Cure‐induced phase separation of epoxy/DDS/PEK‐C composites and its temperature dependency

Abstract

ABSTRACT:The cure-induced phase separation approach for thermoplastic toughened thermosets of epoxy/DDS (4,4 0 -diaminodiphenyl sulfone)/PEK-C (modified polyetherketone) is studied by in situ rheology, real-time TOM (transmission optical microscope) in wide time-temperature space. Rheology studies show that there are two critical gel transformations corresponding to the loose entangled thermoplastic network at the threshold of phase separation and the percolated denser thermosetting network at chemical gelation point, respectively, within broad cure temperature range. The phase separation time may vary by using rheological or morphological methods, but its temperature dependencies can be well described by Arrhenius equation with similar phase separation activation energy E a (ps). It is found in the present systems that E a (ps) keeps unchanged with varying PEK-C content and different epoxy monomers, while changes along the stoichiometric ratio of hardener, which presumably affects the chemical environment of the blends. The quantitative description of time/temperature dependence of phase separation is of practical importance for the design of cure paths in processing and optimizing the properties of TP/ TS composites.

Phase separation time/temperature dependence of some thermoplastics-modified thermosetting systems

“…The moment when the morphological structure appeared was defined as the phase separation time t ps . The value of t ps at any particular temperature is the average of five tests with observation errors of around ¡3% as measured in various TP-modified TS systems [20,22,25]. We find that the phase separation times detected with different resolution optical lens are the same within an accuracy of ¡3% as shown in Table 1.…”

“…The phase separation time versus temperature data based either on rheology, TOM or SALS can be correlated by an equation of Arrhenius of the form [20,22,25]:…”

“…The curves cross at the time for phase separation t ps and the time for chemical gelation t gel where loss tangent becomes independent of frequency [29,30]. We have discussed such critical gel behaviors more systematically in previous work [20,22].…”

“…The morphology evolution may be analyzed qualitatively using the time dependent GinzbergLandau equation (TDGL) of phase separation dynamics [19] but it provides no clues about the temperature dependence of phase separation time. It is important to make experimental studies systematically on the phase separation time-temperature dependence during curing considering the variations of the material parameters in a broad time-temperature space [20].…”

“…Rheology observes certain abrupt mechanical changes upon phase separation while SALS and turbidity trace the change of the optical mismatch between TP and TS rich domains during phase separation. SALS is most widely used to characterize the evolvement of domain size quantitatively in TP and TS blends [6,7,24].The application of SALS is limited by the degree of optical mismatch between blend components and it is not adequate to trace the early stage of the phase separation process [20,25].…”