Toughening of epoxy resins using particles prepared by emulsion polymerization: effects of particle surface functionality, size and morphology on impact fracture properties
✍ Scribed by Day, Richard J.; Lovell, Peter A.; Pierre, Dorian
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 442 KB
- Volume
- 44
- Category
- Article
- ISSN
- 0959-8103
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✦ Synopsis
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 layer 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 diamino-3,5-diethyltoluene. The materials obtained were characterized by transmission electron microscopy, dynamic mechanical analysis and instrumented impact testing. Inclusion of the toughening particles gave rise to a substantial increase in the toughness of piperidine-cured DGEBA, but only a marginal enhancement in the toughness of diamino-3,5-diethyltoluene-cured DGEBA because of the much higher crosslink density of this epoxy resin matrix. The presence of particle surface functionality was essential to optimizing toughness, but above a certain level (about 5 mol%) the concentration of functional groups in the surface layer had no further e †ect on the toughness. Carboxylic acid functionality led to slightly inferior impact toughness compared with epoxide functionality and also gave rise to difficulties in processing the blends of particles and epoxy resin. The e †ects of particle size and morphology were investigated using particles with surface layers containing epoxide functionality. The size of the particles was shown to be important, with the results indicating that the particle diameter at the periphery of the rubbery layer needs to be more than 0É35 km. There also was an e †ect of particle morphology, with toughness decreasing as the size of glassy polymer core was increased.