Effect of nanofillers on the properties of flexible protective polymer coatings

Abstract

Nanofillers with different size, shape, chemical structure, aspect ratio, and purity, including pristine montmorillonite (MMT-Na) and hydrotalcite (HT) lamellar clays, and nonpurified single-walled carbon nanotubes (SWNT) and fullerenes (FUL) were dispersed in a waterborne flexible acrylic coating. SEM and WAXD analysis of drawn-down composite films containing 5 and 10 wt% fillers confirmed the random orientation of the MMT-Na and HT platelets having intercalated or partially exfoliated structures. SEM analysis of composites containing SWNTs revealed the presence of clusters rather than single fibers and irregularly shaped carbonaceous impurities. Low aspect ratio, but well-dispersed particles were observed in the FUL composites. Only the SWNT filler improved the thermal stability of the unfilled polymer; the presence of SWNT and MMT-Na had a negligible effect on the glass transition temperature (T g) of the coating. The presence of all nanofillers increased the tensile secant modulus of the polymer and decreased somewhat tensile strength and elongation at break to different degrees depending on type of filler and concentration. Some nanofillers significantly reduced the water vapor transmission rate of the unfilled matrix. Experimental data are discussed in terms of parameters known to affect mechanical and barrier properties including volume fraction, orientation, aspect ratio, dispersion, interfacial adhesion, and filler hydrophilicity. The results of this work indicate that it is possible to improve certain properties of acrylic protective coatings through the addition of low cost, unmodified nanoclays or by using nonpurified carbon allotropes, without a significant compromise of the strength and ductility of the polymeric matrix. © 2006 Society of Plastics Engineers.