Wang Yue¹， Gu Aotian²， Yang Yi¹

1. School of Environmental and Biological Engineering， Nanjing University of Science and Technology， Nanjing 210094， China；2. School of Chemistry， Chemical and Materials Engineering， Taizhou University， Taizhou 225300， China

Abstract

Objective Epoxy resin （EP） is widely used in aerospace， automotive， electronic packaging， and laminated composite applications due to its mechanical strength， chemical resistance， dimensional stability， and electrical insulation. However， its permanently cross-linked network makes it intrinsically brittle and prevents reshaping or recycling after curing. Covalent adaptable networks （CANs）， particularly epoxy-based vitrimers， overcome this limitation by enabling topological rearrangement through reversible bond exchange while maintaining the cross-link density. Graphene oxide （GO） is a widely adopted reinforcement for such networks. However， existing studies have focused almost exclusively on GO loading， and the role of GO sheet morphology in governing the reinforcement of dynamic covalent networks remains unclear. Therefore， this study aims to reveal the synergistic reinforcement mechanism between GO morphology and dynamic covalent networks， and to establish morphology engineering as a design parameter for sustainable， reprocessable， high-performance thermosets.

Methods Two GO grades with comparable surface chemistry and lateral dimensions but distinctly different aspect ratios were selected as nanofillers： a commercial low-aspect-ratio graphene oxide （GOc） and a laboratory-synthesized high-aspect-ratio graphene oxide （GOH） prepared using a modified Hummers method. The GO powders were characterized using Fourier transform infrared spectroscopy （FTIR）， Raman spectroscopy， scanning electron microscope （SEM）， and transmission electron microscope （TEM） to compare their oxygen-containing functional groups， defect density， lateral dimensions， sheet thickness， and degrees of exfoliation. Four nanocomposites containing 1 wt% filler were then fabricated. For the epoxy system， GO was ultrasonically dispersed in acetone for 30 min and then mixed with Araldite LY564 epoxy under mechanical stirring at 80 ℃ for 18 h. Subsequently， the mixture was combined with Aradur 2 954 hardener at a volume ratio of 100：35， degassed at 60 ℃ for 1 h， and cured at 80 ℃ for 1 h followed by 160 ℃ for 4 h. For the vitrimer system， 4-aminophenyl disulfide was used as the dynamic hardener. The mixture was degassed at 80 ℃ for 1 h and cured at 120 ℃ for 2.5 h， followed by curing at 150 ℃ for 2 h. Unfilled EP and vitrimer controls were prepared following identical procedures. Structure and filler dispersion were assessed by Raman spectroscopy and SEM imaging of cryo-fractured cross-sections. Interfacial chemistry was probed by XPS analysis of the C 1s， O 1s， and S 2p regions. Glass transition temperatures were determined using differential scanning calorimetry （DSC）. Stress relaxation was measured using the same dynamic mechanical thermal analysis （DMTA） instrument at 80 ℃ for 100 min and at 120 ℃ for 30 min. Electrical conductivity was obtained using impedance spectroscopy on silver-painted specimens.

Results and Discussion FTIR and Raman results confirmed that GOc and GOH contained equivalent hydroxyl， carbonyl， and carboxyl groups， as well as comparable I_D/I_G ratios， indicating similar oxidation levels. SEM showed that both grades exhibited lateral dimensions of 5-10 μm， predominantly 6-8 μm. TEM images clearly discriminated between the two morphologies. GOc consisted of flat， multilayer stacks with greater thickness， whereas GOH consisted of thinner， few-layer， strongly wrinkled sheets， indicating that the aspect-ratio difference originated from exfoliation rather than from chemistry. The D and G bands were retained in all four nanocomposites， confirming that GO was incorporated without structural degradation. XPS spectra of the composites showed no chemical shifts relative to the neat matrices， which demonstrated that no new covalent bonds were formed at 1 wt%. Thus， the improved dispersion observed in the vitrimer was attributed to physical polar affinity between the sulfur atoms of the disulfide hardener and the oxygen-containing groups on GO. SEM fractography supported this interpretation： GOc-vitrimer exhibited the most uniform dispersion and the most diffuse filler-matrix interface， while GOH-epoxy showed pronounced agglomerates， sharp interfaces， and voids that served as crack initiation sites. Incorporation of GO lowered T_g in both matrices， from 163 ℃ （DMTA） and 158 ℃ （DSC） for neat EP and from 143 ℃ and 138 ℃ for neat vitrimer. This decrease was attributed to weak filler-polymer interfacial bonding and the additional free volume introduced by GO. All samples remained electrically insulating， with conductivities on the order of 10⁻⁹ S·m⁻¹， because the oxygen-containing groups disrupted the delocalized π-electron system and no percolating network was formed. Mechanically， GOc increased the storage modulus of vitrimer and EP by approximately 30% and 5%， respectively， whereas GOH provided about 20% reinforcement in vitrimer and negligible reinforcement in EP， which was consistent with the lower agglomeration tendency and more efficient load transfer of the flat， thicker GOc sheets. Stress relaxation was markedly faster in vitrimer than in EP at both temperatures owing to disulfide exchange. Among all samples， GOc-vitrimer exhibited the fastest relaxation behavior， revealing a genuine synergy between well-dispersed GOc and the dynamic covalent network.

Conclusion GO morphology is a decisive parameter that governs the overall performance of polymer nanocomposites， while the matrix type further amplifies or suppresses the reinforcement through interfacial affinity and network dynamics. Low-aspect-ratio GOc outperforms high-aspect-ratio GOH in both matrices， and its combination with a disulfide-based vitrimer simultaneously optimizes mechanical stiffness and stress relaxation without compromising electrical insulation. Morphology engineering of GO therefore provides an experimental basis and a practical design route for high-performance， reprocessable， and sustainable thermosetting nanocomposites.

Keywords： graphene oxide； vitrimer； stress relaxation； storage modulus； dynamic covalent networks

Get Citation: Wang Yue， Gu Aotian， Yang Yi. Structure and properties of graphene oxide-reinforced epoxy resins and vitrimers［J］. China Powder Science and Technology， 2027， 33（1）： 1-17.

Received : 2026-05-27， Revised： 2026-08-27， Online： 2026-09-15。

Funding： The research was supported by the National Natural Science Foundation of China (Grant No. 52470120).

CLC No.: TB332； TQ323.5； TB44

Type Code: A

Serial No.: 1008-5548（2027）01-0001-17