N. Agarwal et al., EFFECT OF MOISTURE ABSORPTION ON THE THERMAL-PROPERTIES OF BOMBYX-MORI SILK FIBROIN FILMS, Journal of applied polymer science, 63(3), 1997, pp. 401-410
Films of regenerated Bombyx mori silk are strongly affected by absorbe
d moisture, a phenomenon studied here by differential scanning calorim
etry (DSC). Exposure of previously dried films to environments of cont
rolled relative humidity produces test samples of well-defined equilib
rium moisture content. Ultimate moisture uptake is as high as 20-23% (
by weight) at 75% relative humidity. The glass transition temperature,
T-g, drops by 40 degrees C at moisture uptakes as low as 2%, and T-g
depressions as large as 140 degrees C are observed at higher relative
humidity. The moisture-induced decrease of T-g is completely reversibl
e, as a film remoistened and then red-led possesses an unchanged T-g.
Trends in T-g with water uptake correspond reasonably well to predicti
ons of a classical thermodynamic theory, indicating that the plasticiz
ation effect of moisture on the combined silk-water system can be sati
sfactorily explained from macroscopic properties of the constituents w
ithout any reference to specific interactions. (C) 1997 John Wiley & S
ons, Inc.