Abstract
The purpose of this study was to assess the effects of different aqueous environments (i.e., demineralised, distilled and spring water) on the mechanical properties of a cold-cured bisphenolic epoxy resin modified with the addition of calcium carbonate filler, typically employed as structural adhesive. The parameters selected for the analysis have been; the kind of curing agent employed to cure the epoxy resin at ambient temperature (i.e., Mannich base and triethylenetetramine); the load of calcium carbonate added to liquid epoxy (i.e., from 1 to 3 g per 100 g of resin) and; the duration of the exposure to the different aging conditions (i.e., from 1 to 10 months). Cylindrical specimens of calcium carbonate-modified epoxy systems were tested in compression mode, before and after each of the aging regimes. The effect of the selected curing agents is very small, and they are both suitable for a cure at ambient temperature, on the unfilled epoxy on compressive maximum strength and strain at break; the choice of the hardener affects instead the compressive modulus. The CaCO3 amount was demonstrated to have a significant effect on the mechanical characteristics of un-aged epoxy systems, leading to growth in compressive modulus and maximum strength with reductions in strain at break. Generally speaking, the aging time noticeably affects the compressive properties of calcium carbonate-modified epoxies while almost negligible is the kind of water employed in each exposure regime. Notwithstanding the adverse effects of an aqueous environment on compressive mechanical properties of CaCO3-filled epoxies, these systems keep compressive modulus and maximum strength greater than, and close to, respectively, the same characteristics measured on unaged unfilled control epoxies, demonstrating the positive effect of the addition of this kind of filler to epoxy-based structural adhesives, especially with the addition of 2 and 3 g of CaCO3 per 100 g resin. The results obtained in this study demonstrated that it is possible to contrast the detrimental effects observed in cold-cured epoxy-based structural adhesives due to their aging in water upon the addition of limited amounts (particularly at 2 and 3 g per 100 g resin) of a cheap CaCO3 filler.
Highlights
Epoxy resins are compounds with a broad applicability, which stems from their outstanding properties, in particular, their high mechanical strength, good chemical resistance and thermal stability, and excellent adhesion to different substrates [1,2,3]
Results ofofmechanical mechanical compression mode) tests performed on E5/TFF/100:26 compounds filled with different amounts of and aged for different time spans in demineralised water: (a) compressive modulus; (b) compressive maximum strength; and in demineralised water: (a) compressive modulus; (b) compressive maximum (c) compressive strain at break
Resultsofofmechanical mechanical compression tests performed on E5/TFF/100:26 compounds filled with different amounts of and aged for different time spans in distilled water: (a) compressive modulus; (b) compressive maximum strength; and (c)
Summary
Epoxy resins are compounds with a broad applicability, which stems from their outstanding properties, in particular, their high mechanical strength, good chemical resistance and thermal stability, and excellent adhesion to different substrates [1,2,3]. Polymers 2020, 12, 2541 conditions (namely, heat- or cold-cure) and to properly modify their (chemical, mechanical, functional) properties within a broad range of values. All these features are achieved through an accurate selection of the type and amount of the curing agent, type and quantity of modifiers, as well as curing and aging conditions [3,5,6,7,8,9,10]. Epoxy compounds are usually characterised by resistance to water and to many solvents (i.e., petroleum, oil, organic solvents, diluted acids and bases) (references)
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