Epoxy systems, multicomponent

Other synthetic fibers, as well as natural fibers, were employed in epoxy-based multicomponent systems. Thus, a comparative study between polymeric fibers reinforced epoxy resins and natural fibers reinforced ones, all obtained by UV curing, was performed [186]. Isotactic PP (iPP) fibers modified with 20 wt% EVA and hemp fibers were employed, while the matrices used were epoxy acrylate and epoxy methacrylate. Data indicated that relatively regular distribution of fibers was achieved the addition of fibers caused an increase in Shore hardness of the epoxy methacrylate based composites the epoxy acrylated composites showed a decrease in hardness when EVA-modified iPP fibers were used, whereas hemp fibers caused an opposite effect. Even more, the iPP fibers reinforced photocurable composites displayed a brittle to ductile fracture transition. 

There are several common forms of solid epoxy adhesives. These include film, tape, powder, and preformed shapes. Certain formulations are better suited for specific forms. For example, casting of tape or film adhesive from solvent solutions lends itself to working with multicomponent hybrid systems, where each resin can be solubilized and blended together in a universal solvent. B-staged systems are generally more brittle and better suited for powders or preformed adhesives. 

A comparative study between silica- and CNT-fiUed amine-cured epoxy nanocomposites [249] revealed the opposite behavior of nanocomposites upon UV irradiation. Thus, silica-filled samples underwent a high rate photochemical degradation followed by a significant accumulation of nanoparticles at the surface, which yielded in nanoparticles release. CNT-filled specimens displayed a high density CNT network at the nanocomposite surface, which limited the in-depth photochemical degradation of the material and prevented the nanoparticles release. The conceptual models for the silica nanoparticles release and CNT preservation upon UV exposure may be used for other multicomponent systems based on epoxy resins in order to assess their potential risks. 

The use of modulated DSC for improved interpretation of product characteristics under thermal effects was investigated. Tgs, for example, which are masked by postcuring or enthalpy relaxation, could be detected in a single measurement and compared. The separation of complex transitions in multicomponent systems into individual parts such as melts, transition temps, and relaxations was shown to be feasible. The potential for use of modulated DSC in the field of epoxy resins was demonstrated using examples of the determination of Tg near the regions of enthalpy relaxation, melt and post-curing. 7 refs. 

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