Thermomechanical properties and long-term behavior evaluation of poly(vinylidene fluoride) (PVDF) exposed to bioethanol fuel under heating

DMTA was employed to evaluate the aging of poly(vinylidene fluoride) (PVDF) exposed to ethanol fuel derived from sugarcane. For this purpose, DMTA tests of aged and unaged PVDF were carried out, and the behaviors of E',E '' and tan d curves were carefully investigated. Using the time-temperature superposition principle, the PVDF long-term behavior was evaluated through E' master curves multiple frequencies (T-ref = 25 and 30 degrees C). PVDF suffered significant changes in DMTA properties, mainly in T-g' region. Thus, the T-g' values were shifted toward T-g, ending up as one continuous relaxation. By hydrogen bonds, ethanol attenuated the secondary interactions of the PVDF chains in the constrained and free amorphous phases, reducing E' by plasticization. However, the ethanol molecules also decreased the PVDF long-chain mobility by steric effect, reducing E '' and increasing the T-g activation energy. Since aging in ethanol was accelerated by temperature, annealing in the air was also carried out to separate the thermally induced effects. Although the aging/annealing experiments indicated good compatibility between PVDF and ethanol, both treatments changed the PVDF thermomechanical properties and E' master curves behavior. However, the nature of these changes was different in each case, and the material loses mechanical performance and long-term durability only when exposed to the combination of both.