The Morphology And Rheology During Cure Of Thermoplastics Modified Thermosetting Systems

Improving the toughness of TS (thermosetting resins) through cure induced phase separation is a promising approach with the prerequisite of appropriate control of the phase separated structure. The present work has been focused on the cure induced phase separation process in various TP (thermoplastics) toughened thermosetting systems including systems with UCST (upper critical solution temperature) or LCST (lower critical solution temperature) phase behavior in wide time/temperature window. The phase separation process was detected in situ by means of dynamic rheology and optical microscope, together with the thermal analysis. The morphology evolvement process in constrained space was simulated based on modified TGDL (time dependent Ginzberg Landau) function.An inversed optical microscope system with high resolution and high temperature duration was set up which successfully characterized the onset and evolvement of the phase separation process in various TP/TS systems, including UCST/LCST systems, the liquid crystal monomer modified thermosetting systems.The chemorheology of different TP/TS systems were analyzed and criticalgel transitions were found which arise from different gelation mechanism.Gelation at phase separation is the result of entanglement of TP macromolecules;gelation at chemical gel point corresponds to the branching and cross linking of thermosetting oligomers. Critical gelation transitions were also observed in the post cure stage which is a result of physical gelation arising from the glass transition of TP rich phase. The relaxation exponents of the gels formed at different cure stage show temperature and/or TP content dependence.It was found that the cure induced phase separation time/temperature dependence can be well described by the Arrhenius equation. The phase separation activation energy E_α(ps) keeps constant with the variations of TP content, TP molecular weight, curing rate and phase separation detecting means, while varies with the chemical environments and the time/temperature dependence of the cure reaction. The change of E_α(ps) of some UCST TP/TS systems was elucidated in view of interaction energy density theory. It was shown that E_α(ps) decreases with the deterioration of miscibility of the blends and increase with the increase of the TP/TS miscibility. TTT (time temperature transformation diagram) with morphology was set up which can provide intellectual understanding of the cure process of TP/TS systems.The morphology evolvement of systems in interleaves of TP and TS wassimulated by the modified TGDL (time dependent Ginzberg-Landau) functionwith pre-set concentration ingredient, and the simulated morphology is consistentwith the experimental results qualatitively.The liquid crystal epoxy monomer modified cyanate ester systems wasstudied primarily by rheology, thermal analysis and morphological approaches.The incorporation of liquid crystal monomer will accelerate the cure rate of the matrix resin and also increase the initial viscosity. It was found that the meso-scale phase separated structure is not a necessary condition for the toughness enhancement in the liquid crystal epoxy monomer modified cyanate ester systems.