Nanocomposites based on ethylene-vinyl acetate (EVA) copolymer and expanded graphite (EG) were prepared using direct and two-step melt-mixing processes. The effect of elongational flow on the dispersion of EG nanoparticles in the polymeric matrix was investigated by thermal analysis and electrical conductivity measurements. Two types of EG having different aspect ratio were applied to prepare the nanocomposites. The nanocomposites containing higher aspect ratio nanofiller have shown higher values of transition temperature (Tg) and a stronger reinforcing effect of EG. The evaluation of EVA crystallization behavior has clarified that both the EG loading and particle size have noticeably influenced the crystallization characteristics of EVA. The restrictions imposed by nanoparticles on molecular motion and, correspondingly, the crystal growth stage have been the most notable effect of EG nanopartciles on the EVA crystallization behavior. Moreover, the presence of EG nanofiller has intensified the formation of a second-type of EVA crystals during long annealing time. Furthermore, chemically crosslinking of EVA chains has led to the formation of smaller crystals with more uniform size. J. VINYL ADDIT. TECHNOL., 00:000-000,

Melt electrospinning has been developed in the last decade as an eco-friendly and solvent-free process to fill the gap between the advantages of solution electrospinning and the need of a cost-effective technique for industrial applications. Although the benefits of using melt electrospinning compared to solution electrospinning are impressive, there are still challenges that should be solved. These mainly concern to the improvement of polymer melt processability with reduction of polymer degradation and enhancement of fiber stability; and the achievement of a good control over the fiber size and especially for the production of large scale ultrafine fibers. This review is focused in the last research works discussing the different melt processing techniques, the most significant melt processing parameters, the incorporation of different additives (e.g., viscosity and conductivity modifiers), the development of polymer blends and nanocomposites, the new potential applications and the use of drug-loaded melt electrospun scaffolds for biomedical applications.

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Tissue engineering approaches appear nowadays highly promising for the regeneration of injured/diseased tissues. Biomimetic scaffolds are continuously been developed to act as structural support for cell growth and proliferation as well as for the delivery of cells able to be differentiated, and also of bioactive molecules like growth factors and even signaling cues. The current research concerns materials employed to develop biological scaffolds with improved features as well as complex preparation techniques. In this work, hybrid systems based on natural polymers are discussed and the efforts focused to provide new polymers able to mimic proteins and DNA are extensively explained. Progress on the scaffold fabrication technique is mentioned, those processes based on solution and melt electrospinning or even on their combination being mainly discussed. Selection of the appropriate hybrid technology becomes vital to get optimal architecture to reasonably accomplish the final applications. Representative examples of the recent possibilities on tissue regeneration are finally given.

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.