Jun Lin

Current research on epoxy (EP) vitrimers primarily focuses on enhancing material mechanical properties and self‐healing efficiency. However, EPs with high mechanical strength struggle to reconcile network dynamicity due to their high crosslinking density or substantial content of rigid moieties. Consequently, they often require harsh repair/recycling conditions, exhibit low recycling efficiency. In this study, a series of EP vitrimers with different crosslinking network structures was prepared by reacting a high‐rigidity group‐concentrated multi‐reversible dynamic bond long‐chain curing agent with a flexible epoxy monomer containing polyether bonds. The concept of crosslinking network rigid‐flexible ratio (CRFR) was introduced to quantify the properties. Through structural optimization, the EP vitrimer demonstrated ultrahigh tensile strength (91.6 MPa) and storage modulus (2.65 GPa). Its excellent network dynamicity resulted in an ultra‐fast stress relaxation rate (8.7 s at 120°C), outstanding processability and shape‐memory properties. Furthermore, the EP vitrimer can be fully degraded at 50°C in either an HCl pure H ₂ O/DMF solution. The degradation products can be repolymerized directly, enabling green closed‐loop recycling with full retention of the original mechanical strength. This work provides an important theoretical foundation and a new pathway for the design of high‐strength polymers, as well as for the green recycling of EP vitrimers.

Fe/Co–N–C-GNRs exhibit a high electrocatalytic activity for the ORR (onset and half-wave potentials of 0.95 and 0.83 V, respectively) and high durability, due to the combined effects of Fe–N_x, Co–N_x, FeCo–N_x, and GNR edge sites.

Constructing continuous proton transport channels in proton exchange membranes (PEMs) has been considered as an efficient strategy to improve proton conductivity. In this work, a water‐insoluble hybrid graphene oxide (HDGO) is prepared via the hydrothermal reaction between polydopamine‐coated graphene oxide (DGO) and a strong proton conductor phosphotungstic acid (HPW), in which HPW is chemically bonded onto DGO. The two‐dimensional structure of DGO and the strong acidity of HPW favor the rapid proton transport in the sulfonated poly(ether ether ketone) (SPEEK) membranes. As compared to that of the SPEEK control membrane, the proton conductivity of the SPEEK composite membrane containing 6 wt% HDGO increases from 0.035 to 0.061 S cm⁻¹ at 25°C, an increase of ~75%. The composite membrane containing 10 wt% HDGO exhibits ~49% lower area swelling ratio than the SPEEK control membrane. Meanwhile, the proton conductivity of the composite membrane remains stable during the 1440 h immersing in liquid water.

Phosphotungstic acid (HPW) can retain water in proton exchange membranes to increase proton conductivity; however, its water-soluble nature limits further application. In this work, we combined HPW and graphitic carbon nitride (g-C₃N₄) via sintering to prepare water-insoluble hybrids (HWN), where HPW was chemically linked to g-C₃N₄ to fix HPW. Then, HWN fillers were added to a sulfonated polyether ether ketone (SPEEK) matrix to prepare composite membranes. The conductivity of the composite membrane with 10 wt% HWN is up to 0.066 S cm⁻¹ at room temperature, which is 53% higher than that of the SPEEK control membrane (0.043 S cm⁻¹). The composite membrane also showed stable proton conductivity after being immersed in water for 2000 h. Therefore, our study demonstrates that preparing water-insoluble nanofillers containing HPW components through sintering is a promising approach.

Considering the dilemma of obtaining economic and high-performance composites based on non-polar and main-chain-saturated ethylene propylene diene monomer rubber (EPDM), we proposed an effective and universal filler modification and nanocomposite preparation method. Specifically, the montmorillonite (MMT) surface was coated with polydopamine (PDA) to obtain DMMT, which was confirmed by XRD, XPS, FTIR, and TGA. After compounding DMMT gel with the solid EPDM via the gel compounding method, a silane coupling agent, vinyltrimethoxysilane, was introduced to construct covalent interactions between rubber and filler. Compared with the unmodified MMT filler EPDM, the EPDM/DMMT nanocomposite showed much fewer filler aggregates in the matrix. The highest tensile strength of the composites reached 6.5 MPa with 10 phr DMMT, almost 200% higher than that of pure EPDM.

Natural rubber (NR) composites have been widely applied in damping products to reduce harmful vibrations, while rubber with only a single composition barely meets performance requirements. In this study, rubber blend composites including various ratios of NR and styrene butadiene rubber (SBR) were prepared via the conventional mechanical blending method. The effects of the rubber components on the compression set, compression fatigue temperature rising and the thermal oxidative aging properties of the NR/SBR blend composites were investigated. Meanwhile, the dynamic mechanical thermal analyzer and rubber processing analyzer were used to characterize the dynamic viscoelasticity of the NR/SBR blend composites. It was shown that, with the increase in the SBR ratio, the vulcanization rate of the composites increased significantly, while the compression fatigue temperature rising of the composites decreased gradually from 47 °C (0% SBR ratio) to 31 °C (50% SBR ratio). The compression set of the composites remained at ~33% when the SBR ratio was no more than 20%, and increased gradually when the SBR ratio was more than 20%.

Silicone rubber (SIR) is used in high-voltage insulators because of its insulation, and excellent hydrophobicity is very important in harsh outdoor environments. To enhance the hydrophobicity and low-temperature resistance of silicone rubber, methyl vinyl silicone rubber and fluorosilicone rubber (FSIR) blend composites with different ratios were prepared. The samples were characterized and analyzed using scanning electron microscopy, tensile testing, dynamic mechanical analysis and static contact angle testing. The results showed that after blending, SIR and FSIR were well compatible. FSIR had higher elastic modulus and reduced the tensile strength to some extent in SIR/FSIR composites. The addition of a small amount of FSIR made its crystallization temperature decrease from −30 to −45 °C, meaning that the low-temperature resistance was significantly improved. The breakdown strength of SIR/FSIR composites can still be maintained at a high level when a small amount of FSIR is added. The contact angle of the composites increased from 108.9 to 115.8° with the increase in FSIR content, indicating the enhanced hydrophobicity. When the samples were immersed in water for 96 h, the hydrophobicity migration phenomenon occurred. The static contact angle of the samples with less FSIR content had a weaker decreasing trend, which illustrated that the hydrophobicity was maintained at a high level.