Thermosets particle toughening

In Secs. 13.2-13.3 the principles of toughening of thermosets by rubber particles, and the role of morphologies, interfacial adhesion, composition, and structural parameters on the toughening effect are analyzed. Section 13.4 is devoted to the use of initially miscible thermoplastics for toughening purposes. The effect of core-shell rubber particles is discussed in Sec. 13.5 and, in Sec. 13.6, miscellaneous ways of toughening thermosets (liquid crystals, hybrid composites, etc.), are analyzed. 

In the case of thermosets toughened with thermoplastics particles (Sec. 13.4), this mechanism may be of a considerable importance because of the intrinsic toughness and/or ductility of these particles. 

An improvement in the toughness of thermosets can be favored by rubber or thermoplastic particles, which operate both in crack initiation and propagation mechanisms. The different toughening mechanisms can act simultaneously and can be modeled quantitatively. 

A high degree of toughening may be attained by the use of CSR particles as modifiers of thermosetting polymers. This is because several adjustable parameters - the chemical structure and size of the core the number, chemical structure, and thickness of shells and the possibility of crosslinking... 

A crosslinked rubber may be synthesized at the surface of the glass beads to produce a core-shell structure (glassy core and rubbery shell). Thermosets modified with these particles showed a strong toughening effect for an optimum thickness of the rubbery shell (Amdouni et al., 1992). 

Precrosslinked particles with low crosslink density exhibit elastic properties and ean be applied for toughening thermoplastics or thermosets. The size of the elastic domains in blends consisting of elastic particles and a polymer matrix can be adjusted precisely, provided that the particles are dispersible. Via functional groups, microparticles can be covalently attaehed to a (thermoset) matrix. The grafting of polymer shells onto elastic microparticles improves the compatibility with the polymer matrix to be modified [3]. Thus, after processing of the polymer alloy discrete elastic particles can be observed as disperse phase in a continuous thermoplastic matrix. 

Both thermoset and thermoplastic resins and CF composites have been examined using microhardness techniques. The thermoset resin used was an epoxy, both with and without PA6 particles that served as a toughening agent. 

It was noted in the previous section that the carboxyl end groups on the CTBN elastomer affected the final performance of the material as a toughener since these groups would co-react with the epoxy resin and facilitate stress transfer from the brittle matrix to the phase-separated elastomer. Without this adhesion the particles could debond prematurely, which would lead to poor dissipation of the energy of the growing crack. It has also been noted that excessive adhesion between an epoxy resin and a thermoplastic could be deleterious to the performance (Williams et al, 1997). The process of toughening of a thermoset... 

Brittle thermosets are best toughened by the introduction of a rubbery or thermoplastic dispersed phase (1-4). The dispersed phase can be produced by two methods in situ reaction and adding preformed particles. The first method is used much more because it is easy and it can create specif-... 

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