Thermophysical and adhesive properties of functional polymer materials based on epoxy resin and silicon-containing component

Abstract

The work was aimed at developing an adhesive formulation with increased adhesive strength for metals. It contains an epoxy resin of the bisphenol type СHS-TROXY 520 (an analogue of ED-20), an amine hardener triethanolamine (TEA) and a silicon-containing component (3-isocyanatopropyl)triethoxysilane, designated as NCO-Si, with an optimal ratio of components. The content of NCO-Si in the formulations was 0.5, 1.0, 3.0 and 5.0 wt. %, respectively. The gradual transformation of the epoxy system into a three-dimensional network with the formation of ester and urethane groups was shown by IR spectroscopy method. Tensile and shear strength were determined using the tearing machine R-50 in accordance with current standards. It was found that the maximum values of physical and mechanical parameters were obtained when the amount of NCO-Si was 3 wt. %. The maximum values of adhesion strength to steel substrates δst. = 58.5 MPa significantly exceed those for neat epoxy formulations. The shear strength values for steel plates τst. = 21 MPa increase by 60 %, for aluminium plates they are δAl =14.5 MPa and increase by 48 %. The morphology of the samples has been studied by means of optical microscopy. It is shown that the modified NCO-Si samples are characterised by a phase-separated structure. At a minimum amount of NCO-Si (0.5 wt. %), structurally disordered spherical domains with a size of ~1÷3 μm are observed, an increase in the content of the organosilicon component leads to the formation of interconnected regular structures, which are less pronounced at 1.0 wt. % of NCO-Si and clear at 3.0 and 5.0 wt. % of NCO-Si. Thermogravimetric analysis (TGA) was performed as well. It is shown that the modification of epoxy resin by a silicon-containing component with NCO-Si groups leads to an improvement in thermophysical parameters, a decrease in internal stresses and the formation of a material with a structure close to equilibrium.