Fengshun Zhang

Molecular insights into hydrogen bonds in polyurethane/hindered phenol hybrids: evolution and relationship with damping properties

In this study, a polyurethane/hindered phenol system was prepared as a melt in order to study the yet unclear mechanism of the formation of hydrogen bonds (H-bonds) in analogous systems. The evolution of intermolecular H-bonds between ester carbonyl/phenolic hydroxyl groups and urethane carbonyl/phenolic hydroxyl groups was detected, for the first time, by infrared analysis. Subsequent dynamic mechanical analysis combined with thermal analysis showed the fluctuation of the glass transition temperatures and the damping properties of the hybrids. From X-ray diffraction analysis the existence was observed of only amorphous hindered phenol in the polyurethane, further molecular dynamic simulation, based on an amorphous cell, characterized the number of H-bonds, the H-bond predominant binding energy and the fractional free volume in a quantitative manner. It was observed that the variation of the simulation data was in accordance with the fluctuation change of the damping properties, thus a relationship was established between the evolution of the H-bonds and the damping properties.

Molecular insights into the damping mechanism of poly(vinyl acetate)/hindered phenol hybrids by a combination of experiment and molecular dynamics simulation

The fundamental mechanism of the improved damping properties of poly(vinyl acetate) (PVAc), contributed by the introduction of hindered phenols, was systematically elucidated by two-dimensional infrared (2D IR) spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimeter (DSC), X-ray diffraction (XRD) and molecular dynamics (MD) simulation. The 2D IR results revealed the evolution of hydrogen bonds (H-bonds) from intermolecular H-bonds to H-bond networks of PVAc/hindered phenols. Note that subsequent DMA results revealed that the damping properties of PVAc exhibited two different degrees of improvement due to the addition of hindered phenol. Moreover, DSC results showed that all hybrids were miscible, as concentration fluctuations changed irregularly. In accordance with the XRD observation of only amorphous hindered phenols existing in the PVAc matrix, further MD simulation, based on an amorphous cell, characterized the number of H-bonds, the binding energy and the fractional free volume (FFV) of the hybrids. It was observed that the variation tendency of the simulation data was in accordance with the experimental results. Therefore, the damping mechanism of PVAc/hindered phenol hybrids was proposed through a detailed analysis on the synergistic effect of the number of intermolecular H-bonds and the binding energy between PVAc and the hindered phenol, as well as the FFV or dynamic heterogeneity.

The molecular dynamics of different relaxation modes in asymmetric chlorinated butyl rubber/petroleum resin blends

The relaxation behavior and different modes of molecular motion in the miscible blends of asymmetric chlorinated butyl rubber (CIIR) and petroleum resin (PR) were investigated by dynamic mechanical spectroscopy (DMS) and dielectric spectroscopy (DS). The different modes of CIIR molecular motion, attributed to local segmental motion, sub-Rouse modes and Rouse mode relaxation, have been detected from both of the DMS and DS results, and the relaxation times of local segmental motion and Rouse modes could be fitted by the Vogel–Fulcher–Tammann equation. Due to the increased activation energy with increasing PR content, local segmental motion of CIIR is slightly confined, however, Rouse modes of CIIR, which contain more backbone bonds and need a larger free volume than the local segmental motion, are greatly confined. As a result, the relaxation temperature of local segmental motion moves slightly to high temperature but that of Rouse modes moves to high temperature more significantly.

Puncture characterization of multilayered polypropylene homopolymer/ethylene 1-octene copolymer sheets

This paper presents the studies of the puncture resistances of conventional blend and multilayered structure sheets. The polypropylene homopolymer (HPP)/ethylene 1-octene copolymer (POE) alternating multilayered sheets were prepared though multilayered coextrusion. Polarized optical microscope (POM) photographs revealed that HPP and POE layers aligned alternately vertical to the interfaces and continuously parallel to the extrusion direction, indicating a better laminate structure. Puncture results demonstrated the conventional blend was less puncture-resistant than the multilayered samples. Obvious interfacial delamination occurred in the multilayered structure during crack propagation, causing the puncture behavior to develop into a staged rupture behavior. Hence the puncture resistance was enhanced by the special energy absorbing mechanisms including the plastic deforming independently, interfacial delamination and ductile tearing of the layers.

Comparative Studies on Enhanced Interfacial Adhesion between PE and PA6 through Two Routes in a Sequential Injection Molding Process

The interfacial adhesion of polyethylene (PE) and polyamide 6 (PA6) was enhanced via reactive compatibilization in a sequential injection molding process through PE+PE-MAH/PA6 bilayer system and PE/tie layer/PA6 sandwich system in this article. The experimental results showed that the crack propagation for sandwich system changed from the adhesive interface to a thin layer in the bulk of PE with increasing molding temperature. More copolymers were in-situ formed at sandwich interface. Therefore, stronger interfacial adhesion of PE/PA6 obtained in sandwich system was presumably attributed to higher interfacial temperature formed at sandwich interface during sequential injection molding process.