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Title: Anisotropic Thermal Behavior of Silicone Polymer, DC 745

Abstract

In material applications, it is important to understand how polymeric materials behave in the various environments they may encounter. One factor governing polymer behavior is processing history. Differences in fabrication will result in parts with varied or even unintended properties. In this work, the thermal expansion behavior of silicone DC 745 is studied. Thermomechanical analysis (TMA) is used to determine changes in sample dimension resulting from changes in temperature. This technique can measure thermal events such as the linear coefficient of thermal expansion (CTE), melting, glass transitions, cure shrinkage, and internal relaxations. Using a thermomechanical analyzer (Q400 TMA), it is determined that DC 745 expands anisotropically when heated. This means that the material has a different CTE depending upon which direction is being measured. In this study, TMA experiments were designed in order to confirm anisotropic thermal behavior in multiple DC 745 samples of various ages and lots. TMA parameters such as temperature ramp rate, preload force, and temperature range were optimized in order to ensure the most accurate and useful data. A better understanding of the thermal expansion of DC 745 will allow for more accurate modeling of systems using this material.

Authors:
 [1];  [2];  [2];  [2];  [2]
  1. Univ. of Oregon, Eugene, OR (United States). Dept. of Chemistry; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1312621
Report Number(s):
LA-UR-16-26594
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Adams, Jillian Cathleen, Torres, Joseph Angelo, Volz, Heather Michelle, Gallegos, Jennifer Marie, and Yang, Dali. Anisotropic Thermal Behavior of Silicone Polymer, DC 745. United States: N. p., 2016. Web. doi:10.2172/1312621.
Adams, Jillian Cathleen, Torres, Joseph Angelo, Volz, Heather Michelle, Gallegos, Jennifer Marie, & Yang, Dali. Anisotropic Thermal Behavior of Silicone Polymer, DC 745. United States. doi:10.2172/1312621.
Adams, Jillian Cathleen, Torres, Joseph Angelo, Volz, Heather Michelle, Gallegos, Jennifer Marie, and Yang, Dali. 2016. "Anisotropic Thermal Behavior of Silicone Polymer, DC 745". United States. doi:10.2172/1312621. https://www.osti.gov/servlets/purl/1312621.
@article{osti_1312621,
title = {Anisotropic Thermal Behavior of Silicone Polymer, DC 745},
author = {Adams, Jillian Cathleen and Torres, Joseph Angelo and Volz, Heather Michelle and Gallegos, Jennifer Marie and Yang, Dali},
abstractNote = {In material applications, it is important to understand how polymeric materials behave in the various environments they may encounter. One factor governing polymer behavior is processing history. Differences in fabrication will result in parts with varied or even unintended properties. In this work, the thermal expansion behavior of silicone DC 745 is studied. Thermomechanical analysis (TMA) is used to determine changes in sample dimension resulting from changes in temperature. This technique can measure thermal events such as the linear coefficient of thermal expansion (CTE), melting, glass transitions, cure shrinkage, and internal relaxations. Using a thermomechanical analyzer (Q400 TMA), it is determined that DC 745 expands anisotropically when heated. This means that the material has a different CTE depending upon which direction is being measured. In this study, TMA experiments were designed in order to confirm anisotropic thermal behavior in multiple DC 745 samples of various ages and lots. TMA parameters such as temperature ramp rate, preload force, and temperature range were optimized in order to ensure the most accurate and useful data. A better understanding of the thermal expansion of DC 745 will allow for more accurate modeling of systems using this material.},
doi = {10.2172/1312621},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 9
}

Technical Report:

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  • The purpose of this project is to replace silicone polymer A with silicone polymer B produced by Vendor B. Silicone polymer B and the resulting B-50 cellular silicone have been used to produce cushions for the W87 program. Approximately 5.5 years of stress relaxation aging study data as well as actual part surveillance data have been collected, characterizing the stockpile life performance of the B-50 cellular silicone cushion material. Process characterization of new cellular silicone materials as a result of replacing silicone polymer A with silicone polymer B has been completed. Load deflection requirements for the new cellular silicone materialsmore » based on silicone polymer B have been met. The silicone polymer B based cellular silicone materials must be compounded at densities of approximately 0.03 g/cm{sup 3} less than the silicone polymer A based cellular silicone materials in order to achieve the same load deflection requirements has also been demonstrated. The change in silicone polymers from A to B involved a decrease in volatile content as well as a decrease in part shrinkage.« less
  • Dynamic mechanical thermal analysis (DMTA) of virgin TR-55 silicone rubber specimens was conducted. Two dynamic temperature sweep tests, 25 to -100 C and 25 to -70 to 0 C (ramp rate = 1 C/min), were conducted at a frequency of 6.28 rad/s (1 Hz) using a torsion rectangular test geometry. A strain of 0.1% was used, which was near the upper limit of the linear viscoelastic region of the material based on an initial dynamic strain sweep test. Storage (G{prime}) and loss (G{double_prime}) moduli, the ratio G{double_prime}/G{prime} (tan {delta}), and the coefficient of linear thermal expansion ({alpha}) were determined asmore » a function of temperature. Crystallization occurred between -40 and -60 C, with G{prime} increasing from {approx}6 x 10{sup 6} to {approx}4 x 10{sup 8} Pa. The value of {alpha} was fairly constant before ({approx}4 x 10{sup -4} mm/mm- C) and after ({approx}3 x 10{sup -4} mm/mm- C) the transition, and peaked during the transition ({approx}3 x 10{sup -3} mm/mm- C). Melting occurred around -30 C upon heating.« less
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