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ABSTRACT:The effect of stearic acid modification on the dispersity of silica nanoparticles and the adhesion between the filler and polymer matrix with stearic acid concentration were investigated. The wettability of silica nanoparticles was improved by the addition of stearic acid. The presence of adsorbed stearic acid on the surface of the silica nanoparticles reduced the interaction between silica nanoparticles, and reduced the size of agglomerates with increasing concentration. Silica nanoparticle-reinforced poly(ethylene 2,6-naphthalate) (PEN) composites were melt-blended to investigate their mechanical properties and the processability of the composites. The torque and total torque values of the composites decreased with increasing silica nanoparticle content. The tensile moduli of the composites reinforced with unmodified silica nanoparticles increased with increasing silica content, whereas the tensile strength and elongation decreased. However, the stearic acid-modified silica nanoparticle-reinforced PEN composites exhibited increased elongation and decreased tensile moduli with increasing content because stearic acid, which adsorbs onto the surface of the silica nanoparticles in layers thicker than a monolayer, acts as a plasticizer during the melt-compounding stage.

We added surface-modified silica nanoparticles to poly(ethylene 2,6-naphthalate) (PEN) to investigate their effect on the mechanical properties on the PEN nanocomposite material. The torque and total torque values of the composites decreased in the silica nanoparticle composites. The tensile modulus of the composites reinforced with unmodified silica nanoparticles increased upon increasing the silica content, while the tensile strength and elongation decreased accordingly. In contrast, stearic acid-modified, silica nanoparticle reinforced PEN composites exhibited an increase in elongation and a decrease in tensile modulus upon addition of the silica nanoparticles because the stearic acid that had adsorbed onto the surface of the silica nanoparticle in multilayers could act as a plasticizer during melt compounding. Stearic acid modification had a small effect on the crystallization behavior of the composites. We calculated theoretical values of the tensile modulus using the Einstein, Kerner, and Nielsen equations and compared these values with the experimental data obtained from the composites. The parameters calculated using the Nielsen equation and the Nicolais Narkis model revealed that the interfacial adhesion between silica nanoparticles and the PEN matrix could be improved.

Organic and inorganic hybrid nanocomposites based on poly(ethylene 2,6-naphthalate) (PEN) and silica nanoparticles were prepared by a melt blending process. In particular, polymer nanocomposites consisting mostly of cheap conventional polyesters with very small quantities of inorganic nanoparticles are of great interest from an industrial perspective. The crystallization behavior of PEN/silica hybrid nanocomposites depended significantly on silica content and crystallization temperature. The activation energy of crystallization for PEN/silica hybrid nanocomposites was decreased by incorporating a small quantity of silica nanoparticles. Double melting behavior was observed in PEN/silica hybrid nanocomposites, and the equilibrium melting temperature decreased with increasing silica content. The fold surface free energy of PEN/silica hybrid nanocomposites decreased with increasing silica content. The work of chain folding (q) for PEN was estimated as 7.28 Ý 10 -20 J per molecular chain fold, while the q values for the PEN/silica 0.9 hybrid nanocomposite was 3.71 Ý 10 -20 J, implying that the incorporation of silica nanoparticles lowers the work required to fold the polymer chains.