Composite tubes were filament-wound and cured using a vitrimer epoxy resin and carbon fiber (CF). The matrix was dissolved under mild conditions, and recovered continuous fiber tows were used to rewind a second-generation tube. Property retention and microstructural quality were evaluated by mechanical tests and examination of polished sections. The vitrimer–matrix composite exhibited a higher short-beam shear strength compared to specimens wound with a traditional epoxy, typical of hydrogen tanks. Single-fiber testing revealed that CFs were not degraded by the recycling process. The remanufactured composite exhibited mechanical properties comparable to those of the first-generation material when normalized to the fiber volume fraction. This work demonstrates a circular manufacturing process that includes full fiber recovery and re-use for producing a second-generation filament-wound article.

As energy producers turn towards decarbonization, hydrogen is being explored as an alternative fuel. Hydrogen is stored at high pressures to achieve an efficient energy density, which requires high performance composite tanks. There is currently no end-of-life (EOL) option for these tanks, other than landfills. If we want to sustainably position hydrogen energy for the future, EOL is an imperative consideration. Herein, the authors present a method of producing these composite overwrapped pressure vessels (COPV), via filament winding, with the ability to later unwind and recycle them. A vitrimer matrix was used, which has the ability to dissolve into its monomeric constituents, allowing for reuse of both the continuous fiber reinforcement and the depolymerized matrix. Neat resin analysis included dynamic mechanical analysis and rheometry, following casting in a custom-built tool. Filament winding was used to produce tubular and flat specimens using custom-designed mandrels. Mechanical testing on both neat resin and reinforced material was completed, including tensile and short beam shear loadings, determining the performance of a vitrimer-based COPV compared to existing materials.

Composite overwrapped pressure vessels (COPVs) present a tractable recycling target as the production/recovery methods do not require cutting fibers, permitting recovery and re-spooling of continuous fiber tows. To address the gap between lab-scale recycling methods and commercial COPVs as a target application, an apparatus is required to control the unwinding process during recycling. A fiber management system (FMS) was designed and produced to maintain tension in the fiber tows and prevent tangles during unwinding filament-wound structures. To demonstrate the effects of the FMS, vitrimer composite tubes were produced, the matrix was dissolved, and recovered tows were used to produce a second tube. Second-generation specimens, some produced from tows unwound with the FMS as well as some from tows recovered manually, were cut into coupons and the tubular short-beam strength was measured. Specimens remanufactured with recovered tows unwound with the fiber management system exhibited an 11% increase in strength compared to specimens that were manually unwound (p = 0.048) and were statistically indistinguishable from first-generation tubes (p = 0.22). Maintaining control of the fiber tows resulted in full retention of mechanical properties in addition to automating and simplifying the unwinding process.