Polymer nanocomposite : Structure and its consequences

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Polymer nanocomposite : Structure and its consequences

Polymer

Nanocomposite;

Structure and its consequences

L. A. Utracki

NRCC/IMI, 75 de Mortagne, Boucherville, QC, Canada J4B 6Y4

Invited lecture at the Iran Polymer and Petrochemical Institute (IPPI): Teheran, 2004.10.18-19.

2

Outline

Introduction

Polymeric nanocomposites (PNC)

Diversity of PNC’s

Intercalation and exfoliation methods Morphological features in PNC

PNC performance

Thermodynamics (PVT; modeling)

Rheology (LCP-model; FTR; elongation)

Melt compounding in shear and elongation

Conclusions

3 Nanocomposites (NC) = matrix + dispersed in it nanometer-size 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.).

4

PNC Performance

Property ASTM Units PA-6 PNC

Tensile strength D-638 kg/cm2 800 910 Tensile elongation D-638 % 100 75 Flexural strength D-790 kg/cm2 1100 1390 Flexural modulus D-790 kg/cm2 28,500 35,900 Impact strength D-256 kg cm/cm 6.5 5 HTD (18.56 kg/cm2) D-648 oC 75 140 HTD (4.6 kg/cm2) D-648 oC 180 197 H2O permeability JIS Z208 G/m 2 24 h 203 106 Density D-792 kg/m3 1140 1150

Four main reasons for the development of PNC:

Enhanced rigidity

Improved barrier properties Reduced flammability

Improved heat deflection temperature (HDT)

Examples of published data for various systems are tabulated, starting with PNC (PA-6 with 2 wt% of organoclay) from Ube.

5

Permeability

Addition of 5 wt% of clay with p = 1000-1500 reduces the O₂ 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

500 1000 - 1500 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 aromatic PA-based!

6

Flammability

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 heat of combustion remained the same.

Clay enhances char performance through reinforcement by the 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

7

Definitions

Exfoliated clay: − individual platelets dispersed in a matrix

polymer with the distance d₀₀₁ > 8.8 nm. The platelets can be oriented, forming Short stacks or Tactoids or they can be

randomly dispersed in the medium.

Intercalated clay: − having organic or inorganic molecules

inserted between Platelets, thus increasing the interlayer spacing between them to at least 1.5 nm.

Intercalant: − material sorbed between Platelets that binds with

their surfaces to form an Intercalate.

Interlayer, basal spacing or d-spacing, d₀₀₁ is the thickness of the repeating layers as seen by the XRD = mineral thickness (in MMT = 0.96 nm) + galley thickness.

8 Nano-particles: Clays (e.g., MMT or vermiculite having the aspect ratio p = 10 to 1000 or 1,000 to 15,000, respectively); synthetic silanes (fluoromica, hectorite, tetra-ethoxysilane, POSS, SiO₂);

mineral salts (e.g., CuS, ZrO₂, Fe₂O₃, TiO₂, V₂O₅, Ag or Au); rigid

polymers (cellulosic whiskers, LCP, carbon nanotubes), etc.

Any polymer: viz. PE, PP, PS, PMMA, ionomers, PVE, PEG, PVP,

polypyrrole, SMA, PCL, PVAc, P(tBuA); PA-6, PET, PC, epoxy, PDMS, dendrimers, polyaniline, polyacrylamide, lattices, LCP, etc.

Preparation:

Polymerization (any reaction in any medium).

Melt compounding with organoclay; in TSE or internal mixer. Diverse (complexing and immobilization of dendrimers with

(CuS)_15,; sol-gel processing; solution, latex or suspension; electrochemical preparation of conductive NC), etc.

Strong effects of processing on performance!

9

Clay

Mainly montmorillonite (MMT) [(Na,Ca)(Al,Mg)₆(Si₄0₁₀)₃(OH)₆-nH₂0],

monoclinic, with: Al = 9.98, Si = 20.78, H = 4.10 and 0 = 65.12 (wt%).

sp. surface area, A_sp  800 m2_{/g; Cation Exchange Capacity,}

CEC  1.0 ± 0.2 meq/g; aspect ratio p  300.

Reactive sites:

anions

on the two surfaces with cations and

–OH groups at the edges.

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

10

Intercalation 1

Intercalation − diffusion of intercalant into clay galleries. The

intercalant binds to the platelet surface and expands the interlayer

gallery, facilitating diffusion of macromolecules (exfoliation).

The efficient strategy of intercalation involves reduction of the stack size and a progressive increase of penetrant size, starting with H₂O, then onium, ....

Intercalation methods:

Low-MW solvents and solutions, viz. water, alcohols, glycols, solutions of monomer, … (d₀₀₁  1.7 nm).

Organic cations, mainly ammonium. Intercalation increases the cost of clay from

US$2,000 to US$7,000/ton!

Organic liquids, viz. monomers, epoxies, PEG, PVAl, PDMS, PVP, etc. Inorganic and organo-metallic compounds.

11

Intercalation 2

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 to 77°C. 2. Reaction with onium ions, then removal of salts. 3. Bond strength increases in order:

4. Secondary treatments with a « sizing agent » or compatibilizer.

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

4 3 2 2 3 4

12

Exfoliation – general

Exfoliation transforms an intercalate into dispersion of

individual platelets in a matrix. The system is considered

exfoliated when d₀₀₁ > 8.8 nm.

The methods exfoliation are:

1. Polymerization in the presence of organo-clay.

2. Melt compounding of a polymer with a suitable organo-clay complex (and compatibilizer).

3. Others:

Combining the organo-clays with latex.

Ultrasonic exfoliating of organo-clay particles in a low MW polar liquid followed by either polymerization or melt compounding.

Melt compounding polymer with layered clay in a kinetic energy mixer.

Other methods, viz. sol_¯gel templating, co-precipitation, polyhedral

13 1 .0 3 .0 5 .0 7 .0 0 1 0 2 0 a m ino ac id = NH 2(CH2)n-1CO O H

o nly am ino a cid (AA )

A A an d ca pro la cta m In te rl a y e r S p a c in g ( n m )

# o f C-a tom s p er m olecule , n

In ter calation w ith am in o acid ( AA) a nd ca pro la cta m

O k a d a & U s u k i, 1 9 9 5

Exfoliation 1

The first commercial PNC was developed at the Toyota R&D

Laboratories in the mid 1970’s [Fujiwara & Sakamoto, US Pat.,1988].

The process: (1) intercalation of MMT with -amino-C_12-18 acid,

(2) mixing the intercalate with -caprolactam, and (3) catalyzed

polymerization at T > T_m ( T = 120-250°C) in t < 5 hrs.

The interlayer spacing, d₀₀₁,

changes with alkyl chain

length of -amino acid (AA),

as well as with clay

concentration, temperature and pressure.

Addition of monomer

14

A later patent from AlliedSignal described:

Treating a suspension of clay in aq. solution with organo-silanes, -titanates or -zirconates increasing d₀₀₁ to > 5 nm. Simultaneous or sequential saturation of the clay with

precursor monomer, then polymerizing it under the appropriate conditions.

Compounding the “derivatized” clay with matrix polymer until the desired level of exfoliation is reached.

The complexes of organosilanes, titanates and/or

-zirconates, alone or mixed with primary or secondary

ammonium cations show

prolonged thermal stability at

temperatures greater than about 300°C

, below which

most thermoplastics are polymerized and processed.

15

Circular clay platelets (diameter, d, thickness, h; aspect ratio p = d/h), the geometric calculation for freely rotating platelets gives:

Exfoliation 3

0 4 0 8 0 12 0 0 1 0 2 0 In te rc a la tio n w ith  a m in o a c id = N H 2(C H2)1 1CO O H (AA ) a n d  c a p ro la c ta m R DX T EM d = 1 00 /w d -s p a c in g ( n m ) M M T c on te n t, w (wt% ) da ta: O k ad a & U s u k i, 1 99 5

Ratio of the encompassed to actual volume = 2p/3.

The maximum packing volume fraction f_max = 0.93/p.

The distance between

exfoliated platelets should be:

At f > f_max platelets are not

able to rotate freely. Aligned, they have greater tendency for stacking.

223/

(

%)

16

Exfoliation 4

3.0 4.0 5.0 6.0 0 2 4

Interlayer spacing in the system of:

hydroxylated polybutadiene (Polytail-H; MW = 3,000) and distearyl-dimethylammonium chloride (DSDM)

S p a ci n g ( n m) Concentration, C C = Polytail-H/clay+DSDM complex (g/g) US Pat., 5,973,053

The key to the process is the presence of the compatibilizing guest molecules, e.g., maleated-or hydroxylated PO, of the same type as the matrix or miscible with it.

The process belongs to the melt intercalation category.

PO-based PNC’s. The first patents for elastomers with clay and

CB described polymerization in the presence of intercalated clay particles and a compatibilizer [Usuki et al., 1989].

Later, PNC’s with diverse polymers were prepared using onium ion intercalated MMT (d₀₀₁ = 3 nm). The clay is then compatibilized by mixing at T  250°C with a guest molecule. [Usuki et al., 1999]

17

Thermal instability

The onium intercalant is thermally instable.

Stability decreases with the degree of substitution. The decomposition occurs in steps, from 150o_{C on.}

Oxygen and shear accelerate the degradation.

Branched alkyl chains are more stable than linear.

Aromatic substituents provide better stability than paraffins. The degradation follows the Hofmann elimination reaction:

CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 N CH2 CH3 H3C H3C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH H3C CH2 CH2 N H3C H3C + + H

18

S-S considered liquid was a mixture of holes and occupied sites.

The Helmholtz free energy was expressed in terms of reduced variables:

The S-S theory describes the thermodynamic properties of liquids, explicitly providing information how the hole fraction, h = 1 - y, changes with

independent variables (h is a measure of the free volume fraction, f).

From the Helmholtz , the equation of states was derived as:

, 1 2 2 ( / ) 0 : ( / 3 )[( 1) / ln(1 )] ( 1/ 3) /(1 ) ( / 6 )( ) [2.409 3.033( ) ] V T from F h n c n n y y Q Q y T yV  yV            



 

2

 

2 1 ( / ) : / [1 ] 2 / [1.011 1.2045] T from P F V PV T Q  y T yV  yV         

 

1/ 3 1/ 6 : 2 where Q   y yV  [ , , ( , )] F V T h V T : / *; : / *; : / * : * * / *; * * / ; * * / _o * * / * _o ( / )

pressure P P P temperature T T T volume V V V

where P zq sv T zq Rc V v M P V RT M c s

  

    

19

PVT of PA-6 PNC

PVT data for PA-6 and its PNC (0.64 vol% MMT):

Simha-Somcynsky theory provides a good description. Clay reduced the free volume of PA by ca. 15%.

Interaction parameters in PA, PNC and their 1:1 mixture are:

0.94 0.98 1.02 1.06 480 520 560 600 experimental computed from S-S Sp e ci fic vo lu m e , V (m L /g ) T (K) P = 0.1 - 200 MPa Ube PNC P (MPa) 0.1 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0.95 1 1.05 1.1 480 520 560 600 Ube PA-6 experimental computed from S-S S p e cific vo lu m e , V (m L /g ) T (K) P = 0.1 - 200 MPa P (MPa) 0.1 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 1 1.0 5 1 .1 1.1 5 1 .2 50 0 52 0 54 0 56 0 58 0 60 0 V (P A )/ V (P N C ) a n d h (P A )/ h (P N C ) T (K) 0 .1 5 0 11 0 15 0 19 0 P (M P a) 1 9 0 1 5 0 1 1 0 5 0 0 .1 V (P A )/V (P N C ) h (P A )/h (P N C )

System PA-6 PA/PNC = 1:1 PNC

Contacts *

ij

e (kJ/mol) v_ij*(mL/mol) e_ij*(kJ/mol) v_ij*(mL/mol) e*_ij(kJ/mol) v_ij*(mL/mol)

11 31.23 24.54 31.21 24.54 (26.69) 24.54

12 -- -- 31.53 25.75 (29.16) 25.75

20

Adsorption on solids

The PNC is end tethered. With 1/3 MMT anions used, there is ca. 550 macromolecules attached to each clay platelet.

Due to high surface energy of the crystalline clay, the polymer is adsorbed and the first 6 nm are solid, further away the chain mobility increases. 0 0.2 0.4 0.6 0.8 1 0 20 40 60 80 100 R el at iv e c h ai n m ob ility

Distance from clay surface, z(nm)

Only 100 to 120 nm from the clay surface the bulk mobility is

recovered.

This reduction of macromolecular mobility is reflected in the

measured reduction of free volume, viz. ca. 15% by 0.64 vol% of clay!

21

From the PVT fit the reducing parameters and then the average values of the interaction parameters were calculated:

P* = zq<*>/(s<v*>); T* = zq<*>/Rc; V* = <v*>/M_s

The minimum in the hole fraction (at ca. 2 wt% C10A) corresponds to maximum clay platelets dispersion.

There is a simple relation between the free volume and the average interaction parameter, <*>.

The two average interactions parameters are proportional to each other.

0.93 0.95 0.97 0.99 1.01 0 10 20

PS1301 with Cloisite 10A; P = 10 bar

T = 360 K T = 460 K T = 560 K R el at ive h o le f ract io n , h( PN C )/ h( PS) Organoclay content, w (wt%) 1.00 32.4 32.8 33.2 43.0 43.4 43.8 44.2 44.6 0 10 20

PS1301 with Cloisite 10A

< ij> <v* ij> <  ij > ( kJ /m o l) < v* ij _> ( m L /m o l) Cloisite 10A (wt%) 0.93 0.95 0.97 0.99 1.01 32.4 32.8 33.2 h_r(360) = 3.4589 - 0.075686* ; r2 = 0.99992 h_r(460) = 2.9245 - 0.059237*; r2 = 0.99992 h_r(560) = 2.6834 - 0.051815*; r2 = 0.99994 h r = h( P N C )/ h( P S ) <*> w = 0 w = 1 .4 w = 2 .8 w = 5 .7 w = 1 0 .6 w = 1 7 .1

PVT of PS PNC

22

PP ProFax SR256 from Himont was melt compounded with 0, 1, 2, 3 and 4 wt% of Cloisite 15A (MMT intercalated with 145% 2M2HT).

The ratio of specific volume of PP to that of PNC agrees with density additivity rule. The ratio of free volume of PP to that of PNC slightly decreases with T and strongly increases with P (see left Figure).

The average interaction parameters, <*> and <v*>, demonstrate that in analogy to

PA-6 type PNC here also an assumption of bare clay platelets dispersed in PP melts give bad fit to experimental data (central Figure).

Assumption the “hairy clay platelet” model leads to good agreement (right Figure).

28.5 29.5 30.5 31.5 50 54 58 62 0 1 2 3

PP with Cloisite 15A; bare platelets in PP melt

EAV EAV calc VAV VAVcalc <*> <v*> Clay content, w (wt%) 0.98 1.02 1.06 1.1 1.14 0 1000 2000

PP with 2 and 4 wt% C15A; TTTM series R v(2%) R v(4%) R h(2%) R h(4%) R V = V( P P) /V (PN C ); R h = h (PP )/ h (PN C ) Pressure, P (bar) 28.8 29.2 29.6 30 30.4 50 54 58 62 0 1 2 3

Interactions in PP with Cloisite 15A; coated platelets in diffused melt (experimental error in <*> 1%) <*> calc <*> exp <v*> calc <v*> exp <*> <v*> Clay content, w (wt%)  = 1.57521690 r2 = 0.99907 * 22 =29.95 ± 0.93 V* 22 =57.48 ± 0.91

PVT of PP PNC

23 -10 -5 0 5 10 0 1 2 3 D F A ( m J/ m 2 ) h - h o(nm)  sp, sa = 0  sp, sa = - 4  sp, sa = - 8  sp, sa = - 10

Physics of PNC

Vaia’s thesis of 1995 provided the first thermodynamic description of PNC as a function of distance (h) between

platelets (r_i is radius of interacting segment).

Intercalant entropy gain only up to full stretch (Dolan-Edward). Macromolecule entropy loss within the sandwich (Huggins-Flory). Enthalpy taken from van Opstal et al. (1991).

- 4 - 2 0 2 0 1 2 3 D S A /R ( 1 0 6 /m 2 ) h - h o (nm ) In te rc alant P o lym er Total









1 2 , 2 1 2 2 1 2 1 ˆ ˆ 2 / / ˆ ˆ ˆ 1 1 ( / ) ( / ) sp sa o ap v o h r e r r r h          D  D     DG = DH –TDS

24

Physics of PNC SCF 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 :

Free energy per unit area as a function of surface separation for five different values of the polymer-intercalant interaction parameter, c_ap. Other parameters are: N = 100; N_i = 25 and c_sa

= c_sp = 0. In the LHS and the RHS Figures the grafting density: r = 0.04 and 0.12,

respectively. The cartoons, left and center, show the initial and final state, respectively,

where the surfaces are separated by macromolecules [Balazs et al., 1998].

( ) _i( ) ln _i( ) (1/ 2) _ij ( ') ( ) ( ')_{i j} '

i ij

25

Physics of PNC SCF 2

The system: clay +

functionalized polymer, N_gr =

100, + polymer N_host = 100;

grafting density: r = 0.04

Computed effects of the binary intercalation parameter on the chemical composition of the

lattice layers, z = 1 – 20.

Results:

Even for c = 0 there is miscibility

between intercalant and

polymer.

The miscibility increases with c

and N_gr .

(Work is in progress)

26

Physics of PNC SCF 3

-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 e t 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 “sticker” polymer with N_gr = 75 and

concentration f = 0.05 for four chain lengths of the

non-functionalized polymer, N = 1, 10, 50 and 100 [Balazs et al., 1998].

DF/A

5% is sufficient

27

Physics of PNC SCF 4

Thus, SCF predicts that clay intercalation/exfoliation is reduced by high

grafting density, r, 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 r for intercalation.

SCF was also used to explore two compatibilization strategies:

Compatibilizer between intercalant and polymer, c_ac = c_pc < c_ap .

Compatibilizer to bind directly to the clay surface: N_p = 100, N_c = 75,

c_sc = -75, other interaction parameters c_ij = 0.

The SCF computations indicate that it is advantageous to use a macromolecular “sticker” compatibilizer with highly interactive end-group (see next slide). This prediction agrees with the experimental findings, e.g., by Hoffmann et al. [2000].

28

Computed phase diagrams

Phase structures for CPNC:

(a) isotropic, (b) nematic, (c) smectic, (d) columnar, (e) plastic solid (house of cards), and (f) crystal. The nematic director is in the Z direction, platelets

in X-Y [Ginzburg et al., 2000].

Computed phase diagrams of

polymer-clay mixtures: (a) r= 0.04,

29

Confirmation of theory

At least two US patents (AMCOL, Exxon) follow

Anne Balazs theoretical predictions.

Hoffmann et al. [2000] intercalated in THF/H₂O at

T = 40o_{C 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. Dry organoclay was compounded with 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.

Dynamic moduli of C-APS indicated 3D structures.

C-APS C-PEA

30

Thermodynamics - summary

Clay adsorb and immobilize organic molecules.

The “hairy clay platelet” model (6 nm immobilization +

100 nm diffused layer) explain reduction of 14% free

volume in PA-6 caused by 0.64 vol% MMT.

Because of the negative entropic contribution, the

exfoliation requires energetic interactions between

organoclay and the matrix.

Lower grafting density is beneficial.

Compatibilizing macromolecules with reactive end

group and DP comparable to that of the matrix

31

Melt rheology is used to:

Predict processability

Analyze the structure/interaction in the molten state

Verify theoretical dependencies.

Addition of clay into molten polymer will engender different structures depending on:

The degree of dispersion (filler, aggregates, intercalated, exfoliated)

Degree of bonding with the matrix (end-tethered, adsorbed, non-interacting)

Miscibility between the principal components: organoclay, compatibilizer and the matrix.

PNC’s with PA-6 and PS as matrix will be discussed as two limiting cases.

32

Rheology of PA-6 PNC

Commercial PA-6 and PA-6-based PNC from Ube were

vacuum dried at 80°C for 48 h.

Blends of PA-6 were prepared 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 N₂ [Utracki & Lyngaae-Jørgensen, 2001].

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.

33

Frequency sweep

Frequency sweeps at T = 240°C,

g

= 10 & 40%

G’ and G” were corrected for the time effects using the rates determined in time sweep (t < 600 sec).

The data were fitted to the relation:

where h_o is the zero-shear viscosity, t is the prime relaxation time and the power-law exponent: n = 1 - m₁m₂. 2 1 "/ _o 1 ( )m m G  h _  t _ 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 % P N C 50 % P N C 75 % P N C 10 0% P NC lo g h ' log  T = 240oC ; g = 40 %

Using h_o the relative viscosity vs. clay volume fraction was calculated.

The intrinsic viscosity, [h], is related to the aspect ratio, p: [h] = 2.5 - a(1-pb_).

The calculated value p = 287 ± 9 agrees well with p = 286 determined from the oxygen permeability data.





2 ' ' , / 1 [ ] [ ] r o o PA k h h h   h f  h f

34

LCP model

Flow of PA-6/PNC follows the LCP behavior

The flow of liquid crystal polymers (LCP) is characterized by the presence of three regions [Onogi & Asada, 1980]:

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 & A sa da, 198 0)

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

log (rate of shear)

R e gio n I R e g io n II R e g io n III 20 0 40 0 60 0 80 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 we 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 , h ( P a s ) Rate of shear (1/s) Dt (s )

35

Stress overshoot

Orientation of clay anisometric particles leads to strong stress overshoot effect when the direction of shearing is reversed (left).

The magnitude of the stress overshoot depends on the rest time at 240o_{C (right).}

It takes about 1 hr for the platelets to return to the pre-shear random orientation. 0 100 200 0 1000 2000 3000 4000 experimental computed Dh (Pas ) Rest time, t(s) Dh = a exp{-b/t} a = 212.6 ± 7.4 b = 290.4 ± 28.9 r2 = 0.9967 500 600 700 800 900 1000 0 1000 2000 3000 4000 5000

Flow reversal for PNC at T = 240oC

Rest time = 500 s Rest time = 2000 s Rest time = 4000 s V is cos ity , h ( P as ) Time, t(s)

36

FTR of PA-6 PNC

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 3rd _harmonic.

Right Fig. show the relative intensity of the 3rd harmonic – a measure

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

PNC: time sweep at T = 240°C, 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; g = 20%  = 1 Hz; g = 30%  = 1 Hz; g = 60%  = 1 Hz; g = 70% = 10 Hz; g= 70% R el at ive in te ns ity , R 3 = 10 0( I 3 /I 1 ) Shearing time, t(s)  = 10 Hz = 1 Hz

37

Rheology of PS PNC

PS-based PNC were prepared in solution and by melt compounding

PS (three grades) with 0 to 10-wt% of organoclay (Cloisite® _10A;

C10A) in a CORI (d₀₀₁ = 1.93 to 4.20 nm).

C10A = MMT pre-intercalated with di-methyl benzyl hydrogenated tallow ammonium chloride.

Owing to thermo-oxidative degradation of C10A the degree of

dispersion was poor, viz. the aspect ratio: p = 16 – to be compared

with p = 269 determined for the solution-prepared PNC.

Flow properties were determined in dynamic and steady state shear as

well as under extensional flow conditions.

The Fourier-transform rheology (FTR) indicated strong dependence on strain but weak on time.

The time-temperature superposition held in the full range of variables. Strain hardening in extensional flow of the PNC (with 0 to 10 wt%

38

FTR of PS/C10A PNC

PS1220 (M_w = 310 kg/mol; MFR = 1.9 g/10min) with

2-10 wt% of C10A were used at g = 10, 20, 50 and

75%.

Taking the ratio of the third harmonic to the first, the

dependence shown on the RHS of R₃ = 1000I₃/I₁ vs.

g was obtained.

Note that the melt compounded PNC with 2 wt% organoclay show the same dependence as PS, but specimen prepared in solution shows even stronger non-linearity than the melt compounded specimen with 10 wt% organoclay.

Upper four Figs. show raw data at = 1 Hz and g =

10, 20, 50 and 75%.

Lower Fig. shows R₃ for PS1220 with 10 wt% C10A as a function of frequency and strain at T = 200°C. Solid points are experimental, the open symbols are calculated from: Frequency (Hz) 0 2 4 6 8 10 Int ensit y 0 500 1000 1500 2000 2500 3000 Strain: 10% Frequency (Hz) 0 2 4 6 8 10 Int ensit y 0 500 1000 1500 2000 2500 3000 Strain: 20% Frequency (Hz) 0 2 4 6 8 10 Int ensit y 0 500 1000 1500 2000 2500 3000 Strain: 50% Frequency (Hz) 0 2 4 6 8 10 Int ensit y 0 500 1000 1500 2000 2500 3000 Strain: 75%     3 max L L 3 R ( ) = R 1- exp - - / ; 1 R ( ) = a 1-1 ( )c k or b  g g g g  g         _    0.0 5.0 10.0 15.0 20.0 0 20 40 60 80 PS1220 PS1220+2% PS1220+10% PS1220+10% calc PS1220+ 2% calc PS1220 calc PS1220+2% solution R 3 = 1 00 0 I 3 /I 1 Strain, g (%)

39

Extensional flow of PNC

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 d₀₀₁ = 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 200oC 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 3h+ (shear) h+ E at 0.072 h+ E at 0.167 h+ E at 0.430 h+ E at 0.860 L og ( s tr e ss g row th fu nct io n , Pas)

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 ar d en in g, SH ( -) Hencky strain,  (-) Okamoto et al., 2001 Strain rate,  (1/s)

PP-MA with 4 wt% MMT/ODA

40

PNC rheology: conclusions

The intrinsic viscosity, [h] = f(p), and the initial slopes of the dynamic shear moduli, g’ and g”, may be used to quantify the degree of clay dispersion.

In the power-law region the capillary flow data: . These tests are useless for the characterization of PNC.

Fourier-transform rheology (FTR) is a powerful tool for

studies of the non-linear viscoelastic effects, caused by the presence of 3D structures in PNC.

The time-temperature (t-T) superposition principle has been shown valid for several molten PNC systems.

( ) '( )

41

Melt compounding:

shear vs. elongation

Mixing involves dispersive and distributive flow.

Shear causes rotation, absent in extension.

Fundamentally, on the three accounts:

1. the energy required for mixing (dispersion)

2. the magnitude of the interface increase (distribution)

3. the rate of spatial separation of two material points,

better mixing (by several orders of magnitude) is

expected in extensional than in shear flow.

42

Shear exfoliation in a TSE (co, counter-, intermeshing, non-intermeshing) was studied using 8 screw configurations at T = 240o_{C, Q = 5 kg/h and 200 rpm [Dennis et al., 2001].}

DD vs. residence time (t) correlated

with r2 _{= 0.86.}

Better correlation was obtained when t-distribution of () was included r2 _{= 0.98.}

Thus, exfoliation depends on the residence time, not the stress level

(although stress is necessary).

Exfoliation in extensional flow field should be 4x faster.

Compounding in shear





DD  4.37 exp 0.00972 t ; r  0.86 2 2 DD  4.2 0.21t 564   0.0017 t 4100 ; r 0.98

CORI = co-rotating, intermesh ICRR = intermesh, counter-CRNI = counter, non-intermesh

6 7 8 9 10 20 40 80 120 160 DD = 4.37 exp{0.00972t} R= 0.861 D egre e of dis persion, D D

Residence time in extruder, t (sec)

CRNI CORI ICRR ICRR CRNI CRNI ICRR CORI * * *   in elongation 4x faster???

43

EFM principle

The extensional flow mixer (EFM) and its

dynamic version (DEFM) have:

Converging and diverging zones (CD)

CD elements of different geometries (number and position of the converging zones)

Progressively increasing stress (e.g., by radial flow) Adjustable gap between CD elements.

44

EFM-3, construction details

Futuresoft Technologies Inc., Mississauga, ON,

Canada; <http://www.futuresoft.net/efm>

Modifications of

commercial mixers:

1. Spiral feed for better

feed T-control and added rigidity. 2. Redesigned C-D plates. 3. Redesigned C-D plates mounting. 4. Redesigned attachment to the die.

45

Flow profile in EFM

b h a 120 deg 120 deg c a/R = 0.5 h/R = 0.75 b/R = 2.0 c/R = 0.1 Number of c-d region : 2 Dimensions of c-d region

Tanoue and Iemoto, PPS-17 Annual Meeting Proc. CD (2001)

Without taper ( We = 7)

With taper ( We = 7)

46

Melt compounding 1

The advantage of EFM-3 for melt exfoliation of organoclay in a polymeric matrix was examined using three setups:

TSE (high shear and low shear screw configurations)

TSE + gear pump

TSE + gear pump + EFM-3

The system consisted of PET with 5 wt% of two

organoclays: MMT-1 and MMT-2 [A. Garcia-Rejon & Y. Simard, 2001].

34 mm TSE-CORI with high-shear screw configuration was used, with a side-feeder for organoclay; the residence time varied from 50 to 240 sec.

The extruded PNC was injection molded into ASTM #4 specimens for tensile tests.

Selected compositions were extrusion-blow molded into 500 ml bottles – significant improvement of hot-fill stability were observed (no shape distortion on cooling).

47

Melt compounding 2

The results were repeated at EFM Inc (see next

slide) for PET + MMT-1. Generality of this

observation should be validated using other

PNC systems and diverse processing parameters.

Work is in progress.

The preliminary results indicate that to achieve

exfoliation: (1)

suitable organoclay must be used

,

and (2) use of

EFM leads to better performance

.

1 2 3 4

50 150 250

PET with organocly MMT-1 and MMT-2

MMT1: TSE+GP+EFM MMT1: TSE+GP MMT1: TSE MMT2: TSE+GP+EFM MMT2: TSE+GP MMT2: TSE R e la tive Y o u n g mo d u lu s, E r Residence time, t r(s) error bar: ± 10%

48

Application to PNC: PET

Organoclay MMT w/PET 0 1 2 3 4 5 6 7 8 50 100 150 200 250

Residence time, sec

R e la ti v e Y o u n g M o d u lu s EFM TSE+GP TSE

PET was compounded with 4 wt% organoclay. TSE, TSE with gear

pump (GP) and TSE + GP + EFM were used.

Relative performance is shown (data: EFM Inc.).

0 0.5 1 1.5 2 2.5 3

Flex strength Impact strength

R e la ti v e Str e n g th PET-MMT PET

49

Application to PNC: PP

#1: TSE without EFM; x 50k – large stacks encircled.

#2: TSE + EFM; x 200k – many short stacks.

#3: SSE + EFM; x 200k – few short stacks and

exfoliation

[data from UCL of ITRI, Taiwan]

.

Better dispersion in SSE + EFM than in TSE + EFM is

most likely due to higher thermal degradation in TSE.

#1 #2 #3

400 nm 400 nm

50

DEFM may be used as a torpedo

attached to SSE or as a “stand-alone” unit fed from SSE, TSE, gear pump, etc.

Distributive element Dispersive elements

Sliding barrel

51 1. Smooth, to generate shear flow (S). 2. Sinusoidal, to generate extensional flow (G). 3. Flat-top sinusoidal to generate shear and elongation in proper proportion and

intensity (FG).

4. FG was shown to perform the best.

(S)

(FG)

(G)

52

PNC Summary

MMT with CEC  1 meq/ g and p  300, is the most popular. MMT intercalation involves:

Reacting MMT– with onium+ _{(mainly ammonium).}

Incorporation of a monomer.

Compounding with a compatibilizer and polymer.

Thermal decomposition of R₄N+ _{at T > 180}o_{C is most serious.}

Reactive exfoliation is the easiest, kinetics may be affected, and the dispersion may be thermodynamically unstable!

The PO-type PNC employs “sizing agents”, e.g., organo silanes, titanates or zirconates and/or “compatibilizers” (PO-MAH).

Mixing in extensional flow field is superior to that in shear.

General purpose, inexpensive, static and dynamic extensional flow mixers (EFM

and DEFM, respectively) have been developed.

PNC

Clay-containing

Polymer Nanocomposites

EXTRAS

L. A. Utracki

NRCC/IMI, 75 de Mortagne, Boucherville, QC, Canada J4B 6Y4; Tel.: +1 (450) 641-5182; fax: -5105; <

[email protected] >

54

X-ray diffraction

XRD (WAXS) is used to determine the interlayer spacing, d₀₀₁.

Left Fig.: A = MMT intercalated with di-methyl-stearyl-benzyl

ammonium chloride; B = HDPE melt compounded with A; C = HDPE polymerized on A; D = HDPE [Heinemann et al., 1999].

Right Fig.: A = intercalated MMT; B = LLDPE melt compounded with A; C = LLDPE polymerized on A (LLDPE = polyethylene-co-octene).

55

TEM of PNC

HDPE melt compounded with intercalated clay (A)

HDPE polymerized onto the intercalated clay (B). Noteworthy that clay

reduced catalyst activity by ca. 100.

PNC performance of LLDPE > that of HDPE [Heinemann et al., 1999.

Epoxy PNC (C) shows a better, but still not total exfoliation of MMT

[Giannelis, 1996].

56

Intercalation 3

Molecular modeling of clay layers intercalated with alkyl-ammonium cations (see LHS; Vaia, 1995).

The generated structures were confirmed by FTIR and the XRD d₀₀₁ spacing measurements.

As the alkyl length increases (from the top):

(a) isolated, short chains in a monolayer;

(b) intermediate chains disordered, forming a quasi-bilayer;

(c) long chains with increased order and multi-layer spacing.

57

Intercalation 4

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. Bond strength increases in order:

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

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

4 3 2 2 3 4

58

Commercial intercalated clays contain quarternary amines

(Southern Clay Products, 2000). The cation exchange capacity of MMT: CEC = 100 ± 20 meq/100 g.

Equilibrium of NaMMT 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 to 4 % water and up to 40 wt% of organic compounds.

Intercalation increases the cost of clay from US$2,000 to US$7,000/ton.

59

Exfoliation – general 2

Usuki proposed the following classification:

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

 

60

Hofmann elimination (1851)

CH3(CH2)n N CH2 C CH3 + N CH2 C CH3 + H + CH3(CH2)n-2CH=CH2 CH3(CH2)n-2CH=CH2 O2 CH3(CH2)n-1CH=O CH3(CH2)n-1CH-O -O +

[CH2 CH ]n ₊ CH3(CH2)n-1CH-O -O PS chain scission

Phosphonium ions are more stable than ammonium. Organo-metallic complexes show high stability.

61

Thermodynamics

Lattice-hole model

In 1941 Huggins and Flory calculated the configurational entropy of mixing.

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

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:

62

Adsorption on solids

Owing to high surface energy of crystals (100 x of liquids) the

macromolecules are readily adsorbed (Israelachvili, 1991).

The surface force analyzer measured h of adsorbed PS (from toluene); a

solid-like behavior found for layers with 2H = D < 220 nm (Klein et al., 1993).

The amount of adsorbed polymer depends on PS molecular weight and

c (see insert; Linden & van Leemput, 1978).

2

6 / _H / _o

G  R D F  D h

63

Physics of PNC 2

Since values of the interaction parameters, _ij, are not available,

Vaia replaced them by interfacial energies between interacting species i-j, viz.:

Since for miscibility De_v < 0 is needed, the interfacial tension

coefficients: _sp < _sa must be satisfied.

However, since _ij are also unknown, he suggested calculations

based on surface energies ‒ a bad suggestion.

Vaia’s conclusions: (1) strong energetic interactions between the

diffusing polymer (i = p) and clay (i = s) are required; (2) Since

interactions between intercalant (i = a) and polymer would hindered

kinetics of polymer diffusion, thus they are not desirable, _ap = 0.

ap ap

64

PNC with telechelic sticker

The scaling (non-lattice) theory was used to compute phase diagram of two pre-intercalated clay platelets immersed in a polymer melt of telechelic N-polymer (f and regular P-polymer (1-f). The energy per sticker–clay contact was  [Kuznetsov and Balazs, 2000].

The N-macromolecules are either free (f), anchored by one (t for “tails”) or two ends (l or b for “loops" or "bridges", respectively). The Huggins-Flory interaction parameters were assumed as: c_NN = c_PP = 0, and

c_NP = c.

Left: Phase diagram for PNC containing

f of functionalized polymer (N = 1000) and (1- f) of non-functionalized polymer (P = 100).

The phases are: intercalated (In), exfoliated (Ex), and immiscible (Im).

65

Confirmation of theory 2

The dynamic rheological measurements of C-PEA (5 wt% clay)

caused G’ = G’() to parallel the dependence of the matrix with a

slight increase caused by the filler effect.

The dynamic rheological measurements of C-APS (5 wt% clay) the low frequency slope in the terminal zone was about 0.5 (instead of 2, as in the former case), as predicted by the LCP theories.

66

Strain sweep

Measured at T = 240°C,  = 6.28 (rad/s)

Storage (G’) and loss (G”) shear moduli were corrected for the time effects using the determined rates for actual times of measurements (t < 600 sec). The strain effects were described using non-linearity equation:

An example is shown in the left figure below.

2 3 1 2 '( ) ' / 1_o ' _f ' _f ; _f /100 G g  G _ G g G g _ g g 2 1 03 3 1 03 4 1 03 0 4 0 8 0

E xtrude d P A -6/P N C2 m ixt ure s at T = 2 40 oC ,  = 6.28 rad/s

L o s s m o d u lu s , G " (P a ) Stra in , g(% ) P N C 2 (% ) 10 0 7 5 5 0 2 5 0 (PA -6 ) 0 10 0 20 0 30 0 40 0 0 2 0 4 0 6 0 8 0 10 0

S to rage m o du lu s a t co nsta n t s tra in :

g = 0 a n d 50 % G ' a t g = 0 % G ' a t g = 5 0 % S to ra g e m o d u lu s , G ' (P a ) Co m po sition (w t% o f P NC )

67

Structure

3D structures at low frequency (terminal zone)

The storage modulus (G’) could only be measured at higher frequencies:

 = 1 - 100 rad/s, where the 3D structure is broken.

There is a strong effect of clay concentration on the elastic properties evident in the plot of G’/G” vs. G” and G’/ 2 _vs. _.

1 0-3 1 0-2 1 0-1 1 00

1 01 1 02 1 03 1 04 1 05

S um m ary o f fre qu e cy s w e e p d ata for P A/PN C ble nd s (u n co rrec ted for t);

T = 24 0oC , = 0 .1-1 00 r ad /s sym b o ls fu ll : g = 40 % , em p ty: g = 10% , G'/G "P A G '/G "2 5 G '/G "5 0 G '/G "7 5 G '/G "1 0 0 G '/G "1 0 0  = 0 .1 -1 0 0 G '/G "1 0 0  = 10 0 - 0 .1 G '/ G " G " (P a) 0 .1 1 1 0 10 0 0 .1 1 1 0 10 0

F requ ency depend ence o f G ' fo r P A- 6/P NC m ix tu res

R e d u c e d s to ra g e m o d u lu s , G '/  2 (P a s 2 )

Fre que ncy , (rad/s)

100 % PN C 75 % PN C 50 % PN C 2 5 % PN C P A- 6 T = 24 0oC g = 40 %

68

Dispersing organoclay stacks in a melt:

1.

Incorporation into polymer melt

2.

Wetting and de-aeration

3.

Breaking up the stacks by:

rupture erosion

4.

Stabilization of the resulting dispersion

Dispersion by rupture & erosion

(Manas-Zloczower et al., 1982)

:

Z  2 in shear, Z  1 in pure or biaxial elongation, and Z  0.5 in

uniaxial elongation, k - scalar reflecting geometry of the breakup process

Dispersing in PNC

11 12

( _m ) / _ij / / 4

k Z k Z

69

Exfoliation mechanism

Variation of the XRD with the mixing time for PS/Cloisite10A at 210°C under a shear rate of 65 (1/s); Yoon

et al., 2001.

Dennis et al., 2001

Thermal degradation of organoclay complicates the melt exfoliation

70

Compounding 1

1 mm

TEM Dispersion

Cloisite 30B was melt exfoliated in PA-6, while Cloisite 15A could not, thus deemed suitable for the study. The larger the DD value, the better the delamination and dispersion. DD values were proportional to

XRD data, viz. d₀₀₁ = 3.2 to 3.8 nm, with progressive decrease of the peak high with the compounding time.

The "TEM dispersion method" developed by

Dennis et al., 2000

:

The number of platelets or stacks in 12 squares of TEM were

counted.

The degree of dispersion (DD) = average number of platelets or intercalants per square inch.

71

Velocity Profile in EFM

72

Extensional Flow in EFM

Extensional Rate at CD1 0 2000 4000 6000 8000 10000 12000 0 0.2 0.4 0.6 0.8 1 Relative Gap M ax . Extensional Rate, 1/s Extensional Strain at CD1 0 1 2 3 4 5 6 7 8 9 0 0.2 0.4 0.6 0.8 1 Relativ e G a p M ax . Extensional Strain

Velocity along Streamline

0 100 200 300 400 500 600 700 800 900 1000 0 0.2 0.4 0.6 0.8 1 Relative Gap Max. Velocity, mm/s

73

P & T in EFM

Pressure distribution in EFM

Adiabatic and shear heating by DT  2o_C

Temperature along central streamline

74

The theories predict that mixing in extensional flow field is superior to that in shear, considering:

local strains, increase of the interface, drop deformability, specific energy of mixing,

degradability of polymeric matrix, etc.

General purpose, inexpensive, static and dynamic extensional flow mixers (EFM

and DEFM, respectively) have been developed.

EFM is mainly a dispersive mixer, while DEFM provides adjustable balance of the dispersive and distributive mixing, independent of viscosity ratio.

EFM has been used for blending, homogenization, toughening of thermoplastics, elimination of gel particles, preparation of PNC, etc.

Several new designs of the dispersive elements are being tried to evaluate the importance of: shear and elongational stress, residence time, matrix viscosity and type of organoclay.

The work carried out by a MEng student at McGill, Mr. N. Nassar, confirmed the basic premise.

75

Melt exfoliation of PNC is at an early stage.

There is lack of systematic studies of exfoliation for all but PA-type PNC. Melt exfoliation requires “suitable” organoclay:

Having reactive (preferably) end-groups to bond to clay surface and tails miscible with the matrix polymer.

Alternatively, an organoclay that would readily accommodate a compatibilizer to form an intermediary layer.

Being thermally stable at the processing temperature.

As organoclay dispersion in PET or PP indicate, melt compounding in extensional flow field is more powerful and economic than in shear. For PNC exfoliation EFM with precisely controlled gap and redesigned plates geometry is needed.

DEFM offers several advantages over the static EFM, viz. controllable:

stress level, balance of dispersive and distributive mixing, residence time, diversity of flow geometries.

76

PNC Summary

Na-MMT with CEC = 0.9 -1.2 meq/ g and p = 500 -1000, is the most popular nano-filler.

Success of PNC hinges on intercalation that involves, e.g.: Reacting MMT– with onium+ _{(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 > 200o_C.

Performance depends on exfoliation and the clay-matrix interactions. Easiest to prepare PNC is via polymerization, but the intercalant may interfere with its kinetics, catalyst with exfoliation, and the dispersion may be thermodynamically unstable!

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