System boundary effects in prospective LCA of CFRP recycling: A comparison of pyrolysis and solvolysis across bin-to-gate and circular economy perspectives

Emerging recycling technologies offer promising solutions to the growing end-of-life (EoL) waste of carbon fiber-reinforced polymer composites (CFRPs), especially as incineration and landfill are increasingly phased out under circular economy (CE) frameworks. However, the typically lower and more variable quality of recycled carbon fibers (rCF) limits their applicability in high-performance applications. Life cycle assessment (LCA) is widely used to evaluate recycling pathways, but conventional approaches in CFRP recycling often rely on simplified assumptions regarding system boundaries and material substitution. As a result, they may overlook the non-equivalence of recycled carbon fibers, as well as how modeling choices influence results and their interpretation. To address these gaps, we conduct a prospective LCA comparing selected pyrolysis and solvolysis pathways for CFRP recycling, with time-dependent background scenarios and static foreground recycling inventories. We introduce a flexible LCA design that explicitly represents circular economy (CE) and bin-to-gate (BtG) system boundaries capturing both recycling-stage and value-chain perspectives. Product-level comparisons are based on stiffness equivalence using Young’s modulus as the reference mechanical parameter. The results show that the relative performance of the modeled pyrolysis and solvolysis pathways highly depends on the methodological LCA study designs such as the system boundary. Differences between pathways are less pronounced under CE scenarios than under BtG scenarios because upstream burdens and allocation assumptions dominate the results. These findings underscore the need to match LCA modeling choices with the intended decision context when assessing recycling strategies for CFRPs and other long-lived products.