Peroxide cure systems for silicone
polymers
Reaction: Free radical
Reactants/functionality: Polydimethylsiloxane or SiOH/SiOH
Catalysts: Various peroxides
Stimulus for cure: Heat |
Common applications:
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One-part, pre-catalyzed systems are used to cure silicone
high-consistency rubbers (HCRs), which are extruded or injection molded at
elevated temperatures.
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Two-part systems – where the peroxide catalyst is added during
processing – are used to cure pressure-sensitive adhesives and some paper
coatings.
Advantages
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Room- or low-temperature cure possible.
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Catalyst is not easily poisoned.
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Properties can be modified by manipulating the peroxide level.
Disadvantages
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Cold storage is required to extend peroxide shelf life, short bath life
when catalyzed.
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Oxygen inhibition can occur.
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In HCRs, voids can be formed by volatile residues from the peroxide.
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Post cure may be necessary to remove these volatiles, which can cause
depolymerization at high temperatures.
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Some residual peroxide components can produce toxic peroxide byproducts
(chlorophenyls or PCBs), which could result in “blooming” upon aging;
consequently, post-curing is recommended.
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