Viscoelastic behavior of thermosetting epoxy mixtures modified with syndiotactic polystyrene during network formation

Abstract

ABSTRACT:The rheological behavior of thermosetting epoxy mixtures modified with thermoplastic syndiotactic polystyrene (sPS) was monitored during the curing of the epoxy resin. The selected thermosetting system was diglycidyl ether of bisphenol A cured with 4,4Ј-methylene bis(3-chloro-2,6-diethylaniline) in the presence of various compositions of sPS (from 2.5 to 12.5 wt %). The storage and loss shear moduli of the systems were monitored during network formation. The validity of the Winter-Chambon criterion for the accurate determination at the gelation point from rheological data was demonstrated. The influence of the sPS concentration on the dynamic rheological properties of the samples was investigated. The experimental data showed that at sPS concentrations lower than 7.5 wt %, phase separation induced a quick increase in the viscosity, which was related to a crystallization-induced phase separation of sPS. For sPS concentrations higher than 7.5 wt %, near the phase-inversion composition, the rheological behavior of the mixtures was characteristic of a cocontinuous structure. After the viscosity jumped at the onset of phase separation, a decrease in the viscosity was found, and later on, the viscosity increased again because of gelation. Additionally, the influence of the cure temperature on the rheological properties was studied.

Curing Behavior and Final Properties of Nanostructured Thermosetting Systems Modified with Epoxidized Styrene‐Butadiene Linear Diblock Copolymers

“…Figure 8 shows the evolution of the viscoelastic properties versus curing time for the neat DGEBA/MCDEA system at 140 °C, measured at 1 Hz. It is well known that the simplest method for the estimation of gelation times from rheological measurements is the divergence of the complex viscosity 43. As can be seen in Figure 8, the divergence of the η * magnitude occurs at about 250 min, which is in good agreement with the gelation time reported for the DGEBA/MCDEA system 44–46.…”

“…On the other hand, the divergence of the complex viscosity agrees with the intersection of the G ′ and G ″ moduli. The use of this intersection point as a criterion for the determination of the gelation process, valid only for some kinds of stoichiometrically‐balanced networks,43, 47 has been used to complement the viscosity curves. The complex viscosity profiles and the evolution of the G ′ and G ″ moduli, measured at 1 Hz during isothermal curing at 140 °C for the neat DGEBA/MCDEA system and its blends containing 10 and 30 wt.‐% SepB46 and 30 wt.‐% SB54 block copolymers, are shown in Figure 9(a) and 9(b), respectively.…”

Rheological Study of Epoxy Systems Blended with Poly(ether sulfone) of Different Molecular Weights

“…As it is well-known that different kinds of morphologies have special rheological developing processes, [27][28][29][30][31][32][33][34][35] we studied the effect of PES molecular weight at 14 wt % at first.…”

Mechanical properties of poly(styrene‐co‐acrylonitrile)‐modified epoxy resin/glass fiber composites

“…However, because of their highly crosslinked structure, these materials have some undesirable properties such as low toughness and poor crack resistance, which constraint many of its applications. The most successful methods of improving the toughness of epoxy resin are incorporating secondary rubbery phase particles in to the crosslinked polymer10–12 and the modification with engineering thermoplastics 13, 14. These studies indicate that in most cases, thermoplastic modification resulted in improved toughness of the resin.…”