Extensibility of EVA Based Nanocomposites

Abstract

The structure and deformation characteristics of ethylene-vinyl acetate (EVA)-layered silicate nanocomposites were studied using steady shear and extensional rheology. EVAs with VA contents of 18% and 28% by weight and a commercially modified montmorillonite clay were melt compounded in a twin-screw extruder. Nanocomposites of 2.5%, 5% and 7.5% by weight were produced. WAXS measurements have revealed that EVA chains had intercalated into the silicate layers and expanded the interlayer distance. TEM showed that the morphologies of the nanocomposites were of mixed intercalated/exfoliated. The nanocomposites exhibited an increase in steady shear viscosities compared to the unfilled EVA polymers. At high loading there was a possibility of yield stress owing to network structures. Elasticity of the nanocomposites was compared using first normal stress differenceshear stress plots and the modified Cole-Cole plots, with both methods showing contradictory results. Melt strengths of both EVAs were enhanced with the addition of silicate fillers; however, this was at the expense of the materials' extensibility. Addition of silicate fillers also brought with it flow instabilities like draw resonance and ductile failure, both of which lead to limitations in polymer processing.Compounding of EVA pellets and C30B was carried out using a Brabender twin-screw extruder. The pellets and C30B were initially premixed before introducing into the twin-screw extruder. The compounding temperature was set at 100°C with an extrusion speed of 70 rpm. EVA 18 and EVA28 nanocomposites with clay loadings of 2.5 wt%, 5 wt% and 7.5 wt% were 308 Brought to you by | Purdue University Libraries

Tunable water barrier properties of EVA by clay insertion?

“…A smooth surface is observed for EVA/3 wt% C10A film ( Fig. 16,26,31 For our films, this lack of C10A dispersion in the EVA matrix can be explained by the fact that the VA group is attached to the unmodified region of clay platelets which present a hydrophilic character, as referenced in the literature. In contrast, a roughness of film is noted at higher nanoclay loadings ( Fig.…”

“…2(a)), indicating a homogeneous dispersion of C10A in the polymer matrix. 26,31 Through the analysis of TEM micrographs of the nanocomposite films (Fig. 2(b) and (c)), attributable to agglomerated clay platelets.…”

Anomalous first normal stress difference behavior of polymer nanocomposites and liquid crystalline polymer composites

“…Nonetheless, in a study conducted by Prasad et al on exfoliated ethylene‐vinyl acetate/layered silicate nanocomposites, N 1 demonstrated an inverse relationship with filler contents; i.e., the magnitude of N 1 declined as the silicate filler content increased. They associated this behavior to the reduced mobility of polymer chains due to the enhanced interactions between silicate fillers and polymer chains .…”

“…The near independence of N 1 from filler content at all shear rates in intercalated PNCs has been associated with the intercalation of fillers in the composites, resulting from the preferential orientation of two‐dimensional nanofillers in the direction of flow which could diminish the effect of CC and CP interactions and their influence to elasticity . Nonetheless, in a study conducted by Prasad et al on exfoliated ethylene‐vinyl acetate/layered silicate nanocomposites, N 1 demonstrated an inverse relationship with filler contents; i.e., the magnitude of N 1 declined as the silicate filler content increased. They associated this behavior to the reduced mobility of polymer chains due to the enhanced interactions between silicate fillers and polymer chains .…”

Preparation and Rheological Characteristics of Ethylene‐Vinyl Acetate Copolymer/Organoclay Nanocomposites

“…Even though XRD analyses are useful in examining interlayer d-spacing of ordered layered silicate structures, they may fall short when no scattered intensity peaks are observed and such lack of peaks could be interpreted as exfoliation. Therefore, TEM has been regarded to be essential as it gives a direct evidence of what structure exists in the nanocomposite [23]. All the EVA40/clay nanocomposites were found to indicate individual dispersion of completely delaminated clay sheets in the EVA40 matrix from the TEM.…”