Comparative studies of chemical kinetics of an epoxy‐amine system

Abstract

Chemical reaction kinetics of an aliphatic diepoxy-diamine system (DGEBD14D) has been studied between 50°C and 95 "C by two different calorimetric techniques; DSC in isothermal conditions on the one hand, conservation in thermostated tubes with successive extractions of samples studied by DSC in the dynamic temperature mode on the other hand.Experiments show that the kinetics determined by isothermal DSC are systematically faster than those obtained with the other technique, this advance starting during the initial phase of the reaction. We show that this gap comes from the mass difference between the samples used in the two techniques, and can be explained by two different reasons. On the one hand, there appears a delay in the attainment of the thermal equilibrium at the beginning of the kinetics in the thermostated tubes, the samples having a greater mass. On the other hand, experiments have shown that there is a catalytic effect caused by the contact of reactive system with air (probably due to the action of atmospheric water). The areaholume ratio of samples being greater for samples studied by isothermal DSC, the catalytic effect is favoured to a greater extent in the case of this technique, which induces a faster rate of reaction at the beginning of the kinetics.So, as the kinetic curves x = f (t) have different forms, they are described by different kinetic models. The Spacek-model adequately describes the kinetic curves determined by isothermal DSC, with exponent values p = 1.20 and q = 0.45. The curves obtained by the technique of conservation in thermostated tubes are well described by the second order autocatalytic model, the ratio of the reactivities of primary and secondary amines having the value n = 1.1. Furthermore the Tg variation curve with the extent of reaction in the thermostated tubes agrees very well with the equation proposed by Pascault and Williams. CCC OOO3-3146/95/$07.00 13 J. P. Eloundou, M. Feve, D. Harran, J. P. Pascault ZUSAMMENFASSUNG:Die Reaktionskinetik eines aliphatischen Diepoxy/Diamin-Systems (DGEBDMD) wurde zwischen 50 "C and 95 "C nach zwei unterschiedlichen kalorimetrischen Methoden untersucht, zum einen mit Differentialkalorimetrie (DSC) unter isothermen Bedingungen, zum anderen durch DSC mit Rmperaturerhdhung, nachdem die Proben unterschiedlich lange in thermostatisierten Rohren aufbewahrt wurden.Die kinetischen Parameter aus den isothermen Messungen deuten auf eine schnellere Reaktion, bereits ab der Startphase, hin als die Ergebnisse der dynamischen Methode. Dieser Unterschied wird durch die Massendifferenz der Proben bei den einzelnen Verfahren verursacht und hat zwei Grunde. Erstens verzogert sich die Einstellung des thermischen Gleichgewichts bei den Proben mit der groBeren Masse in den thermostatisierten Rohren. Zweitens wird die Reaktion von der Luft (wahrscheinlich aufgrund der Wirkung der Luftfeuchtigkeit) katalysiert. Das Verhaltnis von Probenoberflache zu Probenmasse ist bei der isothermen Methode grorjer als bei dem dynamischen Verfahren, so daB sich der kata...

Curing of dicyandiamide epoxy resins accelerated with substituted ureas

“…It is clear, from previous observations in the literature, 18,19 that the latency observed is due to the dissociation of URONS into isocyanate and dimethylamine. 8 Sometimes, the difference obtained using the DSC and FTNIR analysis was attributed to a catalytic effect of water moisture or aluminium pans.…”

Simultaneous kinetic and microdielectric studies of some epoxy-amine systems

“…The method of calorimetric study after conservation in thermostated tubes 21 was used to perform the kinetic study.…”

Caracterização do sistema éter diglicidílico do bisfenol A / poliaminas alifáticas

“…Os espectros de ressonância magnética nuclear de carbono-13 (RMN- 13 O equivalente epoxídico (eq.epoxídico) foi determinado por titulação química por método volumétrico usando ácido bromídrico gerado "in situ", segundo as especificações da norma ASTM D 1652. Os resultados são a média de pelo menos três determinações.…”

“…Entretanto, quando se utiliza a proporção estequiométrica, os valores experimen- Determinação da proporção adequada de endurecedor 24 no sistema de resina epoxídica DER 331 por método calorimétrico (DSC). a) ∆H em função da concentração de endurecedor (We, fração em massa), b) Tg em função da concentração de endurecedor (r, razão entre os equivalentes de amina, e os equivalentes de grupos epoxídicos), c) e d) curvas calorimétricas com diferente concentração de endurecedor (phr, partes de endurecedor por cada 100 partes de resina) tais destas magnitudes correspondem aos valores que caracterizam o sistema epoxídico [8][9][10][11][12][13] .O resultado das experiênci-as dinâmicas é apresentado na Figura 2. Nestas experiências, considerou-se o valor de Tg no ponto médio da transição na segunda varredura dinâmica, e o equivalente epoxídico da resina de 187 g eq -1 .…”

“…-1 ) e 124 °C, respectivamente. Estes valores estão em perfeito acordo com o divulgado para os sistemas epoxi-amina, e para os sistemas que utilizam aminas alifáticas como endurecedores, respectivamente [1,2,[8][9][10][11][12][13] . A Tabela 2 apresenta as concentrações dos grupos funcionais da resina epoxídica DER 331 e do endurecedor 24, obtidas por diferentes metodologias.…”