Studies of the Physical Structure of Cured Epoxy Resin Composite Modified with Silicon-Containing Additives

Abstract

Abstract The possibility of regulating the structure and reducing its defectiveness opens great possibilities for controlling the properties of epoxy composite materials. This article reports the results of investigation by X-ray scattering and nuclear magnetic resonance methods and the microstructural changes that occur when silicon-containing additives such as polydimethyl siloxane (PDMS-5) and pyrogenic silica (HDK) are introduced into epoxy resin ED-20. The mechanism of formation of the structure of epoxy binder ED-20 with L-20 curing agent in the presence of complex additives is found. The modifying additive (PDMS-5 + HDK) is located in the epoxy binder because of the chemical interaction of functional polar groups and the developed surface. The additives increase the mobility of the reaction mixture and also facilitate and regulate the spatial orientation of macromolecules during polymerization. This contributes to the formation of a more regular and less defective spatial structure. The epoxy binder is a heterogeneous two-component system, one of which corresponds to a pseudo-crystalline region in which the movement of molecules is suppressed, and the second is found at lower volume fractions and is amorphous. The only maximum in the wide-angle X-ray diffraction pattern of the binder without additives is attributable to the distribution of molecular chains in the para-crystalline lattice. The addition of the HDK additive leads to ordering of the supramolecular structure, in which linear clusters consisting of 5–7 spheres appear. The average size of the spheres is from 8 to 26 nm. The addition of additives in the samples leads to the formation of a more regular and less defective spatial structure because of the interaction of functional polar groups and the surface, which regulate the spatial orientation of macromolecules during polymerization.