysulfidic links, good tensile, fatigue res. low cost
S/Acc<1: efficient vulcanizing (EV), mono and disulfidic crosslinks, good ox ageing, reversion res., poor fatigue bahavior
S/Acc=1: semi-EV, good balance of processing and mecha. prop.
Reversion of NR curing
Reduction of mecha. prop if overcured
Peroxide curing
Initiation (formation of rad.) > Propagation (Proton attraction by a peroxyde) > Termination (recomb. of 2 pol. rad. under form. of crosslink)
vs Sulfur:
+
: tougher, heat res., compression set, corr. res.
-
: tensile strength, less elasticity, dynamic prop.
Measurement of curing time
Phases
: Induction + scorch > Curing > Overcuring (marching or plateau or reversion)
Scorch
: premature vulc., avoided by retarders or pre-vulc. inhibitors or high T
Crosslinking density
-
N'=v/2
with: N' [nb moles/unit vol.], v: effective network chains
vr: volume fraction of rubber
Vs: molar vol. of solvent
X: Flory-Huggings pol-sol interaction parameters, X=Vs/RT.(Sol(solvent)-Sol(pol.))^2
Plasticizers
Synthetic
For polar rubber (NBR, CR)
High cost, large variety
Ester plast.
:
Phtalic > increase elasticity, low T flex.
Adipinic > increase cost, low T flex. (NBR++)
Phosphoric > low fammability
Chlorinated carbohydrates
: low fammablity
Polycondensed products
: high MW, non-volatile, non-migrating
Mineral oils
Types
: Aromatic (TDAE and MES), naphthenic, paraffinic
Most used
Classified according to their density, viscosity
Viscosity gravity constant VGC
: VGC=(D-0,24-0,22log(Vt-35,5))/0,755
D: oil density, Vt: say bolt viscosity
Antioxidant and antiozonant
Ageing of rubber
Can be degraded by reactions with O2, O3, light, metal ions, heat
SBR, NBR, CR, RDPM > cyclization, crosslink >
hardening
NR, IR, IIR > Bond cleavage >
softening
Ren
: no C=C > less sensitive to aerial oxidation
Degradation by O2
: ox. + cut short chains
Key: initial formation of free radicals
High T or high shear forces: Free rad. formed by cleavage of C=C and C-H
Absorption of O2
: :warning: trace of peroxide, free rad. generators, heat, impurities, UV-light > pro-oxidant
Protections
Metal deactivators
: orga. compound forming coordination complexes with metal > EDTA + its various salts
Light absorbers
: protect from photo-ox. by abs. UV > Carbon black, zonc oxide
Peroxide decomposer
: react with initiating peroxide to form inactive prod.
Free rad. chain stoppers
Inhibitor regenerators
Ozone
Ozone cracking
=electrophilic reaction, starts with O3 attack at a location where e density is high
:warning: Unsaturated orga. compounds are highly reactive
Resistant
: EPM, FDM, BIIR, PE
Protection
:
Chemical antiozonants
Waxes
Scavenging mechanism: antiozonant must react more rapidly with O3 than the = of the rubber molecules
Protective film (=waxes)
Combination of both mechanisms
Add an ozone-resistant pol. to the diene rubber
Basics
Definitions
Rubbers
: 3D molecular network, strong chemical bonds, better elasticity, resistance to set and durability
Thermoplastic elastomers
: weak secondary bonds
Rubber Typess
Usual
Butadiene rubber (BR)
Uses
: Tyre treads
+
: resilience, low T porp.
-
: mecha. prop.
Butyl rubber (IIR)
Uses
: Inner tubes, cable sheathing, roofing, thank liners
+
: Air-retention
-
: oil/fuel res., weather res.
Styrene-butadiene rubber (SBR)
Uses
: Tyres, general purposes
+
: Abrasion
-
: Oil res.
Emulsion pol.
: easy to mix, increase strength with C, 23% styrene, wide viscosity range
Solution pol.
: cis, trans, vinyl ratio controllable
more difficult to process
used in treads for low rolling resistances
Chloroprene rubber (CR)
Uses
: rescue suits, conveyor belts, wire/cable
+
: oil/chemical/weather res., strength
-
: process difficult
Natural rubber(NR)/Isoprene rubber(IR)
Uses
: general purposes, tyres, footwear, seals
+
: mecha. prop. ++
-
: oil/weather res., mecha. res.
Types
:
Oil-extended (OENR) > tyres, 20-30% aromatic oil
Sup. procession (SP-rubber) > 20-50% vulcanized, for extrusion
Deproteinized (DPNR) > low creep/stress relaxation
Heveaplus MG rubber > 30-49% methyl-metacrylate, hard++, adhesive
Epoxidized NR (ENR) > 10-25-50%, low air perm., high oil res.
Thermoplastic NR (TPNR) > blend NR+PP, for shoesles, cars
Acrylonite-butadiene rubber (NBR)
Uses
: hoses, seals, gaskets
+
: oil/chemical res.
-
: low T flexibility, weather res.
Types
:
Carboxylated (XNBR) > crosslinking between carboxyl groups
Hydrogenated (HNBR) > increase oil/high T res., peroxide vulc., high H degree, lower Tg
Silicones (Q)
Uses
: Gasket, seals, medical app.
+
: high and low T res.
-
: mecha. prop., electrical insulator
Rem
: inorganic main chain -Si-O-Si-O-
diif. organic side groups: fluoro-, phenyl-, nitrile: increase heat/oil res.
Polyurethanes (AU, EU)
Uses
: Printing roller, sealing, shoe soles
+
: strength, abrasion res., chemical res., O2/O3 barrier, low friction
vary a lot due to processing conditions
Polyester based on PU: better prop. at low T
Rarely used
Chlorosulfonated polyethylene (CM,CSM)
Uses
: wore/cable, chemical plant hose, fabric coating, film
+
: heat/O3/weather res., oil/chemical res., high elasticity, abrasion res.
Chlorine or chlorosulphon groups attached to PE backbone > prevent crystallization > more elastic
CM
: 23-48% chlorine
CSM
: best elasticity at 30-35% chlorine, 1% sulfur, easier to vulcanize > more common
Polysulfide
Uses
: Adhesive, sealants, binders, hose
+
: oil/solvent/water res., impermeability to gases
-
: low strength, odor
Epichlorohydrin (CO, ECO, ETER/GECO)
Uses
: seals, gaskets, wire/cable coatings
+
: O3 res., low resilience, heat/flame/weather res., low air permeability
Fluoroelastomers (FKM, FPM)
Uses
: aerospace, high quality seals, gaskets
+
: heat res., sup. oil/chemical/solvent res., very stable
-
: highest priced
Rem
: strong bonds C=F2
Polyacrylate rubbers (ACM)
Manufactured fom acrylic esters + reactive cure site monomers (1-5%) + Saturated structure
+
: weather/oil/heat res.
-
: low water/alkalis/acid res. due to ester groups
Best
Max T
: EPM,EPDM (120°C)/
FPM (200°C),PMQ (200°C)
Min T
: BR (-75°C)/
AU/EU (-10°C), PMQ (-80°C)
Tear res.
: NR/IR/
AU/EU
Abrasion
: NR/IR, SBR, BR/
AU/EU
Oil/fuel res.
: NBR/
CO/ECO, ACM, AU/EU,FPM
Gas diff.
: IIR/
CO/ECO
Ox. res.
: EDP/EPDM/
AU/EU
Weathering/O3 res
: EPD/EPDM/
AU/EU
Fire res.
: CR/
FPM
Rebound elasticity in cold
: NI/IR, BR/
PMQ/VMQ
Latices (Latex)
NR, SBR, NBR > water-based, other solvent-based
App
: foamed structured, backing for carpets, adhesives, thin-walled products
Thermoplastic elastomers TPE
Definition
Act and look like rubbers, but processed like plastic
No vulcanization
Physical bonds between the molecules
Consist of
hard
(det. strength, heat res., chemical res.) and
soft
(det. low T prop., elasticity) phases (triblock structure ABA)
Styrene-diene block copolymer (TPE-S)
20-40% of styrene, most used TPE
Ex
: SBS, SIS, SEBS
Elastomeric alloyes (EA)
No regular block
TP olefin elastomers (TPO)
: polyolefin + unvulcanized rubber
TP vulcanizates (TPV)
: TP + unvulcanized rubber, higher operating T, mecha. prop, oil res. than TPO
-> Melt processable rubbers (MPR): one-phase system, 2 polymers mixed in molecular-level (1 Tg only)
TP urethane elastomers (TPU)
First TPE
3 compounds: di-isocyanate + polyether/polyester + chain extrender
Factors affecting prop.*
: ratio of isocyanates/hydroxyl, chain diol, polyol, amount of compound
Polyether
: elasticity at low T, good resilience, hydrolytic stability, microbial res.
Polyester
: stiffness, tear strength, abrasion res., oil res., T res.
TP-ester elastomers (TPE-E)
Crystallizable polyester, flexible polyether
TP polyamide elastomer (TPE-A)
Hard segments: aromatic
Soft segments: aliphatic polyester or -ether
TPE vs rubber
Lower chemical res.
Higher compression res.
Lack of soft materials
Recyclable
Simpler processing (no mixing or vulc.)
More expensive