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Effect of rheological behavior of epoxy during precuring on foaming
Author(s) -
Takiguchi Osamu,
Ishikawa Daisaku,
Sugimoto Masataka,
Taniguchi Takashi,
Koyama Kiyohito
Publication year - 2008
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.28727
Subject(s) - rheology , epoxy , materials science , composite material , curing (chemistry) , blowing agent , foaming agent , bubble , porosity , mechanics , physics , polyurethane
In this study, the effect of rheological behavior of epoxy during precuring on foaming was investigated. Dynamic time sweep test of epoxy/curing agent (100/1, w/w) was conducted. The viscosities as a function of time showed extremely rapid increase from the order of 10 2 –10 3 to 10 6 Pa · s at a certain time, followed by slow increase of the viscosities. Dynamic frequency sweep test of precured epoxy with curing agent was conducted at 90°C. The critical gelation time was obtained by using rheological criterion proposed by Winter and Chambon. We found that the slopes of G ′(ω) and G ″(ω) decreased with increasing precuring time. Correspondingly, tan δ showed a change from negative to positive slope at a critical time. By using the results, the critical gelation time was determined as t = 895–935 s. Samples of epoxy/curing agent/blowing agent (100/1/0.5) were precured for 960–1620 s. And then precured samples were foamed at 230°C for 300 s to decompose chemical blowing agent. The formed bubble size distribution becomes sharp with increase of the precuring time. There are roughly two sizes of bubbles when precured for relatively short time ( t < 1080 s) before foaming: large bubbles (>100 μm) and small ones (≅30 μm). On the other hand, foams precured for long time ( t > 1200 s) before foaming, large bubbles disappear, and the average diameter of the bubble becomes small while the porosity is low. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008