Particulate toughening agents

Thermoplastics can be used as particulate toughening agents. Substances used in this way include polyfbutylene terephthalate), nylon 6 and polyfvinylidine fluoride). Toughness can be i ncreased by a factor of 6 by use of these particulates. 

Some inorganic particulate fillers have also been considered as toughening agents for epoxy materials. Glass beads, fly ash, alumina trihydrate, and silica were used early on to improve the toughness of filled epoxy resins. Various studies, however, have demonstrated that the fracture energy of filled epoxies reaches a maximum at a specific filler concentration. 

The word reinforcement will not be applied to particulate fillers, such as quartz or glass beads, because although these additives do increase the modulus, they cannot be relied on to improve the strength of the resin, nor will the word be applied to speciality rubber toughening agents that are used to improve the impact strength only. 

Particulate thermoplastics toughen by crack bridging, crack pinning and by stress concentration which produces shear banding. Amine curing agents are most often used to cure thermoplastic modified epoxies. 

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