FRACTURE-BEHAVIOR OF EPOXY POLYMERS MODIFIED WITH CORE-SHELL RUBBER PARTICLES

Physical and thermomechanical properties of BDMA-catalyzed DGEBA/Dicy epoxy toughened with core-shell particles were studied. Relationships between these properties and the level of toughening are reported. The blends have been made in well-defined processing conditions. In fact, the resulting properties depend on the state of dispersion of the par ticles in the prepolymer matrix before crosslinking and on the cure sc hedule. The considered core-shell particles were of two types: i) poly (butadiene-co-styrene) core/carboxy-functionalized poly(methyl methacr ylate-co-styrene) shell. Such core-shell particles have been dispersed in the epoxy matrix at different volume fractions (from 9.5 to 24%); ii)poly(butyl acrylate) core/carboxy functionalized poly(methyl methac rylate-co-styrene) shell. These particles have been dispersed at a vol ume fraction of 24%. Static mechanical tests were performed in tension and compression modes on these core-shell polyepoxy blends. A slight decrease of Young's modulus and an increase of the ability to plastic deformation were noticed as the volume fraction of the core-shell part icles increased. Using linear fracture mechanics (LEFM), an improvemen t of the fracture properties (K-IC) was measured. Fatigue crack-growth studied for blends demonstrates that the Paris's law can be used to d escribe the behavior of the materials. Increasing the volume fraction of core-shell particles leads to an improvement of the resistance to f atigue crack-propagation. The same trend is noted on the impact behavi or studied by means of high-speed tests performed in a large range of temperatures. (C) 1997 John Wiley & Sons, Inc.