In the current work, the fracture properties of epoxy polymers containing poly-siloxane core shell rubber (CSR) nano-particles were studied. The effect of different cure rates and curing temperatures on the epoxy resin was also investigated. Single edge notched bend tests were performed to evaluate the fracture energy of the polymers. The fracture energy of the unmodified epoxy polymer increased significantly from 339 J/m 2 to 3,922 J/m 2 due to the addition of 9 wt% of CSR nano-particles. Similarly, the fracture toughness for the unmodified polymer increased from 1.27 MPa m 1/2 to 3.42 MPa m 1/2 for an epoxy polymer containing 9 wt% of CSR nano-particles. Faster rates of curing, which can be achieved at higher cure temperatures are found to be detrimental to the toughness of the modified epoxy polymers.
Epoxy resin systems are widely used in composite materials. Epoxy resins can exhibit high moduli and strengths for polymers, whilst being easy to process into fiber reinforced composites. They can also be considered brittle, when compared to many other polymers. Enhancing the toughness of epoxy-based matrices can lead to significant improvements in the toughness and, therefore, damage resistance of fiber reinforced composites. These improvements in toughness can be achieved through the incorporation and/or formation of nano-scale particles or structures in the matrix by the addition of core-shell rubber particles or block copolymers, for example. However, the efficacy of these toughening agents in increasing the toughness of these materials is heavily influenced by their ability to produce a coherent microstructure within the epoxy. It was observed that the fracture energy of toughened epoxies, determined via testing on single edge notched beams, decreased with higher cure temperatures. A loss of coherency in the microstructures, as cure temperature increased, was observed via electron microscopy. This was linked to the reduction in toughness enhancements attained as systematically varied resin formulations were cured more rapidly.
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