Nitrogen/oxygen permeability of natural rubber, epoxidised natural rubber and natural rubber/epoxidised natural rubber blends

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.

Computational Investigation of Dual Filler-Incorporated Polymer Membranes for Efficient CO2 and H2 Separation: MOF/COF/Polymer Mixed Matrix Membranes

Mixed matrix membranes (MMMs) composed of two different fillers such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) embedded into polymers provide enhanced gas separation performance. Since it is not possible to experimentally consider all possible combinations of MOFs, COFs, and polymers, developing computational methods is urgent to identify the best performing MOF-COF pairs to be used as dual fillers in polymer membranes for target gas separations. With this motivation, we combined molecular simulations of gas adsorption and diffusion in MOFs and COFs with theoretical permeation models to calculate H₂, N₂, CH₄, and CO₂ permeabilities of almost a million types of MOF/COF/polymer MMMs. We focused on COF/polymer MMMs located below the upper bound due to their low gas selectivity for five industrially important gas separations, CO₂/N₂, CO₂/CH₄, H₂/N₂, H₂/CH₄, and H₂/CO₂. We further investigated whether these MMMs could exceed the upper bound when a second type of filler, a MOF, was introduced into the polymer. Many MOF/COF/polymer MMMs were found to exceed the upper bounds showing the promise of using two different fillers in polymers. Results showed that for polymers having a relatively high gas permeability (≥10⁴ barrer) but low selectivity (≤2.5) such as PTMSP, addition of the MOF as the second filler can have a dramatic effect on the final gas permeability and selectivity of the MMM. Property-performance relations were analyzed to understand how the structural and chemical properties of the fillers affect the permeability of the resulting MMMs, and MOFs having Zn, Cu, and Cd metals were found to lead to the highest increase in gas permeability of MMMs. This work highlights the significant potential of using COF and MOF fillers in MMMs to achieve better gas separation performances than MMMs with one type of filler, especially for H₂ purification and CO₂ capture applications.

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

At present, high-damping rubber materials, widely used in the field of engineering seismic isolation, generally have the problems such as narrow effective damping temperature range, low damping loss factor and strong temperature dependence, which lead to prominent dependence of temperature and load conditions of the isolation performance of high-damping rubber isolation bearings. Research and development of high-performance high-damping rubber materials with broad effective damping temperature range, high damping loss factor and weak temperature dependence are very urgent and necessary to ensure the safety of the seismic isolation of engineering structures. This paper mainly reviews the recent progress in the research and development of high-damping rubber materials using nitrile butadiene rubber (NBR), epoxidized natural rubber (ENR), ethylene propylene diene rubber (EPDM), butyl rubber (IIR), chlorinated butyl rubber (CIIR), and bromine butyl rubber (BIIR). This is followed by a review of vulcanization and filler reinforcement systems for the improvement of damping and mechanical properties of high-damping rubber materials. Finally, it further reviews the constitutive models describing the hyperelasticity and viscoelasticity of rubber materials. In view of this focus, four key issues are highlighted for the development of high-performance high-damping rubber materials used for high-damping rubber isolation bearings.

Sustainable Epoxidized Guayule Natural Rubber, Blends and Composites with Improved Oil Resistance and Greater Stiffness

Production of petroleum-based synthetic rubbers (SRs) causes an enormous carbon footprint for the rubber industry. Carbon footprint would be reduced if natural rubber (NR) could take a larger market share and replace significant quantities of SR. However, some SRs have higher oil resistance than NRs, and, in applications where these properties are needed, chemically modified NR will be required. Epoxidation is a chemical modification of NR which partially converts unsaturated bonds on the backbone of NR to epoxy groups. In this research, epoxidized guayule natural rubber (EGNR)/guayule natural rubber (GNR) blends and GNR were used to make carbon black (CB) filled composites. The processability, mechanical properties, swelling behaviors and dynamic mechanical properties were characterized at various epoxide fractions. Composites made with EGNR/GNR had higher oil resistance, wet traction and stiffness than GNR composites, although tensile strength and elongation at break were reduced by epoxidation. EGNR is expected to lead to the development of new NR products with similar properties to SR, eroding SR markets and increasing the sustainability of the rubber industry.

Influence of thermal treatment on the properties and intermolecular interactions of epoxidized natural rubber-salt systems

The influence of thermal treatment on the thermal stability, thermal properties, dielectric properties and intermolecular interaction of binary epoxidized natural rubber (ENR)-salt systems, which may be a candidate for solid polymer electrolytes (SPEs) was investigated. Solubility of salt in ENR enhances, which may be due to the disruption of the lightly-crosslinked microgel under heat treatment. The increase in the ionic conductivities of the thermally treated ENR SPEs at constant salt content is correlated to the higher glass transition temperatures, development of percolation network and higher extent of intermolecular interactions between ENR and charged entities in this study.

The Effect of Epoxidation on Strain-Induced Crystallization of Epoxidized Natural Rubber

The effect of epoxidation on strain-induced crystallization (SIC) of epoxidized natural rubber (ENR) and mechanism are studied with synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) and polarized infrared spectroscopy (P-IR). WAXD results reveal that appropriate epoxidation, for example, ENR-25 epoxidized with ≈25% isoprene units, can unexpectedly enhance the SIC of natural rubber (NR), resulting in the improvement of tear resistance. On the other hand, exorbitant epoxidation, for example, ENR-40 epoxidized with ≈40% isoprene units, depresses the SIC and weakens the mechanical properties of NR remarkably. P-IR studies reveal that epoxidation can promote the orientation of chain segments along the stretching direction, which plays a determining role on SIC of NR. Accordingly, hierarchical multiscale schematic models are proposed. This insight into epoxidation on SIC of ENR strongly suggests that ENR with appropriate epoxidation degree is a promising candidate material for the fabrication of high-performance engineering rubber products.

PROBING THE POSTGELATION REACTIONS OF EPOXIDIZED NATURAL RUBBER CROSS-LINKED WITH DODECENYL SUCCINIC ANHYDRIDE

Pregelled mixes of an epoxidized natural rubber, known as ENR50, containing dodecenyl succinic anhydride (DDSA) as cross-linking agent and dimethyl benzyl amine (DMBA) as catalyst, were cured isothermally at 160 °C, and the progress of the reactions was followed by both thermal analysis (differential scanning calorimetry and thermogravimetric analysis [TGA]) and infrared spectroscopy (Fourier transform near-infrared and attenuated total reflection). The curing reactions were found to be approximately first order for both heat of reaction associated with cross-linking and the disappearance of the epoxy groups, even though the reduction of epoxy group concentration was found to be substantially greater than the amount expected from reactions with the anhydride, because of the formation of large quantities of vicinal OH groups. The TGA data have indicated that the pregelled mixes undergo more extensive anaerobic degradation at higher temperatures than the un–cross-linked elastomer, which is accelerated by the presence of the DMBA catalyst.

Chemically crosslinked yet reprocessable epoxidized natural rubber via thermo-activated disulfide rearrangements

Disulfide crosslinks introduced into an ENR matrix enable the thermo-activated reprocessing of the chemically crosslinked rubber, studied in terms of stress relaxation and adhesion experiments.

Breathable Film from Reactive Processing of LLDPE/NR Blends with ENR and Maleic Anhydride

The high oxygen permeability film, so-called breathable film, can be produced via reactive blending and processing of linear-low density polyethylene, natural rubber, and epoxidized natural rubber with a small content of maleic anhydride as a reactive coagent. The foam-like structure of the produced breathable film was created by the reaction between the functional groups during the extrusion. Oxygen permeability of the blended films can be controlled by the blend composition, screw speed, and draw ratio during the chill-roll casting step. The blended films exhibit not only the good breathablility but also the outstanding UV screening with a small transparency trade-off. These properties are suitable for the films to be used in agricultural applications to enhance the growing and production of fruit trees, flowers, vegetables, and even grains, especially during the growing stage of plants.

Autonomic self-healing in epoxidized natural rubber

The development of polymers that can repair damage autonomously would be useful to improve the lifetime of polymeric materials. To date, limited attention has been dedicated to developing elastomers with autonomic self-healing ability, which can recover damages without need for an external or internal source of healing agents. This work investigates the self-healing behavior of epoxidized natural rubber (ENR) with two different epoxidation levels (25 and 50 mol % epoxidation) and of the corresponding unfunctionalized rubber, cis-1,4-polyisoprene (PISP). A self-adhesion assisted self-healing behavior was revealed by T-peel tests on slightly vulcanized rubbers. A higher epoxidation level was found to enhance self-healing. Self-healing of rubbers following ballistic damages was also investigated. A pressurized air flow test setup was used to evaluate the self-healing of ballistic damages in rubbers. Microscope (OM, SEM, and TEM) analyses were carried out to provide further evidence of healing in the impact zones. Self-healing of ballistic damages was observed only in ENR with 50 mol % epoxidation and it was found to be influenced significantly by the cross-link density. Finally, self-healing of ballistic damages was also observed in ENR50/PISP blends only when the content of the healing component (i.e., ENR50) was at least 25 wt %. From an analysis of the results, it was concluded that a synergistic effect between interdiffusion and interaction among polar groups leads to self-healing in ENR.