Viscoelastic behavior and toughness of the DGEBA epoxy resin with 1,2-diaminocyclohexane: effect of functionalized poly(dimethylsiloxane), diglycidyl ether, PDMS-DGE, pre-reacted with 1,2-diaminocyclohexane

There is a great number of reports with the aim to reduce the inherent brittleness of epoxy resins through their modification with different types of reacting and non-reacting additives, in order to diversify their applications. In this work, the toughening effect of polydimethylsiloxane, diglycidyl ether (PDMS-DGE) as well as this rubber functionalized with 1,2-diaminocyclohexane (PDMS-DGE-DCH) on the bisphenol-A diglycidyl ether/1,2-diaminocyclohexane epoxy resin (DGEBA/1,2-DCH) was characterized by differential scanning calorimetry, DSC, and dynamic mechanical analysis, DMA. The results were correlated with those from energy-dispersive X-ray spectroscopy, EDS X-ray, scanning electronic microscopy, SEM, thermogravimetric analysis, and tension tests. The epoxy resin added with 10 phr (parts per hundred of resin) PDMS-DGE underwent phase separation evidenced by voids of c.a. 0.7 µm left after extraction of PDMS-DGE, while Young's modulus and glass transition temperature, Tg, did not decrease significantly. In contrast, the PDMS-DGE-DCH modifier at 10 phr yielded epoxy resins with two lower partially overlapping Tg over a broader temperature range and increased on both the tensile strength and the tensile strain at the break by 2.8- and 16.8-fold, respectively. No voids were observed on the SEM images after subjected to extraction conditions with acetone, and EDS X-ray elemental mapping revealed Si atoms uniformly distributed on all the fracture-surface, proving that PDMS-DGE-DCH took part in the cure reaction into the network of epoxy resin.