Vitrification and physical ageing on isothermal curing of an epoxy resin

Vitrification phenomena and further structural relaxation processes or physical ageing occurring in the isothermal curing reaction of an epoxy resin are studied by Differential Scanning Calorimetry (DSC). The vitrification time,t_v, the limiting conversion degree and the limiting glass transition temperature (T_g) are evaluated at curing temperatures (T_c) between 30 and 100C. The dependence of limitingT_g withT_c permits the determination of the maximumT_g of the resin (109C). The physical ageing, which appears as the the last step of curing reaction for curing times above to vitrification, is analyzed through the endothermic peak superposed to the glass transition temperature. The results obtained in partially reticulated resin show the kinetics of the physical ageing to slow down asT_c increases, as a consequence that the segmental mobility is reduced.

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Zusammenfassung VitrifikationphÄnomeme und strukturelle Relaxations-respektive AlterungsvorgÄnge von Epoxiden wurden mitells isothermer DSC Messungen untersucht. Die Vitrifikationszeit, der Grenzwert des Unwandlungsgrades und die Grenztemperatur der Glasumwandlung wurden in Bereich von 30 bis 100C ermittelt. Werden Epoxide für Temperaturen unterhalb der Glasumwandlungstemperatur einer thermischen Behandlung ausgesetzt, so bilden sich SpannungszustÄnde aus, die bei der ErwÄrmung unmittelbar über der Glasumwandlungstemperatur mit einem endothermen Vorgang relaxieren.

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Financial support of this work has been provided by CICYT (project No. PBO395/85). Special thanks are addressed to CIBA-GEIGY for supplying the materials.