XING M F, XU P, DONG L L, et al． DMF solubilization and recovery of waste carbon fiber prepregs and properties of the products［J］. Journal of Henan Polytechnic University( Natural Science)， doi: 10.16186/j.cnki.1673-9787.2026050006.

doi: 10.16186/j.cnki.1673-9787.2026050006.

Received： 2026-05-07

Revised： 2026-08-06

Online： 2026-08-15

DMF solubilization and recovery of waste carbon fiber prepregs and properties of the products (Online)

XING Mingfei, XU Ping, DONG Lili, ZHAO Li

School of Resources and Environment,Henan Polytechnic University,Jiaozuo 454003,Henan,

China

Abstract: Objectives To address the problem that waste carbon fiber/epoxy prepreg, after long-term storage at ambient temperature, undergoes resin aging caused by solvent evaporation and progressive crosslinking of components, leading to deteriorated re-moldability and a significant decline in the mechanical properties of hot-pressed composites, this study employs a dissolution method using N,N-dimethylformamide (DMF) to achieve efficient separation and recycling of the semi-cured epoxy resin and carbon fiber from the prepreg., Methods After the dissolution characteristics of six common organic solvents were systematically investigated, the dissolution mechanism of N,N-dimethylformamide (DMF) was revealed, and the recycling performance of the solvent and recovered products was comprehensively evaluated. Fourier transform infrared spectroscopy (FTIR) was used to analyze the interaction mechanism between solvent and resin molecules, and scanning electron microscopy (SEM) was used to observe the micromorphology of the recovered carbon fibers and residual resin on their surfaces. A closed-loop solvent recovery system was established by incorporating vacuum rotary evaporation. The mechanical properties of the recovered resin, single carbon fibers, and recycled carbon fiber reinforced polymer (CFRP) plates re-prepared by hot pressing were tested using a universal testing machine and a carbon fiber tensile strength tester. Results For CFRP plates fabricated from waste prepreg stored at ambient temperature for 1–4 months, the flexural strength and tensile strength decreased to 19.44%–76.15% and 44.28%–75.04% of those of the original plates, respectively, while the mechanical properties of the carbon fiber monofilaments in the prepreg remained largely unchanged, retaining 94.70%–98.90% of the original values. Under the optimal conditions of a stirring speed of 40 r/min, a liquid-to-solid ratio of 5:2 mL/g, and dissolution at room temperature for 25 min, the dissolution rate of the semi-cured epoxy resin by DMF reached 98.15%. FTIR analysis revealed that the formyl and N-carbonyl groups in DMF molecules form multiple hydrogen bonds with the hydroxyl and ether bonds of the resin, causing the resin to swell and separate through physical interactions without disrupting its chemical structure. After DMF treatment, the tensile strength and modulus of the recovered carbon fiber monofilaments were retained at 98.2% and 99.96% of those of the original fibers, respectively. When DMF was recovered by rotary evaporation at 90 °C and 0.1 MPa for 10 min, the dissolution rate of the resin using the first recovered DMF was 97.13%, and after five reuse cycles the resin dissolution rate still exceeded 90%. A recycled CFRP plate prepared by hot pressing 8 cm recovered carbon fiber tows with fresh resin exhibited a tensile strength of 227.56 MPa and a flexural strength of 887.31 MPa, whereas a recycled CFRP plate prepared from recovered carbon fiber and recovered resin showed a tensile strength of 204.32 MPa and a flexural strength of 815.35 MPa. Conclusions It can be concluded that the DMF dissolution method can efficiently realize the separation and recycling of resin and carbon fiber from waste semicured carbon fiber prepreg. The recovered fibers and resin suffer minimal damage in structure and mechanical properties, and the solvent can be recycled in a closed loop. The recycled composites demonstrate excellent mechanical property retention, and the process is both feasible and economical, exhibiting a promising prospect for engineering dissemination and resource-oriented application.

Key words: waste discarded carbon fiber prepreg; semi-cured epoxy resin; carbon fiber recycling;DMF dissolution; recycled CFRP plate