In this work, epoxy hybrid materials were synthesized by addition of
thermoplastic segmented aliphatic polyurethanes with good elastic properties.
The modified epoxy samples were obtained by curing of previously homogenized
mixture of prepared polyurethane melts, epoxy resin and crosslinking agent
Jeffamine D-2000. The influence of different weight content of polyurethanes
(5, 10 and 15 wt. % compared to pure epoxy resin) as well the influence of
different hard segments of elastomers (20, 25 and 30 wt. %) on the curing of
modified epoxy systems was studied. The curing was followed by differential
scanning calorimetry (DSC), in dynamic regime from 30 to 300?C, at three
heating rates (5, 10 and 20?C/min). With the increase of hard segments
content of polyurethanes added in higher concentration (10 and 15 wt. %) into
epoxy matrix, the temperature of maximum ratio of curing was shifted to lower
values (from 205 to 179?C). Obtained DSC data were analyzed using two
integral methods (Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose) and one
differential kinetic model (Friedman). The significant differences were
observed in the second part of the epoxy curing (for the reaction degrees
higher than 60 %), where the values of activation energies remarkably
increase. The addition of polyurethane elastomers retarded the curing process
due to decreased mobility of reactant molecules caused by higher viscosity of
reaction mixture. By detailed analysis of determined kinetic parameters, it
is concluded that the influence of slow diffusion is more pronounced in the
presence of thermoplastic polycarbonate-based polyurethanes, which confirmed
their effect on the mechanism of epoxy curing. The highest tensile strength
and hardness showed the DGEBA modified with the polyurethane with highest
hard segment content. Increasing the hard segment content of polyurethane and
its concentration in matrix, the tensile strength of modified epoxy was
increased. The elongation at break of modified epoxy samples was
significantly improved by addition of polycarbonate-based polyurethanes with
low hard segment content, due to higher content of flexible soft segment
chains.