Interpenetrating polymer networks (IPNs) as a branch of multicomponent polymeric materials have gained great attention in the last decades mostly due to their numerous applications. These include ion exchange resins, toughened plastics, adhesives, hydrogels and specially, vibration and noise damping materials. Although polymers possess good damping capability over their glass transition region, the main advantage of IPNs is their ability to widen the glass transition region. This feature makes them a good candidate for vibration and sound damping applications. For instance, IPNs in the form of waterborne latex have shown potential as damping coatings. This latex IPNs are synthesized through emulsion polymerization and usually have a multilayer core/shell structure. Good damping materials should exhibit a high loss factor (tan δ> 0.3) over a temperature range of at least 60–80 °C so as to be efficient in wide temperature and frequency ranges experienced in real damping applications. It has been shown that certain inorganic fillers could enhance the damping properties of IPNs. However, little has been done concerning the effect of nano sized fillers on damping properties of multilayer core–shell latexes. In this study, Latex IPNs with multilayer core-shell structure were synthesized via a three-stage semi-continuous emulsion polymerization technique. A mixture of monomers (Styrene, Methyl methacrylate and Buthyl acrylate) with the crosslinker (Ethylene glycol dimethacrylate) were used to synthesize a three-layer styrene/acrylate core-shell waterborne latex. The composition ratio of monomers in the three layers were changed in a way that Tg was decreased from the core to the last shell. In addition, two types of montmorillonite nanoclays, a natural montmorillonite (Na-MMT) and an organically modified montmorillonite (OMMT) were used to see their effect on the damping properties of styrene-acrylate/nanoclay nano composite. The nanoclays (0.5 wt%) were included in the core during the latex synthesis. The size, size distribution, film topology and the dynamic-mechanical behavior of the dried latex film were studied by dynamic laser scattering (DLS), atomic force microscopy (AFM) and dynamic mechanical analysis (DMA) respectively. Results showed that all the latex particles synthesized in this work were of monomodal distributions confirmed by DLS analysis. Moreover, the spherical morphology of the latex particles was observed via AFM images. The study of the film forming capability of the core, shell 1 and 2 latexes showed that the film formation was mainly controlled by the Tg of the outermost layer of the latex. The maximum loss factor (tan δ max) of the multilayer styrene-acrylate latex was about 1.7 with an effective temperature region of -10.6 - 23.4°C. The addition of OMMT nanoclays to the core, increased the average size of the latex particles from 58.5 to 73.6 nm, whereas the Na-MMT only slightly increased the average particle size (60.7 nm). This result was also confirmed by AFM where larger particles could be observed via incorporation of OMMT in the latex compared to Na-MMT nanoclays. The addition of hydrophilic nanoclay (Na-MMT) decreased both tan δmax and the effective temperature region. However, the OMMT nanoclays could effectively enhance the damping capability of the multilayer latex by a noticeable increase of the tan δmax to 2.5 and also the area under the tan δ curve. This difference in results was ascribed to favorable inclusion of OMMT in the monomer phase due to its hydrophobic nature while the hydrophilic Na-MMT is not possibly incorporated well into the polymer particles during polymerization. Therefore, it seems that the OMMT nanoclays could increase the damping capability via limiting the movement of polymer chains and inducing internal friction between the nanoclay surface and polymer chains.

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