The Morphological Control Of Nonspherical Polymer Particles

Rigid and flexible polymer particles were successfully produced by concentrated emulsion polymerization. Various factors, including the volume percentage of dispersed phase, the crosslinking agent content and the silica colloid content, affecting the generation and stability of the nonspherical shape of polymer particles were investigated. The distinguishing feature of nonspherical particles was preliminarily studied in this paper.A concentrated emulsion possesses a volume fraction of the dispersed phase (Φ) higher than 74%, which represents the most compact arrangement of spheres of the same size. Since 0.74 is the maximum volume which can be occupied by uniform, undeformed spherical particles, the dispersed phase droplets in a concentrated emulsion deformed into polyhedral cells. If the nonspherical shape of each cell could be maintained till the end of polymerization, the nonspherical polymer particles might be produced.For rigid nonspherical polystyrene particles, adding a certain content of crosslinking agent to the dispersed phase to maintain the particles' shape,we can produce nonspherical polystyrene particles with different nonspherical extent. The dispersed phase's volume percentage could reach the maximum of 94.7. The particles' shape was observed by TEM and the nonspherical extent was calculated by roundness formula. And the maximum of roundness value of polystyrene particles was 1.101.The polystyrene nonspherical particles with different roundness values were filled into phenol formaldehyde resin. The composites' impact strength was tested. When the content of polystyrene particles was 3.0 wt%, the impact strength coulJ be improved by filling the particles with high roundness value, reaching 130% of the pure matrix resin.Nevertheless, it is very difficult to retain the nonspherical shape of polybutyl acrylate because of the strong interactions among cells. Then, besides the crosslinking agent in the dispersed phase, a kind of silica colloid was added to the continuous phase to restrain the diffusion of chains and reduce the coalescence by collisions. When the the crosslinking agent content was higher than 5.6 vol% , the silica colloid content was higher than 10 wt%, and the dispersed phase's volume percentage reached 94.7%, the roundness value of pclybutyl acrylate particles was 1.089.The polybutyl acrylate nonspherical particles with different roundness values were filled into cpoxy resin. The composites' impact strength was increased with the rise of particles' roundness values, and the maximum of composites' impact stren^lh was 175% of pure epoxy resin. The photos of...