Assisted heterogeneous multinucleation and bubble growth in semicrystalline ethylene-vinyl acetate copolymer/expanded graphite nanocomposite foams: Control of morphology and viscoelastic properties

Abstract

Abstract. Nanocomposite foams of ethylene-vinyl acetate copolymer (EVA) reinforced by expanded graphite (EG) were prepared using supercritical nitrogen in batch foaming process. Effects of EG particle size, crosslinking of EVA chains and foaming temperature on the cell morphology and foam viscoelastic properties were investigated. EG sheet surface interestingly provide multiple heterogeneous nucleation sites for bubbles. This role is considerably intensified by incorporating lower loadings of EG with higher aspect ratio. The amorphous and non-crosslinked domains of EVA matrix constitute denser bubble areas. Higher void fraction and more uniform cell structure is achieved for non-crosslinked EVA/EG nanocomposites foamed at higher temperatures. With regard to the structural variation, the void fraction of foam samples decreases with increasing the EG content. Storage and loss moduli were analyzed to study the viscoelastic properties of nanocomposite foams. Surprisingly, the foaming process of EVA results in a drastic reduction in loss and storage moduli regardless of whether the thermoplastic matrix contains EG nanofiller or not. For the EVA/EG foams with the same composition, the nanocomposite having higher void fraction shows relatively lower loss modulus and more restricted molecular movements. The study findings have verified that the dynamics of polymer chains varies after foaming EVA matrix in the presence of EG.

Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders

“…The viscoelastic properties of EVA, including the elastic storage and loss moduli, contribute to the resistance of the magnet particles to being rotated into the field direction by the alignment field. Although the viscoelastic properties decrease rapidly above the glass transition temperature, they can still be significant in the temperature range of the present study [15][16][17][18][19]. As a result, the EVA matrix sufficiently limited the rotation of the anisotropic magnet particles by the applied magnetic field at 325 K, compared to alignment at other temperatures.…”

Analysis of dual role of nanographene on the microstructure‐properties correlation of TPU/NG nanocomposite

“…It can be seen that pure TPU exhibits two semi‐arc, as a consequence of a two‐phase structure 52 . By the introduction of NG particles, a tail appears for the nanocomposites, possibly related to the relaxation of tethered polymer chains at the filler‐polymer interface 52‐54 . Figure 7G reveals that, by increasing the NGs content, the Cole‐Cole diagrams shifted to higher η ′, that is, relaxation at lower frequencies or higher times 29,53,54 .…”

A developed, eco-friendly, and flexible thermoplastic elastomeric foam from SEBS for footwear application

“…It has been reported that without crosslinking foam with maximum unfoamed regions are formed, while at a certain limit of crosslinking the foam with more cell structure and very less unfoamed regions are obtained. Beyond the limit, with higher crosslinking again the more unfoamed regions are predominant due to less gas sorption capability of the highly crosslinked rigid polymer matrix [56]. So there is a certain limit of crosslinking to obtain better quality foam with a well-defined cell density and cell size.…”