Thermosetting polymers are extensively used nowadays primarily as matrices for composite materials and durable adhesives. These materials are brittle in nature due to their highly crosslinked networks. In this work, a toughened epoxy thermoset was successfully developed via incorporating partially reacted epoxy (PRE) substructures. For the modified case, stoichiometric amount of polyetheramine (Jeffamine D4000), was reacted with DGEBA (Epon 825) up to 60%, 70% and 80% of epoxide conversion. The precursor further added to the dominant thermoset which is composed of stoichiometric amount of DGEBA (Epon 825) and diethyl toluene diamine (Epikure-W). For the unmodified case, corresponding control samples (0%-PRE) were prepared from similar components with identical compositions where all components were mixed together and then reacted. At some constant concentrations of PRE (10%, 15% and 20% by weight), it was observed that the glass transition temperature starts to deviate from control samples such that, the samples containing substructures with 80% of epoxide conversion (80%-PRE) revealed the largest deviation of Tg from control samples (~25 �C). Values of strain energy release rate (G1c) were implying that the conversion level of the substructures has direct influence on toughening the modified thermosets. Accordingly, 80%-PRE specimens revealed the highest level of toughening.  Additionally, surface morphology of the fracture surfaces support the enhancement in fracture toughness of the network isomers.  In summary, it was shown that addition of one simple step in processing epoxy thermosets enabled us to produce polymer network isomers with improved thermal and mechanical properties.

Toughened epoxy via incorporating pre-reacted network substructures

248th National Meeting (2014)

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