Epoxy resins fracture morphology

Siebert and Riew (4) described the chemistry of the in situ particle formation. They proposed that the composition of the particle is a mixture of linear CTBN-epoxy copolymers and crosslinked epoxy resin. The polymer morphology of the CTBN toughened epoxy systems was investigated by Rowe (5) using transmission electron microscopy by carbon replication of fracture surfaces. Riew and Smith (6) supported the... 

Polymer Morphology and Failure Mechanisms. A failed tensile bar of unmodified piperidine-cured epoxy resin shows shear deformation before tensile failure when strained slowly (0.127 cm/sec). We could not produce stable crazes in specimens of unmodified epoxy resins. At all stress levels, temperatures, and conditions of annealing only fracture occurred after shear band formation. The failure to observe crazes in unmodified epoxy resins may be explained by a fast equilibrium condition which exists between crazing on loading and recovery on unloading. 

Kim et al (1999) examined the morphology and cure of semi-IPN epoxy resin or dicyanate-polyimide/polysulfone-carbon-flbre Aims. Polyimide or polysulfone Aims were inserted into the curing epoxy-dicyanate monomers to form semi-IPNs with sea-island morphology at the thermoset-thermoplastic interface. The final carbon-flbre-thermoplastic-dicyanate Aims had fracture toughness three to five times higher than that of unmodified carbon-flbre-dicyanate composites. 

Martinez et al. (2000) examined the chemorheology and phase separation of polysulfone-modified DGEBA-DDM epoxy-resin mixtures. They found a delay in polymerization due to dilution and viscosity effects. The final morphologies are controlled by curing temperature due to the effect of temperature on phase separation. The fracture toughness increased with increasing immiscibility and was at its maximum for a bicontinuous morphology. 

Zhe Zheng, S., Hu, Y., Guo, Q., Wei, J. Miscibility, morphology and fracture toughness of epoxy resin/poly(vinyl acetate) blends. Colloid Polym. Sci. 274 (1996) 410-417. 

And Andres, M. A., Garmendia, J., Valea, A., Eceiza, A., Mraidragon, 1. Fracture toughness of epoxy resins modified with polyethersuUbne Influence of stoichiometry on the morphology of the mixtures. J. Appl. Polym. Sci. 69 (1998) 183-191. 

Fra Francis, B., Thomas, S., Thomas, S. P., Ramaswamy, R., Rao, V. L. Diglycidyl ether of bisphe-nol-A epoxy resin-polyether sulfone/polyether sulfone ether ketone blends phase morphology, fracture toughness and thermo-mechanical properties. Colloid Polym. Sci. 285 (2006) 83-93. 

It is evident that closely related types of information are conveyed concerning the morphology of CTBN modified epoxy resins by the small deformation data in the upper curves of Figure 8 and the tensile fracture data in the lower curves. Both deformation and fracture data tend to identify a morphological phase change in CTBN modified epoxy above 17% CTBN content wherein the elastomer and epoxy phase become co-continuous. In fact, the curves of Figure 8 appear to imply the essential disappearance of a pure epoxy phase at 50% CTBN as evidenced by loss of the T = 80 C singularities in both E(t) versus T (upper curves) and W versus T (lower curves). 

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