Polystyrenes with Macro-Intercalated Organoclay

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Polystyrenes with Macro-Intercalated Organoclay

Polystyrenes with

macro-intercalated organoclay

M. Sepehr

1

_{, L.A. Utracki}

1

_{, X. Zheng}

2

_{, C.A. Wilkie}

2

1 _{Industrial Materials Institute, National Research Council Canada, 75 de Mortagne,}

Boucherville, QC J4B 6Y4, Canada

2 _{Department of Chemistry, Marquette University, PO Box 1881, Milwaukee,}

WI 53201, USA

Outline

Introduction

Objectives

Preparation of organoclay COPS

Materials and method of compounding

XRD measurements

SEM and TEM observations

Rheological properties

Mechanical properties

Concluding remarks

Introduction

Relatively easy exfoliation of clay platelets by polar polymers

(PA) due to strong interaction, but much more difficult to

exfoliate clays in no polar polymers (PS, PP).

Polymerization in presence of non-reactive organoclay:

•

Slow reaction;

•

Thermodynamically unstable exfoliation → re-aggregation during processing;

•

Process available only to resin manufacturer.

Melt processing providing mechanical exfoliation:

•

Rapidity (< 10 min);

•

Controlled by thermodynamic interactions → no danger of re-aggregation;

•

Need to be miscible with PS and thermally stable organoclay.

(Hasegawa et al. 1999; Hoffman et al. 2000; Yoon et al. 2001; Tanoue et al. 2004)

Objectives

Prepare exfoliated PNC with PS as matrix.

Investigate the degree of dispersion of COPS and the

PNC performance.

COPS organoclay prepared with macromolecular intercalant.

Preparation involved two steps:

Free radical copolymerization of styrene with vinyl-benzyl 3-methyl ammonium chloride Na-MMT intercalation.

TGA measurement from 30 to 700°C at a rate of 10°C/min

shows:

Volatile matter: 1.4-wt% loss at T ≤ 150°C;

Non-volatile matter (MMT): 21.7-wt%. + CHCl3/ETOH 80OC BPO, Cl H₂C N H3C CH3 CH3 X Y Cl H2C N H₃C CH₃ CH₃

Preparation of COPS

Materials and method of

compounding

Materials:

•

PS1301 (Nova Chemicals, M_w = 270 kg/mol);

•

PS20.3 (Delltec, M_w = 116 kg/mol);

•

COPS organoclay dried for 15 d at 60 C;

•

Cloisite 10A (C10A) dried for 24 h at 100 C.

Method of compounding:

•

Melt compounding with:

• MiniLab co- and counter-rotating micro-compounder (ThermoHaake)

• Industrial co-rotating fully intermeshing TSE (Leistritz, TSE-34 mm,

L/D = 40)

•

Solution blending of COPS and PS separately in toluene.

COPS 2θ (degree) 2 4 6 8 Inte ns ity (C ps ) 0 1000 2000 3000 4000 5000 6000

COPS (ground by hand) (run 2)

Interlayer spacing (nm) Main Secondary

8.79 4.42

8.83 4.52

XRD and TEM of COPS

XRD scans of COPS show two peaks: the first at 2θ ≤ 1° (d₀₀₁ = 8.8

nm) and the second at 2θ ≈ 2° (d₀₀₂ = 4.5 nm).

TEM observation of COPS (compression molded then microtomed)

confirm the XRD results of d₀₀₁ = 10 nm (for 96 measures)

x 200k <d₀₀₁> = 8.8 nm N = 7.0 1 001 + − = d d t N θ × λ = cos 9 . 0 2 1_{peak height} W t

The spectra gave:

– The mean interlayer spacing, d₀₀₁ (Bragg):

– The number of platelets per stack, N (Scherer):

001 2 sin n d λ θ = 50 nm

PS/COPS

(Mini-TSE-Co)

Decrease of d₀₀₁ of COPS from 8.8 to 7.4 and 6.9 nm for melt processed PS/COPS;

Decrease of d₀₀₁ with increasing T and/or intensity of mixing conditions; Smaller aggregates of COPS in

PS20.3. x 20k PS 1301/COPS 2 µm PS 20.3/COPS 2 µm PS + 8.7-wt% COPS organoclay Mini-TSE-Co at N = 100 rpm 2θ (degree) 2 4 6 8 10 In te n sity ( C p s) 0 3000 6000 9000 12000 15000 PS20.3/COPS (T = 160°C; t = 0) PS20.3/COPS (T = 160°C; t = 2 min) PS1301/COPS (T = 180°C; t = 0) PS1301/COPS (T = 180°C; t = 2 min) 6.9 nm 7.4 nm 8

PS/COPS

(co-dissolution)

d₀₀₁ of COPS remains in PS/COPS

prepared with co-dissolution;

However large aggregates of COPS were observed in PS (smaller for PS20.3). PS 20.3/COPS 5 µm PS 1301/COPS 5 µm x 10k PS + 8.7-wt% COPS organoclay Co-dissolution preparation 2θ (degree) 2 4 6 8 10 In te n sity ( C p s) 0 1000 2000 3000 4000 5000 PS20.3/COPS (d₀₀₁ = 8.8 nm) PS1301/COPS (d₀₀₁ = 8.1 nm) 9

PS20.3/COPS

Small aggregates of COPS have 10 to 15 platelets;

Individual (exfoliated) clay platelets may be seen also, which are more frequent for co-dissolution prepared blend.

Co-dissolution

100 nm 100 nm

Mini-TS E -Co x 80k

2θ (degree) 2 4 6 8 Inte ns ity (C ps ) 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 COPS PS/COPS (TSE-34) PS/COPS (TSE+GP+EFM) C10A PS/C10A (TSE+GP+EFM)

PS/Clay

(TSE+GP+EFM)

PS/COPS prepared with TSE-34 with

or without EFM show decrease in d₀₀₁

of COPS from 8.8 to 6.5 nm;

Larger aggregates of C10A in PS in comparison with PS/COPS.

PS 1301/COPS 5 µm PS 1301/C10A 5 µm x 10k 4.3 nm 6.5 nm 11

Temperature sweep

with DMTA

The peak of loss modulus (T_g) of PS broadening by adding COPS and

shifts to lower temperature.

At low T, two categories can be distinguished, one for

COPS ≤ 12.5-wt% and another one for higher concentrations.

At high T, the moduli of neat COPS are much higher than those of PS and PS/COPS compounds and show secondary plateaus.

ω = 6.28 rad/s T (°C) 30 50 70 90 110 130 150 170 E" ( G Pa ) 10-4 10-3 10-2 10-1 100 COPS PS/COPS 50/50 PS/COPS 75/25 PS/COPS 87.5/12.5 PS ω = 6.28 rad/s T (°C) 30 50 70 90 110 130 150 170 E' (GP a) 10-3 10-2 10-1 100 101 COPS PS/COPS 50/50 PS/COPS 75/25 PS/COPS 87.5/12.5 PS 12 d_{001 = 7.9 – 8 nm} N = 2.7 N = 4.1 N = 2.5

Frequency sweep with

DMTA

At high frequency (low T), E’ of PS/COPS 50/50 superpose COPS E’.

At high T (T > T_g), the COPS moduli show small peaks, similar to what

has been observed for crosslinked systems.

Considering E” peaks indicates transitions, the secondary peak may originate in the breakup of the ammonium ion pairs or clusters.

T_R = 80°C log ω a_T (rad/s) -15 -10 -5 0 5 10 E' b T ( G Pa ) 10-4 10-3 10-2 10-1 100 101 COPS PS/COPS 50/50 PS T_R = 80°C log ω a_T (rad/s) -15 -10 -5 0 5 10 E " b T ( G Pa ) 10-4 10-3 10-2 10-1 100 COPS PS/COPS 50/50 PS ω = 0.0628 – 62.8 rad/s; γ = 0.0004 T = 30 – 170 °C; ∆T = 10°C

Thermal stability

PS20.3 remains stable during 2 h but the moduli of PS1301 increase by 4.4% (t < 2000 s) then remain stable.

Dynamic shear moduli of PS/COPS increase by 14 – 35% during 6000 s, which can be due to the presence of volatile materials.

γ_o = 0.05; ω = 0.628 rad/s Sweep time, t (s) 0 2000 4000 6000 8000 G' , G" ( k P a) 0 5 10 15 20 G' - PS20.3 (T = 160°C) G" - PS20.3 (T = 160°C) G' - PS1301 (T = 180°C) G" - PS1301 (T = 180°C) G" G' ω = 0.628 rad/s T = 160°C γ_o = 0.05 Sweep time, t (s) 0 1000 2000 3000 4000 5000 6000 G' , G" ( kPa) 0 20 40 60 80 PSCOPS 50/50 PSCOPS 75/25 PSCOPS 87.5/12.5 + G' G" G' G" G' G" 14

Rheological properties of

low clay content blends

Melt structure not affected by the presence of organoclays.

Absence of G’ plateau confirming the XRD and TEM results (not exfoliated COPS).

Increase of G’ and G” by adding C10A to PS (1.2-wt% MMT) due to presence of solid particles, but their decrease in PS/COPS (1.1-wt% MMT) caused by the presence of extractable oligomers.

Frequency sweep ω = 100 − 0.1 rad/s γ₀ = 0.05 T = 180°C ω (rad/s) 0.01 0.1 1 10 100 η ' (kP a. s) 0.1 1 10 100 PS1301+C10A PS1301 PS1301+COPS Frequency sweep ω = 100 − 0.1 rad/s γ₀ = 0.05 T = 160°C ω (rad/s) 0.01 0.1 1 10 100 G' , G " (kPa ) 0.01 0.1 1 10 100 1000 PS1301+C10A PS1301+C10A PS1301 PS1301 PS1301+COPS PS1301+COPS G’ G”

( )

1 0 1 n a _a η η= _ + ⋅τ γ& _ − 15

Concentration of COPS (wt%) 0 10 20 30 40 50 d ln G '/ d ln ω, d ln G '/ d ln ω ω x = ω| G' = G" 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 D ynam ic yi el d s tr es s, σ y ( kPa) 0 2 4 6 8 10 12 14 σ y = 0 at 8. 9-w t% d ln G'/d ln ω d ln G"/d ln ω ω_x = ω|_{G' = G"} σ_y

Rheological properties of

high clay content blends

The partially crosslinked COPS domains are expected to be deformable, the the apparent yield stress can be calculated by:

The extrapolation to zero determines the critical

COPS concentration at 8.9-wt%: the percolation threshold, where the soft gel domains interact. φ = 0.089 < 0.156 shows that the domains have p > 1.

ω = 100 − 0.1 rad/s γ₀ = 0.05; T = 160°C ω (rad/s) 0.01 0.1 1 10 100 G' , G " (kPa ) 0.01 0.1 1 10 100 1000 G' (PS/COPS 50/50) G" (PS/COPS 50/50) G' (PS/COPS 75/25) G" (PS/COPS 75/25) G' (PS/COPS 87.5/12.5) G" (PS/COPS 87.5/12.5) G' (PS) G" (PS)

(

)

0 1 exp u y y y σ ₌σ _{ − − ⋅}τ γ&_ 16

Rheological properties of

high clay content blends

The η’ and G’/ω plots vs. frequency make the structural changes of the melt more evident, the elasticity is in the same level of viscous loss.

The immiscible COPS domains start to interact after the concentration of 8.7-wt% (φ_threshold = 8.9%). ω = 100 − 0.1 rad/s γ₀ = 0.05; T = 160°C ω (rad/s) 0.01 0.1 1 10 100 η ' (kP a. s) 0.1 1 10 100 1000 10000 PS/COPS 50/50 PS/COPS 75/25 PS/COPS 87.5/12.5 PS ω = 100 − 0.1 rad/s γ₀ = 0.05; T = 160°C ω (rad/s) 0.01 0.1 1 10 100 η " (kP a. s) 1 10 100 1000 10000 PS/COPS 50/50 PS/COPS 75/25 PS/COPS 87.5/12.5 PS

Mechanical performance

18

Impact Strength (J/m); Tensile Strength (MPa)

Tensile modulus (MPa)

0 10 20 30 40 50 PS/C10A (TSE+GP+EFM) PS/COPS (TSE+GP+EFM) PS/COPS (TSE) PS (TSE+GP+EFM) PS (TSE) PS As received 3000 3100 3200 3300 3400 3500 3600 3700

Specimen Reference ∆ Tensile

strength ∆ Tensile modulus ∆ Flexural strength ∆ Flexural modulus ∆ Impact strength Error of measurements (%) 1.8 3.6 2.0 1.1 11.0

PS (TSE) PS (as received) -2.0 -2.2 -0.6 1.1 -7.1

PS (EFM) PS (as received) -2.5 -3.2 0.1 1.3 -7.1

PS/COPS (TSE) PS (TSE) -11.3 7.4 -37.4 7.3 -38.5

PS/COPS (EFM) PS (EFM) -9.1 8.0 -35.3 6.1 -30.8

PS/C10A (EFM) PS (EFM) -5.1 7.2 -16.3 3.6 0

(%) 100Yspecimen Yreference 1

∆ = _ − _

Reinforced effect restricted to dispersed domains;

The dispersed domains act as partially solid with low aspect ratio, having low reinforcing effect;

Plasticating effect of

extractable low Mw from COPS.

Concluding remarks 1

COPS organoclay with macromolecular intercalant was prepared in two steps: the free radical copolymerization of styrene with vinyl-ammonium compound followed by Na-MMT intercalation.

Melt compounding of COPS with PS, instead of exfoliation engendered a two-phase dispersion.

The co-dissolution method was also unsuccessful.

The statistic of random copolymerization indicates that a significant proportion of copolymer molecules would have two ammonium

groups, statistically capable of bridging the gap between the adjacent clay platelets. The bridging forms clay/oligostyrene network immiscible with PS.

Concluding remarks 2

The time sweeps indicated an increase of dynamic shear moduli, due to the presence of volatiles in materials containing COPS.

The incorporation of 2-wt% C10A increased the zero-shear viscosity by 20% but that of 5.2-wt% COPS (same amount of MMT) reduced it by 18%, which can be caused by the presence of extractable

oligomers in COPS.

The addition of 12.5-wt% COPS increased the system elasticity as the same level of viscous loss and the material with 50-wt% COPS

behaves in the non-linear VE region. These materials behave like partially crosslinked system.

At high temperatures T > T_g, E’ and E” of COPS show a secondary

plateau, similar to what has been seen for crosslinked systems.

The performance of PS/COPS was slightly inferior of that of PS/C10A. 20

Acknowledgment

Chantal Coulombe

Florence Perrin

Yves Simard

Manon Plourde

This work has been sponsored by NSERC Postdoctoral Fellowship Program.