Primo Baldini

Epoxy polymers: effect of the elastomee in the kinetics of polymerization

Abstract The polymerization kinetics of three epoxy adhesives HX-205, HX-206 and F-185 was defined by means of thermal analysis techniques (DSC and TMA). It was found that the liquid carboxy-terminated butadiene acrylonitriles (CTBN) and the solid rubber elastomer present in HX-206 and F-185 do not affect the phenomenological kinetics of the isothermal cure process by comparison with HX-205, which contains the same epoxy but no elastomer. It was also found that the isothermal (373 K) cure of these adhesives follows a two-range behaviour, i.e., the phenomelogical order of the cure kinetics is close to zero before and close to one after a “critical” time of cure. The trend of the glass transition temperature T g vs the cure degree α for HX-206 and F-185 was always below that for HX-205. T g did not approach the temperature of cure t c for α = 1 for elastomer-added adhesives, whereas HX-205 displayed an almost liear trend, with e.g. T g = 87° C for α. = 85%.

Epoxy polymers: Glass transition/cure degree correlation

The correlation between the glass transition temperature,Tg, and the cure degree, α, of epoxy polymers has been analysed on the basis of an extension of the Vogel-Tamman-Fulcher equation for the viscosity of polymers and glasses.A physical meaning has been given to the coefficients of the series expansion of the functionTg=Tg(α).This analysis allows one to verify that the experimental (Tg,α) data support the conclusion that, in the case of thermoset polymers, the ideal glass transition temperature,To, appearing in the VTF equation, is larger thanTg.This conclusion may be supported by the thermodynamic interpretation ofT0 as the temperature at which the excess entropy of the systems tends to vanish: in the case of partially cured thermosets;T0 would represent the minimum temperature at which the system becomes able to enhance its cure degree.ZusammenfassungDie Korrelation zwischen der Glasumwandlungs-temperaturTg und dem Aushärtungsgrad α von Epoxidpolymeren wurde analysiert, und zwar basierend auf einer Erweiterung der Vogel-Tamman-Fulcher-Gleichung für die Viskosität von Polymeren und Gläsern. Den bei der Reihenentwicklung der FunktionTg=Tg(α) auftretenden Koeffizienten wurde eine physikalische Bedeutung zugeschrieben. Diese Analyse ermöglicht nachzuweisen, daß die experimentellen Daten (Tg),α die Schlußfolgerung stützen, daß im Falle von hitzehärtbaren Polymeren die in der VTF-Gleichung auftretende sogenannte ideale GlasumwandlungstemperaturT0 höher alsTg ist. Diese Konklusion wird auch durch die thermodynamische Interpretation vonT0 gestützt, nämlich als die Temperatur, bei der die Überschußentropie des Systems gegen Null geht: im Falle von teilweise ausgehärteten hitzehärtbaren Polymeren würdeT0 die minimale Temperatur darstellen, bei der eine Erhöhung des Aushärtungsgrades des Systems einsetzt.РезюмеКорреляция между тем пературой расстекловыванияTg и степенью вулканизац ии (α) эпоксиполимеров ана лизировалась на осно вании расширенного уравне ния вязкости ВогеляТ аммана-Фульчера ВогеляТаммана-Фульч ера для полимеров и стеко л. Дано физическое зна чение коэффициентов широкого ряда функци йqTg=Tg(α). Проведенный ан ализ экспериментальных д анныхTg и α подтвердил заключен ие, что так называемая идеальная температура расстек ловыванияT0, появляющаяся в уравн ении Вогеля-Таммана-Ф ульчера, в случае термореактив ных полимеров выше чемTg. Это заключе ние подтверждается т акже термодинамической и нтерпретациейT0, как температуры, при к оторой избыточная эн тропия систем стремится к ну лю. В случае частично вулканизированных т ермореактивных поли меров,T0 представляет ту мини мальную температуру, при которой системы с тановятся способным и к увеличению степени в улканизации.

Epoxy polymers: temperature-time-transformation diagram by means of DSC investigations

Abstract The aim of this work is to show that isothermal and non-isothermal DSC investigations allow the temperature-time-transformation diagram of a polymer system to be drawn. DSC data can be worked out according to a simple model which supports the interpretation of the gelation process in terms of viscosity. It is seen that the degree of cure attained at the gelation point depends on the temperature of cure and that this crucial process is similar to the formation of a glass phase from a melt.

Thermodynamic properties and thermoelectric power of solid electrolytes

Abstract Thermoelectric power determinations may significantly improve the characterization of the solid electrolytes, if a convenient procedure is followed to work out the experimental results. The peculiar physical properties of a solid electrolyte are generally due to a single fastly moving ionic species; therefore, thermocells assembled with proper electrodes reversible to the mobile ion allow to evaluate its partial molar entropy at various temperatures and, if side informations about the structure of the solid electrolyte are available, to compute other thermodynamic properties.

Thermoelectric Power of the Solid Electrolyte Cu16Rb4I7Cl13

— 6] planned a thorough investigation of the binary and ternary system containing copper and alkali halides. The expectation underlying those studies was to recognize promising solid electrolytes characterized by the high mobility of Cu+ ions: analogous investigations for the systems containing Agi had given important results, such as RbAg4I5 and similar high ionic conductivity compounds. At present the solid electrolyte showing the highest ionic conductivity at

Molar Heat Capacity of AgI: Evaluation of the Cationic and Anionic Contributions from Thermoelectric Power Data

Thermoelectric power data provide a useful tool for the evaluation of the thermodynamic properties of ionic species of both solid and molten electrolytes in equilibrium with electrodes of thermocells; however a previous evaluation of the heat of transport of the mobile ions is necessary. This is the case of AgI. whose standard modifications have been investigated with silver electrode thermocells some years ago. The interpretation of the thermoelectric power change at the melting point allows one to recognize that the heat of transport of the silver ions in the high conductivity bcc modification is practically the same as in molten Agl. This result has been used to evaluate the molar heat of the silver ions in the bcc phase from the corresponding thermoelectric power data reported in the literature. The analysis of the thermoelectric power change at the transition point, from the wurtzitic to the bcc phase, as well as a more speculative interpretation of thermoelectric power data obtained with iodine electrode thermocells, allows one to evaluate the molar heat of the iodide ions in the bcc modification of AgI. The summation of the ionic contributions so computed reproduces rather satisfactorily the trend of AgI molar heat data obtained with adiabatic calorimetry.