TOUGHENING OF EPOXY-RESINS USING PARTICLES PREPARED BY EMULSION POLYMERIZATION - EFFECTS OF PARTICLE SURFACE FUNCTIONALITY, SIZE AND MORPHOLOGY ON IMPACT FRACTURE PROPERTIES

A range of sub-micron size three-layer toughening particles have been prepared by sequential emulsion polymerization. each type of particle comprising a glassy polymer core, a rubbery inter-layer and an outer l ayer of glassy polymer, which was functionalized using either glycidyl methacrylate or methacrylic acid. Each type of particle was dispersed at a range of levels in a commercial diglycidyl ether of bisphenol-A (DGEBA), which then was cured using either piperidine or commercial di amino-3,5-diethyltoluene. The materials obtained were characterized by transmission electron microscopy, dynamic mechanical analysis and ins trumented impact testing. Inclusion of the toughening particles gave r ise to a substantial increase in the toughness of piperidine-cured DGE BA, but only a marginal enhancement in the toughness of diamino-3,5-di ethyltoluene-cured DGEBA because of the much higher crosslink density of this epoxy resin matrix. The presence of particle surface functiona lity was essential to optimizing toughness: but above a certain level (about 5 mol%) the concentration of functional groups in the surface l ayer had no further effect on the toughness. Carboxylic acid functiona lity led to slightly inferior impact toughness compared with epoxide f unctionality and also gave rise to difficulties in processing the blen ds of particles and epoxy resin. The effects of particle size and morp hology were investigated using particles with surface layers containin g epoxide functionality. The size of the particles was shown to be imp ortant, with the results indicating that the particle diameter at the periphery of the rubbery layer needs to be more than 0.35 mu m. There also was an effect of particle morphology, with toughness decreasing a s the size of glassy polymer core was increased.