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manias@ psu.edu
The role of nmThe role of nm--thin layeredthin layeredinorganic fillers asinorganic fillers as
flame retardants in polymersflame retardants in polymers
E. Manias E. Manias && T.C. ChungT.C. ChungMaterials Science & Engineering dept.Materials Science & Engineering dept.
Penn State University, University Park, PAPenn State University, University Park, PA
J.W. GilmanJ.W. GilmanBuilding & Fire Research Lab, NISTBuilding & Fire Research Lab, NIST
OutlineOutline
Flame retardancy by layered silicate filler addition
✦ brief review of previous findings
✦ clues about the physical origins of FR
Effect of polymer & surfactant chemistry in FR
Syndiotactic Polystyrene / montmorillonite
nanocomposites as a promising high-T material
Concluding RemarksBuilding & Fire Research Laboratory
2
Flame Retardant CharacterFlame Retardant Character
0
200
400
600
800
1000
1200
1400
1600
0 120 240 360 480 600
PP intercalated (2 % silicate) PP pure (PP-g-MA, 0.4 % MA)PP intercalated (4 % silicate)
Hea
t Rel
ease
Rat
e (k
W/m
2 )
Time (seconds)
Flux = 35 kW/m2
Cone calorimeter studies(at NIST)
Gilman, J. W.; et al Chemistry of Materials 12, 1866 (2000)
“Universal” Enhancement:✦ PS ✦ nylon-6 ✦ PE✦ PP ✦ PI ✦ various epoxies
Origins:
formation of surface-char✦ barrier (O2, fumes)✦ thermal isolation
Char StructureChar Structure
Gilman, J. W.; et alChemistry of Materials 12, 1866 (2000)
nanocomposite structure char structure
3
Effect of filler dispersionEffect of filler dispersion
Flux = 35 kW/m 2
0
200
400
600
800
1000
1200
1400
1600
0 40 80 120 160 200 240 280
PS purePS immiscible (3 % NaMMT)
PS intercalated/delaminated (3 % 2C18-MMT) extruded at 170 oC
PS intercalated (3 % C14-FH) extruded at 170 oC
Hea
t Rel
ease
Rat
e (k
W/m
2 )
Time (seconds)Gilman, J. W.; et al
Chem. Mater.12, 1866 (2000)
Origins of the flame retardancyOrigins of the flame retardancy
Gilman, J. W.; et al Chemistry of Materials 12, 1866 (2000)
Nanoscale Dispersion is important/necessaryGeneral Improvement for many polymers
HRRs of thermoplastic/thermoset are reduced by 40-60% in nanocomposites of only 2-6% filler. This approach does not increase the carbon monoxide or soot produced during the combustion, and oftentimes it retards “dripping”.
The physical properties are not degraded by the sillicateadditive, instead many of them are improved.. FR originates from a surface char developmentduring combustion.
This char layer acts as an insulator and a mass transport barrier, as the polymer decomposes.
4
Achieving Dispersion Achieving Dispersion (for melt blending)(for melt blending)
Generally, Polymers and Clays do not mix
and thus, clays must be organically modified
“Rule of thumb” : favorable excess interactionsi.e. polymer-clay interactions better than
clay-surfactant interactions
Vaia & Giannelis, Macromolecules, 30, 7990 (1997)Balazs et al, Macromolecules, 31, 8370 (1998)
General Hybrid StructureGeneral Hybrid Structure
For naturally occuring fillers (e.g. montmorillonite)there coexist intercalated/exfoliated filler structures
A: intercalated layersB: exfoliated/disordered
5
Barrier propertiesBarrier properties
0 2 4 6 8
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
wat
er p
erm
eabi
lity
[10-5
g*m
/m2 h]
φ MMT [wt%]
0 1 2 3 4 5 6 7
0
10
20
30
40
neat PVA φ MMT : 2 wt% 4 wt% 6 wt%
Wat
er V
apor
Tra
ns.
[mg
H2O
]
time [ 103 min ]
Poly(vinyl-alcohol) / montmorillonite hybrid
K. Strawhecker & E. ManiasChemistry of Materials 12, 2943 (2000)
GeneralEnhancement:
PDMS nylon-6PP PE PETPU PUU PSPVA ...
water vapororganic solventsgases (e.g. O2 )
Origin of barrier propertiesOrigin of barrier properties
Origins:
✦ path tortuosity
✦ dispersion✦ filler effect on
polymer nature
R. Xu, E. Manias, A.J. Snyder & J. Runt Macromolecules, 34, 337-339 (2001)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
vol. fraction silicate (φ)
Rel
ativ
e Pe
rmea
bilit
y P
com
posi
te/P
poly
mer
poly(vinyl alcohol) poly(dimethyl siloxane) poly(urethane-r-urea)
α = 300
α = 1000
theoretical prediction- - - -
Origins:path tortuosity
filler effect on polymer nature
mechanicalthermalsolubility
6
Effect of polymer “chemistry”Effect of polymer “chemistry”
0
200
400
600
800
1000
1200
1400
1600
0 120 240 360 480 600
PP intercalated (2 % silicate) PP pure (PP-g-MA, 0.4 % MA)PP intercalated (4 % silicate)
Hea
t Rel
ease
Rat
e (k
W/m
2 )
Time (seconds)
Flux = 35 kW/m2
0 10 20 30 40 50 60 70 80 90 100 110 1200
200
400
600
800
1000
1200
1400
1600
1800
PP pure (PP-g-OH , 0.5% OH) PP hybrid (2C18-mmt, 5.5% silicate) PP hybrid (Cloisite15A, 5.5% silicate)
Hea
t Rel
ease
Rat
e (k
W /m
2 )
Time (seconds)
PP-g-MA 0.4% / 2C18MMT PP-g-OH 0.5% / 2C18MMT
Cone calorimeter studies at NIST
Effect of surfactant chemistryEffect of surfactant chemistry
100 200 300 400 500 600 700
0
20
40
60
80
100
2C18ammmoniummmt
sPS/2C18am -mmt nanocomposite
neat sPS
Wei
ght (
%)
Temperature (oC)
nanocomposite
formation with
alkyl-ammonium
modified mmt
can deteriorate
the response of
high T polymers
(e.g. syndio-PS)
7
Cationic Surfactants for Cationic Surfactants for sPSsPS
NN H
NN C16H33
NN C16H33
H+
N+
N C16H33
C16H33
C16H33I
C16H33I
THF
THF
2C16imm
C16imm
ImmidazoliumImmidazolium--alkyls as surfactantsalkyls as surfactants
nanocomposite
formation with
alkyl-immidazolium
modified mmt
can improve
the response of
syndio-PS
200 300 400 500 600
0
20
40
60
80
100
sPS / 2C16im-mmtnanocomposite
2C16-immidazmmt
neat sPS
Wei
ght (
%)
Temperature (oC)
8
200 300 400 500 600
0
20
40
60
80
100
C16imm -mmtnanocomposite
C16 immidazmmt
neat sPS
Wei
ght (
%)
Temperature (oC)
ImmidazoliumImmidazolium--alkyls as surfactantsalkyls as surfactants
Melt Processable Melt Processable sPSsPS/o/o--mmtmmt
0 5 10 15 20 25
sPS / 2C16imm-mmt nanocomposite(melt blending @ 270oC)
sPS / 2C16imm-mmtmixture
XRD
Inte
nsity
2θ
9
Melt Processable Melt Processable sPSsPS/o/o--mmtmmt
0 5 10 15 20 25
sPS / C16imm-mmt nanocomposite(melt blending @ 270oC)
sPS / C16imm-mmt mixture
XRD
Inte
nsity
2θ
Concluding RemarksConcluding Remarks
Nanoscale Dispersion is important/necessary
General Improvement for many polymers due toa surface char development during combustion
Chemistry is also importantpolymer chemistry/functionalizationorganic modification of mmt
syndio-Polystyrene / alkyl-immidazolium mmtnanocomposites seem promising high-T materials
10
AcknowledgementsAcknowledgements
Who actually did the work:Who actually did the work:
Zhiming WangAhmed TounyLixin Wu
Jeff Gilman (NIST)
T.C. Chung (Chemistry)
Financial Support:Financial Support:NIST (Building & Fire Research) Air ProductsKulicke & Soffa/PolysetArrow BiomedicalCoca-Cola papers at: http://zeus.plmsc.psu.edu/
or email: manias @ psu.edu/
100 nm