Hongbo Dai

Vitrimers are covalent adaptable networks (CANs) that undergo thermally activated topological rearrangement via dynamic bond exchange, enabling reprocessability and intrinsic self-healing. However, precise, real-time identification of the topological transition temperature (T_v) remains challenging, as conventional methods are inherently stress- and protocol-dependent. Here, we present a hierarchically structured piezoresistive sensing strategy based on dual-scale CNT-integrated conductive networks. A mesoscale CNT-decorated glass fibrous web (G-CNT) and a nanoscale CNT/EPON percolation network are synergistically integrated to enable in situ, external-stress-free electrical tracking of disulfide-containing epoxy vitrimer network formation and topological transitions. These multiscale conductive architectures exhibit distinct resistance signatures throughout vitrimer evolution, with pronounced inflection features at T_v arising from bond-exchange-driven rearrangements of conductive pathways. Comparative analysis reveals that interfacial G-CNT meso-networks fabricated via ultrasonic atomization exhibit substantially higher sensitivity, manifested by pronounced resistance decreases at T_v (ΔR_v = −10.9% to −20.0%), enabling instant detection of local topological rearrangements. In contrast, bulk CNT/EPON networks display attenuated resistance responses (ΔR_v = −4.3% to −9.4%) associated with matrix-level percolation restructuring. These electrical signatures are corroborated by differential scanning calorimetry, dynamic mechanical analysis, rheology, and dielectric analysis, establishing a direct structure-dynamics-signal correlation. This stress-free, multiscale sensing paradigm provides a scalable route for intrinsic T_v identification and process-aware diagnostics in recyclable and adaptive vitrimer-based composites.

Carbon fiber-reinforced epoxy composites are widely used in engineering applications owing to their excellent specific strength, modulus and cost performance. However, the brittleness and poor recyclability of the thermosetting epoxy matrix severely limit their sustainability. In this study, bisphenol A-type epoxy resin and bisphenol A were used as raw materials, and a 2-methylimidazole/tetrabutylammonium bromide catalytic system was employed to successfully prepare a high strength and toughness thermoplastic epoxy resin (TPE) via solution polymerization. The resulting TPE exhibited a weight-average molecular weight (Mw) of 43078 g/mol and a polydispersity index of 1.29. In addition, the TPE exhibited outstanding mechanical and thermal performance, with high tensile strength of 76 MPa, toughness of 30.7 MJ·m−3 and Td5% of 423 °C. Carbon fiber-reinforced thermoplastic epoxy composites (CF/TPE) were fabricated via the prepreg compression molding process. The CF/TPE composites exhibited a tensile strength of 1022.7 MPa, flexural strength of 1042.5 MPa and interlaminar shear strength (ILSS) of 65.2 MPa. The TPE matrix can be efficiently dissolved in polar solvents, enabling the intact recovery of both carbon fibers and the TPE matrix. This approach provides a TPE to replace conventional thermosetting epoxy while also enabling an effective preparation-recycling route for sustainable use of carbon fiber composites.

The attainment of both high mechanical strength and good toughness has always been the ultimate goal for developing viable fiber-reinforced thermoplastic (FRTP) composites for critical structural applications in the aerospace and automobile fields. Most sized glass fiber reinforced polypropylene composites exhibit higher tensile and flexural strengths but lower impact resistance than commercial glass fiber reinforced polypropylene composites, which limits their future utilization in industry. In this work, an amphiphilic sizing agent as the interfacial modifier and a β-nucleating agent (NA) as the added toughener were simultaneously used to improve the mechanical properties of short glass fiber reinforced polypropylene (GF/PP) composites and addition of a β nucleating agent improved the impact resistance of the sized glass fiber reinforced polypropylene composite without degrading the tensile and flexural strengths. Additionally, polarized light microscope and differential scanning calorimetry demonstrated that the improved mechanical properties of the composites were attributed to the improved compatibility between glass fibers and polypropylene and the enhanced crystallization ability of polypropylene. Thus, the proposed method provides a way to balance the strength and toughness of composites.

Purpose: The purpose of this study is to reduce the cost of poly(butylene adipate-co-terephthalate) (PBAT) and obtain biodegradable composites with good interface compatibility, mechanical properties and shape memory properties. The unmodified and modified bamboo powder/poly(lactic acid)/PBAT (B/PLA/PBAT) composites were prepared, respectively. The effects of bamboo powder and modifiers on the interfacial compatibility, mechanical properties and shape memory properties of the B/PLA/PBAT composites were systematically investigated. Design/methodology/approach: The B/PLA/PBAT composites were prepared by melt extrusion and hot-pressing with ADR 4370 and SMA-2025 as chain extender and compatibilizer, respectively. Findings: The experimental results showed that the section roughness of the B/PLA/PBAT composites increased after addition of bamboo powder, but the surface roughness was slightly improved after the addition of chain extender and compatibilizer. At the same time, bamboo powder and PLA particles were well dispersed in PBAT, and the interface compatibility between the three was improved. With the increase of bamboo powder content, the tensile strength and elongation at break of the B/PLA/PBAT composites generally showed a decreasing trend, and the Young’s modulus generally showed an increasing trend. The addition of bamboo powder and modifier have little effect on the thermal stability of the PLA/PBAT composites. The B/PLA/PBAT composites have good shape memory properties and the Rf and Rr decreased slightly with the increase of bamboo powder at prestrain of 300%. From 100 °C to 120 °C, the Rr of the composites only added with ADR 4370 increased more significantly, especially when the content of bamboo powder was 10 Wt.%, the Rr of the composites was still 75.50 ± 2.61%. In general, the Rf and Rr of the typical B/PLA/PBAT composites exceeded 60.56 ± 3.47% and 71.83 ± 0.68%, respectively. Research limitations/implications: The B/PLA/PBAT composites have good mechanical properties and shape memory properties, and have good application potential in biodegradable plastics and other fields. In the context of the increasing pressure on the environment caused by the proliferation of non-degradable plastic products. It is important to promote research efforts to replace traditional non-biodegradable materials with biobased or biodegradable materials that are more environmentally sustainable. Originality/value: In this study, the unmodified- and modified PBAT-based composites with good mechanical properties, shape memory properties were obtained by using PLA as the filler, bamboo powder as the low-cost natural functional filler, ADR 4370 and SMA-2025 as chain extender and compatibilizer, respectively.

Advanced flexible dielectric materials have long been sought to meet the growing demands of high-frequency and high-speed applications. In this study, a composite system was first synthesized by blending water-soluble fluorinated poly (amic acid) ammonium salt (FPAAs) with polytetrafluoroethylene particles (PTFEP), namely PTFEP-FPAAs. Then, unique and freestanding PTFEF/PTFEP-fluorinated polyimide (FPI) composite sandwich films (50-90 μm thick) combining PTFE fiber film (PTFEF) core with PTFEP-FPI film sheets were fabricated via a facile layer-by-layer process. The influence of varying PTFEP and PTFEF volume fractions on the dielectric, thermal, mechanical, and hydrophobic properties of the composite films was systematically investigated. The optimal performance was achieved at specific volume ratios: 30 vol% PTFEF in PTFEF/PTFEP-FPI and 40 vol% PTFEP in PTFEP-FPAAs, resulting in exceptional dielectric properties in the high-frequency range (8.2 to 12.4 GHz and 12 to 18 GHz) including an ultra-low dielectric constant of 1.84 (at 10 GHz), dielectric loss factor of 0.005, and dielectric strength of 213.0 kV/mm. Theoretical analyses, based on dielectric constant and dipole polarization models, provided further insights into the observed dielectric behavior. The incorporation of PTFEF, PTFEP, and the sandwich structure synergistically enhanced the dielectric performance. In addition, a large-deformation (in terms of 15% and 45% compressive strain) cyclic buckling test was conducted to evaluate the mechanical robustness of the sandwich films. This work successfully demonstrates the fabrication of a flexible dielectric composite film with superior overall thermal and mechanical properties, offering a solid theoretical and experimental foundation for the development of advanced dielectric composite materials.