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moisture dependence of positron lifetime in kevlar-49Because of filamentary character of Kevlar-49 aramid fibers, there is some concern about the moisture uptake and its effect on plastic composites reinforced with Kevlar-49 fibers. As part of continuing studies of positron lifetime in polymers, we have measured positron lifetime spectra in Kevlar-49 fibers as a function of their moisture content. The long lifetime component intensities are rather low, being only of the order of 2-3 percent. The measured values of long component lifetimes at various moisture levels in the specimens are as follows: 2072 +/- 173 ps (dry); 2013 +/- 193 ps (20.7 percent saturation); 1665 +/- 85 ps (25.7 percent saturation); 1745 +/- 257 ps (32.1 percent saturation); and 1772 +/- 217 ps (100 percent saturation). It is apparent that the long component lifetime at first decreases and then increases as the specimen moisture content increases. These results have been compared with those inferred from Epon-815 and Epon-815/K-49 composite data.
Document ID
Document Type
Conference Paper
Singh, Jag J.
(NASA Langley Research Center Hampton, VA, United States)
Holt, William H.
(NASA Langley Research Center Hampton, VA, United States)
Mock, Willis, Jr.
(U.S. Navy, Naval Surface Weapons Center Dahlgren, VA, United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1984
Subject Category
Distribution Limits