Main methods for the modification of epoxy composites that aim to increase their impact and crack resistances are considered with the main attention focused on modification with the use of thermally stable thermoplastics as additives. The influence of various factors (the modifier-matrix chemical bond and the morphology and molecular weight of the modifier) on the physicomechanical characteristics of the composites is discussed. New approaches to the toughening of polymeric composite materials based on epoxy thermosets that involve the use of modified binders or the introduction of a modifier between layers of the composite prepreg are advanced.
Catalyzed epoxy systems have been studied consisting of an ED 20 epoxy diane oligomer ED 20, a curing catalyst (dicyandiamide (DCDA)), and an accelerator (an asymmetric urea based on toluene diiso cyanate). The chemical composition and structure of the catalyzed epoxy systems have been established by IR and NMR spectroscopy in the initial and cured states. The influence of the composition of the complex catalyst system of curing on the mechanisms of chemical transformation of epoxy system has been consid ered. It is shown that the products of interaction of epoxydiane oligomers with DCDA in the presence of the accelerator-asymmetric urea of Dyhard UR500 brand-is a complex system consisting of chains of poly esters produced by a chain growth mechanism and amine sites, as well as interaction products of epoxy groups with imines, isocyanates, and hydroxyl groups with nitriles.
Ha spectral observations of flares and moustaches using linear polarization analyser have been carried out. It is found that some flare knots and moustaches show strong polarization.
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