Microscale Structures and Mechanical Properties of Rubber-modified Epoxy Resins
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Danube Vltava Sava Polymer Meeting
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Epoxy resins are often used because of their wide-ranged properties and resulting numerous application possibilities. The properties can easily be modified by adding different additives - e.g. rubber additives are added to modify the toughness of epoxy resins. In the microscopic range a separation between epoxy matrix and rubber additive occurs. Scanning force microscopy (SFM) is an appropriate method for the examination of this separation.
Epoxy resins based on bisphenol A diglycidyl ether and various amounts of nitrile rubber were cured isothermally at 80 °C to complete hardening with diethyltoluenediamine. The addition of rubber was varied between 5 and 45 phr. Both, the phase morphology and nanomechanical properties were investigated with SFM. To obtain smooth specimen surfaces, ultramicrotome cuts were performed at -80 °C.
The epoxy and the rubber phase can be easily distinguished in SFM phase images. The nitrile rubber forms soft spherical particles in the hard epoxy matrix. They have a diameter of around 2 µm. The size and shape of the rubbery domains remain the same even with increasing addition of rubber. The mechanical properties of the two phases were investigated with nanoindentation. Furthermore, the influence of the varying amounts of rubber additive on the toughness of the epoxy resin was quantified.