Introduction to PNC Science and Technology

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Introduction to PNC Science and Technology

Introduction to PNC Science

and Technology

L. A. Utracki

2 2

Outline

Introduction to polymeric nanocomposites

(PNC)

Applications

Definitions

Clay intercalation & exfoliation methods

Compounding/dispersing PNC

Elements of the science & technology

Mathematical modeling

Thermodynamics of PNC

Rheology of PNC

PNC performance (mechanical, barrier, flammability)

Conclusions

3 2

PNC market

The PNC annual growth rate

is AGR  18.4%/y.

The growth rate for

thermoplastics is 20%, and

that of thermosets 10%.

The thermoplastic matrices

constitute ca. 77%, thus

thermoplastic PNC market

AGR  24%/y.

According to BCC (2004), the global market for CPNC increased

from US$90.8M in 2003, to 195 in 2004, and it is expected to

increase to US$311M by 2008.

0 50 100 150 200 250 300 350 2003 2004 2005 PNC market size TP (M US$) TS (M US$) Total (M US$) Million US$ Yea r 3

4 2

Use of CPNC in 2004

GM has been using CPNC since 2002. In 2004, the company introduced body side molding in Chevrolet Impala. The latest application is the 2005 GM Hummer H2 using a TPO-clay formulation.

PP-based CPNC are used in seat backs of the 2004 Acura TL. They are to be used for interior consoles of a 2006 light trucks.

PolyOne has commercialized CPNC masterbatches with high impact strength and stiffness for consumer disposable applications. Its formulations combine chemical resistance and stiffness and dramatically reduce cycle time.

Semi-aromatic PA-based CPNC (with PA-mXD6) have been used by Eastman as a barrier layer in multi-layer PET bottles and films for food packaging, e.g., in Europe for alcoholic beverage bottles, carbonated soft-drink bottles and

thermoformed deli meat and cheese containers.

Nanocomposite concentrates are being evaluated in films not only for enhancing barrier, but also to control the release and migration of additives such as

5 2

Other uses of CPNC’s

Unitica produces injection-molding grades of PA-6 based PNC used for the production of car engine and converter covers for Mitsubishi & Toyota.

The same grade is also used for injection molding of highly rigid bases for the electronic control tray & cover.

Ube PNC is used for rear mirror housing and timing belt cover.

Bayer manufactures PA-6 nanocomposites for transparent barrier film packaging.

Kabelwerk Eupen uses EVAc/organoclay for wire & cable applications. Drastic reduction of heat release

(flammability) at 3 to 5 wt% clay loading.

Showa Denko produces PA-66 and POM

nanocomposites for improved flame retardancy and

rigidity at 0.4 mm thickness. The flex moduli are 30-80% higher, and HDT 30 to 80 C higher, than those of neat resins.

6 2

Nanocomposites (NC) = matrix + dispersed in it nanometer-sized

(< 50 nm) particles.

The matrix may be single- or multi-phase.

It may comprise additives that complement functionalities of the

system (reinforcement, electrical conductivity, toughness, etc.)

Depending on the nature of matrix, NC is:

Polymeric NC (PNC)

Ceramic NC (CNC)

Metallic NC (MNC)

To generate high enhancement of properties, the nano-particles

ought to be anisometric, viz.

Lamellar

, Fibrillar, Tubular, etc.

Spherical particles have been used to produce functional NC (e.g.,

for electrical conductivity, optical or magnetic properties, etc.).

7 2

Definitions 2

Exfoliated clay:

− individual

platelets dispersed in a matrix

with spacing d

₀₀₁

> 8.8 nm.

The platelets may form Short

stacks randomly dispersed.

Intercalated clay:

− having

organic or inorganic molecules

inserted between Platelets, thus

with d

₀₀₁

> 1.5 nm.

Intercalant:

− material sorbed between Platelets that binds with their

surfaces to form an Intercalate.

Interlayer, basal spacing, or d-spacing, d

₀₀₁

is the thickness of the

repeating layers as seen by the XRD = mineral thickness

8 2

Mainly montmorillonite (MMT)

ADVANTAGES Well-established technology Availability Lower cost DISADVANTAGES Variability of composition

Platelets welded together by fault in crystal structure

Variable color

Contaminants (grit & amorphous clay)

Semi- or fully-synthetic

MMT, hectorite or saponite

Hydrothermal or molten glass

Example: fluoro mica (FM, FH)

ADVANTAGES Aspect ratio: p  6,000 Stable composition Non-toxic Absence of color DISADVANTAGES

Limited and uncertain sourcing Evolving technology

Higher cost

Mineral vs. synthetic clay

9 2

Cell unit MW (g/mol.) 540.46 Density (g/mL) 2.3 to 3.0 Mohs Hardness @20°C 1.5- 2.0

Cleavage Perfect in one direction, lamellar Characteristic Expands up to 30 times in volume

in H2O

Appearance Light yellow with dull luster Field Indicators Softness, and soapy feel

Montmorillonite (MMT)

TEM of MMT

At T < 500°C smectites have 4 layers:

Outer layer with H₂O and Na+_{, K}+_{, Ca}++_{, Mg}++ _ions.

3-layer sandwich: octahedral central between two tetrahedral: SiO₂-(Al/Mg)-SiO₂; 0.956 nm thick.

Monoclinic, (Na,Ca)(Al,Mg)₆(Si₄0₁₀)₃(OH)₆-nH₂0], has: Al = 10, Si = 21, H = 4, and O = 65 (wt%); p  100 to

300; A_sp  750 m2_{/g (football stadium = 17 g MMT);}

Cation exchange capacity: CEC  1.0 ± 0.2 meq/g.

Reactive sites: anions and –OH groups on the surface and cations and –OH groups at the rim.

10 2

Intercalation 1

Intercalation

− diffusion of intercalant into clay galleries.

The intercalant binds to the platelet surface.

The aim of intercalation: to expand the interlayer space,

facilitating diffusion of macromolecules (exfoliation).

Intercalation depends on the balance of forces: positive that

drives the molecules to bond with the solid surface and

negative that requires breaking the solid-solid interaction

and loss of entropy.

Intercalation is a process of simultaneous expansion of ca.

200 clay platelets that form a tactoid. The layers are elastic,

but there is a limit to the amount of bending they can

undergo.

The efficient strategy of intercalation involves reduction of

the stack size and a progressive increase of the penetrant

size, starting with H

₂

O, then an onium cation, ....

11 2

Intercalation 3

Several routes have been used to intercalate clay particles:

Low-MW solvents and solutions, viz. water, alcohols, glycols,

monomers.

Freeze-drying of expanded clay.

Organic cations, viz. ammonium, phosphonium or sulfonium.

Complexing of aromatic or cyclical (crown ether) compounds by Cu

++

or Ag

+

_.

Compounding with organic liquids, viz. monomers, epoxies, PEG,

PVAl, PDMS, PVP, and their solutions.

Inorganic compounds that form inter-layer pillars

– stable porosity,

but no exfoliation

.

Mechanical or ultrasonic delaminations in aq. medium.

By cyclic compression/decompression.

12 2

Intercalation 4

For CPNC organoclay must be thermodynamically miscible with

the matrix

, hence

great diversity of the intercalating agents have

been described in the patent literature

.

They mainly comprise primary, secondary, tertiary or quarternary

onium salts, viz.

ammonium, phosphonium, sulfonium

or their

mixtures, with or without organosilane as a coupling agent.

Process:

1. Dispersion in aqueous medium at T = 60-77°C.

2. Reaction with onium ions.

3. Bond strength increases in order:

4. Secondary treatments, e.g., with a « sizing agent ».

5. Addition of a monomer (then polymerization) or polymer (then melt compounding).

4 3 2 2 3 4

13 2

Intercalation 5

The d₀₀₁-spacing depends on: (1) Intercalant and its (2) concentration, (3) temperature and (4) pressure

1 .0 3 .0 5 .0 7 .0

0 1 0 2 0

In te rc ala tio n w ith   am in o a c id = N H 2(C H2)n -1CO O H (AA ) a n d   cap rolactam o n ly a m in o acid (A A ) A A a nd ca pr ola ctam I n te rl a y e r S p a c in g ( n m )

# of C-a toms per m olecule, n

da ta: O kad a & U suki, 1 99 5

1 .2 1 .4 1 .6 1 .8 2 0 80 0 1 60 0 Ca -smectite Na -smectite Ca-ve rmiculite Na-ve rmiculite d -s p a c in g ( n m ) P (b a r)

d e Siqu ira et al., 199 9

3 .8 4 .2 4 .6 5 2 0 6 0 10 0 B e id e llit e : Al 2.17[Al0.33N a0.33Si3.17] O10(O H )2 w ith : te t rad e c y l a m m o n iu m - te t rad ec y l a m in e ( TA T A) o r d im e th y ld it e tra d e c yl am m o n iu m ( D M T A) T AT A D MT A d 0 0 1 ( n m ) T (°C ) da ta : L aga ly e t al., 1 97 5 1 2 3 4 5 0 4 0 8 0

In terc a la tio n o f N a M M T w ith

p o lyvin ylp y ro llid o n e (P V P ) o r p o lyvin yla lc o h o l (PV A l)

PVP PVA l X R D b a s a l s p a c in g , d 001 ( n m ) C o n c e n tra tio n o f P V P o n d ry we ig h t o f N a -M M T (w t% ) O p tim u m ra n g e : 3 - 4 .5 n m

da ta: Be all e t al., 1 99 6

1

₂

14 2

Commercial intercalated

mineral

or

synthetic

clays contain

quarternary amines

MMT cation exchange capacity:

CEC = 100 ± 20 meq/100 g.

Equilibrium of Na-MMT reaction

with ammonium salt is shifted left,

hence excess of onium salt is

often used, i.e., 0.9 to 1.4 meq/g

or 23 to 40 % of the organic

modifier.

Intercalated clay contains 2 - 4 %

water and up to 44 wt% of

organic compounds (Southern

Clay Products, 2000).

Organoclays 1

d₀₀₁= 2.96; 2.39 nm org. = 43; 38-wt% d001 = 1.93 nm d₀₀₁ = 1.87 nm d₀₀₁ = 2.02 nm

15 2

MD indicates that the ammonium ion charge is dislocated and it

spreads all over the molecule; the paraffin chains are straight.

There is immiscibility between the non-polar intercalant chains and

polar PA-66 molecules.

The polymer has a limited access to the clay surface.

Best miscibility is between PA macromolecules and bare clay

.

Organoclay structure

Molecular dynamics (MD)

of clay (

stick model

)

intercalated with



-amino

acid (

space-filled model

),

dispersed in PA-6 or -66

(

cylinder model

)

[Tanaka & Goettler 2002; Brown D. et al., 2003].

The intercalant lays flat on

the clay surface.

16 2

Consider solid surface grafted with end-terminated polymers (MW = N), dispersed in chemically identical polymer (MW = P), where N  P.

The grafting density, (# of N per surface area), and MW control the shape. For low , the phase diagram show swollen (S) and ideal (I) mushrooms (M). At higher , S-, and I-stretched brush, as well as non-stretched brush (NSB). At high  > N-½_{, and high P > N the brush is non-penetrating} – the grafted clay

phase separates from the melt [Gay, 1997].

Immiscible

Mushrooms

Stretched brush

17 2

Organoclays are expensive, viz. Na-MMT $1/kg; organoclay > $14/kg.

Organoclays are immiscible with most polymers of industrial interest.

Organoclays are thermally instable

– stability decreases with the degree of

substitution.

The decomposition occurs in steps, starting at 125 to 150

o

_{C. Oxygen and}

shear accelerate the degradation.

Stability may be improved by:

Using phosphonium instead of ammonium intercalants. Using branched alkyl chains instead of linear.

Using aromatic substituents instead of paraffins. Using metallo-organic complexes.

Other methods.

Organoclays are expensive, and any attempt to improve thermal stability

further increases the cost.

18 2

Hofmann elimination (1851)

Degradation of intercalants at T > 150

o

_{C is a major}

problem in CPNC technology

Phosphonium ions are more stable than ammonium.

Organo-metallic complexes show high stability.

Bulky, aromatic ammonium (e.g., dyes) form stable organoclays.

Thermal degradation

in the presence of O

₂

of ammonium

intercalant in PS

matrix resulted in

formation of

peroxy-radicals

and subsequent

degradation of the PS

matrix.

19 2

The Figure illustrate these two

processes: melt exfoliation (

#1

)

and degradation (

#2

)

The XRD data are for

PS/Cloisite

®

_{10A mixed at}

T = 200 to 210°C, shear rate of

65 (1/s), for up to 30 min

[

Yoon et al., 2001; Tanoue et al., 2004

].

Shear compounding results in two parallel processes:

Mechanical intercalation/exfoliation

Thermal degradation via

Hofmann elimination reaction

The result is a complex variation of the interlayer spacing as

a function of stress, time, and temperature.

Degradation effects

20 2

Compatibilization

Compatibilization is a method of the interface control in

PNC, especially these based on PO or PS resins.

As in blends, the compatibilization must:

1.

Reduce interfacial tension coefficient,



₁₂

.

2.

Stabilize morphology against stress-destruction during forming.

3.

Provide adhesion between the phases in the solid state.

Compatibilization is accomplished by:

1.

Addition of reactive macromolecular species that are miscible with

the matrix polymer and have (preferably) a terminal group that

reacts with the organoclay.

2.

For example, maleated-PO, acrylic acid grafted PO or PS,

copolymers with glycidyl methacrylate serve as compatibilizers

.

Since compatibilizers’ cost is higher than that of the

matrix polymer, they must be used in small quantities.

21 2

Hasegawa et al. [2003] described direct compounding of PA-6 with aqueous slurry of Na-MMT in JSW TSX-77.

During the PNC-2003 symposium at NRCC/IMI, Kato et al. described a New

Production Method for a PP-Clay Nanocomposite.

Melt-compounding in TSX-77 of PP + PP-MA + Na-MMT (with or without

octadecyl trimethyl ammonium chloride, OTM), than injecting H₂O to exfoliate. The performance of these new PNC’s was reported comparable with that for the ―classical‖ ones based on PA-6 or PP, respectively.

22 2

Exfoliation

– general

The principal exfoliation methods for the production of CPNC

are: (1) Reactive, (2) In solution, and (3)

Mechanical

.

The

mechanical

exfoliation method is the most promising, as

it potentially offers the capability to produce suitable CPNC to

any compounder or manufacturer of plastics part.

It

starts with a polymeric matrix, suitably intercalated clay, and

(often) a compatibilizer.

The controlling factors are:

Interactions between organo-clay and polymer, e.g., in PA-6 methyl

tallow bis-hydroxy ammonium-MMT is relatively easy to exfoliate, while

di-methyl di-hydrogenated tallow ammonium-MMT is difficult.

Viscosity of the polymeric matrix.

Residence time in the processing equipment

[Dennis et al., 2000].

Type and intensity of stress fields.

Thermodynamics controls the exfoliation

–

23 2

Usuki’s classification

Exfoliation methods

with increasing difficulties:

1. Hydrophilic matrix with strong polar groups, e.g., P2VP:

2. Hydrophobic matrix with strong polar groups, e.g., PA-6:

3. Hydrophobic matrix with strong polar groups, e.g., PA-6:

4. Hydrophobic non-polar matrix, e.g., PP:

water polar organic compound

clay swollen clay CPNC

int ercalant (s) monomer

polymerization

clay int ercalated clay

exp anded clay CPNC

 



int ercalant (s)

compounding

clay int ercalated clay

polar polymer CPNC



 

int ercalant (s)

compounding

clay int ercalated clay compatibilizer

non polar polymer CPNC

 

24 2

Assuming that clay platelets are circular discs with diameter, d,

and thickness, h (

aspect ratio p = d/h

),

the geometry

of the freely

rotating platelets gives:

Concentration effects

Ratio of the encompassed to

actual volume = 2p/3, and the

maximum packing volume

fraction

f

_max

= 0.93/p.

At

f

>

f

_max

platelets are not able

to rotate freely, thus locally they

form short stacks with :

For Ube PA1015C2 the factor is

(ca. 100); hence twin platelets

are to be expected.

Exfoliation is feasible only for

w(clay)

 1.1 wt%.

001



223/

(

%)

d

w wt

0 10 20 30 0 10 20 30 XRD TEM d 001 = a0 + a1/w In te rl a y e r s p a c in g , d 001 ( n m ) MMT content, w (wt%)

data: Okada & Usuki, 1995

Intercalation with -amino acid, NH

2-(CH2)11-COOH (AA) and

25 2

Clay platelets are unable to exfoliate at higher concentration.

As clay resides only in non-crystalline domain exfoliation in

semi-crystalline polymers is more difficult:

Data for PP + PP-co-PE with 2 or 4-wt% Cloisite 15A (C15) followed the

dependence with



= 0.115 & r

2

_{= 0.9994}

_{(Ton-That, 2003).}

Exfoliation in

crystalline matrix

1 2

10 5 0 6

0 39 0 05

0 11 0 01

0 0 001 001 1 clay 2 001

d

= d

- a C

- a X ; d



.



. , a



.



.

, a



.



.

In the experiments, the crystallinity

ranged from X = 46 to 60%.

Since d

₀₀₁

of C15 is 2.96, no

expansion of the interlamellar

galleries is to be expected at:

X  60% crystallinity.

2.5 3.5 4.5 2.5 3.5 4.5 C15 = 2% C15 = 4% d 001 = 0.071 + 0.98d001, calc; r = 0.99 d 00 1 , exp ( nm ) d 001, calc (nm)

26 2

Mixing

— to combine ingredients into one mass, so that the

constituent parts are indistinguishable, a synonym for

homogenization

.

Blending

— the processes that lead to formation of polymer

blends.

Compounding

indicates preparation of ―a compound‖,

frequently comprising fillers and reinforcements.

Polymer mixing occurs only within the

laminar

flow region

where the Reynolds number << 2000.

Within the laminar region there are two mechanisms to be

distinguished:

distributive

(or extensive) and the

dispersive

(or

intensive).

27 2

Molecular adsorption 1

Adsorption of polymer on solid

surface has been predicted by

numerical methods.

Klein showed that from toluene

solution PS is adsorbed on mica

flakes to a layer of ca. 110 nm

thick!

Luengo et al. [1997] observed a

3-layer structure of PBD on

mica:

z

_s

< 6 nm

– solid-like

6 < z < 100

– elastomeric

z

_b

> 100 nm

– bulk behavior

Thickness of the adsorbed

solid-like layer, z

_s

, depends on

M

_w

for M

_w

> M

_e

Surface Force

Analyzer (SFA)

28 2

The PVT data indicate that addition of

clay results in reduction of free

volume,

D

h

[Utracki & Simha, 2003; 2004].

At constant clay content (

2-wt%

organoclay)

D

h

linearly depends on

the interlayer spacing,

d

₀₀₁

(standard

deviation ± 0.15 nm).

The Figure shows the correlation

between d

₀₀₁

, and computed from PVT

reduction of h

(at 100 MPa & 500 K)

for

CPNC’s based on PS, PP, and PA-6.

Free volume in CPNC

2 6 10 14 0 4 8 12 16

Correlation for 2 wt% organoclay

PNC without compatibilizer: Dh = 2.50 + 0.833d 011; r = 1 PP-PNC with compatibilizer: Dh = -21.73 + 9.38d 001; r = 0.927 D h ( % )= 1 00 [1 h (P N C )/ h (p o ly )] d 001 (nm) PA-6 PP PS

Two dependencies are seen:

For a two component CPNC (polymer/organoclay)

For three component: PP/organoclay/compatibilizer systems.

The loss of free volume depends on the total clay surface capable to

adsorb the macromolecules

– equivalent to lowering T by  50

o

_C!

_.

29 2

The heart of EFM = two converging/diverging (C-D)

plates separated by adjustable gap

The C-D plates of different geometries (number, position, and

shape of the converging zones) have been used

They generate radial flow of progressively increasing velocity

and stress field.

Since dispersion of clay stacks and liquid drops in flow are

fundamentally different, new geometry of C-D plates was

designed for the nanocomposites (EFM-N).

Generation of

30 2

Extensional Flow Mixer, EFM-3

Commercial mixers

:

1. Spiral feed for better

T-control & rigidity.

2. Redesigned C-D plates and mounting.

4. Redesigned attachment to the die.

31 2 Transverse Longitudinal 20%w mPE 15%w mPE +5%w. 36A

EFM: 2A2M, 14 MPa; Fractured surfaces in  and // direction to flow TSE; Fractured surfaces in  and // direction to flow

32 2

PA + 2-wt% organoclay Medium shear TSE

2 (degree) 2 4 6 8 10 In te nsit y (Cp s) 0 5000 10000 15000 20000 25000 30000 35000 C 15A Master batch TSE TSE + GP TSE + GP + EFM (Gap = 5 µm) Interlayer spacing (nm) Main Secondary 3.21 1.95/1.22 3.87 1.91 4.44 1.98 4.42 2.02 4.39 1.94

Diluting 4-wt% C15A master-batch

with PA-6 in a TSE+EFM (

small gap

)

dramatically changed the degree of

clay dispersion (

Figure A

).

Dilution increased d

₀₀₁

and reduced

N to a constant value, independent

of the compounding method

[Sepehr, 2004]. 2 (degree) 2 4 6 8 10 Inten sity (kCps) 0 5 10 15 20 TSE SSE+EFM-3 SSE+EFM-N

As the EFM gap decreased the

diffraction intensity diminished,

indicating increased exfoliation (ex).

Figure B

shows that the best

dispersion in TSE+GP+EFM

(gap 5 mm) is worse than that

obtained in SSE+EFM-3 or

SSE+EFM-N (gap 30 mm).

A

B





        1 2 00 n 0 hkl 001 peak height d n /( 2 sin ) ex 100 1 A A 0.9 N 1 W cos d    

XRD of PA-6/C15A

33 2

Part

2

Elements of the science &

technology

Mathematical modeling

Thermodynamics of PNC

Rheology of PNC

PNC performance (mechanical, barrier,

34 2

Balazs SCF model 1

The self-consistent field (SCF) lattice model considers

adsorption on a solid surface hence the properties change with

the short range interactions,



, and the distance from clay

surface, h

_o

< z < h.

The theory predicts that clay intercalation/exfoliation is reduced

by high grafting density,



, the latter being related to:

Clay CEC (CEC = 0.02 for kaolin, 1 for MMT, 2.5 meq/g for hectorite), Intercalant structure, viz. PA-6 with Cloisite-15A (2xC₁₈) or -30B (1xC₁₈).

SCF shows that as the packing density increases it becomes

harder for the macromolecules to diffuse into the gallery and

mix with the intercalant chains

‒

there is an optimum



for

intercalation

.

The SCF computations indicate that it is advantageous to

use a macromolecular

“sticker” compatibilizer with highly

35 2

Balazs SCF model 2

-0 .8 -0 .4 0 0 1 0 2 0 0 % 5 % 1 0% 3 0% 7 0% D F /A h a fte r: B a la z s et al., 1 99 8 0 4 8 0 1 0 2 0 N p = 5 0, 10 0 N p = 1 0 N p = 1  (h ) h

Free energy vs. gallery

height for

clay-polymer-‖sticker‖ system (its

content is indicated).

Thus, 5 wt% of ―sticker‖ is

sufficient for exfoliation.

The amount of adsorbed

functionalized ―sticker‖ polymer

with N = 75 and concentration

f

= 0.05 for four chain lengths of

the non-functionalized polymer,

N

_p

= 1, 10, 50 and 100

DF/A

5% is sufficient

36 2

Confirmation of theory

1. At least two US patents (AMCOL, Exxon) follow

Anne Balazs theoretical predictions.

2. Hoffmann et al. [2000] intercalated synthetic

fluoromica (Somasif) with:

1. 2-phenyl-ethyl amine (M_n = 121 g/mol) = C-PEA.

2. amine-terminated PS (M_n = 5.8 kg/mol) = C-APS.

Dried organoclays were compounded with the PS at 200o_C

The intercalation expanded the interlayer

spacing d₀₀₁ to 1.4 nm with PEA and to > 4 nm with APS.

Compounding with PS produced large

aggregates for C-PEA and full exfoliation for C-APS.

In C-APS clay platelets were ca. 600 nm long and

100 nm wide hence the aspect ratio: p ≅ 245.

C-APS C-PEA

37 2

4-component systems

D

F =

D

H - T

D

S

System

:

1. Clay platelet (s);

2. Host polymer (h);

3. Compatibilizer (g);

4. Organic modifier (o).

Conformational Entropy,

D

S:

Number of ways to occupy free lattice site

Mixing Enthalpy,

D

H:

Huggins-Flory short-range

parameters

solid-liquid :



hs

,



hs

,



os

Long-range interactions for

solid-solid

:

Van der Waals force between clay plates

with Hamaker constant, A:

liquid-liquid :



_hg

,



_hg

,



_ho d s 2

12

A s

F

d







38 2

The influence of the bare-solid

area-lattice ratio () and grafting

density (

_g

,



_o

) on the excess free

energy (h = z  ).

Statistical chain length

N_g = 200, N_h = 400, N_o = 10

Surface properties



_g

 [0, 0.2];



_o

 [0.5, 0.9]; and



_v

 [0.02, 0.05]

Influence of solid-solid

interactions

A = 20(k

_B

T),



 [0, 20]

Binary interaction parameters



_hg

= 0,



_ho

= 0,



_go

= 0,



_hs

= 0.01,



_gs

=



0.01,



_os

=



0.02

39 2

S-S Lattice model

2D lattice containing two types of

molecules and holes or vacancies

(open circles). The binary

interaction parameters,



_ij

, are

also indicated.

Lattice model is a base for many

theories, e.g., free volume,

cell-hole, tunnel, etc. For example:

In 1941 Huggins & Flory calculated the configurational entropy of

mixing.

In 1969 Simha and Somcynsky (S-S) derived Helmholtz free energy, then PVT equation of state, etc.

40 2

S-S lattice-hole theory



















 















 

1 _{2 2} 2 2 1 1 6 1 3

1

2

0

3

1 3

1

3

2

6

1

1

0

1 011

1 2045

2

T V ,T / /

P

F / V

PV / T

yG

AQ

B / T

F / y

c

/

/

yQ

AQ

B / T

s

s ln

y / y

where :

A

.

; B

.

;

yQ

; Q

yV













  

 



 

















_









_

  



_





_











The S-S theory describes the thermodynamic properties of

liquids, explicitly providing information how the hole fraction

(h = 1 - y) changes with independent variables.

From the Helmholtz free energy, F, using standard

definition of P and thermodynamic equilibrium condition the

coupled equation of states (eos) was derived:

41 2

PVT measurements 2

To directly compare the specific volume and the hole fraction

variations with T and P for PA and PNC, the ratios V(PA)/V(PNC)

and h(PA)/h(PNC) at identical T and P for each point are shown.

1 1.05 1.1 1.15 1.2 500 520 _{T (K)}540 560 580 600 0.1 50 110 150 190 P (MPa) 190 150 110 50 0.1

V(PA)/V(PNC)

h(PA)/h(PNC)

Theoretical V-ratio

for PNC with 0.64

vol% clay is:

V(PA)/V(PNC)

= 1.0088

.

The holes ratio:

h(PA)/h(PNC)

= 1.125 to 1.159

.

The experimental

ratio

V(PA)/V(PNC)

42 2

Rheology of PNC

Thermodynamics suggest the hairy-clay platelet (HCP) model

for PNC.

PA-6 and PA-6-based PNC from Ube were dried and then

compounded in a TSE with: 0; 25; 50; 75; and 100% of PNC.

The rheological tests were carried out at 240°C under blanket of dry

N

₂ [Utracki & Lyngaae-Jørgensen, Rheologica Acta, 41, 394 (2002)].

During the time sweep the storage (G

’) and loss (G‖) shear moduli

increased with time, due to polycondensation & exfoliation.

The rates of these two processes differently depended on the

intercalated clay content.

All raw data were corrected for the polycondensation effects

by extrapolating the measured signal to t = 0.

43 2

Time-effects

T = 240oC _o = 0.10  = 6.28 rad/s dried for 48h at 80°C Time (s) 0 2000 4000 6000 8000  ' (Pa.s) 200 400 600 800 1000 1200 UBE1015C2 TSE TSE+GP Gap = 1000 µm Gap = 60 µm Gap = 30 µm Gap = 5 µm T = 240oC _o = 0.10  = 6.28 rad/s dried for 48h at 80°C Time (s) 0 2000 4000 6000 8000 G' ( Pa) 0 500 1000 1500 UBE1015C2 TSE TSE+GP Gap = 1000 µm Gap = 60 µm Gap = 30 µm Gap = 5 µm

The dynamic viscosity (left Figure) and the storage modulus (right Figure) for PA-6 with 2-wt% organoclay are presented [M. Sepehr, 2004].

The polycondensation rate decreases with the increasing degree of clay dispersion.

44 2

Dynamic flow 1

Frequency sweeps at T = 240°C,  = 10 & 40%

G’ and G‖ were corrected for the time effects using the rates determined

in time sweep (t < 600 sec).

2 1

"/

_o

1 (

)

m m

G

 





_







_

 2.4 2.5 2.6 2.7 2.8 -1 0 1 2

Su m m a ry of dyn am ic visc osity d ata

P A 25 % PN C 50 % PN C 75 % PN C 10 0% P NC lo g  ' log  T = 240oC ;  = 40 %

The data were fitted to the

relation:

where 

_o

is the zero-shear

viscosity,  is the prime relaxation

time and the power-law

exponent: n = 1 - m

₁

m

₂

.

Thus, the shear viscosity data

were separated into a

pseudoplastic flow and yield-like

contributions.

45 2

Dynamic flow 2

Zero-shear viscosity of PA-6/PNC mixtures

The concentration dependence of _o was described the relation derived for dilute suspensions:

where [] is the intrinsic viscosity, k is a constant.





2 ' ' ,

/

1 [ ]

[ ]

r o o PA

k

  



 

 f



 f

1 1.4 1.8 2.2 0 0.002 0.00 4 0.006

R e lative ze ro -s h ea r vis cos ity fo r PA-6/PN C m ix tures at: T = 24 0oC a nd  = 1 0 & 40% R e la ti v e v is c o s it y ,  r (-)

C lay volu m e fra ction , f (-)

0 2 0 4 0 6 0 8 0 10 0 12 0 0 5 0 10 0 15 0 20 0 25 0 30 0 e xp erime nt [] = 2 .5 + a (1 + pb) In tr in s ic v is c o s it y , [  ] Asp e ct ratio, p For anisometric particles: [] = 2.5 - a(1-pb_), where p is the aspect ratio

Computed from the flow data value of

p = 287 ± 9 agree

with the nominal

p = 286

determined from the barrier

46 2

Stress overshoot 1

The LCP model also predicts the stress overshoot:

PNC was pre-sheared at = 0.1 s

-1

for 5 min;  = 30.

The shearing stopped for the rest time, t

_r

< 4000 s.

Shearing re-started, but in opposite direction, at the same

rate, , and for the same time of 5 min.



In the Figure, stress overshoot vs. t_r is plotted:

First peak shows overlapping data for three separate specimens.

Other peaks were determined after rest time, t_r = 500, 2000 & 4000 s.

Due to polycondensation the base line is shifted.

Stress overshoot is the peak height above base line.

500 600 700 800 900 1000 0 1000 2000 3000 4000 5000

Flow reversal for PNC at T = 240 oC

Rest time = 500 s Rest time = 2000 s Rest time = 4000 s Vi s c o s ity ,  (P a s ) Time, t(s)

Base line (polycondensation) 3 initial peaks

47 2

The stress overshoot is related to orientation of anisometric elements

during steady-state shear flow.

Resuming shearing after rest time probes the extent of disorientation.

0 100 200 0 1000 2000 3000 4000 experimental computed D  (Pa s ) Rest time, t(s) D = a exp{-b/t} a = 212.6 ± 7.4 b = 290.4 ± 28.9 r2 = 0.9967

The magnitude of the stress

overshoot depends on the rest time

at 240

o

_C.

There is but a small difference when

shearing (after rest) is in the same or

opposite direction.

It takes about 1 hr for the platelets to

return to the pre-shear random

orientation.

Experimental data follow a simple

exponential relation hence one type

of anisometry.

48 2

Steady-state flow

Flow of PA-6/PNC follows the LCP behavior:

The flow of LCP is characterized by the presence of three regions reflected by interactions between mesogenic groups:

I – the poly-domain structure gradually destroyed by shear.

II – rotation of nematic domains dispersed in a mono-domain continuous matrix,

III – flow by the tumbling motion, gradually replaced by flow alignment.

0 .1 1 1 0

- 3 -2 - 1 0 1 2 3

T h re e re g io n s o f flo w o f n e m a tic L C P (after O n ogi & Asa da, 198 0)

lo g ( n em a tic v is co si ty )

log (rate of shear)

R e gio n I R eg io n II R e g io n III 2 0 0 4 0 0 6 0 0 8 0 0 0 .0 1 0 .1 1 1 0 S t e a d y -s t a te s h e a rin g o f P N C w it h Dt ( s ) b e t w e e n d a t a p o in ts (T = 2 4 0oC ) 54 0 36 0 18 0 9 0 0 S h e a r vi sc o si ty ,  ( P a s) Rate of shear (1/s) D t (s )

49 2

Fourier-transform

rheology 1

The Fourier-transform rheology (FTR) has been used to analyze non-linear viscoelastic response in large amplitude oscillatory shear (LAOS) tests.

The FTR measures higher harmonics that in the past were only qualitatively characterized by the Lissajou stress-strain loops [Wilhelm, 2002].

Considering complex rheological behavior of molten PNC application of FTR may provide quantitative measure of the non-linear viscoelastic response caused by the time dependent ordering and orientation effects.

According to FTR, the stress is a sum of odd harmonics:

The simplest method for the analysis of FTR signal is to plot the relative magnitude of the odd harmonic peaks divided by the first one:

R_n() = I(n)/I₁(), with n = 3, 5, 7, …

For non-linear materials R_i() = 1/n, thus the strongest third harmonic, R₃(),

contains all pertinent information.

1

cos3

2

cos5

3

cos7

...

A

t

A

t

A

t

50 2

The Fourier-transform rheology (FTR) is a new method for

quantifying the non-linear viscoelastic behavior of matter.

Left Fig. shows the raw data: input peak and 3

rd

_harmonic.

Right Fig. show the relative intensity of the 3

rd

_harmonic

– a measure

of non-linearity as a function of frequency, strain and shearing time.

PNC: time sweep at T = 240°C,   10 Hz Frequency (Hz) 0 10 20 30 40 Inten s ity 0 600 800 1000 0 1 2 0 400 800 1200

Fourier transform rheology for PNC

 = 1 Hz;  = 20%  = 1 Hz;  = 30%  = 1 Hz;  = 60%  = 1 Hz;  = 70%  = 10 Hz;  = 70% Rel at ive in tens ity , R 3 = 100( I 3 /I 1 ) Shearing time, t(s)  = 10 Hz  = 1 Hz

Fourier-transform

rheology 2

51 2

Extensional flow

of PNC’s

PS-based PNC was measured in RER and in RME.

Strain hardening (SH) was strain-rate ( ) independent.

Strong effects of



were calculated from nanocomposites based on

PP-MA, indicating strain and strain-rate dependent structure in

this PNC.

Since

d

₀₀₁

= 3.0 nm

,

aggregation of MAH-groups is suspected.

0.0 0.2 0.4 0.6 0.8 1 3 5 7 PS1220 + 10 wt% at 200o_C 0.074 0.269 0.453 0.899 S tr ai n h ar d en in g, SH ( P a s ) Hencky strain,  (-) SSH = 0.11 ± 0.03 Strain rate (1/s) 4 5 6 0 1 2 PS1220 with 2 wt% at 200oC 3+ _(shear) + E at 0.072 + E at 0.167 + E at 0.430 + E at 0.860 L o g (s tr e ss g ro w th f u n ct io n , P a s)

Log (deformation time, s)

0.5 1.5 2.5 3.5 0 0.5 1 1.5 2 1.0 0.5 0.1 0.05 0.01 0.005 0.001 St ra in h a rd e n in g , SH ( -) Hencky strain,  (-) Okamoto et al., 2001 Strain rate,  (1/s)

PP-MA with 4 wt% MMT/ODA



52 2

Summary of

PNC Rheology

The characteristic feature of the PNC flow is the presence an

yield-like behavior at low deformation rates, i.e., the viscoelastic

non-linearity (VNL).

The better dispersed is the system, the higher is the VNL.

The flow of exfoliated PNC resembles that of lamellar LCP with very

large mesogens (relaxation time of ca. 60 min).

Fourier-transform rheology (FTR) is a useful tool for characterization

of VNL hence the degree of dispersion.

To interpret the PNC flow behavior the hairy-clay platelet (HCP)

model was used:

The clay are enrobed in solidified organic phase, from which emanate long, able to entangle macromolecules

Consequently, for well dispersed PNC the VNL behavior is observed at

concentration below that calculated from the encompassed volume principle. Owing to large aspect ratio (p  300) there is a strong orientational effect

53 2

PNC Performance

Four main reasons for the development of PNC: Enhanced rigidity (100% at 5 wt% clay)

Improved barrier properties (by a factor of 100 at 10 wt%) Reduced flammability (PHRR reduced by 2/3 at 5 wt% clay) Improved heat deflection temperature (HDT)

Examples of published data for various systems are tabulated for PA-6 and its CPNC’s with 2 wt% organoclay (mineral & synthetic):

Mechanical properties of PA-6 and based on it PNC.

Data from [Ube Industries, Ltd., 2002, and Unitika Plastics, 2004].

Property ASTM Units Ube Unitika

PA-6 PNC PA-6 PNC

Tensile strength,  D-638 kg/cm2 800 910 810 930

Tensile elongation, b D-638 % 100 75 100 4

Flexural strength, f D-790 kg/cm2 1100 1390 1080 1580

Flexural modulus, Ef D-790 kg/cm2 28,500 35,900 29,000 45,000

Impact strength, NIRT D-256 kg

cm/cm

6.5 5 4.9 4.5

HTD (18.56 kg/cm2) D-648 oC 75 140 70 172

HTD (4.6 kg/cm2) D-648 oC 180 197 175 193

H2O permeability, PH2O JIS Z208 G/m2 24

h

203 106 -- --

54 2

Relative tensile

modulus

Fig. 1: Relative modulus vs. clay content for CPNC with PDMS as the matrix. Experimental data [Shia et al., 1998] and theoretical prediction from Brune-Bicerano(B-B) relations (see center).

B-B derived a relationship between tensile modulus & clay content for exfoliated and intercalated systems. In the Eqs. p’ = the aspect ratio, f’ = clay volume

fraction, and E’ = the tensile modulus in platelet stack composed of N-clay layers, each with thickness t and the interlamellar gallery spacing, .

Fig. 2: E_R vs. clay content for CPNC of PA-6, PP, PLA and PS with MMT, and PP with fluoromica (FM): 1 2 3 0 4 8 E RPA E RPP E RPLA E R PP (with FM) E RPS R e la ti ve m o d ulu s , E R ( -) Clay content, w (wt%) E R = 1 + 0.2w E R = 1 + 0.07w E R = 1 + 0.13w Hard sphere 1 2 3 0 0.02 0.04 experimental B-B theory E r = E c /E m ( -) f (-) PDMS/clay Shia et al., 1998









' ' ( / ') / 1 (1 1/ ')( / ) ' 1 (1 1/ ')( / ) (1 1/ ')( / ) 1 (1 1/ ')( / ) ' (1 )( / ) 1 r r p p N N s t N s t E N s t E N s t N N N s t f f f f                001 0.96 s d  nm Fig. 1 Fig. 2

 

 

R m E  E / E  1  f  1 awa  / 314

55 2

Mechanical performance

Tensile strength (, and modulus (E) of PA-66 vs. organoclay (MMT-3MHDA-DGEBA (di-glycidyl ether of bis-phenol-A). Points – experimental, lines –

polynomials [Liu and Wu, 2002]. At 5-wt% loading: E and  increased by 26%.

Tensile modulus (E) tensile strength (, and elongation at break ( of polyimide (PI) with MMT-ODA [Tyan et al., 2000]. The properties are well approximated by

straight lines – their parameters are given. At 5-wt% loading: E, , and  increased by ca. 139, 40, and 16%, respectively.

75 85 95 105 2.5 3.5 4.5 5.5 0 4 8

Liu and WU, 2002  = 78 + 4.4w - 0.16w2 ; r = 0.99 E = 3.01 + 0.39w - 0.016w2_{; r = 0.99} Ten s ile modulus , E (GP a ) Organoclay content, w (wt%) Ten s ile s tre n gt h,  (MP a) 75 85 95 105 115 1 3 5 7 9 0 2 4 6  = 74.4 + 5.88w; r = 0.985  = 7.06 + 0.207w; r = 0.978 E = 1.41 + 0.390w; r = 0.996 Ten si le st re ng th,  (M Pa ) Eo ng a tio n at b rea k,  (% ) T e ns ile mo du lu s, E (GPa ) Organoclay content, w (wt%)

56 2

Permeability control 2

The relations specify, that the relative permeability, P

_r

, depends

on the clay platelets aspect ratio, p, their volume fraction in the

matrix,

f

, and the orientation factor, S

[Bharadwaj, 2001]

.

In the definition of S,



is an angle between platelet and the wall

surfaces; S = 1, -½, and ¼ for flux perpendicular to platelet





 0, in parallel 



 /2; P

_r

= 1!

, and random





 /4, respectively.

Evidently, the degree of dispersion (exfoliation) enters into p.

The second equation linearized the dependence (at low

f



.

2

1

;

3cos

1 / 2

1

(

1/ 2) / 3

r o

P

P

S

P

p S

f

_

f

















1/

P

_r



1



1

p S

(

1/ 2) / 3

 

f

/(1

f

)





  







57 2

Fig.1: Relative permeability of polyimide containing 2 wt% of clays vs. aspect ratio

[Yano et al., 1997]. Line was calculated from the presented relation.

Fig. 2: Relative permeability of di-chloro methane through PCL-type CPNC, plotted

as Y = 1/P_r vs. X = f/(1 – f). Data [Gorrasi et al., 2002]. The line is the least square fit to

the relation: Y = 1 + (1 +<p>/2)X + bX2_{, with the average aspect ratio:<p> = 197}

and the parameter b = 1240, indicating enhanced barrier properties at higher

clay loadings (overlap?).

Permeability control 3

0 20 40 60 80 0 0.1 0.2 Gorrasi et al., 2002 (1/ P r ) 1 X = 1/((1/f)-1) Fig.1 Fig.2 0 0.4 0.8 0 400 800 1200 Experimental P r = 1/(1 + fp/2) R ea lti ve p erme a b il ity, P r (-)

58 2

Addition of 5 wt% of clay with p = 1000-1500 reduces the O

₂

permeability

by

two orders of magnitude

[Tetra Laval, 1999].

Exfoliated clay increases container barrier properties and stiffness not

affecting its transparency. Only

0.1-2 mm thick layer

of a PNC is required.

0 .0 0 1 0 0 .0 1 0 0 .1 0

0 2 4

Permeability of O

2 through PET nanocomposites

50 0 10 00 - 1 50 0 P e r m e a b il it y (m L /2 4 h a t 0 .2 a tm O 2 ) w t% of m on tm o rillon ite As pec t ratio, p =

The process involves

polymerization in the presence

of intercalated clay with a

―swelling -&-compatibilizing‖

agent being present.

Currently, the inner PNC layer

in PEST containers is PA-based

(MXD-6 = meta-xylene di-amine + adipic acid)

!

59 2

Flammability 1

In 1965 Blumstein reported that presence of MMT increased the thermal decomposition temperature of PMMA by 40-50°C.

In 1997 Gilman labeled the PNC ―a revolutionary new flame retardant‖:

5 wt% clay reduced the peak heat release rate by 63% (but the kinetic and the total heat of combustion remained the same).

Clay enhances char formation. Owing to reinforcement by clay particles there is a significant reduction of the gas diffusion rate.

By contrast with the customary flame retardants that reduce the resin performance, in PNC the other physical properties are greatly improved.

Incorporation of dispersed clay significantly increases the char (composed of clay + graphitized carbon) content:

60 2

Flammability 2

Flammability reduction of CPNC with PA-6, PP-g-MA or PS as the matrix, were measured in a cone calorimetry at NIST [Gilman et al., 2000; Kashiwagi et al., 2004].

Peak heat release rate (PHRR) was reduced by 50%-75%.

To affect flammability, MMT should be well dispersed, but not necessarily fully exfoliated. Synthetic fluorohectorite was ineffective at reducing the flammability of PS.

Extrusion of PS with 3-wt% of 2M2ODA-MMT at 170o_{C reduced flammability, but at 185}o_C

it did not (degradation of organoclay!).

TEM and XRD were used to study the mechanism of flammability reduction.

The type of clay, clay dispersion, and processing degradation influenced the flammability reduction.

61 2

Na-MMT with CEC = 0.9 -1.2 meq/g and p = 200 - 500, is the most popular nano-filler.

Success of PNC hinges on intercalation that involves, e.g.:

Reacting MMT– anion with onium cation (ammonium, phosphonium or

sulfonium).

Reacting acidified MMT with basic groups of a monomer. Adsorbing a polar liquid (e.g., PVP, PVAl or PEG)

Inorganic structures by hydrolysis of metal-alcoholates

Most common is intercalation with a quarternary ammonium ion –disadvantage:

decomposition at T > 180o_{C, and inherent immiscibility with most polymers.}

Performance depends on exfoliation and the clay-matrix interactions.

The easiest to prepare PNC is via polymerization, but the intercalant may interfere with its kinetics, and catalyst with exfoliation!

For PO’s the MMT has been reacted with ―sizing agents‖, e.g., organo silanes, titanates or zirconates and/or ―compatibilizers‖ (PO-MAH).

Melt-compounding is the preferred method of PNC manufacture.

62 2

Common strategy for melt-compounding is:

Compatibilization, sizing or intercalation (under N₂, then devolatilization) DISPERSIVE mixing, based on microrheology

DISTRIBUTIVE mixing, based on the theories of laminar flows

Theoretically, extensional mixing in is superior to shear mixing, viz.:

High strains, interface, aggregate deformability, specific energy of mixing Low degradability of polymers, attrition of solid particles,

Strong orientation of anisometric particles, etc.

PNC morphology depends on the thermodynamics, kinetics and flow.

In PNC’s the clay platelet might be treated as a large molecule, which first

should be chemically modified to induce miscibility, and then mechanically

dispersed.

A precarious alternative is to use organoclay with partially bare surface

(by partial intercalation or by degradation) and graft it either with a polar

polymer (e.g., PA), or with functionalized macromolecules (e.g., PP).

63 2