Jeffrey W. GilmanGroup Leader

Materials and Products GroupNIST

Flame Retardant Polymer Nanocomposites

General Flame Retardant Approaches for Polymers

I- Gas Phase Flame Retardants- Reduce Heat of Combustion (ΔHc ) resulting in incomplete combustion.- Inherent Drawbacks: Negative Public Perception!

II- Endothermic Flame Retardants- Function in Gas Phase and Condensed Phase- Via endothermic release of H2 O, polymer cooled and gas phase diluted.- Inherent Drawback: High loadings (30-50%) degrade mechanical properties.

III- Char Forming Flame Retardants- Operate in Condensed Phase- Provides thermal insulation for underlying polymer and a mass transport

barrier, preventing or delaying escape of fuel into the gas phase.- Inherent Drawback: High loadings (20-50%) degrade mechanical properties.

Goal: develop cost effective, environmentally friendly approacheGoal: develop cost effective, environmentally friendly approaches to s to reduce flammability reduce flammability andand improve physical propertiesimprove physical properties

Polymer clay NanocompositePolymer clay NanocompositeMaterials:Layered silicates, organic modifier, polymer matrix

Processing Techniques:•Solution mixing and film casting•Melt mixing (extrusion, injection molding)•In situ polymerization

Morphologies (Simplified picture):

Properties:•Flame resistance•Improved gas permeability•Higher stiffness•Scratch resistance•Higher glass transition•Improved thermo-mechanical response

Usuki et al. 2001, Nano LettersL. F. Drummy -AFRL

PPPP--clay Nanocomposite: TEMclay Nanocomposite: TEM

Gilman, et al, Chemistry of Materials; 2000; 12; 1866-1873

0

200

400

600

800

1000

1200

1400

1600

0 120 240 360 480 600

PP intercalated + delaminated (mass fraction 2 % silicate) PP-g-MA (mass fraction 0.4 % MA)

PP intercalated + delaminated (mass fraction 4 % silicate) H

eat R

elea

se R

ate

(kW

/m2 )

Time (seconds)

Flux = 35 kW/m 2

PPPP--clay Nanocomposite: Cone Calorimetryclay Nanocomposite: Cone Calorimetry

Gasification of Polystyrene LayeredGasification of Polystyrene Layered--silicate Nanocompositessilicate Nanocomposites

Char or

Coke Formation

Critical criteria for formation of homogeneous char

Kashiwagi et al., Polymer, 2004

Homogeneous clay dispersion in polymer

Unstable and inhomogeneous clay dispersion in polymer

Pyrolysis and phase separation

homogeneous char:thermal barrier

discontinuous char:Poor thermal protection

Depends on: clay loading, dispersion, polymer Mw, viscosity, degradation mechanisms, carbonaceous char formation

Nanocomposite + Conventional Flame Retardant Approach

Nanocomposites + additional flame retardants have resulted in fiNanocomposites + additional flame retardants have resulted in final nal materials that pass regulatory tests and have superior balances materials that pass regulatory tests and have superior balances of of properties. properties.

Successful commercial approaches remove some of existing FR Successful commercial approaches remove some of existing FR package, replace with nanocomposite. package, replace with nanocomposite.

DupontDupont 1980s 1980s ––PBT + PBT + OMMtOMMt + + OrganoOrgano BrBr-- UL94 V0UL94 V0Showa Denko Showa Denko –– PBT PBT SynMicaSynMica + + MealmineCYMealmineCY-- UL94V0UL94V0KabelwerkKabelwerk EupenEupen: EVA + : EVA + OrganomontmorilloniteOrganomontmorillonite + Al(OH)+ Al(OH)33. . ––UL1666UL1666PolyOne: (polyolefin nanocomposite PolyOne: (polyolefin nanocomposite –– ULUL--94 V94 V--0 @ 3.0mm) 0 @ 3.0mm) StrathclydeStrathclyde ––PU Foam + PU Foam + OMMtOMMt + FR + FR –– pass cribpass crib--5 5 NanocorNanocor –– PhosPhos. Clay . Clay -- UL94 V0UL94 V0U mass Lowell U mass Lowell –– ClayClay-- ELO as substitute for ELO as substitute for PbPb in PVCin PVC

ChallengesChallenges1)1) Furniture and mattress firesFurniture and mattress fires

still causestill cause~1000 deaths/yr and cost $ 500 M/yr~1000 deaths/yr and cost $ 500 M/yr

1)1)

Objective:Objective:

to evaluate the effectiveness of to evaluate the effectiveness of nanoadditive based flame retardantsnanoadditive based flame retardants

in reducing in reducing the flammability of flexible foams.the flammability of flexible foams.

2)2)

Objective :Objective :

To improve the ability of barrier To improve the ability of barrier fabrics to prevent flame spread in mattresses and fabrics to prevent flame spread in mattresses and furniture using furniture using nanoadditivesnanoadditives..

Melt Pool Fires During Foam Burning

240 kW in 540 sec240 kW in 540 sec

0

100

200

300

400

500

600

0 100 200 300 400 500 600 7000

100

200

300

400

500

600

Time Since Start of Ignition (s)

Polypropylene fabric

Cotton fabric

Cal 117 PU Foam

550 kW in 280 sec550 kW in 280 sec

Nano-additives

Layered Double Hydroxide

Mg(OH)64-

Al(OH)63

-

POSSCarbon nanotubes

Coughlin-U MassBellayer - NIST

Zammerano-Chimteclab

Layered Silicates

Nano silica

Kashiwagi - NIST

Flame Retardant MechanismHigh aspect ratio nanoadditives (e.g. CNF) properly dispersed in the polymeric matrix form a percolated jammed structure, due to particle- particle interactions, so that the melt behaves rheologically like a gel

-

Inhibition of dripping

1 10 100 10001

10

100

Rel

ativ

e vi

scos

ity

Shear Rate (1/s)

C30B CNF POSS

6.6 parts of Br-P FR in the standard formulation are replaced by 6.6 parts inorganic additive (e.g., CNF, Na+ MMT, LDH and Boehmite)

When organo-modified additive are used (e.g., OMMT) the amount of additive is increased in order to keep constant the inorganic fraction of the additive.

Modified/Nano Formulations

Br-P FR (wt.%)

Nano-additive (wt.%)

Br-P FR (Control 1) 6.2 0Talc (Control 2) 2.3 3.9CNF 2.3 3.9Boehmite 2.3 3.9LDH 2.3 3.9OMMT (C30B) 2.3 5.1POSS 2.3 5.1

Foam Processing Optimization

Control POSSFire-

quench Boehmite C30B

Non-optimized foam samples with various additives.

Each formulation needsto be individually tuned to match the control formulation.

1. Adjustment of the polyol – nanoparticle dispersion viscosity by coupling agents.

2. Optimization of the curing and blowing reaction through suitable catalysis ratios.

3. Prevention of collapse and shrinkage by appropriate surfactants and cell openers.

4. Monitoring of the foam rise and curing with a FOAMAT foam qualification system.

5. Evaluation of the foam quality by optical analysis, density and air flow measurements.

Characterization of Nanoparticles Dispersions

0 1 2 3 4 5

2.0 nm

1.9 nm4.0 nm

3.8 nm

I(q)

q (nm-1)

Cloisite 30B in liquid polyol Cloisite 30B Foam

Median Size (μm)

Cloisite

30B 100Boehmite 0.2POSS 8CNF -

Small Angle X-Ray ScatteringAggregate size estimation by means of Static Laser Scattering

Foam Characterization

POLYOL

FOAM

OPTICAL MICROSCOPY

SEM

Talc OM-Clay CNF

Br-P FR OM-Clay CNF

CNF

Cloisite 30B FoamCNF Foam

Modified Cone Calorimetry

Nanoadditive Flame Retardants for Polyurethane Foam

Tom Ohlemiller, Richard Harris, J. Randy Shields, Tom Ohlemiller, Richard Harris, J. Randy Shields, Mauro Mauro ZammaranoZammarano (GR), Roland (GR), Roland KrKräämermer (GR)(GR)

PoolPool--fire fire

PU FRPU FR--foam controlfoam controlnono

PoolPool--fire fire

PU FRPU FR--foam + 4% Carbon Nanofoam + 4% Carbon Nano--Fibers:Fibers:

Catch Pan

ViscosityNano-Graphite

HRR by Modified Cone Calorimetetry

0 50 100 150 200

0

1000

2000

3000

4000

5000

6000

HR

R (W

)

Time (s)

Cloisite 30B POSS Talc

35% reduction in PHRR with CNF

External Heat Flux: 11 kW/m2

0 50 100 150 200

0

1000

2000

3000

4000

5000

6000

HR

R (W

)

Time (s)

Talc Br-P FR CNF

Flame Retardant Mechanism of CNF

*Takashi Kashiwagi, BFRL, NIST

High aspect ratio nanoadditives (e.g. CNF) properly dispersed in the polymeric matrix form a percolated jammed structure, due to particle- particle interactions, so that the melt behaves rheologically like a gel*.

-

Inhibition of dripping-

Heat shield effects of network structured protective layer

1 mm1 mm1 mm

Residue of CNF foam after Cone

1 10 100 10001

10

100

Rel

ativ

e vi

scos

ity

Shear Rate (1/s)

C30B CNF POSS

CNF Foam Residue - SEM

1 mm1 mm1 mm

Residue of CNF foam after Cone

b) 4 μm

10 μmc)

Environmentally Friendly, Nano-based Polyurethane Fire Retardant Systems

Professor Richard A. Pethrick,

Department of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham

Building, 295 Cathedral Street Glasgow G1 1XL.

"Pollution Prevention through Nanotechnology" September 25-26, 2007, in Arlington , VA

1 10 100 1000

0.1

1

10

Shear thinning of sonicated glycol blends of Strath A / Strath B

1% Strath B 2% Strath B 3% Strath B 1% Strath A 2% Strath A 3% Strath A

Vis

cosit

y (P

a.s)

Shear Rate (1/s)

Effect of dispersion methods -study of PU monomers

Alignment of Platelets Due to Shear

Applied Shear

Alignment of the platelets in the shear field leadsto a lowering of the viscosity.

Flame Retardancy in Polymer Foams.

Nano platlets compositestructures within cellwalls to inhibit volatilediffusion and enhancethe viscoelasticity ofthe melt phase .

Flexible Foam Systems

• A series of flexiblefoam system have beenproduced with therequired flexibilityand incorporatingnanocompositeorganically modifiedclay materials.{Patents have beenapplied for thesesystems}

What do the materials look like?

• Electron microscopy has been performed and they show the nano material is present in the foam walls and has effected the rheology in the foam formation

• The materials have comparable mechanical properties to current flexible foam formulations

Electron Micrograph of PU foam

Electron Micrography of PU Foam Structure

CL592 CL594

Daly, Lewicki, Liggat, McCulloch, MacRitchie, Pethrick, Rhoney

The Challenge:

The Process:Formulation design

Toavoid this

Obtain this

Escalating Self-extinguishing

Crib 5 Testing

From these

Nano Composites

I hope this short presentation has shown that by recognising the natural nano dimensions which exist in natural materials it is possible to enhance the properties of conventional materials which we produce and achieve a greater use of these materials.

Nano composites are not all about new exotic materials but can be about using traditional materials more effectively.

Acknowledgements

• Dr J.J. Liggat, Dr John Daly,• Dr Ian Rhoney, Dr Sharon Ingram, • EPSRC.• Scottish Enterprise. • Southern Clay.

Layer by layer assembly of nanoparticles

Collaborator: Jaime Grunlan, Texas A&M

University

Deposition of nanoparticles using layer by layer assembly technique.

Coated Control Foam: 2 wt. % coating

Movie Speed: 10x

Amphipholis squamata• Common echinoderm• Diet consists of particles• Bioluminescence under

nervous control, and produced only under stimulation

• Commonly used in the Deheyn lab to assess sub- lethal effect

Dimitri D. Deheyn, Ph.D. Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego

Methodologies to Determine Health and Methodologies to Determine Health and Environmental effects of Environmental effects of NanoNano--particlesparticles

Experimental setup in aquariums

Nanoparticles* Concentration (ppm) Abbreviations

Single-Wall Carbon Nanotubes 1 and 10 SNT

Multi-Wall Carbon Nanotubes 10 MNT

Surfactant: Carboxymethyl cellulose 0.1 CMC

Layered Double Hydroxide Colloidal 1 and 10 CLD

Micro Layered Double Hydroxide 10 MLD

Surfactant: Sodium acetate ~10 SA

* Received from Jeff Gilman group at NIST, National Institute for Standard and Technology

Time variation of the spontaneous light Nanoparticles

Time variation of the spontaneous light Nanoparticles

Parameter Space for Polymer Nanocomposites

Polymer Nano-additive

Organic Treatment

Processing Conditions

Other additives

Flame Retardant

PE PP PS

PA6 PU

PVC PC PEO

PMMA EVA

Epoxy . .

clay POSS

Carbon Silica LDH

.

.

.

.

.

.

.

.

AlkylammoniumImidazolium

Chelates Silated Alkyl

Carboxylate . . . . . . .

Temperature Shear

Residence time sonication

.

.

.

.

.

.

.

.

.

Stabilizers Processing

UV Antioxidant

Fillers Pigments

.

.

.

.

.

.

.

Phosphate Halogenated Silicon Based

.

.

.

.

.

.

.

.

.

.

• We will use a small-scale automated high throughput liquid handling equipment with the capability of mixing dozens of polyol, nanoadditive combinations to screen for nanoscale mixing with polyols.

NanoNano--dispersiondispersion

ConclusionsAn An important applicationimportant application of polymer clay nanocomposites is of polymer clay nanocomposites is as a flame retardant in polymers. as a flame retardant in polymers.

flame retardant mechanism of polymer clay nanocomposites flame retardant mechanism of polymer clay nanocomposites appears to be the maintenance of a appears to be the maintenance of a homogeneous homogeneous dispersiondispersionStrathclydeStrathclyde -- Clay in Foam passes crib 5Clay in Foam passes crib 5 test for UK test for UK upholstered furnitureupholstered furniture

Carbon Carbon NanoNano FibersFibers inhibit melt dripping and reduce the inhibit melt dripping and reduce the flammabilityflammability

GrunlanGrunlan -- LBLLBL Coating can be used to remove dripping in Coating can be used to remove dripping in foamsfoams

DeheynDeheyn/Scripps preliminary data show /Scripps preliminary data show possiblepossible toxic effects toxic effects from surfactants and from surfactants and nanotubesnanotubes

Acknowledgments

Dimitri

D. Deheyn, Marine Biology Research Division,

Scripps Institution of Oceanography, University of California, San DiegoRoland Krämer

School of Chemical Science and Engineering, Fibre and Polymer Technology,Royal Institute of Technology, SE-100 44 Stockholm, Sweden

Jeffrey W. Gilman, Richard Harris, Jr., Thomas J. Ohlemiller, Sameer

S. Rahatekar, John R. Shields, Takashi Kashiwagi

Building and Fire Research Laboratory, NIST, Fire Research Division, Gaithersburg, MD

Jaime C. GrunlanDepartment of Mechanical Engineering & Polymer Technology Center (PTC)

Texas A&M University, College Station, TX

Professor Richard A. PethrickDepartment of Pure and Applied Chemistry, University of Strathclyde, Thomas

Graham Building, 295 Cathedral Street Glasgow G1 1XL

Methane ice burning http://http://www.geomar.dewww.geomar.de

Thank you