ABSTRACT:In this study an attempt was made to improve the rebound resilience and to decrease the density of ethylene-vinyl acetate copolymer (EVA) foam. For this purpose, EVA was blended with natural rubber (NR), and EVA/NR blends were foamed at 155°C, 160°C, and 165°C. To investigate the correlation between crosslinking behavior and physical properties of foams, crosslinking behavior of EVA/NR blends was monitored. The physical properties of the foams were then measured as a function of foaming temperatures and blend compositions: 165°C was found to be the optimal temperature for a crosslinking of EVA/NR foam. As a result, the density of EVA/NR blend foamed at 165°C was found to be the lowest. EVA/NR (90/10) blend, foamed at 165°C, showed lower density, better rebound resilience, and greater tear strength than EVA foam.

Hydrophobic polymers such as polyethylene and polypropylene are very difficult to use for preparing nanocomposites without a compatibilizer. However, in this study, polybutadiene rubber (BR; a hydrophobic polymer) nanocomposites were produced successfully without a compatibilizer with a melt-compounding method. Transmission electron microscopy showed an intercalated and exfoliated clay morphology in the polymer matrix, which led to increased mechanical properties. The tensile and tear strengths of the BR/Cloisite 20A hybrids were 4.4 times and 2 times larger than that of BR, respectively. The rebound resilience, compression set, and abrasion resistance were also improved by the addition of organoclay. The abrasion resistance of BR/Cloisite 20A was approximately 2 times larger than that of BR. The cure time (t 90 ), scorch time (t 2 ), and their difference (t 90 Ϫ t 2 ) of the BR/organoclay hybrids were much reduced than those of BR. Thus, organoclays behaved as good fillers and effective accelerant agents for BR vulcanization.

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Introducing additional elements into Ni‐rich cathodes is an essential strategy for addressing the instability of the cathode material. Conventionally, this doping strategy considers only the incorporation of additional elements into the bulk structure of the cathode in terms of fortifying the crystal structure. However, high‐valence elements such as Nb5+, Ta5+, and Mo6+ are likely to be insoluble in the crystal structure, resulting in accumulation along the interparticle boundaries. Herein, a new mechanism for doping high‐valence elements into Ni‐rich cathodes and their effects on the morphology and crystal structure are investigated by calcining LiNiO2 (LNO) and X‐doped LNO cathodes (X = Al, Nb, Ta, and Mo) at various temperatures. Operando X‐ray diffraction analysis reveals that the temperature at which the content of Li‐X‐O compounds declines is higher for the dopants with high oxidation states, reinforcing segregation at the grain boundary and widening the calcination temperature range. Thus, the highly aligned microstructure and high crystallinity of the LNO cathode are maintained over a wide calcination temperature range after doping with high‐valence elements, enhancing the electrochemical performance. As next‐generation dopants, high‐valence elements can fortify not only the crystal structure, but also the microstructure, to maximize the electrochemical performance of Ni‐rich cathodes.