ABSTRACT Recycled carbon fibers (rCFs), typically recovered in short and randomly oriented forms, are often limited to downgraded applications with reduced commercial value. Here, we demonstrate their effective upcycling into shape memory polymers (SMPs) with enhanced multifunctional performance. SMP composites containing rCFs of varying lengths (0.5 and 4 mm) and loadings (0–3 wt.%) were systematically investigated under tensile test, thermal radiation, hot‐water, and electro‐activation. rCFs significantly improved mechanical properties, with 4 mm fibers yielding the highest strength and modulus. At 2 wt.% loading, rCFs accelerated heating to T g (≈52°C) from 0.15°C/s to 0.52°C/s, reducing full‐recovery time from ~240 to ~100 s. Increasing the loading to 3 wt.% yielded a more uniform temperature distribution, albeit with a slightly reduced heating rate (0.45°C/s). Hot‐water activation enabled complete recovery within 10 s for all samples, whereas electro‐activation exhibited a pronounced length effect, such that only 4 mm rCFs formed conductive networks enabling full recovery within 20 s. These findings establish a sustainable strategy for transforming rCFs into high‐value, multi‐responsive SMP actuators, highlighting their potential in advanced smart materials and sustainable manufacturing.
Lin et al. (2026) studied this question.