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The semi-hyperbolic (SHPB) die with and possibly without wall lubrication has been proposed as a device for measuring the elongational viscosity of polymeric fluids. Using numerical simulation under the condition of complete wall slip, it was found for two polyethylenes (LDPE and LLDPE) that the calculated elongational viscosity values agreed well with strain-averaged values, , obtained from independent measurements in stretching type rheometers. This is in agreement with the original hypothesis of Everage and Ballman (E-B). Numerical simulations showed that the Baird and Huang (B-H) approach for calculating , which accounts for the shear stress due to geometric considerations in the presence of complete slip, agreed with data better than did the E-B approach. Numerical simulations using varying degrees of wall slip indicated that reasonable values of could be obtained using the B-H approach with wall slip levels which could be most likely reached using a coating such as a flouroelastomer. The numerical simulations provided an explanation as to why the elongational viscosity values determined in the SHPB die for resins such as LDPE, which are extensional-strain hardening, are less sensitive to wall slip than non-strain-hardening resins such as LLDPE.

ABSTRACT The compressive stress relaxation tests of butadiene rubber (BR) at different thermo-oxidative aging temperatures were carried out. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) was used to observe the variations of internal groups before and after the thermo-oxidative aging. Magnetic resonance-crosslink density (MR-XLD) spectroscopy was used to measure the crosslink densities. The results showed the compressive stress relaxation of BR during thermo-oxidative aging was dominated by chemical reactions: crosslinking, chain scission, and oxidation. Then an empirical model and an amendatory standard linear solid (SLS) model were put forward to describe the compressive stress relaxation behavior of BR. Both models fitted the data well. The SLS model, based on the aging mechanism of BR, not only made up the disadvantages of the empirical model, but also considered the changes of intrinsic viscosity (η) during the thermo-oxidative aging of BR. The SLS model showed that the thermo-oxidative aging of BR was mainly dominated by the crosslinking and oxidation reactions. This research proposes the amendatory SLS model and has important significance for study the stress relaxation behavior of crosslinked rubbers during thermo-oxidative aging. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44630. [ABSTRACT FROM AUTHOR]

Natural rubber (NR) composites highly filled with nano-α-alumina (nano-α-Al2O3) modified in situ by the silane coupling agent bis-(3-triethoxysilylpropyl)-tetrasulfide (Si69) were prepared. The effects of various modification conditions and filler loading on the properties of the nano-α-Al2O3/NR composites were investigated. The results indicated that the preparation conditions for optimum mechanical (both static and dynamic) properties and thermal conductivity were as follows: 100 phr of nano-α-Al2O3, 6 phr of Si69, heat-treatment time of 5 min at 150°C. Furthermore, two other types of fillers were also investigated as thermally conductive reinforcing fillers for the NR systems: (1) hybrid fillers composed of 100 phr of nano-α-Al2O3 and various amounts of the carbon black (CB) N330 and (2) nano-γ-Al2O3, the particles of which are smaller than those of nano-α-Al2O3. The hybrid fillers had better mechanical properties and dynamic performance with higher thermal conductivity, which means that it can be expected to endow the rubber products serving under dynamic conditions with much longer service life. The smaller sized nano-γ-Al2O3 particles performed better than the larger-sized nano-α-Al2O3 particles in reinforcing NR. However, the composites filled with nano-γ-Al2O3 had lower thermal conductivity than those filled with nano-α-Al2O3 and badly deteriorated dynamic properties at loadings higher than 50 phr, both indicating that nano-γ-Al2O3 is not a good candidate for novel thermally conductive reinforcing filler. POLYM. COMPOS., 37:771-781, 2016. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

A combined study of experimental and molecular dynamics (MD) simulation methods is presented for hindered phenol AO-80/nitrile-butadiene rubber/poly(vinyl chloride) (AO-80/NBR/PVC) composites with different AO-80 contents to establish the microstructure-damping property relations. MD simulation found that the AO-80/NBR/PVC composite (abbreviated as AO-80/NBVC) with an AO-80 content of 99 phr had the largest hydrogen bonds (H-bonds) and highest binding energy, indicating a good compatibility between NBR and AO-80 and good damping performance of AO-80/NBVC composites. Experimental results from SEM, DSC, and DMA were in good agreement with the MD simulation results. The tensile test results showed that the AO-80/NBVC composite with an AO-80 content of 99 phr had high tensile strength because of the strong H-bonds of the composites and the disintegration and reintegration of the H-bonds. The MD simulation technique proves to be a promising tool for the design and prediction of high damping properties of advanced composites in a microscopic view. [ABSTRACT FROM AUTHOR]

In this paper, graphene oxide/styrene-butadiene rubber (GO/SBR) composites with complete exfoliation of GO sheets were prepared by aqueous-phase mixing of GO colloid with SBR latex and a small loading of butadiene-styrene-vinyl-pyridine rubber (VPR) latex, followed by their co-coagulation. During co-coagulation, VPR not only plays a key role in the prevention of aggregation of GO sheets but also acts as an interface-bridge between GO and SBR. The results demonstrated that the mechanical properties of the GO/SBR composite with 2.0 vol.% GO is comparable with those of the SBR composite reinforced with 13.1 vol.% of carbon black (CB), with a low mass density and a good gas barrier ability to boot. The present work also showed that GO-silica/SBR composite exhibited outstanding wear resistance and low-rolling resistance which make GO-silica/SBR very competitive for the green tire application, opening up enormous opportunities to prepare high performance rubber composites for future engineering applications. [ABSTRACT FROM AUTHOR]

The use of conductive polymer composites (CPCs) as strain sensors has been widely investigated. A wide range of strain sensitivities and high repeatability are vital for different applications of CPCs. In this study, the relations of the conductive filler network and the strain-sensing behavior and electrical stability under fatigue cycles were studied systematically for the first time based on the conductive polymethylvinylsiloxane (PMVS) composites filled with both carbon nanotubes arrays (CNTAs) and carbon black (CB). It was proved that the composites could be fabricated with large strain-sensing capability and a wide range of strain sensitivities by controlling the volume ratio of CNTA/CB and their amounts. Additionally, the CNTA/CB/PMVS composite with 3 vol % content of fillers showed high sensitivity (GF is 10 at 60% strain), high repeatability (the relative standard deviation (RSD) of the max R / R ₀ value is 3.58%), and electrical stability under fatigue cycles (value range of R / R ₀ is 1.62 to 1.82) at the same time due to the synergistic effects of the dual conductive network of CNTAs and CB. This could not be achieved by relying on a single CNTA or CB conductive network. This study may provide guidance for the preparation of high performance CPCs for applications in strain sensors.