Thermal and Chemical Analyses of Silicone Polymers for Component Engineering Lifetime Assessments
Accurate predictions of a polymer component's functional lifetime at best arc tenuous when one has only relatively short term chemical or mechanical property data to extrapolate. We have analyzed a series of silica-filled siloxanes to determine the chemical and microstructural signatures of aging, and we are incorporating these data into rational methodologies for assessing a component's lifetime measured against as-designed engineering properties. We are monitoring changes in mechanical properties, crystallization kinetics, cross-link density changes, and motional dynamics with a variety of analysis methods: Modulated DSC, Dynamic Mechanical Analysis, and Solid-state Nuclear Magnetic Resonance. Previous work has shown that the addition of phenyl side groups to polydimethylsiloxane (PDMS) polymer chains reduces the rate and extent of crystallization of the co-polymer compared to that of pure PDMS. Crystallization has been observed in copolymer systems up to 6.5 mol % phenyl composition by DSC and up to 8 mol % phenyl by XRD. The PDMS-PDPS-silica composite materials studied here are silica reinforced random block copolymers consisting of dimethyl and diphenyl monomer units with 11.2 mol. % polydiphenylsiloxane. Based on this previous work, it is not expected that this material would exhibit crystallization in the polymer network; however, these silicones do, in fact, exhibit crystallization phenomena. This report focuses primarily on our efforts to assess the information content of the crystallization phenomena with respect to aging signatures and mechanisms that may be limiting the functional lifetime of the composite materials.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15005291
- Report Number(s):
- UCRL-JC-143691; TRN: US200322%%358
- Resource Relation:
- Conference: 3rd Heat Flow Calorimetry Symposium, French Lick, IN (US), 04/08/2002--04/12/2002; Other Information: PBD: 14 May 2002
- Country of Publication:
- United States
- Language:
- English
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