Solvent Resistance and Mechanical Properties in Thermoplastic Elastomer Blends Prepared by Dynamic Vulcanization

J.D. (Jack) Van DykeTrinity Western University, Langley, B.C., Canada

Marek GnatowskiPolymer Engineering Co. Ltd, Burnaby, B.C., Canada

Andrew BurczykDefence R&D Canada-Suffield, Canada

Mixing Methods

High shear melt mixing

Without curing agents non-vulcanized blends Continuous phase dependent on proportions in the

blend

With curing agents dynamic vulcanization Non-vulcanized component becomes continuous

phase, almost independent of proportion in blend

Non-Vulcanization vs. Dynamic Vulcanization

Objective of Present Work

Dynamic Vulcanization on a Variety of Thermoplastic / Rubber Combinations

Thermoplastics (PA, PP, and PBT)

Rubber (CIIR, NBR)

Measure

Mechanical properties

Exposure to solvents (hexane and CHCl3)

% insolubility, swelling index

DSC and SEM

Effect of % Thermoplastic on Properties

PP-CIIR Blends

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

18 20 25 30 35 40 50 60 100

% Polypropylene

Ten

sile S

tren

gth

(M

Pa)

Tensile Strength

(MPa)PP-CIIR Blends

0

10

20

30

40

50

60

70

80

18 20 25 30 35 40 50 100

% Polypropylene

Hard

ness (

Sh

ore D

)

Hardness (Shore D)

60-90 50-90

Tensile Strength Comparison in Blends

PA-

CIIRPP-

CIIRPA-

NBRPP-

NBRPBT-

NBR

0

15

20

25

30

35

4050

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

Tensile Strength

Blend Type

% Plastic

DSC Results – Thermoplastic Phase

Tm (°C) ΔHf (J/gplastic)

PA 178.7 60.6

PA/CIIR 175.6 58.1

PA/NBR 176.5 58.5

PP 163.3 80.9

PP/CIIR 161.6 83.1

PP/NBR 161.5 80.6

PBT 223.0 38.1

PBT/NBR 222.6 46.0

Phase separation

Dynamic vulcanization effects

rubber phase (curing, particle formation)

thermoplastic phase (MW reduction, graft formation, crystallization effects)

SEM OF PA/NBR BLEND

PA-NBR Blend PP-NBR Blend

0

1

2

3

4

5

6

0 8 16 24 32 40 48 56 64 72 80 88 96

Time (hrs)

Sw

elli

ng Index

100 NBR

40 PA /60 NBR

Solvent Uptake – Kinetic Studies

Rate of solvent uptake determined on rubber and blend samples

Blends achieve equilibrium relatively quickly

Example of 100 NBR and 40 PA/60 NBR

Swelling Index: PA – CIIR Blend at Different Compositions

S.I. Values consistently below theoretical line (physical mixture)

Continuous thermoplastic phase prevents solvent expansion of cured rubber phase

PA-CIIR Blends

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70 80 90 100

% Polyamide

Sw

ell

ing

In

dex

Swelling Index

Swelling Index Values for Other Blends

PP-CIIR Blends

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70 80 90 100

% Polypropylene

Sw

ellin

g In

dex

Swelling Index PA-NBR Blends

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80 90 100

% Polyamide

Sw

ellin

g In

dex

Swelling Index

Swelling Index Values for Other Blends

PP-NBR Blends

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80 90 100

% Polypropylene

Sw

ellin

g In

de

x

Swelling Index PBT-NBR Blends

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80 90 100% PBT

Sw

ellin

g In

dex

Swelling Index

Relationship Between Swelling Index and % Elongation

Minimum elongation reached at similar composition as change in S.I. Curve

Phase inversion

Similar results for all blends studied.

PBT-NBR Blends

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80 90 100

% PBT

Sw

ellin

g In

dex

0

100

200

300

400

500

600

Elo

ng

ati

on

(%

)

Swelling IndexElongation (%)

Conclusions

1. Dynamic vulcanization – variety of rubber plastic blends, many with elastomeric properties. Elastomeric properties seen between 20-40%

thermoplastic

2. Both rubber and plastic phases affected during the dynamic vulcanization process.

3. Solvent exposure – rapid swelling upon exposure to solvent (tested on hexane and CHCl3). Similar performance expected with other solvents.

Conclusions (continued)

4. S.I. values of blends are significantly less than expected “theoretical” values. “caging effect” at higher thermoplastic

compositions.

5. Minimum elongation values reached at phase inversion.

6. Increased compatibility in blends reduced particle size (discrete phase)

frequently produces less caging effect on the rubber phase

Acknowledgements

Defence R&D Canada – Suffield

Laboratory staff at PEC

Dave Lesewick, Christine Mah, Beverley Start

Laboratory staff at TWU

Leanne Edwards, Simon Moore, Kim Klassen

DRDC – Esquimalt (SEM results)

Bruce Kaye

Website: www.polymer-engineering-co.com/