Eugene Chang
Chem 4491
Dr. Buckley
Fall 2010
MANIPULATING CROSSLINK DENSITY OF EPM/EPDM POLYMER
EPM/EPDM is an ethylene propylene (diene) monomer that is a synthetic rubber and has
a wide range of applications. The difference between the two compounds is found in the diene,
in which a double bond is formed during the vulcanization process and increases the crosslink
density; this will increase tensile strength without subtracting from any other properties.
During the special problems class with Dr. Buckley, we performed several tests to refine
data from previous experiments. Small samples of EPM/EPDM, containing various cured
content, was placed in a soxhlet extractor with a xylenes solution. The samples were immersed
in fresh xylenes solution at intervals proportional to the setting of the potentiometer. This
provided continuous extractions over the course of a week. Samples were allowed to dry for a
week and the xylenes pot was distilled using a simple distillation apparatus and recycled for
additional soxhlet extractions. The EPM/EPDM samples no longer contained traces of the cured
packages, assisted in the homozygous blending of the polymer, and was immersed in
cyclohexane for a week. Cyclohexane would cause the polymer to swell and the samples could
then be weighed to determine the gel fraction. The gel fraction would reveal the cross link
density or the double bond formation from the blending process.
DATA
Table 1 – Swelling data
SAMPLE
initial mass
gel mass
SWELLING
MASS
EPM50C200GB#2
EPDMC30GB2
EPM0C200GB
EPM50C60GB
EPDMC80GB2
EPM50C125GB
EPM50C2256B
EPM50C40GB
0.3014
0.3806
0.2936
0.2508
0.398
0.39
0.3983
0.3607
0.1775
0.3521
0.2715
0.1542
0.383
0.2354
0.2327
0.226
0.9463
2.5075
0.9031
1.016
1.6017
1.2668
1.26
1.7717
Table 2- Gel fraction determination
volume
rubber
0.20882353
0.41423529
0.31941176
0.18141176
0.45058824
0.27694118
0.27376471
0.26588235
mass of
solvent
0.7688
2.1554
0.6316
0.8618
1.2187
1.0314
1.0273
1.5457
molar
volume
volume
volume
network
solvent
fraction
solvent
density
0.986906
0.174641
108.0359
0.007404
2.766881
0.130217
108.0359
0.005776
0.810783
0.282617
108.0359
0.011553
1.10629
0.14088
108.0359
0.006166
1.564442
0.223614
108.0359
0.009239
1.324005
0.172986
108.0359
0.007343
1.318742
0.171908
108.0359
0.007303
1.984211
0.118165
108.0359
0.005335
Figure 1 – Network density
The network density was determined by using the equation:
-[(LN(1-Vr)+ Vr+X Vr2) = V Vs(Vr1/3-2 (Vr/f))
The term Vr is the volume fraction of the rubber sample, X is a constant of 0.35, v is the
network density, and Vs is the molar volume of the solvent. The density of the polymer is 0.85
g/cc and the solvent was 0.779 g/cc. Dimensional analysis was used to determine the molar
content of the solution and polymer. The equation was rearranged to solve for v (network
density).
The numbers of crosslinks have now been identified and the samples can be placed under
a tensile stress test to determine the ideal blending process.