Mechanical and dielectric properties of epoxy resin modified using reactive liquid rubber (HTPB)

Abstract

In the present study, hydroxyl-terminated polybutadiene (HTPB) liquid rubber was employed to modify epoxy resin using 2,4,6-tri (dimethylaminomethyl) phenol as a catalyst, and methyl hexahydrophthalic anhydride as a curing agent. The reactions between HTPB and epoxy were monitored by Fourier transform infrared (FTIR); the mechanical and dielectric properties of HTPB modified epoxies were evaluated and the morphology was investigated through scanning electronic microscopy (SEM). The FTIR analysis evidenced the occurrence of a chemical reaction between the two components. The mechanical results indicated that the impact strength of HTPB-modified epoxy was superior to that of the pure epoxy. As the HTPB content increased up to 10 phr the best mechanical performances in terms of tensile and flexural properties were achieved when compared to the unmodified epoxy. Higher concentration of HTPB resulted in larger particles and gave lower mechanical strength values. The incorporation of HTPB into epoxy decreased the dielectric constant and dissipation factor over a wide frequency range from 1 to 10 6 Hz, and improved the electrical resistivity. SEM micrographs showed that the modified epoxy exhibited a two-phase morphology where the spherical rubber domains were dispersed in the epoxy matrix.

A Carboxyl-Terminated Polybutadiene Liquid Rubber Modified Epoxy Resin with Enhanced Toughness and Excellent Electrical Properties

“…The peaks at 915 cm À1 and 831 cm À1 related to oxirane functionality of neat EP (Fig. 1b), 14 while a new, but small peak at 1667 cm À1 (Fig. 1c) and the decrease in the intensities of the peaks at 915 cm À1 and 831 cm À1 clearly confirm that the addition of CTPB into EP caused chemical interaction between the terminal oxirane group of EP and the terminal carboxyl groups of CTPB.…”

“…Because of its weak polar molecular structure and high electrical insulations, CTPB can prohibit and reduce the space charge accumulation at the phase interface and the formation of electric current inside the network under applied high electric voltages. 13,14 Therefore, the dielectric strength significantly was enhanced when CTPB was added to EP. However, no further increase was found on further loading of CTPB.…”

“…The initial decrease in dissipation loss might be because the dipoles get much less time to orient themselves in the direction of the applied electric field and hence the effect of the orientation polarization reduces with the increase in frequency. 14,21 The dissipation factor tends to increase again at frequencies above 10 4 Hz, which are mainly associated with the relaxation movement of the EP. It is evident from Fig.…”

“…However, not all samples were obviously sensitive to the change of frequency. The main reasons for the decrease of dielectric permittivity may be: (1) the low dielectric constant of the CTPB, 14,21 (2) the weak interfacial polarization caused from the addition of non-polarity CTPB rubber to the strong polar EP, 13 and (3) the relative low number of dipoles of CTPB compared with pure EP. So, the dipoles polarization is weaken by the use of CTPB in the blend, thus leading to a reduction in the dielectric constant.…”

“…Just like the hydroxyl-terminated polybutadiene (HTPB)-modified EP, 14 the obvious characteristic of CTPB is also its immiscible nature with EP: it stays in a phase-separated state from the major EP matrix throughout the cure reaction. So, in this work, in order to enhance the compatibility between the two components, EP prepolymers were first prepared by means of the chemical interaction between the oxirane ring of EP and the terminal carboxyl functional groups of the CTPB using 2,4,6-tri (dimethylaminomethyl) phenol as a catalyst.…”