Modification of epoxy resins with thermoplastic segmented polycarbonate-based polyurethanes)

Abstract

© 2014, Association of Chemists and Chemical Engineers of Serbia. All Rights Reserved. In this paper, the 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 in 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 analysed 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 the highest hard segment content. The tensile strength of modified epoxy was increased by increasing the hard segment in content of polyurethane and its concentration in matrix. 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.