ABSTRACT 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 less than 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 non-isothermal 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 non-isothermal 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.

ABSTRACT 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 and viscous modulus to capture critical aspects of the material’s response. The is further divided into two components: the first harmonic, representing linear elasticity, and a nonlinear modulus , 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 and , 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.

ABSTRACT The maturation process is an important means of industrially regulating NR. It is of great significance to understand the change rule of properties in the maturation process for the production and processing of NR. In this study, the effects of maturation time on the nonrubber components, microstructure, and macroscopic properties of NR were examined. The test results of nitrogen content showed that the protein content of NR decreased with the extension of maturation time. The results of the solid NMR and gel content test showed that the molecular chain entanglements of the rubber increased and that the natural network structure increased during the maturation process. The test results of the vulcanization curves showed that the scorching time of the rubber was significantly shortened with the prolongation of the maturation time; The test results of crosslinking density showed that the crosslinking density decreased with the extension of maturation time. The test results of compression heat build-up and Akron abrasion showed that the heat build-up of the rubber increased and that the wear resistance deteriorated during the maturation process. In addition, when the maturation time was 2 days, the rubber had the highest molecular weight, highest storage modulus, smallest loss factor, best dispersion of carbon black, and best mechanical properties and aging resistance.

ABSTRACT I was honored by the award of the 2024 Charles Goodyear Medal 42 yr after I received my PhD in plant biology and thank Drs Judit Puskas and Adel Halasa for their nominations and support over several yr as well as the selection committee. As the second woman and first biologist to receive this recognition, I will describe some of the basic and applied research that led me to my admiration of plants and subsequent focus on the biological and geographical diversification of the global natural rubber (NR) supply. My focus across federal, industrial, and academic appointments has continuously been on making research meaningful, and my basic research has always been tethered to strongly applied research translation and goals. Achieving domestic rubber production means that the entire value chain from seed to product must be validated, and every part presented and still presents specific research and development challenges. Fortunately, core scientific and engineering principles are constant and readily adaptable to new areas. Many people were happy to advise me in areas in which I had no formal training. My innovative research has led to 10 start-up companies, about 36 issued or pending patents, many with student inventors, over 310 published papers, and an H-index of 51. Working in NR is not only very interesting but has left me with an unshakable belief that my research is meaningful. Failure is not an option because the consequences of relying on a single clonal tree species for this critical material could be unimaginably bad if the rubber tree crop collapses and no alternatives have previously been established at a rapidly scalable level.

ABSTRACT We report synthesis of nitrogen-containing silane coupling agents (N-SCAs) and their use in a 1:1 mixture by weight with bis(triethoxysilylpropyl)tetrasulfide in preparation of silica/solution SBR (SSBR)/BR composites. These N-SCAs contain in their structures, inter alia, a tertiary amine center (N1, N2), a carbamate (N3), or a urea (N4) group. In addition, N1, N3, and N4 were equipped with allyl side arms to increase the hydrophobization effect of silica particle as well as to achieve a balance between the filler–filler and filler–matrix networks being formed. By contrast, N2 consists of glycidyl side arms that contribute to the filler–filler interaction even more. The silica/SSBR/BR blends and subsequent vulcanizates were prepared and then thoroughly investigated via dynamic mechanical analysis, rubber process analysis, and tensile testing. The composite based on N1 (V/N1) exhibited exceptionally great tensile strength, abrasion resistance, and winter traction, accompanied by soft hysteresis. Therefore, N1 has potential applications in preparation of winter tire tread materials.

ABSTRACT The segregation of carbon black within a blend of NR/EPDM rubber at different mixing proportions (especially 70/30 and 30/70) was investigated via various microscopic techniques—transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM)-mapping, field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM)—to analyze the characteristics of the rubber matrix in pristine rubber to final filled rubber blends. The investigation spans from the unfilled rubber to ultimate filled blends with low (25 phr) and high (50 phr) carbon black content. The use of OsO4 for selective chemical staining, in conjunction with microscopy, made it possible to distinctly understand each rubber phase within the blend, greatly aiding in the identification of filler migration to the preferred rubber phase. In addition, STEM-mapping confirmed the phase distribution by identifying the continuous and dispersed phases through precise detection and validation of the stained areas. The combined outcome of the microscopic studies (TEM, FESEM, and AFM) revealed that the carbon black filler is more inclined to move toward the unsaturated NR phase due to its active graphitic edges, making it more compatible with the NR phase, which has a higher degree of unsaturation than EPDM.

ABSTRACT Carbon blacks are electrically conductive; however, when carbon black is used as particulate reinforcement in a rubber compound, the compound electrical conductivity can vary from insulative to fully conductive depending on the loading level and properties of the carbon black. An investigation of the influence of three fundamental properties of carbon black—particle size, structure, and porosity—on rubber compound electrical conductivity was conducted. The deconvolution of these three parameters within the study allows for conclusive results to be drawn on what drives compound electrical conductivity and the underlying principles. The work is split into two parts: (1) a determination of the influence of particle size and structure and (2) the influence of porosity. Particle size traces its influence back to the number particles that are in a given volume of rubber compound. Structure’s influence on electrical conductivity varies with the particle size of the carbon black and is for the first time traced back to the aspect ratio of the aggregates. Porosity is separated as a variable in this work by introducing discrete levels of porosity to nascent carbon blacks via gasification. The results show that the impact of carbon black porosity on electrical conductivity in rubber compounds arises from a change in its envelope density and is not due to any change in the inherent aggregate conductivity.

ABSTRACT Silica is a reinforcing filler commonly used in the production of environmentally friendly tires, because tires reinforced with silica have lower rolling resistance that translates into reduced energy consumption and improved fuel economy. However, achieving the optimal dispersion of silica within the rubber matrix is crucial for maximizing its reinforcing effects. In this study, a three-dimensionally networked silica (NS) was introduced in various amounts to rubber inks to improve their tensile strength and increase miscibility to enable their use in additive manufacturing. The results show that synthetic rubber ink with a high content of SBR (90%) and reinforced by NS possesses adequate viscosity for use in the direct ink write (DIW) process. NS was confirmed to have an impact on the rheological properties and printability of the rubber ink as well as improve the tensile strength of the printed parts. Different formulations were tested to study and facilitate the vulcanization process and identify the optimal curing conditions as well as the print parameters to use in DIW printing. The successful printing and vulcanization of various printed structures demonstrate the potential for using the developed printable ink in additive manufacturing. This study opens up new possibilities for creating rubber products (such as tire treads) with adequate flexibility and high tensile strength.

Abstract The recycling of waste rubber is very important for environmental protection, but the compatibility problem restricts the recycling and application of waste rubber powder. Devulcanization of waste rubber powder (WRP) has been proven to be an effective method to improve the solubilization effect. The use of environmentally friendly non-toxic solvents can not only improve the devulcanization effect, but also avoid secondary pollution. Thus, in this paper, an environmentally friendly deep eutectic solvent (DES) is first prepared, and then applied to the devulcanization treatment of WRP. The results show that the prepared DES has a positive devulcanization effect, and the devulcanization rate can reach 50%. The devulcanization mechanism can be divided into two aspects. Firstly, adsorption and removal of sulfur- containing low molecular compounds. Secondly, destruction of the crosslinking structure and improvement of the fluidity. The microstructure observation showed that the rougher the surface of the desulfurized rubber powder was, the more conducive to the crosslinking reaction with the matrix material to form a uniform whole. The devulcanization mechanism of DES is divided into destroying the sulfur-containing cross-linked structure and adsorbing the sulfur-containing low molecular compounds. The surface of WRP after DES treatment is rougher and more porous, which is beneficial to the cross-linking reaction with the matrix material. Finally, the optimum process conditions for the decrosslinking effect are determined by orthogonal test as follows: liquid-solid ratio 15∶1, temperature 120°C, time 0.5 h.

ABSTRACT Rubbers and elastomers have a rich history that spans many eras of human civilization dating back to 1600 AD. Upon their introduction into Europe, they became common materials in shoes and fabrics. With the invention of vulcanization by Charles Goodyear in 1839, rubbers became widely used in many new applications, ranging from tires to industrial machine parts. Today, rubbers and elastomers are essential in the development of innovative, emerging technologies. This review exemplifies how rubbers and elastomers have been used to advance the emerging fields of soft robotics through soft grippers and dielectric elastomer actuators, stretchable and wearable devices through conductive elastomers and smart elastomers used in thermal camouflage and sensors, biomedical applications through tissue scaffolding and stretch-triggered drug delivery, and energy harvesting through piezoelectric elastomers and wave harvesting triboelectric nanogenerators. This review also briefly summarizes other developments in these fields as well as glimpses into other emerging fields that are advancing through the incorporation of rubbers and elastomers.