Rheology, morphological evolution, thermal, and mechanical properties of epoxy modified with polysulfone and cellulose nanofibers

In this work, the epoxy systems modified with polysulfone (PSF) and cellulose nanofiber (CNF) cured at different temperatures are prepared to investigate the effect of CNF on curing reaction, morphology evolution, rheology, thermal, and mechanical performance of composites. The reaction rate is increased and the activation energy is decreased with CNF incorporation, implying an accelerating effect of CNF on the epoxy-amine reaction. The phase separation and gelation of the epoxy/PSF/CNF system start earlier compared with the binary system of epoxy/PSF. While it is displayed by rheology that both the system viscosity and relaxation time are elevated with CNF, presenting an inhibiting effect on phase evolution. Morphologies with smaller domain size are finally freezed by the epoxy gelation. The enhancement of impact performance for the epoxy/PSF/CNF composites is indicated by 40.2% increase in the impact strength, which is attributed to the finer phase-separated morphology, the uniformly distributed CNF within the polymer matrix and the good load transfer between phases. In addition, the thermal stability of composites is improved as the CNFs existed in the phase-separated polymer matrix can restrict the thermal motion of molecules during decomposition process. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48628.