Experimental investigation of the linear viscoelastic response of EVA‐based nanocomposites

Abstract

Linear viscoelastic behaviors of ethylene-vinyl acetate (EVA)-layered silicate nanocomposites were investigated. EVA with vinyl acetate (VA) content of 18 and 28% by weight and commercially modified montmorillonite clay (Cloisite® 30B) were melt blended in a twin-screw extruder. Nanocomposites of 2.5, 5 and 7.5% by weight were produced. Wide angle X-ray scattering was used to ascertain the degree of layer swelling that could be attributed to the intercalation of polymer chains into the interlayer of the silicates. Transmission electron microscopy was used to analyze the dispersion and extent of exfoliation of the layered silicates in the polymer matrix. All nanocomposites were found to have mixed intercalated/exfoliated morphologies. Both storage and loss moduli and complex viscosity showed improvement at all frequencies tested with increase in silicate loading. Terminal zone behavior was also shown to disappear gradually with silicate content. Increase in silicate loading had caused the divergence of viscosity profile from low-frequency Newtonian plateau to non-Newtonian slope corresponding to a possible finite yield stress. The gradual disappearances of terminal zone and Newtonian homopolymer-like characteristics with silicate loading were attributed to the formation of lattice spanning three-dimensional network structures.

The Degradation Kinetics of EVA‐Clay Nanocomposites

“…Samples of EVA nanocomposites were available from materials produced in previously reported research . Three different EVA compositions were used with vinyl acetate (VA) contents of 9, 18 and 28 wt% (denoted EVA9, EVA18 and EVA28 respectively).…”

“…Wide‐angle X‐ray scattering (WAXS) and transmission electron microscopy (TEM) revealed the EVA9 nanocomposite were intercalated in nature but the EVA18 and EVA28 nanocomposires were a mixture of intercalated and defoliated morphologies. Details are reported in the previous literature …”

“…Samples of EVA nanocomposites were available from materials produced in previously reported research. [9,10] Three different EVA compositions were used with vinyl acetate (VA) contents of 9, 18 and 28 wt% (denoted EVA9, EVA18 and EVA28 respectively). These were melt blended with organically modified montmorillite (OMMTs) to produce nanocomposites (of 2.5, 5 and 7.5 wt% nano-clay loading).…”

“…Details are reported in the previous literature. [9,10] The mass-loss kinetics of the EVA was measured by TGA experiments conducted using a Perkin Elmer STA 6000. The experiments were performed over a temperature range of ambient to 700 C under laboratory grade nitrogen (flow rate ¼ 20 mL/min) using a constant heating rate of 1, 2, 5, 10 or 20 K/min.…”

Use of purified and modified bentonites in linear low‐density polyethylene/organoclay/compatibilizer nanocomposites

“…The processing of polymer nanocomposites necessitates knowledge of their rheology. Because the rheological properties of particulate suspensions are responsive to the feature of the dispersed phase, they provide information about the internal microstructure of nanocomposites, such as the state of dispersion of clay and the confinement effect of silicate layers on the motion of polymer chains 19, 20. Consequently it can be used as a supplementary tool for other characterization techniques, such as X‐ray diffraction (XRD), transmission electron microscopy (TEM), and mechanical testing.…”