The role of poly (ethylene-co-methacrylic acid) (EMAA) on cure kinetics and thermomechanical properties of epoxy

The addition of thermoplastic to thermosetting matrix systems has been proposed as a successful strategy to produce polymers with self-healing ability. Curing mechanism of diglycidyl ether of bisphenol A/triethylene-tetramine epoxy system modified with poly(ethylene-co-methacrylic acid) (EMAA) thermoplastic healing agent was investigated in this work. The effects of thermoplastic content, particle size and dispersion on thermomechanical properties were studied. Specimens were produced with 5 wt. %, 10 wt. % and 15 wt.% EMAA with particle sizes ≤ 125 μm or ≤ 425 μm. The addition of thermoplastic produced a reduction in E’ of about 27% for samples with particles ≤ 125 μm and about 45% for samples with particles ≤ 425 μm. Samples with particle size ≤ 125 μm showed a reduction in Tg of up to 37 °C as compared to neat epoxy. In the case of samples with particle size ≤ 425 μm, no direct correlation between Tg and mass fraction of added EMAA is found. Thus, particle size played an important role on thermomechanical properties and cure kinetics of epoxy. The greater the interfacial area, the greater was the change in final properties as compared to the unmodified material. It was also observed that the mass fraction and particle size can interfere in the curing reactions, where results suggest deceleration when smaller particles (≤ 125 μm) are added in larger fractions and acceleration with increasing mass fraction of larger particles (≤ 425 μm). All experimental reactions could be fit to the autocatalytic Sourour and Kamal model with good agreement; the model was able to predict the effects of thermoplastic addition in different particle sizes and mass fractions.