Improving Performance of Rubber Materials Through Blending

C.M. RolandNaval Research Laboratory

Gary S. BuckleyCameron University

Outline

•A little terminology

•Work with hydrogels

•Can this shift to rubber materials?

•Materials used in rubber work

•Results

•Conclusions

A Little Terminology

Crosslink – a covalent bond between two separate polymer molecules

Work with Hydrogel Materials

Jing Ping Gong and Yoshinori Katsuyama, Advanced Materials, 15(14), 2003.

Single Network Double Network

Single Network Double Network (0.4 MPa) (17.2 MPa)

Key factors: 1. The two networks were homogeneous. 2. The difference in crosslink densities was maximized.

Can this idea translate to rubber materials?

Two selected rubber materials:

EPDM – contains double bonds and can be crosslinked with sulfur

EPM – contains no double bonds and cannot be crosslinked with sulfur

The idea:Blend EPDM and EPM followed by crosslinking with sulfur to see if mechanical properties are improved

0 0.5 1 1.5 2 2.5 3 3.5 40

0.5

1

1.5

2

2.5

3

3.5

Comparison of Higher Modulus Materials

0% EPM 0.625 phr S 50% EPM 1.4 phr S

Strain (mm/mm)

Str

ess

(MP

a)

Tensile Strengths

Is the EPM chemically a part of the network?

Did EPM become a bonded part of the network?

All EPM should be soluble if not a chemical part of network

Soxhlet extraction to determine gel fraction

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60.5

0.6

0.7

0.8

0.9

1

1.1

Gel fractions vs. phr Sulfur

0% EPM 50% EPM

phr S

Gel

Fra

ctio

n

Gel fractions

Indicates that EPM was not a chemical part of the network

Network Density

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60.0E+001.0E-052.0E-053.0E-054.0E-055.0E-056.0E-057.0E-058.0E-059.0E-051.0E-04

Network Density vs. phr S

0% EPM 50% EPM

phr S

Net

wo

rk D

ensi

ty (

mo

l/cc

)

Tensile Strength and Network Density

0.0E+00 1.0E-05 2.0E-05 3.0E-05 4.0E-05 5.0E-05 6.0E-05 7.0E-05 8.0E-05 9.0E-050

0.5

1

1.5

2

2.5

3

3.5

4

Mechanical Properties vs. Network Density

0%EPM (TS) 50%EPM (TS)

Network Density (mol/cc)

Ten

sile

Str

eng

th (

MP

a)

Is there a homogeneity issue?

Are EPDM and EPM homogeneous initially?

C-C bond length:

~ 0.15 nm

Potential Applications – Ballistics

Bad response Good response

Conclusions

•Blended EPDM and EPM crosslinked with sulfur provides better tensile strength than crosslinked EPDM

•Blended EPDM/EPM tensile strengths continue to increase even as the network density levels off

•The increase in tensile strength of the blended material is modest – not on the order of the hydrogel work

•The EPDM/EPM system is not particularly homogeneous - work remains to be done to see if its homogeneity increases as the cure package increases

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