Search Results (46)

Modern trends in advanced material design increasingly emphasize sustainability and the use of naturally derived resources. One promising approach involves replacing synthetic additives with natural compounds that exhibit stabilizing properties. The aim of this study was to evaluate the effects of selected natural auxiliary substances—thymol (2-isopropyl-5-methylphenol), quercetin (3,3,4,5,7-pentahydroxyflavone) and caffeic acid (3-(3,4-dihydroxyphenyl)prop-2-enoic acid)—on the properties of elastomeric composites based on natural rubber. Biochar was used as the filler in the composites, serving as an eco-friendly alternative to conventional carbon black. The evaluation included measurements of crosslink density, hardness, mechanical properties and microstructural analysis of the resulting materials. The samples were also subjected to accelerated aging under thermo-oxidative conditions and UV radiation to assess their resistance to degradation. For comparison, the commonly used synthetic antioxidant BHT (2,6-di-tert-butyl-4-methylphenol) was also analyzed. The results enabled the assessment of the potential of natural additives as environmentally friendly stabilizers in elastomeric systems, with respect to their effectiveness and impact on material durability. Full article

Diabetic foot ulcers (DFUs) represent a critical global health issue, necessitating the development of advanced smart, flexible, and wearable sensors for continuous monitoring that are reimbursable within foot orthotics. This study presents the design and characterization of a pressure sensor implemented into a shoe insole to monitor diabetic wound pressures, emphasizing the need for a high sensitivity, durability under cyclic mechanical loading, and a rapid response time. This investigation focuses on the electrical and mechanical properties of carbon nanotube (CNT) composites utilizing Ecoflex and polydimethylsiloxane (PDMS). Morphological characterization was conducted using Transmission Electron Microscopy (TEM), Laser Confocal Microscopy, and Scanning Electron Microscopy (SEM). The electrical and mechanical properties of the CNT/Ecoflex- and the CNT/PDMS-based sensor composites were then investigated. CNT/Ecoflex was then further evaluated due to its lower variability performance between cycles at the same pressure, as well as its consistently higher capacitance values across all trials in comparison to CNT/PDMS. The CNT/Ecoflex composite sensor showed a high sensitivity (2.38 to 3.40 kPa⁻¹) over a pressure sensing range of 0 to 68.95 kPa. The sensor’s stability was further assessed under applied pressures simulating human weight. A custom insole prototype, incorporating 12 CNT/Ecoflex elastomeric matrix-based sensors (as an example) distributed across the metatarsal heads, midfoot, and heel regions, was developed and characterized. Capacitance measurements, ranging from 0.25 pF to 60 pF, were obtained across N = 3 feasibility trials, demonstrating the sensor’s response to varying pressure conditions linked to different body weights. These results highlight the potential of this flexible insole prototype for precise and real-time plantar surface monitoring, offering an approachable avenue for a challenging diabetic orthotics application. Full article

Thermoplastic polyurethane (TPU) combines elastomeric and thermoplastic properties but suffers from insufficient rigidity and strength for structural applications. Herein, we developed novel carbon fiber-reinforced TPU (CF/TPU) composites filaments and utilize melt extrusion for 3D printing to maintain elasticity, while achieving enhanced stiffness and strength through multi scale-the control of fiber content and optimization of printing parameters, reaching a rigid–elastic balance. A systematic evaluation of CF content (0–25%) and printing parameters revealed optimal performance to be at 220–230 °C and 40 mm/s for ensuring proper flow to wet fibers without polymer degradation. Compared with TPU, 20% CF/TPU exhibited 63.65%, 105.51%, and 93.69% improvements in tensile, compressive, and impact strength, respectively, alongside 70.88% and 72.92% enhancements in compression and impact energy absorption. This work establishes a fundamental framework for developing rigid–elastic hybrid materials with tailored energy absorption capabilities through rational material design and optimized additive manufacturing processes. Full article

In this paper, thermal and mechanical properties of ablative thermal protective material (TPM) as inhibitors for a free-standing propellant grain based on phenolic resin (PR) and acrylonitrile butadiene rubber (NBR) were investigated. NBR elastomerized PR composite, reinforced with chopped carbon fibers (CFs) (PR/NBR/CF), was prepared by homogenization of 90 parts by weight (PBW) PR in 100 PBW NBR (28 wt.% of acrylonitrile content). PR/NBR/CF composite was blended in two-roller open and closed mixers and in a twin-screw extruder. Carbon black, aluminum(III)-oxide, and fumed silica were added as promoters of thermal and mechanical properties of PR/NBR/CF. The structural analysis was studied using Fourier transform infrared spectroscopy (FT-IR). Thermal properties of the prepared PR/NBR/CF composite inhibitor were studied by ablation and firing tests, while a morphological analysis of the char layer formed after the ablation test was conducted via scanning electron microscopy (SEM). A low erosion rate of 2.00 × 10⁻⁴ m·s⁻¹ and high tensile strength and elongation at break of 6.7 MPa and 419.92%, respectively, indicate that the developed materials can be applied as a thermal insulation/inhibitor of free-standing rocket propellant grains. Bond strength between PR/NBR/CF composite and aluminized composite rocket propellant (ACRP), determined via a standard peel test, showed higher adhesion forces between the PR/NBR/CF composite and the ACRP compared to the cohesion between the ACRP molecular chains. Full article

This paper investigates the use of glass and carbon fiber-reinforced polymer composites with epoxy matrices for non-pneumatic tires (NPTs), as an alternative to conventional elastomer-based designs. A novel NPT design approach was developed in three steps: (i) a finite element model with isotropic material properties was constructed to identify suitable spoke geometries; (ii) an anisotropic parametric study quantified key parameters influencing the load-bearing capability of two selected concepts from step (i); and (iii) a preferred version was chosen from step (ii) and evaluated under multiple load cases to ensure it met all requirements. The final tire design incorporates thick spiral spokes superimposed with a cosine-like function, showcasing the strengths and limitations of non-elastomeric reinforced polymers for NPT design. This study provides innovative insights into reducing the mass of NPTs and demonstrates the potential of fiber-reinforced polymer composites to achieve more lightweight, durable, and efficient NPT designs in comparison to pneumatic ones. Full article

Carbon nanomaterials, particularly carbon nanotubes (CNTs), are widely used as reinforcing fillers in rubber composites for advanced mechanical and electrical applications. However, the influence of rubber functionality and its interactions with CNTs remains underexplored. This study investigates electroactive elastomeric composites fabricated with CNTs in two common diene rubbers: natural rubber (NR) and acrylonitrile-butadiene rubber (NBR), each with distinct functionalities. For NR-based composites containing 2 vol% CNTs, mechanical properties, such as elastic modulus (2.24 MPa), tensile strength (12.48 MPa), and fracture toughness (26.92 MJ/m³), show significant improvements of 125%, 215%, and 164%, respectively, compared to unfilled rubber. Similarly, for NBR-based composites, the elastic modulus (5.46 MPa), tensile strength (13.47 MPa), and fracture toughness (82.89 MJ/m³) increase by 94%, 22%, and 65%, respectively, over the unfilled system. Although NBR-based composites exhibit higher mechanical properties, NR systems show more significant improvements, suggesting stronger chemical bonding between NR chains and CNTs, as evidenced by dynamic mechanical, X-ray diffraction, thermogravimetric, and thermodynamic analyses. The NBR-based composite at 1 vol% CNT content exhibits 261% higher piezoresistive strain sensitivity (GF = 65 at 0% ≤ Δε ≤ 200%) compared to the NR-based composite (GF = 18 at 0% ≤ Δε ≤ 200%). The highest gauge factor of 39,125 (1000% ≤ Δε ≤ 1220) was achieved in NBR-based composites with 1 vol% CNT content. However, 1.5 vol% CNT content in NBR provides better strain sensitivity and linearity than other composites. Additionally, NBR demonstrates superior electromechanical actuation properties, with 1317% higher actuation displacement and 276% higher electromechanical pressure compared to NR at an applied electric field of 12 kV. Due to the stronger chemical bonding between the rubber and CNT, NR-based composites are more suitable for dynamic mechanical applications. In contrast, NBR-based CNT composites are ideal for stretchable electromechanical sensors and actuators, owing to the high dielectric constant and polarizable functional groups in NBR. Full article

In recent years, the search for more sustainable fillers for elastomeric composites than silica and carbon black has been underway. In this work, silanized starch was used as an innovative filler for elastomeric composites. Corn starch was chemically modified by silanization (with n-octadecyltrimethoxysilane) via a condensation reaction to produce a hydrophobic starch. Starch/natural rubber composites were prepared by mixing the modified starch with elastomer. The morphology, hydrophobicity, and chemical structure of starch after and before modification were studied. The results showed that starch after silanization becomes hydrophobic (θ_w = 117.3°) with a smaller particle size. In addition, FT-IR spectrum analysis confirmed the attachment of silane groups to the starch. The modified starch dispersed better in the natural rubber matrix and obtained a more homogeneous morphology. The composite achieved the best dynamic (ΔG′ = 203.8 kPa) and mechanical properties (TS_b = 11.4 MPa) for compositions with 15 phr of modified starch. In addition, the incorporation of silanized starch improved the hydrophobicity of the composite (θ_w = 117.8°). The higher starch content allowed the composites to achieve a higher degree of cross-linking, resulting in better resistance to swelling in organic solvents. This improvement is due to enhanced elastomer–filler interactions and reduced spaces that prevent solvent penetration into the material’s depths. The improved mechanical properties and good dynamic properties, as well as improved hydrophobicity, were mainly due to improved interfacial interactions between rubber and starch. This study highlights the potential and new approach of silane-modified starch as a sustainable filler, demonstrating its ability to enhance the mechanical, dynamic, and hydrophobic properties of elastomeric composites while supporting greener material solutions for the rubber industry. Full article

This contribution focuses on electroconductive elastomeric composites based on styrene–butadiene rubber filled with graphite, conductive carbon blacks, and a mixture of these fillers to investigate changes in their conductivity during cyclic deformation. Static conductivity, mechanical properties, and conductivity with simultaneous recording of the stress-strain curve were measured to characterize the composites. The composites containing higher amounts of graphite showed an increase in maximum stress and a decrease in conductivity dependency starting from the second cycle. The results show the potential to design and construct flexible conducting composites based on styrene–butadiene rubber in broad applications such as in the automotive industry. Full article

This study investigates the effectiveness of polyether block amide (PEBA) thermoplastic elastomeric nanofibers in reducing low-velocity impact damage across three carbon fiber composite lay-up configurations: a cross-ply [0°/90°]2s (CP) and a quasi-isotropic [0°/45°/90°/−45°]s (QI) lay-up utilizing unidirectional plies, and a stacked woven [(0°,90°)]4s (W) lay-up using twill woven fabric plies. The flexural strength and interlaminar shear strength of the composites remained unaffected by the addition of nanofibers: around 750 MPa and 63 MPa for CP, 550 MPa and 58 MPa for QI, and 650 MPa and 50 MPa for W, respectively. The incorporation of nanofibers in the interlaminar regions resulted in a substantial reduction in projected damage area, ranging from 30% to 50% reduction over an impact energy range of 5–20 J. Microscopic analysis showed that especially the delamination damage decreased in toughened composites, while intralaminar damage remained similar for the cross-ply and quasi-isotropic lay-ups and decreased only in the woven lay-up. This agrees with the broad body of research that shows that interleaved nanofibers result in a higher delamination resistance due to toughening mechanisms related to nanofiber bridging of cracks. Despite their ability to mitigate delamination during impact, nanofibers showed limited positive effects on Compression After Impact (CAI) strength in quasi-isotropic and cross-ply composites. Interestingly, only the woven fabric composites demonstrated improved CAI strength, with a 12% improvement on average over the impact energy range, attributed to a reduction in both interlaminar and intralaminar damage. This study indicates the critical role of fiber integrity over delamination size in determining CAI performance, suggesting that the delaminations are not sufficiently large to induce buckling of sub-layers, thereby minimizing the effect of nanofiber toughening on the CAI strength. Full article

Objectives: Using toothpaste with activated carbon might increase the decay of orthodontic elastomeric chains’ (ECs) tensile strength, thereby compromising orthodontic treatment. Therefore, this study aimed to evaluate the influence of activated charcoal toothpaste on orthodontic ECs. Materials and Methods: A total sample of 180 EC segments from 3M Unitek^®, Ormco^® and Ortho Classic^® brands were equally divided into 12 groups, each comprising 15 specimens. These pieces were kept in artificial saliva at 37 °C and brushed twice daily for 28 days, with three distinct types of toothpaste: Colgate^® Total, Colgate^® Max White, and Dr Organic^® Extra Whitening Charcoal Toothpaste. The latter two toothpastes contain activated charcoal. Tensile strength, resistance to rupture and colour variation were evaluated at time zero and day 28. Descriptive statistics, one-way ANOVA and Tukey HSD tests were performed at p ≤ 0.05. Results: Toothpaste with and without activated carbon significantly reduced the tensile strength and resistance to rupture of the ECs, and altered EC colour (p < 0.0001). There was inconsistency in the effect of the activated carbon on EC characteristics, most probably due to the different compositions of the ECs and percentages of whitening agents in the toothpastes. Conclusions: The material composition of ECs contributes to their tensile strength decay, resistance to rupture and colour change over time. The variable percentage of activated carbon in a toothpaste likely underlies the different effects observed, depending on the EC brand. Clinical Relevance: It might be reasonable to advise patients wearing ECs to avoid using toothpaste with activated carbon until further evidence becomes available. Full article

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. Full article

Ablative composites serve as sacrificial materials, protecting underlying materials from high-temperature environments by endothermic reactions. These materials undergo various phenomena, including thermal degradation, pyrolysis, gas generation, char formation, erosion, gas flow, and different modes of heat transfer (such as conduction, convection, and radiation), all stemming from these endothermic reactions. These phenomena synergize to form a protective layer over the underlying materials. Carbon, with its superb mechanical properties and various available forms, is highlighted, alongside phenolics known for good adhesion and fabric ability and elastomers valued for flexibility and resilience. This study focuses on recent advancements in carbon-and-phenolic and carbon-and-elastomeric composites, considering factors such as erosion speed; high-temperature resistance; tensile, bending, and compressive strength; fiber–matrix interaction; and char formation. Various authors’ calculations regarding the percentage reduction in linear ablation rate (LAR) and mass ablation rate (MAR) are discussed. These analyses inform potential advancements in the field of carbon/phenolic and carbon/elastomeric ablative composites. Full article

Composites revolutionize material performance, fostering innovation and efficiency in diverse sectors. Elastomer-based polymeric composites are crucial for applications requiring superior mechanical strength and durability. Widely applied in automotives, aerospace, construction, and consumer goods, they excel under extreme conditions. Composites based on recycled rubber, fortified with reinforcing fillers, represent a sustainable material innovation by repurposing discarded rubber. The integration of reinforcing agents enhances the strength and resilience of this composite, and the recycled polymeric matrix offers an eco-friendly alternative to virgin elastomers, reducing their environmental impact. Devulcanized rubber, with inherently lower mechanical properties than virgin rubber, requires enhancement of its quality for reuse in a circular economy: considerable amounts of recycled tire rubber can only be applied in new tires if the property profile comes close to the one of the virgin rubber. To achieve this, model passenger car tire and whole tire rubber granulates were transformed into elastomeric composites through optimized devulcanization and blending with additional fillers like carbon black and silica–silane. These fillers were chosen as they are commonly used in tire compounding, but they lose their reactivity during their service life and the devulcanization process. Incorporation of 20% (w/w) additional filler enhanced the strength of the devulcanizate composites by up to 15%. Additionally, increased silane concentration significantly further improved the tensile strength, Payne effect, and dispersion by enhancing the polymer–filler interaction through improved silanization. Higher silane concentrations reduced elongation at break and increased crosslink density, as it leads to a stable filler–polymer network. The optimal concentration of a silica–silane filler system for a devulcanizate was found to be 20% silica with 3% silane, showing the best property profile. Full article

Elastomer composites for dynamic mechanical applications with a low dissipation of energy are of great importance in view of their application in tire compounds. In this work, furnace carbon black functionalized with 2-2,5-dimethyl-1H-pyrrol-1-yl-1,3-propanediol (SP) was used in place of silica in an elastomer composite based on poly(styrene-co-butadiene) from solution anionic polymerization and poly(1,4-cis-isoprene) from Hevea Brasiliensis. The traditional coupling agent used for silica was also used for the CB/SP adduct: 3,3′-bis(triethoxysilylpropyl)tetrasulfide (TESPT). The composite with the CB/SP + TESPT system revealed a lower Payne effect, higher dynamic rigidity, and lower hysteresis, compared to the composite with CB + TESPT, although the latter composite had a higher crosslinking density. The properties of the silica and the CB/SP + TESPT-based composites appear similar, though in the presence of slightly higher hysteresis and lower ultimate properties for the CB/SP-based composite. The use of CB in place of silica allows us to prepare lighter compounds and paves the way for the preparation of tire compounds with lower environmental impacts. Full article

Fiber-reinforced elastomeric isolators (FREIs) are composite devices consisting of an alternation of elastomer layers and fiber reinforcement layers. They have mechanical properties comparable to those of conventional Steel-Reinforced Elastomeric Isolators (SREIs). The mechanical and construction characteristics of FREIs, together with their lower cost, make them potentially usable on a large scale. However, for their actual use, it is necessary to take into account the current regulations regarding seismic isolation. The application of FREIs provides the absence of anchoring to the structure, but the European Technical Standard UNI EN 15129 requires that the isolators are attached to the structure by mechanical fastening only. In this research work, a constraint device that fulfills this requirement but, at the same time, does not significantly alter the mechanical behavior of FREIs is investigated. The properties of the selected device and its installation method are presented. The results of both a simple compression test and a combined compression and shear test performed on two isolators reinforced by quadri-directional carbon fiber fabrics and two isolators reinforced by bi-directional fabrics are presented. The tests were performed in the absence and presence of the constraint device in order to investigate the modifications produced by the device. Full article