Agglomerate toughening

The above hypothesis, that the toughening efficiency is enhanced by the formation of local agglomerations, requires intensive theoretical calculations of stress distributions as well as the preparation and characterization of morphologies with a controlled level of dispersion and local agglomeration respectively. 

Figure 4.2 Reinforcement mechanism of a ZTA (zirconia-toughened alumina) duplex ceramics with agglomerated Y-PSZ particles.

There are far fewer options for preparing the second-phase particle distribution by precipitation within the uncured resin matrix. This approach, again, is not ideal for solvent-based adhesives. Any such toughener must be soluble in the base resin system at elevated temperature and then give an even precipitation, without agglomeration, as the matrix cools back to ambient temperature. 

Recently, Wills et al. [16,17] proposed a novel agglomeration method. Core/shell impact modifiers, useful in toughening polyfvinyl chloride) and other thermoplastics, are prepared at small particle size by an emulsion polymerization process, agglomerated by the novel technique which has little effect on emulsion solid, are further encapsulated by a final shell, and are isolated by spray drying or coagulation. The isolated particles are readily redispersed to their original particle size in the matrix polymer. 

Typical tensile stress-strain curves of neat PP and its filled version are shown in Figure 3.2, indicating that both a reinforcing and a toughening effect of the Iianoparticles on the polymeric matrix was brought into play. That is, a structural weakness, which would have resulted from the agglomerating behavior of the nanopai ticles, has been eliminated by the grafting macromolec-ular chains. 

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