Search Results (293)

The effect of thermo-oxidative aging on the hyperelastic behavior of ethylene propylene diene monomer (EPDM) rubber was investigated by a combined experimental and theoretical modeling approach. Firstly, the uniaxial tensile test of aged and unaged EPDM rubber was carried out. The test results show that the unaged EPDM rubber had the nonlinear large deformation characteristic of a “S” shape. The stiffness of the EPDM rubber was found to increase with the aging time and aging temperature. Then, in order to quantitatively characterize the hyperelastic behavior of unaged EPDM rubber, the fitting performances of the Mooney–Rivlin, Arruda–Boyce, and Ogden models were compared based on a uniaxial tensile stress–strain curve. The results show that the Ogden model provided a more accurate representation of the hyperelastic behavior of unaged EPDM rubber. Subsequently, the Dakin dynamic equation was adopted to associate the parameters of the Ogden model with the aging time, and the Arrhenius relationship was utilized to introduce the aging temperature into the rate term of the Dakin dynamic equation, thereby establishing an improved Ogden constitutive model. This improved model expanded the Ogden model’s ability to explain aging time and aging temperature. Finally, the improved model prediction results and the test results were compared, and they indicate that the proposed improved Ogden constitutive model can accurately describe the hyperelastic behavior of aged and unaged EPDM rubber. Full article

Sustainable ethylene propylene diene monomer (EPDM) elastomers are gaining traction as eco-friendly sealing materials in fuel cell applications. This study evaluates the mechanical degradation behavior of two ECO EPDM formulations—one reinforced with circular carbon black (CCB EPDM), and the other with recycled carbon black (RCB EPDM)—under conditions representative of acidic fuel cell environments. The samples underwent thermal aging at 90 °C for 1000 h, and were immersed in aqueous H₂SO₄ solutions of varying concentrations (1 M, 0.1 M, and 0.001 M) for 1000 h at the same temperature. Gravimetric and volumetric swelling measurements revealed that RCB EPDM experienced significantly higher mass and volume uptake, particularly at intermediate acid concentration, indicating greater susceptibility to fluid ingress. Mechanical testing, including measurement of tensile strength, Shore A hardness, and IRHD microhardness, showed that while RCB EPDM exhibited higher initial strength, it degraded more severely under thermal and acidic exposure. SEM-EDS analysis revealed microstructural damage and compositional changes, with RCB EPDM displaying more pronounced oxidation and surface erosion. In contrast, CCB EPDM demonstrated greater retention of mechanical integrity, greater dimensional stability, and lower variability across aging conditions. These findings highlight the advantages of circular carbon black in enhancing the durability of ECO EPDM compounds in acidic and thermally dynamic fuel cell environments. Full article

Polypropylene carbonate (PPC) is a biodegradable material derived from propylene oxide (PO) with the renewable resource CO₂. In this study, PPC was prepared by the catalytic polymerization of CO₂ with PO using a zinc glutarate/zinc cobalt double metal cyanide (ZnGA/DMC) composite catalyst prepared from two heterogeneous catalysts, zinc glutarate (ZnGA) and zinc cobalt double metal cyanide (Zn-Co DMC). High selectivity of PPC was achieved among the polymer and propylene carbonate. The prepared PPC had high molecular weight. The thermal stability of the PPC product was obviously improved by the optimization of the reaction conditions. The catalytic effect of the composite catalyst was superior to that of individual ZnGA and Zn-Co DMC, overcoming the shortcomings of those two catalysts. And the composite catalyst also stimulated some synergistic effects between the two composites, which significantly improved the catalytic effect. Full article

This study reports an efficient and low-cost hydrothermal method for synthesizing vanadium oxide/graphene nanocatalysts. Field-emission scanning electron microscopy (FESEM) revealed the formation of nanostructured catalysts with consistent and directional shapes, as confirmed by X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectroscopy indicated the presence of V₂O₅ and graphene, highlighting their bonds and structures. Thermogravimetric analysis (TGA) identified three stages of weight loss in the nanocatalysts, corresponding to water molecule evaporation, decomposition of residual organics, and the formation of yellow vanadium pentoxide particles due to the oxidation of vanadium V⁴⁺. Gas chromatography analysis from 450 °C to 600 °C showed that ethylene selectivity increased with temperature, while propylene selectivity showed the opposite trend. The effectiveness of these nanocatalysts was assessed in the oxidative dehydrogenation of propane using temperature programmed reduction. The approach of graphene-based vanadium oxide nanostructures will open up a new insight into the fabrication of high-performance catalysts. Full article

Carbon dioxide-based copolymers such as polypropylene carbonate (PPC) can offer the double environmental benefit of capturing CO₂ and replacing oil-based raw materials in the plastics industry with renewable ones. However, their production at an industrial level is still limited by the range of applications in which their physicochemical properties are competitive and ideally surpass those of fossil-based polymeric commodities. This work introduces PPC materials with high-stretch and self-healing properties that were prepared by copolymerization of CO₂ and propylene oxide using tailored Zn glutarate catalysts. The PPC materials were analyzed in terms of composition, molecular weight, thermal and mechanical behavior, particularly focusing on their tensile properties, strain recovery, creep response, and self-healing ability. All the prepared PPC materials showed good ductility and self-healing properties. The most promising ones achieved excellent and fast recovery of extremely high elongations (>700%), still reaching remarkable values (>600%) after proper self-healing. These high-stretch and self-healing PPC materials are completely amorphous, present good optical transparency, and can be processed using techniques normally used for other thermoplastics. Therefore, they are promising for a variety of applications, including shrink films and self-healing packaging, thus providing new, valuable perspectives for the industrialization of these CO₂-based polymers. Full article

To enhance the dispersion of silica within a natural rubber (NR) matrix and improve the modification efficiency of the silane coupling agent, a novel interfacial dispersant composed of block polyether with a PEO-PPO-PEO structure is employed in this study. This block polyether, consisting of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), serves to reduce the surface energy of silica and improve its compatibility with the rubber matrix. Three types of block polyethers with different hydrophilic–lipophilic balance (HLB) values of 8, 13, and 22 are selected to regulate the surface tension of silica. Subsequently, bis[γ-(triethoxysilyl)propyl] tetrasulfide (TESPT) is used to further modify the silica surface, aiming to prepare high-performance rubber composites. The results indicate that the HLB value of the block polyether has a significant influence on the system. Compared with block polyethers having HLB values of 8 and 22, the block polyether with an HLB value of 13 demonstrated superior silica dispersion, leading to enhanced filler–rubber interfacial interactions. Consequently, both the mechanical properties and processability of the NR composites were substantially improved. When the dosage of this block polyether was 1 phr, the composite exhibited a tensile strength of 28.9 MPa and an elongation at break of 523%. Full article

Natural rubber is widely used in various engineering fields due to its excellent properties, particularly as an anti-corrosion and wear-resistant lining for metal pipelines. The defects in rubber linings are typically detected using the electrical spark test. Carbon black can enhance the strength, modulus, and wear resistance of natural rubber. However, conventional carbon black-filled natural rubber composites exhibit a certain level of electrical conductivity, making them unsuitable for defect detection via the electrical spark test. In this study, a silica/carbon black hybrid filler system was selected, and different types of amino-terminated poly(propylene oxide) were employed as novel interfacial dispersants to develop a low-conductivity natural rubber composite suitable for electrical spark testing while meeting general industrial mechanical performance requirements. The role of amino-terminated poly(propylene oxide) was first explored in a pure carbon black system, and then the optimized types and dosages of amino-terminated poly(propylene oxide) were added into a mixed filler system of silica and carbon black to explore the silica dosage that could balance the resistivity and mechanical properties. The results showed that the amino-terminated poly(propylene oxide) could improve the dispersion of carbon black and silica, thus increasing the mechanical properties of natural rubber composites. In the pure carbon black system, the tensile strength of natural rubber composites increased by 18.2%, the 300% modulus increased by 74.6%, and the Akron abrasion decreased by 42.7%. In the mixed filler system, the tensile strength of the natural rubber composites with 20 phr of silica and 30 phr of carbon black was 24.03 MPa, the 300% modulus was 15.16 MPa, and the Akron abrasion was 0.223 cm³. In addition, the volume resistivity was 5.52 × 10⁹ Ω·cm, which is suitable for detecting defects with the spark test. Full article

Due to the high saturated vapor pressure of low-boiling-point flammable liquids, it is difficult to make fire extinguishers for storage tanks containing them. Air foam extinguishing technology has been recommended by several standards. However, the effectiveness of air foam against low-boiling-point flammable liquid is still limited due to a lack of experimental data. To validate the reliability of air foam, fire-extinguishing measures for three low-boiling-point flammable liquids including propylene oxide, n-pentane, and condensate oil were carried out for the first time in this work. The results show that air foam fails the fire extinguishment of the studied liquids even at higher supply intensities. To address the challenge of fire extinguishment in storage tanks containing low-boiling-point flammable liquids, a novel method using heptafluoropropane (HFC227ea) phase change foaming to substitute air was proposed in this work. The experimental system of HFC227ea foam fire extinguishment was constructed. In addition, two low-boiling-point flammable liquids propylene oxide and n-pentane were selected as the research subjects, the fire extinguishment measures were conducted. The results show that the proposed method can realize rapid and effective extinguishment of flames for the studied liquids. Full article

Tropospheric ozone (O₃) and other pollutants significantly affect Chile’s Metropolitan Region, posing risks to human health. As a secondary pollutant and a major photochemical oxidant, O₃ formation is driven by anthropogenic volatile organic compounds (AVOCs) from the residential and transport sectors, the main sources of gaseous emissions. This study evaluated the AVOC capture capacity of leaf material from two tree species, Quillaja saponaria (native species) and Robinia pseudoacacia (exotic species), as potential urban biomonitors. Leaf samples were collected near nine SINCA official monitoring stations and the Antumapu University Campus, stored frozen, and analyzed by HS-SPME-GC/MSD for AVOC quantification. Photochemical reactivity and O₃ formation potential were assessed using equivalent propylene concentration (Prop-Equiv) and Ozone Formation Potential (OFP) methods. The results showed that both species captured atmospheric AVOCs, confirming their role as bioindicators. However, Q. saponaria adsorbed significantly higher AVOC concentrations and exhibited greater tropospheric O₃ formation potential than R. pseudoacacia. Given the AVOC adsorption capacity of both tree species, they could be used as biomonitors for styrene and also as a biomonitor for toluene in the case of Q. saponaria. This research highlights the importance of selecting tree capacity to improve urban air quality. Full article

The spray pyrolysis deposition of nanostructured Pb_1−xSn_xSe alloy films, x = 0.0 to 1.0, from as-prepared Pb_1−xSn_xSe alloy colloids as the starting solution is reported. The colloidal dispersions were prepared by dissolving selenium in an amine–thiol mixture, reacted with the Sn and Pb precursors in propylene glycol, and subsequently sprayed onto glass substrates at 300 °C. Structural characterization indicated the formation of the alloyed rock-salt cubic phase for 0.0 ≤ x ≤ 0.75, oxidized Pb and Se phases produced during the deposition, and only orthorhombic SnSe for x = 1.0 with Se and SnSe₂ as impurities. Nanocrystalline films ranging from 16 to 16.5 nm in size were obtained. The films displayed a shift in their optical structure and a non-monotonic variation in the band gap energy, first a decrease, reaching the minimum at x = 0.30 and a further increase in the Sn content. The decrease in the optical band gap resembles that of a topological insulator behavior. The morphology of the alloyed films confirmed the large nanocrystal formation by self-assembly processes in both the PbSe and SnSe phases and segregated PbSnSe platelets for x ≥ 0.30. Seebeck coefficient revealed that a typical semiconductor behavior dominated by bipolar transport, and p-type conductivity, but only for x = 0.0 n-type conductivity was exhibited. The maximal Seebeck coefficient magnitude behaved similarly to the band gap energy, evidencing the influence of energy band structure and the topological character. Full article

V-doped ZrO₂ support materials were synthesized through a hydrothermal method, followed by a deposition–precipitation process to load Au clusters using an H₄AuClO₄ precursor. This study investigated the impact of vanadium doping on propylene epoxidation over the corresponding Au-supported catalysts. Vanadium incorporation significantly enhanced propylene conversion and promoted acrolein production, leading to reduced propylene oxide selectivity. Propylene epoxidation at higher temperatures accelerated the decomposition of oxygenates into CO₂. Vanadium addition to ZrO₂ altered the interactions between Au and V-doped ZrO₂, thereby modifying the chemical states of Zr, Au, and V and forming surface oxygen vacancies and active oxygen species. These changes defined the catalytic performance of the materials. Full article

St. John’s wort (Hypericum perforatum) has been used for centuries in traditional medicine owing to its high content of various bioactive metabolites and wide geographic occurrence. Nowadays, it plays an important role in the pharmaceutical industry and is increasingly significant in modern cosmetology. The objective of this study was to assess the antioxidant activity and compare the content of polyphenolic compounds in two commercial extracts of H. perforatum, glycerol–water and propylene glycol–water, which are used as cosmetic raw materials. The HPLC method was used to determine phenolic compounds. The total polyphenol content and total flavonoid content of H. perforatum extracts were determined using spectrophotometric methods. Free radical-scavenging properties were analyzed using a 2,2-diphenyl-1-picrylhydrazyl radical assay with electron paramagnetic resonance spectroscopy (DPPH-EPR assay), as well as the ferric reducing antioxidant power (FRAP) method. St. John’s wort extracts were able to scavenge free radicals, indicating beneficial cellular protection against oxidative stress. The use of non-toxic extractants makes it possible to obtain extracts with high antioxidant potential, which can be safely used in the pharmaceutical and cosmetics industries. The results of this study, i.e., the values for TPC, TFC, and antioxidant activity (DPPH and FRAP), suggest that Hypericum perforatum, especially the glycerol–water extract, has antioxidant potential. Full article

A series of 5 wt.% Cr/SiO₂ catalysts were prepared through incipient wet impregnation using different chromium salts as a source of Cr (chromium (III) sulfate, acetylacetonate, nitrate, ammonium dichromate). The obtained catalysts were characterized by SEM-EDX, TEM, DRIFT-CD₃CN spectroscopy, UV-VIS diffuse reflectance spectroscopy, and the N₂ low-temperature adsorption–desorption technique. The catalysts were tested in propane, and isobutane dehydrogenation assisted with CO₂ at 600–750 °C. The highest activity in propane dehydrogenation was observed for the catalyst obtained from chromium acetylacetonate, the yield of propylene was 32% at 750 °C, and in the isobutane dehydrogenation reaction, the catalyst obtained from chromium sulfate was the best one; the yield of isobutene was ~30% at 600 °C. The obtained results show that the type of chromium precursor has a significant effect on the efficiency of the catalyst in the propane and isobutane dehydrogenation with CO₂. Full article

Multifunctional materials requiring low functional voltages are the main goal of new industrial smart technologies. Polypyrrole (PPy) was chemically synthesized by a simple dip-coating process on glucose–porcine skin gelatin nanofibers, accelerating mass production, here shown on nanofiber scaffolds (NFs) with those consisting of composites. The isometric and isotonic characterizations by electro-chemo-mechanical deformation (ECMD) of NFS-PPy are obtained from cyclic voltammetric and chronoamperometric responses in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium triflouromethanesulfonate (LiTF) and sodium perchlorate (NaClO₄) in propylene carbonate (PC). The results indicate a prevalent anion-driven actuation of the linear actuator (expansion by oxidation and contraction by reduction). Different stress (4–2 kPa) and strain (0.7–0.4%) gradients are a function of the anion Van der Waals volume. During reversible actuation (expansion/contraction), the material stores/releases energy, obtaining greater specific capacitance, 68 F g⁻¹, in LiTFSI solutions, keeping 82% of this capacity after 2000 cycles. The sensitivity (the slope of the linear sensing equation) is a characteristic of the exchanged anion. The reaction of the PPy-coated nanofiber is multifunctional, developing simultaneous actuation, sensing, and energy storage. The materials were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Full article

This work concerns a study of the thermomechanical behaviour of a commercial thruster for aerospace use. The thruster, operated using a bipropellant liquid mixture, is used for the motion and in-orbit altitude control of small telecommunications satellites. The mixture used in the combustion process is composed of propylene and nitrous oxide, while the wall of the thruster is made of PH15-5 stainless steel. A computational fluid dynamics analysis of conjugate heat transfer determines the spatial–temporal distribution of temperature within the thruster wall. This information is passed to a finite element mechanical model that simulates the stress and the equivalent plastic strain distribution within the thruster wall. Full article