ABSTRACT EPDM is recognized for its outstanding flexural resistance, resilience, low-temperature performance, and chemical stability, making it suitable for applications in the automotive, sealing, and waterproofing industries. However, a key challenge for this type of rubber-based compound is its susceptibility to thermal, mechanical, or oxidative stressors, even under standard operating conditions. Consequently, accurately predicting the service life of these materials is critical to ensure their reliability in practical applications. We propose an accelerated aging methodology to estimate the lifespan of EPDM under thermal and hygrothermal environments. Accelerated thermal aging tests were performed at 70, 80, and 100 °C. For hygrothermal conditions, the tests were conducted at 23, 70, and 80 °C, with relative humidity levels between 50 and 95%. In both cases, the exposure durations varied from 22 to 672 h. Properties such as tensile strength, elongation at break, tear strength, compressive strength, and hardness, specific gravity, and X-ray photoelectron spectroscopy analysis of the rubber were systematically studied before and after aging. Nevertheless, using the Arrhenius, Peck, and Luo, Wu, and Wu models, shelf life was predicted from the laboratory-based aging data, with a compression set at 25% selected as the failure criterion. It was observed that hygrothermal conditions had a more significant effect on deterioration than thermal aging alone. Thus, this approach provides a valuable framework for assessing the durability of polymeric materials, instilling confidence in their application under specified service conditions.
ABSTRACT Tread wear is one of the indicators determining the service life of tires. Because electric vehicles are heavier overall and exhibit greater starting torque than fuel cars, tread wear is more severe. This study aims to clarify and establish the correlation between laboratory abrasion and tire road wear. Specifically, we compared tire road wear against several standard abrasion metrics: Laboratory Abrasion Tester 100 (LAT 100) (at various slip angles), Akron, Lambourn, and Deutsches Institut für Normung (DIN) methods. LAT 100 abrasion at 5.5° slip angle exhibits the strongest correlation with tire road wear. The causes are analyzed in combination with the tire service conditions of the tread. The Lambourn abrasion at 15% longitudinal slip ratio shows a similar trend with the tire road wear. The Akron abrasion condition is 15° slip angle, and the DIN abrasion condition is 100% longitudinal slip ratio, both of which are different from the tread of passenger vehicle service conditions; therefore, their correlations with tire road wear are poor. This study clarified the correlation between different laboratory abrasions and tire road wear and demonstrated the importance of selecting the proper laboratory test condition reflecting service driving conditions. Furthermore, the influence of friction energy and the proportions of longitudinal and lateral friction energies on the abrasion patterns are analyzed to understand the roles of the longitudinal and lateral friction in abrasion.
ABSTRACT The devulcanization of rubber vulcanizates and rubber waste products remains a major technological and environmental challenge, particularly in achieving selective network breakdown without significant main chain degradation. From a novel and unusual perspective, we introduced liquid metal gallium (Ga) as a mechanochemical devulcanizing agent to induce selective devulcanization of sulfur-crosslinked NR, prepared using a semi-efficient curing system. Ga-filled NR compounds exhibited significant network degradation in the 150–170 °C range compared with similar compounds without Ga, realized by rheometric torque. This rheometric investigation revealed that at 160 °C, a sharp drop in torque occurs after a certain torque value is reached and that a quasi-stationary state is established after ∼30 min. This effect became even more pronounced at higher temperatures, indicating active degradation of the sulfur networks during the postcuring process. The extent of network degradation was quantified through sol fraction, crosslink density, and degree of devulcanization at different thermal treatment times and temperatures. The Ga-based compounds showed an increase in sol fraction and degree of devulcanization with increasing cure time and temperature, whereas the crosslink density decreased as expected under the same conditions. To understand the nature of the crosslinked network degradation, a comparative analysis was performed using Horikx’s model: the model predicted selective chain degradation while preserving the main chain of the rubber. These results demonstrated a new mechanochemical pathway for the selective devulcanization of sulfur-crosslinked NR.
ABSTRACT Superhydrophobic materials have significant industrial application value in self-cleaning and oil–water separation. Thus, a β-nucleating agent–modified polypropylene (PP)/EPDM terpolymer thermoplastic vulcanizate (TPV) was fabricated, and a rough surface texture was constructed using metallographic sandpaper as a template. The resulting material exhibited superhydrophobicity, self-cleaning capability, and pressure-responsive oil–water separation performance. The results show that after hot-pressing PP/EPDM TPVs with W10 metallographic sandpaper, the surface contact angle of the TPVs increased to 154.3°, the sliding angle decreased to 3.1°, and the surface energy decreased to 12.2 mN·m −1 , indicating a remarkable improvement in superhydrophobic performance. Furthermore, with the incorporation of a β-nucleating agent into the PP phase of PP/EPDM TPVs, the loose stacking of β-crystal molecular chains facilitated plastic deformation, leading to a further enhancement of surface roughness after sandpaper templating. Consequently, the surface contact angle increased to 157.8°, the sliding angle decreased to 2.8°, and the surface energy was reduced to 11.3 mN·m −1 . Under both sliding and rolling self-cleaning test modes, the TPVs with β-nucleating agent exhibited excellent self-cleaning behavior. In oil–water separation experiments, the β-nucleating agent–modified superhydrophobic TPV films demonstrated rapid separation, high selectivity, and pressure-responsive characteristics across various oil–water mixtures. The critical pressure difference between oil and water phases reached as high as 4.10 kPa, and the separation efficiency remained >95.0%, even under strong suction forces. New insights are presented on the development of efficient and sustainable materials for oil–water separation and self-cleaning applications.
ABSTRACT The quest for sustainable, greener, low-cost energy storage has propelled solid-state sodium-ion batteries as a vital alternative to lithium-based systems. A solid polymer electrolyte (SPE) comprising a poly(ethylene oxide) (PEO) and 50% epoxidized NR (ENR50) blend doped with NaCF 3 SO 3 was investigated. Incorporation of the biobased ENR50 elastomer improves flexibility and promotes ion transport by suppressing PEO crystallinity and enhancing amorphous conduction pathways. An optimal salt loading of 25 wt% NaCF 3 SO 3 delivered the highest room temperature ionic conductivity of 1.00 × 10 −5 S cm −1 . Temperature-dependent conductivity followed Arrhenius behavior, with two distinct regions at 30–60 °C ( E a1 = 1.27 eV) and 60–100 °C ( E a2 = 0.19 eV; σ 2 = 8.57 × 10 −2 S cm −1 ), suggesting a temperature-driven structural transition. Differential scanning calorimetry confirmed a semicrystalline-to-amorphous transition with a melting temperature event at ∼60 ± 10 °C, consistent with the observed increase in ionic mobility. Compared with lithium analog (PEO-ENR50-LiCF 3 SO 3 ), the sodium-based system exhibited improved electrochemical performance, achieving a higher sodium-ion transference number (0.23) than the lithium-ion transference number (0.06). Both systems showed dominant ionic conduction, with total ion transport numbers approaching 0.99. Attenuated total reflectance Fourier transform infrared spectroscopy confirmed polymer–salt coordination at the PEO ether group (∼1099 cm −1 ), whereas thermogravimetric analysis demonstrated improved thermal stability upon salt incorporation. Linear sweep voltammetry revealed a wide electrochemical stability window up to 5.0 V. Overall, these results demonstrate the synergistic role of ENR50 in combining mechanical compliance with improved ionic transport, highlighting its potential as a high-voltage SPE for next-generation sodium-ion batteries.
ABSTRACT The construction of the matrix polyurethane (PU) network during the curing process of solid rocket propellants critically determines the mechanical properties, aging behavior, and service life of the propellant. The molecular weight of hydroxyl-terminated polybutadiene (HTPB), a key structural parameter, significantly influences the curing reaction kinetics of HTPB with toluene diisocyanate (TDI) and the ultimate network architecture. The curing reaction mechanism, curing reaction kinetics, and the properties of HTPB-TDI system are systematically investigated using molecular dynamics simulation, isothermal infrared spectroscopy, isothermal rheology, equilibrium swelling method, dynamic mechanical analyzer, and differential scanning calorimetry. The results demonstrate that the curing reaction of the HTPB-TDI system follows second-order reaction kinetics, and with the decrease of molecular weight, the specific reaction rate constant of HTPB-TDI curing system increases, the reaction rate increases significantly, and the crosslinking density increases, glass transition temperature ( T g ) increases, and loss factor (tan δ) decreases. The decrease of molecular weight makes the curing reaction easier to carry out, and the rigidity of material was improved. These findings provide theoretical guidance and reference for optimizing materials and processes in the production of HTPB-TDI PU curing.
ABSTRACT The performance of silica-filled SBR nanocomposites is strongly governed by the ability of organosilane coupling agents to promote favorable silica–polymer interactions while suppressing filler–filler association. We used fully atomistic molecular dynamics simulations to compare eight coupling agents in a range of surface grafting densities and to quantify silica–SBR compatibility by using two complementary metrics: a solubility-distance parameter and the silica–polymer interaction energy. Both approaches yield consistent trends, showing that increasing grafting density strengthens interfacial affinity with diminishing returns at high surface coverage due to steric crowding and saturation. Clear chemistry-dependent differences are observed: for example, 4-methyl-1-(3-triethoxysilylpropyl)-piperazine provides efficient surface shielding already at intermediate grafting densities, whereas simpler alkyl- and thiol-based agents deliver weaker stabilization despite comparable extension into the polymer phase. Interfacial analysis further shows that chain extension alone is not predictive of compatibility; rather, the organization of the grafted layer and the resulting shielding of the silica surface are key determinants. Finally, a cost-accuracy comparison supports the solubility-distance metric as an efficient first-pass screening tool, whereas interaction-energy calculations and targeted structural descriptors provide deeper mechanistic insight for selected organosilane candidates.
ABSTRACT A systematic study was conducted to investigate the structure–property relationship of polytetrahydrofuran ether glycol (PTMG) based thermoplastic polyurethane (TPU) elastomer upon varying the polydimethylsiloxane (PDMS) segment proportion from 1.98% to 8.40%. A series of polyurethane elastomers containing PDMS and PTMG segments was synthesized by two-step method. The performance improvement mechanism of PDMS segments for the TPU elastomer was deeply analyzed through multiple methods such as Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The macro properties of TPU were further evaluated by mechanical property tests, static contact angle tests, and so on. The experimental results demonstrated that the introduction of PDMS significantly promoted microphase separation. The glass-transition temperature of the TPU elastomer decreased to as low as −127.9 °C, reflecting improved segmental mobility at cryogenic temperatures. Meanwhile, the TPU elastomer exhibited obviously improved surface hydrophobicity, and its water contact angle increased from 82.17° to 111.80° with increasing PDMS content.
The long-term durability of natural rubber (NR) in demanding applications depends critically on the stability and evolution of its sulfur crosslinked network, as thermo-oxidative aging alters both the polymer backbone and the crosslink structure. Post-curing treatments—often referred to as maturation—can reshape the sulfur network architecture and, in turn, influence resistance to degradation. While some studies have considered how the topology of the initial sulfur crosslink network affects aging, the specific effects of maturation remain underexplored. To address this gap, this study examines the impact of maturation on the aging behavior of NR vulcanizates cured to t’95 at 180 °C. The evolution of the elastically active chain (EAC) density and mechanical properties was tracked using equilibrium swelling experiments and tensile testing under both thermal and thermo-oxidative conditions.Findings show that post-curing enhances crosslink density, reduces network defects, and delays the onset of oxidative degradation. In contrast, unmatured samples exhibit an initial crosslinking phase, driven by residual curatives and oxygen, followed by accelerated degradation. Ultimately, both systems converge to similar EAC densities, underscoring the overriding influence of oxidative degradation on long-term material performance.
High-precision curing kinetics models are of great significance for the rubber curing simulation. To establish a mature curing model, five sets of isothermal curing experiments were conducted to evaluate the traditional Kamal–Sourour (K-S) model. The results show that this model exhibits relatively large prediction deviations during both the initial curing stage and the thermal curing stage. To improve the model, two modifications were proposed: (1) introducing the initial degree of cure and proportional parameters and (2) treating the reaction order and proportional parameters as linear functions of temperature. The prediction error of the modified model is <5%, and its universality has been verified through experiments on five different rubber compounds. To simulate the nonisothermal curing process of thick-walled rubber products, the nonisothermal process was discretized into a finite number of isothermal steps and an ABAQUS UMATHT subroutine based on FORTRAN was developed to achieve coupled simulation of nonisothermal curing and heat transfer in thick-walled rubber products. Finally, the reliability of the numerical simulation method was verified through thermocouple experiments and rubber process analyzer tests.
The tire inner liner is a thin, air-impermeable layer composed of natural or synthetic rubber engineered to retain internal air pressure, thereby enhancing fuel efficiency and prolonging tire service life. We present a comprehensive and timely review of the current state of research on tire inner liners, with particular emphasis on material development and performance optimization. We introduce the fundamental role and design principles of inner liners, followed by a critical analysis of recent advancements in the selection of elastomers and functional fillers; and address the recycling and reuse of inner liner materials, highlighting environmentally sustainable and economically feasible approaches. A key novelty of this work lies in its coverage of a research area that has received minimal attention in the literature. Despite the critical importance of inner liners in tire performance and sustainability, comprehensive reviews on this topic are scarce, resulting in a significant knowledge gap. By systematically synthesizing historical research and identifying emerging trends and challenges, this review not only fills a crucial void in the academic and industrial literature but also provides valuable guidance for researchers, entrepreneurs, and tire manufacturers seeking to develop next-generation sustainable tire technologies. [doi:10.5254/rct.25.00028]
The strengthening effect of carbon black (CB) and silica dual-filler in solution polymerized styrene butadiene rubber (SSBR) was studied. SSBR composites with different silica/CB filler ratios were prepared under the condition of constant filler amount. The vulcanization efficiency and crosslinking degree of rubber were evaluated by vulcanization experiments. The filler dispersion and network strength of rubber were comprehensively analyzed by linear and nonlinear rheological tests. The crosslinking characteristics of rubber were studied based on the tube model. The results show that the mixing of the dual filler can reduce the agglomeration between the filler particles, improve the dispersion of the filler, and improve the force between the filler and polymer molecules. The excellent dispersion and the interaction force inside the polymer improve the vulcanization degree of the rubber, and the crosslinking density of the rubber is improved. The results showed that the optimal ratio of silica to CB was 4:1. From the macro point of view, the uniaxial tensile test of vulcanizate samples was carried out, and it was found that the tensile strength, tensile stress and elastic modulus of SSBR vulcanizate were improved. [doi:10.5254/rct.25.00036]
We evaluated the performance of thermomechanical devulcanized ethylene-propylene-diene terpolymer rubber (dEPDM), obtained from postconsumer automotive weather seal rubber, as a functional additive in plasticized poly(vinyl chloride) (PVC) formulations. The formulations contained 0-40 phr dEPDM by varying the dEPDM-to-plasticizer ratio. The effect of poly(ethylene-co-propylene-co-5-ethylidene-2-norbornene) grafted with maleic anhydride (EPDMg-MAH) on compatibility was evaluated at concentrations of 1.5, 3, and 6 phr. The results indicated that the inclusion of dEPDM led to a reduction in elongation at break while simultaneously enhancing mechanical properties, such as hardness, tensile strength, Young's modulus, and wear resistance. Differential scanning calorimetry (DSC) confirmed an increase in glass transition temperature (Tg). Scanning electron microscopy (SEM) demonstrated significantly improved interfacial adhesion between PVC and dEPDM in the PVC containing 20 phr of dEPDM after modification with 1.5 phr of EPDM-g-MAH. These findings were further substantiated by dynamic mechanical analysis (DMA), which revealed an increase in Tg and a decrease in tan d peak height. Overall, dEPDM was shown to be an effective functional additive for improving strength and wear resistance in PVC, but its content should not exceed 20 phr to maintain flexibility and achieve a balanced performance suitable for shoe sole applications. [doi:10.5254/rct.25.00027]
The rebound test is a widely used method for evaluating hysteresis losses in rubber samples. However, the fundamental limitation of the conventional rebound test is that only a proportion of dissipated energy is measured. An improvement to the traditional rebound elasticity test is presented, with a focus on implementing a high-resolution measurement technique and optimizing the mechanical setup. The present extension of the classic setup focuses on the precise detection of the contact between the pendulum hammer and the rubber sample. The high-resolution detection of the contact between the hammer and the sample enables the exact analytical determination of the time-dependent deformation on the sample. We present a special method for the analytical description of the measured, discrete, time-dependent deformation of the sample that enables direct calculation of the forces acting on the sample. Using the theoretical description of the Hertzian contact for viscoelastic media by Argatov, the complex Young's modulus for the pulse-like deformation occurring during contact can be calculated from the time-dependent deformation. Experimentally, a series of measurements were carried out on vulcanizates filled with carbon black, varying the filler type and the filler content and crosslinking densities. The results confirm that this extended measurement and analysis technique provides access to the characterization of the complex mechanical behavior of filled vulcanizates in the millisecond time range at high deformations, making it highly relevant for a wide range of industrial applications and to strains not accessible with conventional measurement techniques.
Rubber compounds containing soft rubber and hard reinforcing filler have been shown to exhibit superior properties compared with neat rubber. Invariably, the macroscopic properties of such nanocomposites are controlled by the interfacial layer formed between the matrix and the filler. Because the interactions within these compounds are complex, unravelling the underlying factors affecting strong intrinsic heterogeneity in the interfacial region is still a long-standing controversial topic. Therefore, a comprehensive survey is presented herein to report the latest experimental, simulation, and theoretical results that characterize interface structure and probe polymer chain mobility in these materials. The review begins by describing intermolecular forces and filler-mediated interactions, including the role of filler attributes and rubber–filler interactions, and discussing appropriate methods to investigate segmental mobility. Next, measurements of microscopic details of segmental motion in various rubber compounds reinforced with fillers, such as nanocarbon, silica, and hybrid fillers, are presented, highlighting why and how fillers interact with elastomers and arguing for an urgent need to consider the filler-mediated interactions for better and accurate rubber reinforcement. In addition, the latest studies regarding bound rubber and wet-mixed compounds are discussed. Quantitative correlation of microscopic interactions and macroscopic properties is also provided. Finally, several open challenges in probing the interfacial layer and polymer chain mobility of rubber compounds are discussed.
Autonomously repairing tire sealants are critical for vehicle safety; however, conventional self-healing formulations frequently fail under prolonged high-speed tire operation due to excessive flowability, resulting in compromised sealing performance and dynamic imbalance. We have designed a dual-crosslinked butyl rubber-based interpenetrating network (IPN) incorporating dynamic hydrogen bonds and imine bonds, which collectively ensure excellent self-healing capability, reprocessability, and high-temperature structural integrity. The fabricated IPNs exhibit an ultimate stress of 1.4-3.1 MPa and a breaking strain of 1450-2600%. The imine-crosslinked network ensures structural integrity at elevated temperatures, while the hydrogen-bonded network significantly enhances strength and toughness via reversible hydrogen bond breakage and reformation, facilitating efficient energy dissipation. Moreover, the designed IPNs achieve a high healing efficiency of X85% after 4 h at 80 degrees C. Such a healing efficiency stems from the synergistic interaction between imine-bond exchange reactions and hydrogen-bond dissociation/reformation dynamics. The IPN architecture harnesses the rapid reversibility of hydrogen bonds and the robust exchangeability of imine bonds, while the imine-bond-crosslinked network preserves the structural integrity of the material. This design effectively mitigates the flow behavior observed in conventional self-healing sealants during high-speed operation, providing a versatile platform for developing high-temperature-resistant, healable tire sealants with tunable mechanical properties. [doi:10.5254/rct.25.00024]
This paper presents macrostructural analysis of NR from transgenic Parthenium argentatum (guayule) in comparison with commercial Hevea brasiliensis (Hevea) and wild-type guayule by using high-resolution size exclusion chromatography (HR-SEC). Analysis of the soluble fraction of commercial Hevea demonstrated a bimodal distribution in the high molecular weight range, with a compact branched structure, and some oligomer content. By contrast, earlier HR-SEC analysis of samples isolated from enzymatically active washed rubber particles of Hevea that are closest to the in vivo state showed linear conformation in the high molecular weight range, with substantial oligomer content. Thus, branching in Hevea is likely due to processing conditions. Simple drying (evaporation of water) of wild-type guayule latex and coagulation and drying of transgenic guayule lattices did not result in branching in the soluble fraction. Our HR-SEC analysis demonstrated for the first time that transgenic modification of the guayule plants can produce NR with lower weight average molecular weight, eliminating the need to "masticate" NR to reduce the viscosity for compounding before using it for tire building and the production of rubber goods. We also propose a new model of in vivo rubber particles where the interior contains high molecular weight rubber swollen in oligomers. [doi:10.5254/RCT.25.00038]
The rubber-producing species Scorzonera tau-saghyz Lipsch et. Bosse (mountain gum) was used as a significant source of NR between 1930 and 1950 by the USSR because this perennial can accumulate up to 40% rubber in its roots on a dry weight basis. Wild stands of rubber plants were harvested and then various root metrics (length, diameter, weight) and compound contents (rubber, resin, and carbohydrates) were quantified in both nursery and field trials at multiple locations. Most of the historical data were lost, but a few rare early reports were discovered and translated by our co-authors in Kazakhstan. In this paper, these early data from different sites have been plotted and analyzed to guide modern cultivation efforts in Kazakhstan and in the United States. The use of a nitrogen, phosphate, and potassium complex fertilizer appeared most effective in increasing overall yield, promoting growth, and enhancing the content of rubber, resin, and carbohydrates in the plants. The highest rubber and the lowest resin concentrations were observed in September-October. The greatest yields of root biomass and rubber were obtained on relatively acidic, magnesium-rich soils (pH 5.35-7.45) with a mild climate (Krasnograd, Ukraine). However, S. tau-saghyz was able to perform quite well even when winter temperatures dropped to--20 degrees degrees C (Poltavka, Kazakhstan). Good plant performance on the Poltavka, Krasnograd, and irrigated Almaty (Kazakhstan) sites suggests that adequate water is needed for good yield. Lack of water and higher pH both appeared to be detrimental to yield in Balashov (Russia) and nonirrigated Almaty sites.
Fatigue crack growth (FCG) tests were performed on 11 SBR vulcanizates by using pure-shear specimens at a frequency of 5 Hz and a strain ratio of 0.1, in air at room temperature. The vulcanizates were either unfilled, carbon black (CB) filled, or silica (SC) filled, with filler contents ranging from 5 to 25 vol%. Although the FCG data for all vulcanizates could be fitted using power-law equations, deviations from the fitted curves were observed in the high tearing energy regime when the filler content exceeded 15 vol%. This deviation is attributed to a transition in the crack growth mechanism from cycle-dependent to time-dependent behavior. For both CB-and SC-filled vulcanizates, the threshold tearing energy increased and the power-law exponent decreased with increasing filler content; however, both values tended to plateau beyond 15 vol%. Notably, at equivalent filler contents, SC-filled vulcanizates exhibited threshold tearing energy values approximately three times higher than those of CB-filled compounds, despite comparable hysteresis ratios. This unique threshold behavior was interpreted in terms of crack tip deformation, as evaluated by crack opening displacement, and the underlying fracture mechanisms, namely chain scission and interfacial delamination. [doi:10.5254/rct.25.00032]
This study investigates the transition from linear to nonlinear viscoelastic behavior in polymers and rubber compounds under cyclic sinusoidal shear deformation. By using Fourier series decomposition, we define the generalized elastic modulus G'0(c0) and viscous modulus to capture critical aspects of the material's response. The G'0(c0) is further divided into two components: the first harmonic, representing linear elasticity, and a nonlinear modulus G'NL, derived from higher harmonic contributions. To quantify the degree of nonlinearity, we introduce the nonlinearity index (NLI), defined as the ratio of the nonlinear modulus to the first harmonic elastic modulus G'NL and G', providing a precise metric for nonlinear viscoelastic behavior. We demonstrate the high sensitivity and utility of NLI in distinguishing different polymer topologies, particularly to differentiate between linear and branched macrostructures. Furthermore, we explore the influence of silica loading in silica-filled tread solution SBR (s-SBR) compounds, revealing the pronounced nonlinearity induced by filler content and the sensitivity of NLI in detecting filler-rubber interactions. The study also examines functionalized s-SBR in silica-based tread formulations for high-performance tires, emphasizing the critical role of polymer-filler interactions in dynamic reinforcement. Our findings establish NLI as a robust analytical tool for characterizing viscoelastic properties, offering valuable insight into molecular architecture and rubber-filler interactions for functionalized s-SBR compound. [doi:10.5254/rct.25.00022]
