Looking over Liquid Silicone
Rubbers: (2) Mechanical
Properties vs Network Topology
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Abstract
In the previous paper of this series, eight formulations
were analyzed
under their uncross-linked forms to relate liquid silicone rubber
(LSR) chemical compositions to material network topologies. Such topologies
were confirmed by swelling measurements and hardness evaluation on
vulcanized samples. In this article, characterization of cross-linked
materials is further done using different mechanical measurements
on final materials, including dynamic mechanical analysis, compression
set, stress–strain behavior and tear resistance. It was shown
that the compression set value is mainly related to the chains motion:
increasing the filler–polymer interactions and/or decreasing
the dangling/untethered chains content positively impact the compression
resistance. Elongation at break depends on the molar mass between
cross-linking points, showing an optimum value set at around 20 000
g mol<sup>–1</sup>, i.e., the critical mass between entanglements.
The distribution of elastic strands into the network has strong implications
on the stress–strain curves profiles. By generating bimodal
networks, the ultimate properties are enhanced. The materials cured
by hydride addition on vinyl groups catalyzed by peroxide exhibit
poorer compression set and tensile strength values, respectively,
because of post-cross-linking reaction and broad polydispersity index
of elastic network chains