Research and Development of High-Performance High-Damping Rubber Materials for High-Damping Rubber Isolation Bearings: A Review

Natural Rubber/Styrene-Butadiene Rubber Blend Composites Potentially Applied in Damping Bearings

Natural rubber (NR) composites have been widely applied in damping products to reduce harmful vibrations, while rubber with only a single composition barely meets performance requirements. In this study, rubber blend composites including various ratios of NR and styrene butadiene rubber (SBR) were prepared via the conventional mechanical blending method. The effects of the rubber components on the compression set, compression fatigue temperature rising and the thermal oxidative aging properties of the NR/SBR blend composites were investigated. Meanwhile, the dynamic mechanical thermal analyzer and rubber processing analyzer were used to characterize the dynamic viscoelasticity of the NR/SBR blend composites. It was shown that, with the increase in the SBR ratio, the vulcanization rate of the composites increased significantly, while the compression fatigue temperature rising of the composites decreased gradually from 47 °C (0% SBR ratio) to 31 °C (50% SBR ratio). The compression set of the composites remained at ~33% when the SBR ratio was no more than 20%, and increased gradually when the SBR ratio was more than 20%.

A Novel Method to Characterize the Damping Capacity of EPDM/CIIR Blends Using Vibrating Rubber Balls

An experimental device fixed with a laser displacement sensor was assembled to investigate the rebound behaviors and damping mechanism of rubber balls prepared with ethylene-propylene-diene monomer (EPDM)/chlorinated butyl rubber (CIIR) blends. The result showed that a prediction model was proposed to characterize the damping capacity by using the rebound height of the rubber balls. The lower rebound height corresponded to better damping capacity. A modified equation relating to the rebound height has been obtained from the theoretical derivation on the basis of the dynamic mechanical analysis, showing that the rebound height was affected by the deformation frequency, the external excitation, and the nature of rubber blends. Furthermore, the energy dissipation rate (EDR), defined by the ratio of the height loss to the rebound time, was proposed to further characterize the damping capacity. The EDR value was shown to be highest for the pure CIIR and lowest for the pure EPDM, exhibiting a decreasing trend with the increase in EPDM content in the rubber blends. It can be expected that the damping capacity of the EPDM/CIIR blends decreases with the decrease in external excitation, the conclusion of which plays a key role in the formulation design of viscoelastic damping rubber materials.

Synergistic Development of Natural Rubber/Butyl Rubber Composites for Improved Interfacial Bonding and Enhanced Shock-Absorbing Capabilities

Shock-absorbing materials play a vital role in various industrial sectors, including construction and transportation. Among these materials, natural rubber (NR) stands out due to its exceptional elastic and mechanical properties, coupled with its robust crack resistance. Nevertheless, with the rising demand for enhanced damping capacities, there is a need to further optimize the damping performance of NR. One direct approach is to blend it with high-damping rubber. Butyl rubber (IIR) is a prominent member of the high-damping rubber category. Integrating IIR effectively with the NR, however, presents challenges. These challenges arise from IIR's inherent characteristics, such as its low unsaturation, slower vulcanization rate, and restricted compatibility with NR. Addressing these challenges, our study employed isoprene and isobutene to synthesize a variant of butyl rubber with a higher degree of unsaturation-achieving an unsaturation level between 4 and 6 mol %. Notably, this heightened unsaturation significantly expedited the curing time of IIR and facilitated the concurrent vulcanization of both IIR and NR. Utilizing atomic force microscopy, we observed that the introduction of unsaturated double bonds ameliorated the compatibility between NR and IIR, leading to an interfacial region extending up to 1000 nm. Our tests using a dynamic mechanical analyzer and rubber processing analyzer demonstrated the material's damping temperature range. Furthermore, there was a noticeable rise in the loss factor (tan δ) at ambient temperature, which remains over 0.1 across both a frequency window of 0.2 to 5 Hz and a strain spectrum of 10 to 200%. This tan δ enhancement ensured the potential of these rubber composites for shock-absorbing applications.

Developing a New Constitutive Model of High Damping Rubber by Combining GRU and Attention Mechanism

High damping rubber (HDR) bearings are extensively used in seismic design for bridges due to their remarkable energy dissipation capabilities, which is critical during earthquakes. A thorough assessment of crucial factors such as temperature, rate, experienced maximum amplitude, and the Mullins effect of HDR on the mechanics-based constitutive model of HDR is lacking. To address this issue, we propose a deep learning approach that integrates the Gate Recurrent Unit (GRU) and attention mechanism to identify time series characteristics from compression-shear test data of HDR specimens. It is shown that the combination of GRU and attention mechanism enables accurate prediction of the mechanical behavior of HDR specimens. Compared to the sole use of GRU, this suggested method significantly reduces model complexity and computation time while maintaining good prediction performance. Therefore, it offers a new approach to constructing the HDR constitutive model. Finally, the HDR constitutive model was used to analyze the impact of experienced maximum amplitudes and cycles on following processes. It was observed that maximum amplitudes directly influence the stress-strain relationship of HDR during subsequent processes. Consequently, a solid foundation is laid for evaluating the responses of HDR bearings under earthquakes.

The Contribution of BaTiO3 to the Stability Improvement of Ethylene-Propylene-Diene Rubber: Part I-Pristine Filler

This study presents the functional effects of BaTiO₃ powder loaded in ethylene-propylene-diene rubber (EPDM) in three concentrations: 0, 1, and 2.5 phr. The characterization of mechanical properties, oxidation strength, and biological vulnerability is achieved on these materials subjected to an accelerated degradation stimulated by their γ-irradiation at 50 and 100 kGy. The thermal performances of these materials are improved when the content of filler becomes higher. The results obtained by chemiluminescence, FTIR-ATR, and mechanical testing indicate that the loading of 2.5 phr is the most proper composition that resists for a long time after it is γ-irradiated at a high dose. If the oxidation starts at 176 °C in the pristine polymer, it becomes significant at 188 and 210 °C in the case of composites containing 1 and 2.5 phr of filler, respectively. The radiation treatment induces a significant stability improvement measured by the enlargement of temperature range by more than 1.5 times, which explains the durability growth for the radiation-processed studied composites. The extension of the stability period is also based on the interaction between degrading polymer substrate and particle surface in the composite richest in titanate fraction when the exposure is 100 kGy was analyzed. The mechanical testing as well as the FTIR investigation clearly delimits the positive effects of carbon black on the functionality of EPDM/BaTiO₃ composites. The contribution of carbon black is a defining feature of the studied composites based on the nucleation of the host matrix by which the polymer properties are effectively ameliorated.

Blending to Make Nonhealable Polymers Healable: Nanophase Separation Observed by CP/MAS 13 C NMR Analysis

Can commodity polymers are made to be healable just by blending with self-healable polymers? Here we report the first study on the fundamental aspect of this practically challenging issue. Poly(ether thiourea) (PTUEG₃ ; T_g =27 °C) reported in 2018 is extraordinary in that it is mechanically robust but can self-heal even at 12 °C. In contrast, poly(octamethylene thiourea) (PTUC₈ ; T_g =50 °C), an analogue of PTUEG₃ , cannot heal below 92 °C. We found that their polymer blend self-healed in a temperature range above 32 °C even when its PTUEG₃ content was only 20 mol %. Unlike PTUEG₃ alone, this polymer blend, upon exposure to high humidity, barely plasticized, keeping its excellent mechanical properties due to the non-hygroscopic nature of the PTUC₈ component. CP/MAS ¹³ C NMR analysis revealed that the polymer blend was nanophase-separated, which possibly accounts for why such a small amount of PTUEG₃ provided the polymer blend with humidity-tolerant self-healable properties.

Influence of Alternating Multi-Layered Design on Damping Characteristics of Butyl Rubber Composites and a New Idea for Achieving Wide Temperature Range and High Damping Performance

This paper investigates the influence of an alternating multi-layered design on the material loss factor and effective temperature range of free/constrained-damping butyl rubber, and then proposes a new method of designing materials with high damping properties and a wide temperature range. First, the wide-temperature rubber IIR-0, the low-temperature rubber IIR-1, the medium-temperature rubber IIR-2, and the high-temperature rubber IIR-3 are prepared and characterized. Second, the influences of an alternating multi-layered design on the damping peak values and temperature range of free damping and micro-constrained damping of the rubber types are investigated. Finally, different methods for broadening the damping temperature range and improving the damping loss factor are discussed. The results show that the loss factor of the alternating multi-layered, constrained damping structure is increased to 0.488, while that of the free-damping structure is increased to 0.845. Their damping-temperature ranges are increased to 89.4 °C and 93.2 °C, respectively. A wide temperature range and high damping performance can be achieved by the alternating multi-layered design of rubber/plastic micro-constrained damping composites.

Modeling of Hyper-Viscoelastic Properties of High-Damping Rubber Materials during the Cyclic Tension and Compression Process in the Vertical Direction

With the rapid development of the economy and urbanization, the construction of the urban rail transit system has had a great impact on the work, life, and health of residents in buildings along the rail transit line. Thus, it is particularly urgent and necessary to develop base isolation technologies to control and reduce the impact of vibrations of rail transit systems on building structures. High-damping rubber isolation bearings have shown significant effectiveness in the reduction of this impact, and their isolation performance mainly depends on the mechanical and damping energy dissipation characteristics of the high-damping rubber material. This paper aims to investigate the hyper-viscoelastic properties of the high-damping rubber material used for high-damping rubber isolation bearings during the cyclic tension and compression process in the vertical direction. These properties include hyperelastic parameters, viscoelastic coefficients, and the relaxation times of the material. For this purpose, uniaxial cyclic tension and compression tests were conducted. A three-element Maxwell rheological model combining a strain energy density function was proposed for modeling the hyper-viscoelastic behaviors of the materials during the cyclic tension and compression process. Based on the obtained results, an iterative identification procedure was used to determine the constitutive parameters of the material for each loading-unloading cycle. The aforementioned parameters were further expressed as a function of the number of cycles. New insights into hyper-viscoelastic property changes in this high-damping rubber material during the cyclic tension and compression process were gained in this work. These investigations could facilitate the development of computational tools, which would regulate fundamental guidelines for the better controlling and optimization of the isolation performance of the high-damping rubber material used for high-damping rubber isolation bearings, which have a wider perspective of applications in the urban rail transit system.

Mesoporous Spherical Silica Filler Prepared from Coal Gasification Fine Slag for Styrene Butadiene Rubber Reinforcement and Promoting Vulcanization

Coal gasification fine slag (CFS) is a solid contaminant produced by an entrained flow gasifier, which pollutes fields and the air in the long term. CFS is a potential polymer reinforcement filler and has been used in polypropylene and acrylonitrile butadiene styrene resins. Coal gasification fine slag mesoporous silica (FS-SiO₂) was prepared by acid leaching, calcination, and pH adjustment, with a larger specific surface area and less surface hydroxyl compared to the commercial precipitated silica (P-silica). The cure characteristics, crosslink density, mechanical properties, the morphology of the tensile fractures, dynamic mechanics, and rubber processing of the prepared styrene butadiene rubber (SBR) composites filled with P-silica and FS-SiO₂ were analyzed, respectively. The results indicated that FS-SiO₂ was dispersed more uniformly in the SBR matrix than P-silica owing to its smaller amount of surface hydroxyl and spherical structure, resulting in a better mechanical performance and wet skid resistance. In particular, the SBR composites with a filler pH of 6.3 exhibited the highest crosslink density and tensile strength, being superior to commercial P-silica. Significantly, the curing time decreased with the increase in the pH of FS-SiO₂, which caused the rubber processing to be more efficient. This strategy can reduce the cost of rubber composites and the environmental pollution caused by CFS.