No abstract

In this study, polyurethane (PU)/nano-silica nancomposite foams were prepared. The effects of isocyanate index, cell size, density, and molecular weight of polyols on the sound absorption ratio of PU/nano-silica foams were investigated. With increasing nano-silica content, the sound absorption ratio of PU/nano-silica foams increases over the entire frequency range investigated in this study. Decrease of isocyanate index, cell size, and increase of density leads to the increase of sound absorption ratio of PU/ nano-silica foams. PU/nano-silica foams have a broad T g centered around room temperature by decreasing molecular weight of polyol resulting in good sound absorbing ability.

A series of polynorbornenes (PNBEs) with 1,4-bis[(3‘-fluoro-4‘-n-alkoxyphenyl)ethynyl]benzene mesogens (n = 9−12) laterally attached to the polymer backbone through a one-carbon spacer were previously synthesized by ring-opening metathesis polymerization of the corresponding norbornene-based monomers. Wide-angle X-ray diffraction (WAXD) experiments demonstrate that the mesogens organize into the tilted layer structure of a smectic C (SC) phase at room temperature, and polarized light microscopy demonstrates that the highest temperature ordered phase is a nematic (N) phase. Upon heating above room temperature, the tilt angle of the SC phase of all of the PNBEs (n = 9−12) continuously decreases, especially at temperatures above 70 °C for the PNBEs (n = 9−11) and 60 °C for the PNBE (n = 12). However, the SC phase of the PNBEs (n = 9−11) transforms to a N phase before the tilt angle reaches zero. That is, the SA phase is never actually achieved in the PNBEs (n = 9−11), although the decrease in the tilt angles corresponds to a broad endotherm in the differential scanning calorimetry (DSC) experiments in the same temperature region. This speculation is proven by the stable SA phase of PNBE (n = 12) observed by WAXD at temperatures above 83 °C. The transition between the SC and SA phases is not a first-order transition according to DSC measurements and is instead a second-order transition based on the gradual decrease to 0° in the tilt angle, which serves as an order parameter.

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.