Macromol. Mater. Eng. 2001, 286, 191–195 191 Adhesive Properties of Epoxy Resin with Chromic Hardener Igor Nova ´k,* 1 Jarmila S ˇ imonı ´kova ´, 2 Ivan Choda ´k 1 1 Polymer Institute, Slovak Academy of Sciences, Du ´bravska ´ cesta 9, 842 36 Bratislava, Slovak Republic 2 Poleng, Prlovska ´ cesta 2488, 760 01 Zlı ´n, Czech Republic Introduction Epoxy resins are considered as an important group of engineering materials [1] applied mainly as adhesives and sealants for metals and metal alloys. [2, 3] They are rarely used as unmodified resins, usually various additives are used such as reactive solvents, fillers, pigments, etc. The curing of epoxy resins occurs due to reaction of epoxy moieties with reactants containing reactive/abstractable/ labile/basic/acidic hydrogen. [4] Quite a number of various hardeners can be used for curing, based on amines, thiols or carboxylic compounds. [5] The properties of cured epoxy resins depend to a large extent on the nature of the hardener. Besides amines, e.g., diethylenetriamine or triethylenetetraamine, various orga- nometallic compounds can be used such as triethylalumi- nium, aryl- or alkylmetal borides, halogenides of either metals or boron (e. g. boron fluoride). Some of these com- pounds act as latent catalyzers that are active after heat- ing to higher temperature. [6, 7] Primary and secondary amines react with epoxy groups at room temperature to form adducts with a reduced vapor pressure and less criti- cal mix ratios. Furthermore, from a practical point of view it is important that these systems are less sensitive to scatter in the resin: hardener ratio compared to hard- eners of other nature. Complexes, especially chelates of certain metals repre- sent a viable alternative for hardening of epoxy resins at room temperature. A possible structure of such a complex of chromium with an organic acid can be proposed by us as a compound with two Cr 3+ atoms connected with a bridge formed by a bidental carboxylic group of an organic acid. Four oxygen atoms of the two carboxylic moieties bound in the chelate occupy the remaining coor- dination sites of the chromium atom. A different structure of chromium chelate was proposed by Uri. [8, 9] In the molecular complex formed the COO – groups are bound to the chromic atom according to the formula: In this paper the adhesive and cohesive properties of an epoxy resin cured with a hardener based on a chromic che- late have been investigated. The properties are compared to the resin cured with a conventional amine hardener. Full Paper: Cohesive and adhesive properties have been compared of epoxy resins crosslinked either with chro- mic-based hardener or with conventional amine-type hardener. Higher cohesive parameters, such as yield strength, Young’s modulus and impact resistance were observed for the material cured with chromic hardener. The adhesive strength of metal-metal joints (steel-alumi- nium) has been also found to be higher for chromic hard- ener containing epoxy compared to conventional curing systems. The time dependencies of adhesive strength after thermal treatment at 140 8C of the joints showed a higher thermal resistance of the epoxy with chromic hardener when compared to the amine cured resin. Macromol. Mater. Eng. 2001, 286, No. 3 i WILEY-VCH Verlag GmbH, D-69451 Weinheim2001 1438-7492/2001/0303–0191$17.50+.50/0 Strength of adhesive joints aluminium-aluminium versus curing agent concentration: a – chromium chelate, b – amine-based hardener.