Pure Rubber Research Articles

A flexible thermal interface composite of copper-coated carbon felts with 3d architecture in silicon rubber

Thermal interface materials (TIM) are key thermal management components to enhance the performance of electronic products, and how to improve thermal conductivity is a key issue to consider. As a high thermal conductivity material, it is difficult for copper to have both high thermal conductivity and high elasticity when filled into the polymer. In this paper, by growing copper nanoparticles on the surface of carbon felt (Cfelt), a three-dimensional interoperable thermally conductive copper network is formed with carbon fibers as the support, which makes the material both better thermally conductive and elastic at the same time. The vertical thermal conductivity of the prepared Cu-Cfelt/silicon rubber composite material reached 7.3230 W/mK. It is 23 times higher than pure silicon rubber(0.3130 W/mK), 18 times higher than Cu/silicon rubber composite (0.4120 W/mK) and 12 times higher than CFelt/silicon rubber composite (0.6200 W/mK), and successfully improves the thermal conductivity of the interface. The three-dimensional Cu network structure of the prepared Cu-CFelt/silicon rubber composite maximized the thermal conductivity of Cu, and the composite also showed excellent mechanical properties, indicating that the composite has broad application prospects in thermal management and other aspects.

Effect of hydroxylated boron nitride and boron nitride nanosheets on the properties of doped organosilicone rubber composites

As the electronic industry develops rapidly, the miniaturisation, integration and multifunctionality of electronic devices have resulted in a dramatic increase in power density, and the heat dispersal of electronic devices has attracted much attention. In this work, hydroxylated hexagonal boron nitride (BN-H) was obtained by hot alkali treatment, and boron nitride nanosheets (BNNS) with a thickness of about 4 nm were obtained by boric acid-assisted ball milling stripping. The effects of different types of fillers as well as filler contents on the thermally conductive and mechanical performance of organosilicon composites were also compared. Notably, when BN-H and BNNS thermally conductive fillers were added at 12 wt%, the thermally conductive coefficients of the composites were 0.4831 W·m−1·K−1 and 0.7131 W·m−1 K−1, respectively, which were 183% and 318% of higher than that for the pure silicone rubber (SR, with a thermally conductive coefficient of 0.1706 W·m−1·K−1). In addition, in respect of mechanical performance, the tensile strengths of SR/BN-H and SR/BNNS composites with a filling level of 12 wt% were 3.59 MPa and 3.89 MPa, respectively, and the storage moduli were 4501 MPa and 4583 MPa, respectively, which were improved to a certain extent compared with pure SR. The present work provides an effective way to develop organosilicone rubber composites with good thermal conductivity and mechanical properties by boric acid assisted ball milling to strip boron nitride in the field of electronics packages.

Multi‐Interfacial Heterostructure Design of Carbon Fiber/Silicone Rubber‐Oriented Composites for Microwave Absorption and Thermal Management

AbstractIn order to ensure the operation and longevity of electronic devices, the design of multifunctional composites integrating microwave absorption (MA) and thermal conduction has become the key to solving the problem. However, the superior MA properties and thermal conductivity are usually incompatible in the blend system. In this study, a modified carbon fiber/silicone rubber‐oriented structure is designed based on the multiscale design concept of heterostructures with multiple interfaces. The forward deposition‐reverse growth mechanism is utilized at the microscopic level to construct multi‐interfacial heterogeneous structures on the surface of 1D carbon fibers (CFs). The magneto‐electric coupling network of the multi‐interfacial heterostructure induces interfacial polarization and enhances MA properties and heat transfer. Subsequently, the structural design of the modified CFs is carried out on a macroscopic scale using the ice template method. The directionally aligned modified CFs/silicone rubber aerogel composites are obtained by backfilling with silicone rubber (SR). The samples achieved an effective absorption bandwidth of 4.41 GHz and a maximum reflection loss of −42.29 dB with ultra‐thin thickness (1.3 mm). The thermal conductivity of the sample is improved to 200% compared to pure silicone rubber. The composites with directional alignment have promising applications in lightweight and flexible electronic packaging.

Sulfur and Peroxide Vulcanization of the Blends Based on Styrene-Butadiene Rubber, Ethylene-Propylene-Diene Monomer Rubber and Their Combinations.

Rubber blends based on styrene-butadiene rubber, ethylene-propylene-diene monomer rubber and a combination of both rubbers were cured with different sulfur and peroxide curing systems. In sulfur curing systems, two type of accelerators, namely tetramethylthiuram disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, and combinations of both accelerators were used. In peroxide curing systems, dicumyl peroxide, and a combination of dicumyl peroxide with zinc diacrylate or zinc dimethacrylate, respectively, were applied. The work was aimed at investigating the effect of curing systems composition as well as the type of rubber or rubber combinations on the curing process, cross-link density and physical-mechanical properties of vulcanizates. The dynamic mechanical properties of the selected vulcanizates were examined too. The results revealed a correlation between the cross-link density and physical-mechanical properties. Similarly, there was a certain correlation between the cross-linking degree and glass transition temperature. The tensile strength of vulcanizates based on rubber combinations was higher when compared to that based on pure rubbers, which points out the fact that in rubber combinations, not only are the features of both elastomers combined, but improvement in the tensile characteristics can also be achieved. When compared to vulcanizates cured with dicumyl peroxide, materials cured with a sulfur system exhibited higher tensile strength. With the application of co-agents in peroxide vulcanization, the tensile strength overcame the tensile behavior of sulfur-cured vulcanizates.

Properties and Mechanism of Friction‐Reducing Silicone Rubber Modified with Hyperbranched Polysiloxane

AbstractDuring the utilization of silicone rubber, excessive friction can cause damage to the contact surface and the material itself. Therefore, friction‐reducing modification of silicone rubber has attracted much attention. In this paper, hyperbranched polysiloxanes with different structures is synthesized for friction‐reducing modification of silicone rubber. Infrared spectroscopy, nuclear magnetic resonance spectroscopy, and amine titration tests reveal that hyperbranched polysiloxanes are successfully synthesized by the hydrolytic condensation of 3‐aminopropyltriethoxysilane and their Michael addition with four acrylates with different alkyl chains. The friction coefficients and mechanical properties of silicone rubber are evaluated. Hyperbranched polysiloxanes significantly reduces friction and maintained excellent mechanical properties of silicone rubber. Silicone rubber with butyl‐ester‐secondary‐amino hyperbranched polysiloxane displays the best overall performance, with static and dynamic friction coefficients decreasing by 33.99% and 43.16% compared with that of pure silicone rubber, respectively, and a tensile strength of 10.80 MPa. The friction‐reducing mechanism of hyperbranched polysiloxanes on silicone rubber is investigated by contact angle test and dynamic mechanical analysis. Hyperbranched polysiloxanes migrates to the surface due to the incompatibility of alkyl chains with silicone rubber matrix. Consequently, the shielding effect produced by hyperbranched polysiloxanes on the surface depresses the adsorption activity of silicone rubber surface thereby reducing friction.

Investigation of Macroscopic Mechanical Behavior of Magnetorheological Elastomers under Shear Deformation Using Microscale Representative Volume Element Approach.

Magnetorheological elastomers (MREs) are a class of smart materials with rubber-like qualities, demonstrating revertible magnetic field-dependent viscoelastic properties, which makes them an ideal candidate for development of the next generation of adaptive vibration absorbers. This research study aims at the development of a finite element model using microscale representative volume element (RVE) approach to predict the field-dependent shear behavior of MREs. MREs with different elastomeric matrices, including silicone rubber Ecoflex 30 and Ecoflex 50, and carbonyl iron particles (CIPs) have been considered as magnetic particles. The stress-strain characteristic of the pure silicon rubbers was evaluated experimentally to formulate the nonlinear Ogden strain energy function to describe hyper-elastic behavior of the rubbery matrix. The obtained mechanical and magnetic properties of the matrix and inclusions were integrated into COMSOL Multiphysics to develop the RVE for the MREs, in 2D and 3D configurations, with CIP volume fraction varying from 5% to 40%. Periodic boundary condition (PBC) was imposed on the RVE boundaries, while undergoing shear deformation subjected to magnetic flux densities of 0-0.4 T. Comparing the results from 2D and 3D modeling of isotropic MRE-RVE with the experimental results from the literature suggests that the 3D MRE-RVE can be effectively used to accurately predict the influence of varying factors including matrix type, volume fraction of magnetic particles, and applied magnetic field on the mechanical behavior of MREs.

Bioinspired helical fiber/elastomer composites with high strength

For general composites, fiber can improve the strength of rubber matrix, but it will damage the original high deformation that affect the toughness. Therefore, to solve this problem, we propose a strategy of constructing rubber-helical fiber composite, which can not only improve the strength of rubber, but also maintain the original high deformation of rubber. Inspired by helical structure in nature, we convert straight fibers into helical fibers by winding. The helical fibers with spring characteristic have high strength and large deformation matching with rubber. The tensile strength and fracture toughness of the composite are 3.51 and 3.41 times those of the rubber matrix, respectively. When the aramid fiber was used instead of nylon fiber, the strength of the composite is 12.81 MPa, which is 17.8 times that of pure rubber matrix, and the mass fraction of the fiber is only about 1.60 %. Furthermore, by analyzing the reinforcement and toughening effect of helical fiber, we have determined that helical fiber plays the role of bearing stress and dispersing stress into three-dimensional space in composites.

Fabrication and investigation of graphene‐loaded triiron tetraoxide/silicone‐rubber electromagnetic shielding composites based on static magnetic‐field–induced orientation

AbstractGraphene‐loaded triiron tetraoxide/silicone‐rubber composites containing highly loaded graphene‐loaded Fe3O4 (Fe3O4@RGO) particles were fabricated using static magnetic field‐induced alignment. The Fe3O4@RGO particles were characterized through Fourier transform infrared, x‐ray diffraction, SEM, and XPS analyses. Subsequently, the influence of added material and the strength of the magnetic field on the alignment distribution of the filler were examined through a synergistic combination of SEM and Raman spectroscopy. The electrical conductivity and electromagnetic shielding properties of the composites were assessed. The electrical conductivity of the composites increased with increasing filler addition, the 25 wt% filler mixture had the fastest curing rate and the maximum torque, and the continued increase in filler addition led to the occurrence of many defects. Concurrently, the alignment distribution of the filler progressively enhances with the augmentation of magnetic field strength. The composites synthesized at 180 mT exhibit the most substantial alignment, facilitating the establishment of effective conductive pathways. This results in a notable enhancement in electromagnetic shielding effectiveness, approximately 400% greater than that of pure silicone rubber and around 40% higher than that of non‐aligned composites. This approach introduces a novel concept for shaping the structural design of flexible electromagnetic shielding materials.Highlights Highly loaded Fe3O4@RGO was prepared by self‐assembly. The continuous phase structure of Fe3O4@RGO oriented was assessed. Fully oriented Fe3O4@RGO promotes the formation of conductive pathways. Fully oriented Fe3O4@RGO reduced the SER by 13% and increased the SEA by 67%.

Variation of Stem CO2 Efflux and Estimation of Its Contribution to the Ecosystem Respiration in an Even-Aged Pure Rubber Plantation of Hainan Island

The stem CO2 efflux (Es) plays an important role in the carbon balance in forest ecosystems. However, a majority of studies focus on ecosystem flux, and little is known about the contribution of stem respiration to ecosystem respiration (Reco) for rubber (Hevea brasiliensis) plantations. We used a portable CO2 analyzer to monitor the rate of Es in situ at different heights (1.5 m, 3.0 m and 4.5 m) in an even-aged rubber plantation from 2019 to 2020. Our results showed that Es exhibited a significant seasonal difference with a minimum value in April and a maximum in September. The mean annual rate of Es at 3.0 m in height (1.65 ± 0.52 μmol·m−2·s−1) was slightly higher than Es at 4.5 m in height (1.56 ± 0.59 μmol·m−2·s−1) and Es at 1.5 m in height (1.51 ± 0.48 μmol·m−2·s−1). No obvious differences in vertical variations were found. An area-based method (Ea) and a volume-based method (Ev) were used to estimate stem respiration at stand levels. One-way ANOVA showed that Ea had no obvious differences in vertical variation (p = 0.62), and Ev indicated differences in vertical variation (p < 0.05). Therefore, the Ea chamber-based measurements at breast height were reasonable and practical extrapolation proxies of stem respiration in an even-aged rubber plantation. With the use of the area-based method, the stem carbon values released from a mature rubber forest were estimated to be 1.214 t C·hm−2·a−1 in 2019 and 1.414 t C·hm−2·a−1 in 2020. Ea/Reco and Ev/Reco showed seasonal changes, with a minimum value in April and a maximum value in December. The leaf area index (LAI) and soil volumetric moisture content (VWC) were the major impact factors of Ea/Reco in an even-aged pure rubber plantation.

Eco-Friendly Natural Rubber-Jute Composites for the Footwear Industry.

Nowadays, biocomposites represent a new generation of materials that are environmentally friendly, cost-effective, low-density, and not derived from petroleum. They have been widely used to protect the environment and generate new alternatives in the polymer industry. In this study, we incorporated untreated jute fibers (UJFs) and alkaline-treated jute fibers (TJFs) at 1-5 and 10 phr into TSR 10 natural rubber as reinforcement fillers. These composites were produced to be used in countersole shoes manufacturing. Untreated fibers were compared to those treated with 10% sodium hydroxide. The alkali treatment allowed the incorporation of fibers without compromising their mechanical properties. The TJF samples exhibited 8% less hardness, 70% more tensile strength, and the same flexibility compared to their pure rubber counterparts. Thanks to their properties and ergonomic appearance, the composites obtained here can be useful in many applications: construction materials (sound insulating boards, and flooring materials), the automotive industry (interior moldings), the footwear industry (shoe soles), and anti-static moldings. These new compounds can be employed in innovative processes to reduce their carbon footprint and negative impact on our planet. Using the Lorenz-Park equation, the loaded composites examined in this study exhibited values above 0.7, which means a competitive load-rubber interaction. Scanning electron microscopy (SEM) was used to investigate the morphology of the composites in detail.

Tensile stress relaxation behavior of a novel wide‐angle fabric/EPDM composite at room temperature

AbstractThe main purpose of this study is to analyze the fundamental deformation and relaxation mechanisms responsible for the stress relaxation behavior of a novel wide‐angle fabric/ethylene propylene diene monomer (EPDM) composite (W‐60 composite) at room temperature with different initial strain. The designed and constructed stress relaxation test device can test five samples simultaneously. The stress relaxation curves of the W‐60 composite are in general agreement with those of the pure rubber. It is proved again that the wide‐angle fabric has good formability. Through the slope calculation, the stress relaxation curves of the W‐60 composite can be divided into two stages: rapid relaxation stage (RRS) and slow relaxation stage (SRS). The cross‐sections are observed using photographic tracking techniques and CT scans. The stress relaxation mechanism of the W‐60 composite is dominated by the internal physical relaxation. It shows many more correlations under the experiment results for the three‐component Maxwell's model with parallel‐connect nonlinear spring (NS‐TCM model). However, in the mechanical models with more parameters, the computational problem also increases due to the accumulation of local minima, which makes it harder to find global minima.Highlights This study builds stress relaxation testing equipment for flexible composite. This study uses a 7‐day stress relaxation pre‐experiment. The stress retrogradation and elastic recovery have occurred. The deformation and strengthening mechanisms of stress relaxation are revealed. The NS‐TCM model shows a positive correlation with the experimental results.

Molecular simulation of the effect of dioctyl phthalate on the properties of nitrile rubber

The mechanical and tribological properties of pure nitrile rubber (NBR) and dioctyl phthalate/nitrile rubber (DOP/NBR) composite materials with mass ratios of 5/95, 10/90, 15/85, 20/80, 25/75, and 30/70 were studied through molecular dynamics simulations at the molecular level. The root mean square displacement (RMSD) and gyration radius of the composite materials were investigated to explore the mechanism of DOP plasticizing NBR. Different models of pure NBR and DOP/NBR composite materials with different mass ratios were established, and the mechanical properties of the materials were calculated by using the constant strain method. The tribological properties of the materials were studied by applying shear velocity on the surface of the materials. The research results showed that the shear resistance of the DOP/NBR composite material increased and then decreased with the increase of the DOP mass ratio, and the same pattern was observed for the shear modulus. Compared with pure NBR materials, DOP/NBR composite materials demonstrated better mobility and flexibility, and the RMSD and gyration radius of the material increased and then decreased with the increase of the DOP mass ratio. The DOP plasticization of NBR reduced the intermolecular interaction forces and changed the molecular conformation, increasing the softness and plasticity of the polymer chains.

Preparation and properties of SBR/PPTA nanocomposite via in‐situ interfacial polycondensation

AbstractIn this article, Styrene butadiene rubber/poly‐p‐phenylene terephthamide (SBR/PPTA) nanocomposite was synthesized via in‐situ interfacial polycondensation of para‐phenylenediamine (PPD) and para‐benzoyl chloride (TPC) between the interface of SBR‐containing cyclohexanone (CYC) solution and water. Fourier transform‐infrared spectroscopy (FTIR) and x‐ray diffraction (XRD) confirmed the formation of PPTA in SBR matrix. Transmission electron microscopy (TEM) indicated PPTA nanosheets were uniformly dispersed in the SBR matrix. The thermal stability and mechanical properties of SBR/PPTA nanocomposite were also studied. Results showed that PPTA significantly improved the mechanical properties and thermal stability of SBR. The tensile strength and 200% tensile stress of SBR/PPTA‐3 were 120.9% and 150.8% higher than those of Pure rubber, respectively. The tensile strength and elongation at break of SBR/ PPTA‐3‐30% were 187.2% and 36.9% higher than those of Pure rubber, enabling promising applications of this new composite rubber material.

On the experimental investigation of silicone-based soft composites under mode I loading using Digital Image Correlation

There is a growing interest in understanding the mechanical behavior of fibrous soft biological materials under several loading conditions. Due to difficulties in manipulating and testing these materials, synthetic composites have already been employed in literature. In this work, a fiber-reinforced soft composite was manufactured and tested to extract its mechanical behavior at two different fiber orientations under mode I loading. The domain J-integral was evaluated by means of DIC using a pure shear (planar) configuration. The coefficients of the fourth-order strain energy function proposed by Luo and Chou were adjusted to describe the mechanical behavior of the considered soft composite and its isolated components (i.e., pure silicone rubber and extensible cotton knit fabric) under tensile loading. The values of the J-integral were validated using a classical formulation for homogeneous rubber-like materials. For the soft composite with fibers oriented at θ0=90°, in which the fiber contribution was not considerable, a satisfactory matching was found between J-integral and classical results in the absence of fiber reinforcement (homogeneous materials), resulting in approximately 13.67% of mean relative error. In fact, the J-integral obtained by DIC and the fourth-order hyperelastic strain energy function can be employed to estimate the energy release rate of fiber-reinforced soft composites.

Preparation and characterization of CNTs/CaCu3Ti4O12/silicone rubber composites with improved dielectric and mechanical properties

AbstractThe dielectric performance of Silicone rubber (SR) composites can be significantly enhanced by carbon nanotubes. However, carbon nanotubes are easy to agglomerate in the polymer matrix. Adding low‐dimensional materials of different dimensions may be a solution. In this article, one‐dimensional multiwall carbon nanotubes (CNTs) and zero‐dimensional copper calcium titanate (CaCu3Ti4O12, CCTO) ceramic fillers were simultaneously added to prepare silicone dielectric elastomer composites. SEM results showed that the CNTs were distributed uniformly in the SR matrix due to the addition of CCTO. When 2 wt% CNTs and 10 wt% CCTO were added, the dielectric constant of the composite increased from 2.79 (pure silicone rubber) to 5.72, with a low loss tangent of 0.0012. Due to the uniform dispersion of CNTs with the addition of CCTO particles, dielectric performance of the composites were enhanced. The tensile stress was 986 kPa, the elongation at break was 333%, while the elastic modulus was not more than 613 kPa (2 wt% CNTs and 5 wt% CCTO in the SR composite). In addition, the composites had a wide temperature range up to 400°C. Therefore, the prepared CNTs/CCTO/SR composites have good dielectric and mechanical properties, and good thermal stability. It has a good reference value for this kind of composites as dielectric elastomer materials.

Low velocity impact performance of 3D auxetic composites embedded with re‐entrant triangle inclusions

AbstractThis paper reports the low‐velocity impact performance of 3D auxetic composite embedded with re‐entrant triangle inclusions by both experiments and finite element (FE) simulations. Both auxetic and non‐auxetic samples were manufactured by embedding inclusions made from carbon fiber/epoxy laminates into silicone rubber matrix. The pure silicone rubber was also manufactured for comparison. All samples were subjected to low‐velocity impact with an impact energy of 147 J and an impact speed of 5.42 m/s and their impact load‐time and energy‐time curves were compared between the experimental results and FE simulation. The impact performances under different impact energies from 60 to 120 J were further investigated based on the validated FE models. The results show that the auxetic composites show better energy absorption capacity and impact resistance than non‐auxetic composites with the same number of inclusions at all energy levels. More inclusions can result in better impact resistance of auxetic composites when the impact energy is under 120 J. The auxetic composites possess 10% higher crash efficiency than non‐auxetic samples. The embedding of inclusions leads to easier damage of the composite under impact energy of 147 J. The research provides a better understanding on the impact performance of auxetic composites made from random inclusions.

Vulcanization and stress analysis of heat vulcanizing bonding joints in fabric rubber seals

Vulcanization has a great impact on the performance of rubber products, which is difficult to analyze due to its complicated process and boundary conditions, especially for complex rubber products like aircraft fabric rubber seals. In this paper, an optimized relationship between reaction order and temperature was first developed based on the comparative study of the existing vulcanization kinetic equations, showing improved accuracy and wider applicable temperature ranges. In the temperature range of 160 °C ∼ 190 °C, the determination coefficient of the model can reach 0.9973. Then, finite element models of pure rubber and fabric rubber were established with Abaqus UMATHT and UMAT subroutines to simulate the vulcanization process and analyze the relationship between the stress in the vulcanization process and the non-uniformity of the vulcanization degree field. Finally, the process of mold core synchronous heating was adopted to reduce the non-uniformity of the vulcanization degree field for the heat vulcanizing bonding joint, so as to reduce the residual stress at the joint. Compared with the traditional upper and lower surface heating mode, the residual stress is reduced by about 20 %. This study provides a theoretical guidance for improving the quality of heat vulcanizing bonding joints of seals.

Flame retardancy, combustion, and ceramization behavior of ceramifiable flame‐retardant room temperature vulcanized silicone rubber foam

AbstractTwo types of ceramifiable flame‐retardant room temperature vulcanized (RTV) silicone rubber foam containing mica power (MP) were prepared by using glass powder (GP) as fluxing agents and aluminum hydroxide (ATH) as flame‐retardant agent, respectively. The flame retardant, combustion behavior, and thermal stability of ceramifiable flame‐retardant RTV silicone rubber foams were investigated. The results show that GP is not conducive to the flame retardancy and thermal stability improvement of the foams. On the contrary, MP and ATH can significantly improve the flame retardancy and thermal stability at high temperatures of the foams. The foams with addition of MP and ATH can reach to a high limiting oxygen index value of 35.8 with V‐0 rating in the vertical combustion test, and the total heat release and total smoke production of the foams are 21.0% and 61.7% lower than of the pure RTV silicone rubber foam, respectively. Furthermore, the structural and morphological changes of the foams under different pyrolysis conditions were studied, so as to reveal its ceramifiable mechanism under different fire scenarios. The results show that GP does not promote the formation of more char residue during pyrolysis, but it can greatly lower the ceramifiable temperature, resulting in a superior ceramic phase char residue. The foams including MP and ATH have a high char residue content; nevertheless, a comparatively higher temperature is necessary to create ceramic phase char residue.

Synergism Effect between Nanofibrillation and Interface Tuning on the Stiffness-Toughness Balance of Rubber-Toughened Polymer Nanocomposites: A Multiscale Analysis.

As the design and scalable technology development of tough, yet stiff, polymer nanocomposites receive attention in the automotive industry, fundamental understating of underlying toughening mechanisms at the nanoscale is inevitable. However, mechanical tests on rubber-toughened nanocomposites have shown that their overall fracture properties are significantly smaller than theoretical predictions. Our previous study showed that major factors in this regard are the simultaneous operation of different toughening mechanisms and the nanostructural features of the interface. As a result, it may be necessary to employ multiscale and multimechanism modeling strategies to accurately account for the contribution of each toughening mechanism. In this study, the effects of nanofibrillation (i.e., size, orientation, and dispersion) and interfacial tuning on the mechanical properties of nanofibrillated rubber-toughened nanocomposites are examined using molecular dynamics (MD) simulations. We report that by interfacial modification via grafting compatibilizer at the interface, nanofibrillated rubber-toughened polypropylene (PP) nanocomposite can achieve superior mechanical properties as a result of enhanced interfacial load transfer. Compared to pure ethylene propylene diene monomer rubber (EPDM)/PP system, an increase of 49% in energy absorbed per unit volume during fracture was achieved for 30% functionalized nanocomposites. Such an increase in energy dissipation was caused by a transition in the dominant crack propagation mechanism from interfacial slippage to crack-arresting behavior, owing to enhanced interfacial adhesion. MD simulations in conjunction with the multiscale model revealed that such a change in mechanism is caused by the formation of strong covalent bonds, interfacial friction, and the presence of a highly entangled polymeric network at the interface. Although the multiscale framework can be viewed as a road map for modeling the interface of various nanocomposite systems, the results obtained from our study may offer valuable insights for developing robust and scalable fabrication processes for nanofibrillated rubber-toughened nanocomposite structures, which pose significant technological challenges.

Constitutive modeling of stress relaxation for fabric reinforced rubber composites

Establishing an unsteady fractional order Zener model with degradation parameters has significant meaning for predicting stress relaxation of fabric reinforced rubber composites. Based on the experimental results, an integer order Zener model was deduced to demonstrate the stress relaxation behaviors of fabric reinforced rubber composites and pure rubber. Due to the limitations, however, the integer order Zener model could not explain the stress relaxation behavior of the fabric reinforced rubber composites (the FRR) very well. Therefore, a Zener model was developed based on the viscoelasticity theory and the fractional calculus theory to characterize the stress relaxation behavior, but errors still existed in the initial and final stages. With more reasonable physical interpretation, an unsteady fractional order Zener model degraded by parametric aging with 7 parameters is proposed in this paper to accurately capture the stress relaxation behavior of the FRR, whose correlation coefficient is over 99.99%. The parameter sensitivities of the seven-parameter model were analyzed. Present study may provide a critical step for designing and evaluating the fabric reinforced rubber composites.