C.M. Roland
Naval Research Laboratory
Gary S. Buckley
Cameron 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
Single Network
Double Network
Single Network
(0.4 MPa)
Double Network
(17.2 MPa)
Jing Ping Gong and Yoshinori Katsuyama, Advanced Materials, 15(14), 2003.
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
Tensile Strengths
Comparison of Higher Modulus Materials
3.5
Stress (MPa)
3
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
3
3.5
Strain (mm/mm)
0% EPM 0.625 phr S
50% EPM 1.4 phr S
Is the EPM chemically a part of the network?
4
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
Gel fractions
Gel fractions vs. phr Sulfur
Gel Fraction
1.1
1
0.9
0.8
0.7
0.6
0.5
0
0.5
1
1.5
phr S
0% EPM
50% EPM
Indicates that EPM was not a chemical part of the network
Network Density
Network Density (mol/cc)
Network Density vs. phr S
4.0E-04
3.5E-04
3.0E-04
2.5E-04
2.0E-04
1.5E-04
1.0E-04
5.0E-05
0.0E+00
0
0.2
0.4
0.6
0.8
1
phr S
0% EPM
50% EPM
1.2
1.4
1.6
Tensile Strength and Network Density
Mechanical Properties vs. Network Density
Tensile Strength (MPa)
4
3.5
3
2.5
2
1.5
1
0.5
0
0.0E+00
5.0E-05
1.0E-04
1.5E-04
2.0E-04
2.5E-04
3.0E-04
3.5E-04
Network Density (mol/cc)
0%EPM (TS)
Is there a homogeneity issue?
50%EPM (TS)
4.0E-04
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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