Fiber Reinforced Epoxy Resin Composite Materials Using Carboxylate-Alumoxanes as Cross-Linking Agents
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Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
We have previously reported that aluminum-oxide nanoparticles (5 to 80 nm) may be prepared by the reaction of the mineral boehmite with carboxylic acids. 6 The identity of the carboxylic acid appears to control the size of the nanoparticles. 7 These materials are termed carboxylate-alumoxanes and may be prepared with an almost limitless variety of functional groups. One of the more common classes of organic resins is the epoxide-based materials. Epoxy resins are easily extruded and/or molded, have moderate strength, and low hardness. 8 Common resin systems usually consist of two parts, a resin and a hardener, which are mixed and cured at elevated temperatures (50 - 100 °C). 9 The resin component is often a bi-functional epoxide while the hardener contains a cross-linking agent along with a catalyst. Using such commercial resin systems, two classes of alumoxane-based materials are possible. First, a chemically functionalized carboxylate-alumoxane may be incorporated as an additional cross-linking agent into an existing resin/hardener system. Second, the chemically functionalized carboxylatealumoxane may be used in place of the hardener (cross-linking agent). We have investigated both classes of material. In the present case two carboxylate-substituted alumoxanes were investigated: those derived from para-hydroxybenzoic acid (I) and lysine (II). 00 % 'C
HO
II
HO
0OH
NH2
HO, (I)
(II)
We have investigated two classes of epoxy-alumoxane materials. First, a chemically functionalized carboxylate-alumoxane was directly cross-linked with a common epoxy resin, the diglycidyl ether of bisphenol-A (Dow Chemical DER 332, III). This material has been termed a "hybrid alumoxane resin." The second class of material, referred to as a "composite alumoxane resin," is formed by the incorporation of the functionalized carboxylate-alumoxane into a commercially available resin/hardener system. Our results in these areas are reported herein.
(III) RESULTS AND DISCUSSION Hybrid Epoxy-Alumoxane Resins The diglycidyl ether of bisphenol-A (DER 332, III) may be cross-linked directly with either para-hydroxybenzoate-alumoxane (p-HB-alumoxane) or lysine-alumoxane in the presence of a suitable base catalyst (e.g., 1-methylimidazole). By comparison with known epoxide reactivity 10 and model compound studiesI 1 it is proposed that the hydroxy group in p-HBalumoxane and the amine groups in lysine-alumoxane undergo a ring opening reaction with the epoxide groups. By reacting varying quantities of p-HB- and lysine-substituted alumoxanes with DER 332 an optimal weight ratio, based on a qualitative assessment of the physical properties of the cured materials, was found to be 1 part alumoxane to 2 parts resin. Variations of this ratio were found to yield cured materials with different properties ranging from extremely solid to almost "rubbery" in form. Neither p-HB-alumoxane or lysine-alumoxane are soluble in DER 332,
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however, uniform mixtures may be readily prepared by
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