Elastomer Composites Research Articles

Room temperature self-healing and high gas barrier properties of elastomer composites incorporated with liquid metal

Flexible electronic devices require stretchable packaging materials that provide a hermetic seal. However, conventional soft materials often exhibit strong gas permeability, making it difficult to achieve stable operation, which requires films with high deformability, self-healing capability, and gas barrier functionality. In this study, a layer by layer (LBL) method was employed to uniformly coat a controllable thickness of liquid metal (LM) onto a designed and synthesized self-healing thermoplastic polyurethane (TPU) film, successfully developing a stretchable gas barrier film (TPU/LM) with high gas barrier properties. The designed polyurethane film significantly enhanced the adhesion of the liquid metal, effectively preventing leakage. The experimental results show that the water vapor transmission rate (WVTR) of the TPU/LM composite film with a thickness of 40 μm is 4.04g/(m2·day). Compared to the film without LM, the gas barrier performance has been improved by approximately 16 times. Additionally, there is a significant enhancement in nitrogen (N2) barrier, with a permeation rate reaching 4.0*10−17 cm3 cm/(cm2·s·Pa), effectively blocking the N2 permeation. This demonstrates the universality of the TPU/LM in gas barrier applications. Furthermore, the TPU/LM film also demonstrated excellent electromagnetic shielding effectiveness. The self-healing capability of the stretchable gas barrier film allows it to recover its initial gas barrier performance after mechanical damage. Humidity-sensitive resistors encapsulated with TPU/LM exhibited stable operation in both air and 90 % humidity environments, confirming the superior barrier properties of the TPU/LM. Generally, the developed TPU/LM is suitable for packaging applications in the next generation of flexible electronic devices.

Direct Ink Write 3D Printing of Fully Dense and Functionally Graded Liquid Metal Elastomer Foams

AbstractLiquid metal (LM) elastomer composites offer promising potential in soft robotics, wearable electronics, and human‐machine interfaces. Direct ink write (DIW) 3D printing offers a versatile manufacturing technique capable of precise control over LM microstructures, yet challenges such as interfilament void formation in multilayer structures impact material performance. Here, a DIW strategy is introduced to control both LM microstructure and material architecture. Investigating three key process parameters–nozzle height, extrusion rate, and nondimensionalized nozzle velocity–it is found that nozzle height and velocity predominantly influence filament geometry. The nozzle height primarily dictates the aspect ratio of the filament and the formation of voids. A threshold print height based on filament geometry is identified; below the height, significant surface roughness occurs, and above the ink fractures, which facilitates the creation of porous structures with tunable stiffness and programmable LM microstructure. These porous architectures exhibit reduced density and enhanced thermal conductivity compared to cast samples. When used as a dielectric in a soft capacitive sensor, they display high sensitivity (gauge factor = 9.0), as permittivity increases with compressive strain. These results demonstrate the capability to simultaneously manipulate LM microstructure and geometric architecture in LM elastomer composites through precise control of print parameters, while maintaining geometric fidelity in the printed design.

Strong and Healable Elastomers with Photothermal-Stimulus Dynamic Nanonetworks Enabled by Subnano Ultrafine MoO3-x Nanowires.

One-dimensional nanomaterials have become one of the most available nanoreinforcing agents for developing next-generation high-performance functional self-healing composites owing to their unique structural characteristics and surface electron structure. However, nanoscale control, structural regulation, and crystal growth are still enormous challenges in the synthesis of specific one-dimensional nanomaterials. Here, oxygen-defective MoO3-x nanowires with abundant surface dynamic bonding were successfully synthesized as novel nanofillers and photothermal response agents combined with a polyurethane matrix to construct composite elastomers, thus achieving mechanically enhanced and self-healing properties. Benefiting from the surface plasmon resonance of the MoO3-x nanowires and interfacial multiple dynamic bonding interactions, the composite elastomers demonstrated strong mechanical performance (with a strength of 31.45 MPa and elongation of 1167.73%) and ultrafast photothermal toughness self-healing performance (20 s and an efficiency of 94.34%). The introduction of MoO3-x nanowires allows the construction of unique three-dimensional cross-linked nanonetworks that can move and regulate interfacial dynamic interactions under 808 nm infrared laser stimulation, resulting in controlled mechanical and healing performance. Therefore, such special elastomers with strong photothermal responses and mechanical properties are expected to be useful in next-generation biological antibacterial materials, wearable devices, and artificial muscles.

Manufacturing of Stretchable Wavy-Patterned Fiber-Reinforced Elastomer Composites and Its Behaviors Under Tensile Loading Conditions

The wavy-patterned carbon fiber reinforced elastomer composites that offered both the elongation characteristic of the elastomer and the stiffness of the fiber reinforcement before the elastomer reached its elongation at failure was introduced in this study. The goal of this study was to develop and demonstrate the manufacturing process of the wavy-patterned fiber-reinforced elastomer composites and investigate its behaviors under tensile loading conditions. A carbon fiber tow was impregnated with a silicone elastomer and placed in the test specimen manufacturing mold with a specific pattern using a wavy-patterned fiber placing jig. The silicone elastomer was then poured into the mold to cast test specimens. Various wavy-patterned fiber-reinforced elastomer composites, each with different allowed elongation levels and different amount of fiber, were designed and fabricated. Due to fiber slippage during the tensile test with the traditional test grip fixture, a roller grip fixture was used for the tensile test. The test results showed a unique behavior of the wavy-patterned fiber reinforced elastomer composites that elongated until the patterned fiber became straightened, providing additional stiffness to the test specimen under tensile loading. It was observed that the maximum strength and elongation at failure varied with different patterns and amounts of fiber. The unique failure mechanisms of the fiber-reinforced elastomer composite during the tensile test were analyzed and discussed. Despite the fiber being fully impregnated with the elastomer, weak adhesion between the fiber and elastomer led to disbonding between them.

CROSSLINK DENSITY AND ITS DISTRIBUTION IN HEAT AND OIL RESISTANT ELASTOMERS BY DOUBLE QUANTUM NUCLEAR MAGNETIC RESONANCE

ABSTRACT Double quantum (DQ) nuclear magnetic resonance (NMR) was used to characterize the crosslink density, crosslink density distribution, and defect level in a series of heat and oil resistant elastomers. A wide range of defect levels, crosslink densities, and crosslink density distributions was measured, and results depended on elastomer type and compound formulations, including the vulcanization system. The sol fraction defect level generally correlated with the concentration of added plasticizer in the formulation. The presence of polar side chains appeared to cause additional dynamic contributions to the dangling chain end fraction. The large differences in elastomer composition and rubber formulations prevented meaningful correlation of the measured crosslink densities with the low strain modulus. Fast Tikhonov regularization and log normalization fitting of the corrected DQ build-up curve was extremely useful to provide insight into the modality and widths of the crosslink density distributions. A high degree of heterogeneity of the crosslink network of heat and oil resistant elastomers was found. Crosslink density distributions were explained in terms of the polymer chain structure comprised of monomer sequencing coupled with the position of the crosslinking sites. The type of vulcanization system had a lesser effect of the nature of the crosslink density distribution. The primary polymer chain crosslinking sites may become segregated from the continuous phase due to polarity differences seen in the microstructure of oil and heat resistance elastomers. The development of such micromorphologies can favor curative partitioning. The sole use of DQ NMR can provide valuable insight into the nature of the polymer chain structure and crosslink network in rubber.

Wireless driven and self-sensing flexible gripper based on piezoelectric elastomer/high-entropy alloy magnetoelectric composite

The mechanical gripper shows significant importance as an alternative to manual work, but presents certain limitations in its gas or electric power with complex wire connection, presents limited available area and loud working noise, and lacks sensing function for feedback to the environment. In the present work, a novel magnetically driven and self-sensing flexible gripper was prepared based on piezoelectric elastomer and high-entropy alloy composite. The high-entropy alloy is prepared as FeCoNi(AlGa)0.5 to realize high permeability, while the piezoelectric elastomer is synthesized with superior elasticity and low modulus. The incorporation of FeCoNi(AlGa)0.5 into the piezoelectric elastomer exhibits high flexibility, magnetostriction performances and piezoelectric responses, reaching maximum strain of 1534.5 %, maximum magnetostrictive coefficient of 320 ppm and maximum piezoelectric response of 0.28 V/N. Meanwhile, the flexible gripper achieves synchronous wireless driven gripping function with a maximum lifting ratio to dead load over 41.38, and self-sensing function of target physical size with accuracy over 95 %. The flexible gripper shows maximum work power as low as 5 W. Thus, the magnetically driven and self-sensing flexible gripper shows great potential in intelligent industrial equipment.

Study of the effect of hexagonal boron nitride addition to thermoplastic polyester elastomer composites reinforced with carbon, glass and basalt fibers

Study of the effect of hexagonal boron nitride addition to thermoplastic polyester elastomer composites reinforced with carbon, glass and basalt fibers

Bio-functionalization of fillers with natural phytic acid for sustainable flame-retardant agents for natural rubber composites

The current challenge for sustainable flame retardants has led to innovative approaches, including the utilization of natural substances to enhance the fire resistance of elastomer composites. This paper presents the design of eco-friendly hybrid flame-retardant additives based on mineral fillers (hydrotalcite (LDH) and sepiolite (SEP)) modified with aminosilane (APTS) and phytic acid (PA) for natural rubber (NR) biocomposites. The synergistic effects of the PA and silanized mineral fillers resulted in NR composites with improved thermal, mechanical, and barrier properties, as well as increased flame retardancy. Importantly, it was proven that direct in-situ application of PA into elastomer cured with sulphur-based crosslinking systems is ineffective, due to its negative effect on the curing process (significantly reducing torque moment). Binding the PA onto silanized fillers enabled the creation of hybrid additives that leverage the flame-retardant benefits of PA without compromising the other properties of the polymer. The addition of PA-modified fillers to NR reduced the heat release rate (HRR) by around 40 %, indicating outstanding flame retardancy. This work makes a significant contribution and expands the understanding of using eco-friendly natural compounds to reduce the flammability of sulfur-cured elastomers.

Elastomeric Compositions of Ethylene-Norbornene Copolymer Containing Biofillers Based on Coffee and Tea Waste.

The development of eco-friendly elastomeric materials has become an important issue in recent years. In this work, thermoplastic elastomer samples of an ethylene-norbornene copolymer (EN) with coffee and tea biofillers mixed with typical fillers such as montmorillonite (MMT), silica (SiO2), and cellulose were investigated. The aim of this research was to determine the effect of fillers on the properties of the materials and to assess their degradability after two ultraviolet (UV) aging cycles (200, 400 h). The scientific novelty of this work is the assessment of the anti-aging effect of simultaneous biofillers-stabilizers based on coffee and tea waste. The surfaces of the obtained polymer compositions were examined using infrared spectroscopy (FTIR-ATR). Contact angles were determined, and surface energy was calculated. The mechanical properties were tested, and the influence of plant fillers and aging on the color change in the materials was analyzed. The combination of coffee with silica, MMT, and cellulose fillers limited the migration of fatty acids and other compounds from the biofiller to the EN surface (FTIR analysis). Based on the aging coefficients K, it was shown that all coffee- and tea-based fillers stabilized the polymer compositions during UV aging (400 h). The results allowed the authors to determine the importance and impact of waste plant fillers on the degradability of the synthetic EN.

Магнетит как функциональный наполнитель эластомерных композитов: эффекты размерности и структурирования

Samples of composite materials based on Fe3O4 magnetite with different particle sizes (natural and crushed in a planetary mill) and various elastomeric matrices (chloroprene rubber of sulfur regulation – PCP, styrene butadiene rubber - BSK and cold-cured polydimethylsiloxane – SKTN-A) in the concentration range of 10...200 weight parts per 100 weight parts of elastomeric matrices. The kinetics of curing of the elastomeric compositions under consideration has been studied, on the basis of which optimal molding modes have been proposed. The samples were formed both in the presence of a magnetic field up to 0.3 T and without it. The functional (electrophysical and magnetic) properties of the samples were studied and it was shown that these properties in a wide range of values can be regulated by changing the size of magnetite particles and/or structuring them by means of a magnetic field during the molding of elastomeric composites.

Design of High-Temperature Packaging Insulation for Power Modules Using Grafted Nanostructured Silicone Elastomer Composites

Design of High-Temperature Packaging Insulation for Power Modules Using Grafted Nanostructured Silicone Elastomer Composites

Effects of Egg and Snail Shells on Biodegradation and Tensile Properties of Waste Plastics Fabricated Thermoplastics Elastomer Composites

The essence of this study is to proffer solution on the degradation of the environment caused by non-degradable plastics waste. A novel approach on plastic waste management was adopted by fabricating a thermoplastic natural rubber (TPNR) composite using waste Polyethyleneterephthalate {PET}plastics and eggshell as biofillers to initiate degradation by microorganism.Waste Polyethylene Terephthalates (PET) was grinded andmelted blended with Natural Rubber with 40pphr of Eggshell to fabricate a Natural Rubber Thermoplastic elastomer (TPNR) composite. The resultant thermoplastic elastomer composite was prepared for soil burial for a period of 90 days to obtain percentage weight loss as an indication of biodegradation. The NR/PET composite was evaluated for tensile properties. The results obtained were of the new that the tensile strength, elongation at break and modulus decreases with increase in soil burial duration time. The eggshell as a biopolymer has been shown to initiate biodegradation. There was a reduction in tensile strength at a blend ratio of 50/50 NR/PET blend, an indication that degradation has occurred, hence tensile properties are useful tools for the evaluationof biodegradation of polymeric materials

Smart mechanoluminescent phosphors: A review of zinc sulfide‐based materials for advanced mechano‐optical applications

AbstractThe quest for mechanoluminescence (ML) in zinc sulfide (ZnS) spans more than a century, initially sparked by observations of natural minerals. There has been a resurgence in research into ML materials in recent decades, driven by advances in optoelectronic technologies and a deeper understanding of their luminescent properties under mechanical stress. ZnS, in particular, has garnered attention owing to its remarkable ability to sustain luminescence after more than 100,000 mechanical stimulations, positioning it as a standout candidate for optoelectronic applications. In contrast to conventional photoluminescent and electroluminescent light sources, ZnS composite elastomers have emerged as flexible, stretchable self‐powered light sources with considerable practical implications. This review introduces the development history, ML mechanisms, prototype ML devices, ZnS‐based ML material preparation methods, and their diverse applications spanning environmental mechanical‐to‐optical energy conversion, E‐signatures, anti‐counterfeiting, wearable information sensing devices, advanced battery‐free displays, biomedical imaging, and optical fiber sensors for human–computer interactions, among others. By integrating insights from ML‐optics, mechanics, and flexible optoelectronics, and by summarizing pertinent perspectives on current scientific challenges, application technology hurdles, and potential solutions for emerging scientific frontiers, this review aims to furnish fundamental guidance and conceptual frameworks for the design, advancement, and cutting‐edge application of novel mechanoluminescent materials.

Soft, Tough, Antifatigue Fracture Elastomer Composites with Low Thermal Resistance through Synergistic Crack Pinning and Interfacial Slippage.

Soft elastomer composites are promising functional materials for engineer interfaces, where the miniaturized electronic devices have triggered increasing demand for effective heat dissipation, high fracture energy, and antifatigue fracture. However, such a combination of these properties can be rarely met in the same elastomer composites simultaneously. Here a strategy is presented to fabricate a soft, extreme fracture tough (3316J m-2) and antifatigue fracture (1052.56J m⁻2) polydimethylsiloxane/aluminum elastomer composite. These outstanding properties are achieved by optimizing the dangling chains and spherical aluminum fillers, resulting in the combined effects of crack pinning and interfacial slippage. The dangling chains that lengthen the polymer chains between cross-linked points pin the cracks and the rigid fillers obstruct the cracks, enhancing the energy per unit area needed for fatigue failure. The dangling chains also promote polymer/filler interfacial slippage, enabling effective deflection and blunting of an advancing crack tip, thus enhancing mechanical energy dissipation. Moreover, the elastomer composite exhibits low thermal resistance (≈0.12K cm2 W-1), due to the formation of a thermally conductive network. These remarkable characteristics render this elastomer composite promising for application as a thermal interface material in electronic devices.

Elastomeric Fire and Heat-Protective Materials Containing Functionally Active Microheterogeneous Systems.

This research aims to explore how functionally active structures affect the physical, mechanical, thermal, and fire-resistant properties of elastomeric compositions using ethylene-propylene-diene rubber as a base. The inclusion of aluminosilicate microspheres, microfibers, and a phosphorus-boron-nitrogen-organic modifier in these structures creates a synergistic effect, enhancing the material's heat-insulating properties by strengthening coke and carbonization processes. This results in a 12-19% increase in heating time for unheated sample surfaces and a 6-17% increase in residual coke compared to existing analogs. Microspheres help counteract the negative impact of microfibers on composition density and thermal conductivity, while the phosphorus-boron-containing modifier allows for controlling the formation of the coke layer.

Hydroxyapatite-Filled Acrylonitrile-Butadiene Rubber Composites with Improved Cure Characteristics and Reduced Flammability.

The goal of this work was to develop acrylonitrile-butadiene (NBR) elastomer composites filled with hydroxyapatite (HAP) characterized by improved cure characteristics and resistance to burning. Silane, i.e., (3-aminopropyl)-triethoxysilane, ionic liquid, i.e., 1-decyl-3-methylimidazolium bromide and surfactant, i.e., cetyltrimethylammonium bromide, were used to improve the filler's dispersibility in the elastomer matrix and to reduce the time and temperature of vulcanization. The effects of HAP and dispersants on the cure characteristics, crosslink density and physico-chemical properties of NBR composites were explored. The additives used, especially the ionic liquid and surfactant, effectively improved the dispersion of HAP in the NBR matrix. The amount of HAP and the dispersant used strongly affected the cure characteristics and crosslink density of NBR. The optimal vulcanization time significantly increased with HAP content and was pronouncedly reduced when ionic liquid and surfactant were applied. In addition, ionic liquid and surfactant significantly lowered the onset vulcanization temperature and improved the crosslink density and hardness of the vulcanizates while impairing their elasticity. HAP and dispersants did not significantly affect the damping properties or chemical resistance of NBR vulcanizates. Above all, application of HAP considerably enhanced the resistance of vulcanizates to thermo-oxidative aging and reduced their flammability compared with the unfilled NBR.

Response Properties of Electrorheological Composite Hydrophilic Elastomers Based on Different Morphologies of Magnesium-Doped Strontium Titanate.

As smart materials, electrorheological elastomers (EREs) formed by pre-treating active electrorheological particles are attracting more and more attention. In this work, four Mg-doped strontium titanate (Mg-STO) particles with spherical, dendritic, flake-like, and pinecone-like morphologies were obtained via hydrothermal and low-temperature co-precipitation. XRD, SEM, Raman, and FT-IR were used to characterize these products. The results showed that Mg-STOs are about 1.5-2.0 μm in size, and their phase structures are dominated by cubic crystals. These Mg-STOs were dispersed in a hydrogel composite elastic medium. Then, Mg-STO/glycerol/gelatin electrorheological composite hydrophilic elastomers were obtained with or without an electric field. The electric field response properties of Mg-doped strontium titanate composite elastomers were investigated. We concluded that dendritic Mg-STO composite elastomers are high-performance EREs, and the maximum value of their energy storage was 8.70 MPa. The significant electrorheological performance of these products is helpful for their applications in vibration control, force transducers, smart structures, dampers, and other fields.

Tailoring molecular structure and electromechanical properties of polydimethylsiloxane elastomer for enhanced energy conversion efficiency

AbstractThe molecular structure of dielectric elastomers dictates their mechanical, electrical, and properties to react under external stimuli, influencing their suitability for applications such as actuators, sensors, and energy harvesting devices. The molecular structure of polymers can be tailored by incorporating plasticizers and particulate fillers to achieve multifunctional properties. However, achieving a balance between flexibility and maintaining mechanical strength due to incorporation of fillers induced phase separation and compromised intermolecular interactions remains challenging. In the present work, polydimethylsiloxane (PDMS) composites are synthesized using plasticizer and particulate fillers, polyethylene glycol (H‐(OCH2CH2)nOH) and titanium diboride (TiB2) respectively in various concentrations using shear mixing and doctor blade casting technique. Molecular structure of synthesized PDMS composite is confirmed by observing peaks of Raman spectra sift, which exhibits robust CO bonds dominating for both fillers. Chain entanglement due to filler incorporation significantly affects the crosslink density of PDMS composite, it increases with the concentration of plasticizer and possesses inverse relation for particulate. Furthermore, interdependence of the filler types and concentration are found on the mechanical as well as electrical properties. The specific deformation energy exhibits a significant increase of 118.9% when comparing particulate to the plasticizer at concentration of 8 wt.%. Although plasticizer increases the actuation strain and energy conversion efficiency but decreases the electrical breakdown voltage in comparison to particulate. By systematically varying fillers concentration, subtle changes in multifunctional properties are achieved. Overall, this investigation provides a framework for tailoring dielectric elastomer composites with desired electromechanical characteristics through the amalgamation of filler types and crosslinking densities, all intricately tied to the molecular architecture for electromechanical sensors.Highlights Filler incorporation changes DE molecular structure and materials properties. Formation of additional bonds and micro‐capacitors in DE enhances capacitance. Actuation strain in DE depends on filler type and concentration. Energy conversion efficiency varies with the concentration of filler.

Sustainable and multifunctional polyurethane green composites with renewable materials

Polyurethane materials are characterised by an ever-expanding range of application possibilities due to their versatility. Currently, the management of leftovers as well as post-production and post-consumer waste for the production of biocomposites is one of the most obvious, effective and profitable solutions. Due to the renewable nature of biofillers such as cellulose, lignin, and chitin, their use to obtain composite polyurethane elastomers is a real perspective for the dissemination of more environmentally friendly materials and, at the same time, contributes to additional economic profit. The key aspect for further development of the polyurethane/biopolymer biocomposite concept is to fulfil of a number of currently functioning industry standards, mainly those regarding functional properties. In the presented research, an attempt to obtain advanced polyurethane elastomers with the addition of biopolymers (cellulose, lignin, and chitin) was conducted for the first time. The innovative biocomposites obtained in this way were characterised by good processing parameters (processing times, density) and improved functional properties compared to the standard without the addition of fillers (abrasion resistance, tensile strength, contact angle, hardness). Due to the above-mentioned facts, the described biocomposites can be successfully used for the production of multifunctional elastomeric materials with a wide range of potential applications. Moreover, it is worth noting that the management of waste materials in this way will reduce production costs while indirectly contributing to the protection of the natural environment.Graphical abstract

Effects of Filler Modification on the Properties of Elastomeric Composites

Effects of Filler Modification on the Properties of Elastomeric Composites