Sustainable benzoxazine-based phase change materials: from bio-based to upcycling

Currently, the mainstream organic phase change materials (PCMs) like paraffin are almost petroleum-derived and typically incinerated at end-of-life, raising sustainability concerns. Herein, a bifunctional PCM (C-ah-HDI) was synthesized from renewable cardanol which also shows high-value upcycling characteristics. The incorporation of reversible intermolecular hydrogen bonds yields a high melting temperature ( T m ) of 104.9 °C, outperforming most organic PCMs. The acceptable latent heat (Δ H m ) of 110.1 J g −1 and excellent cycling stability (>50 cycles) ensure reliable thermal storage application. When encapsulated in expanded graphite (EG), the composite demonstrates significant potential for photothermal conversion. Crucially, under thermal runaway conditions, C-ah-HDI undergoes ring-opening polymerization (ROP) to form a crosslinked network, imparting intrinsic flame retardancy that reduces the peak heat release rate by 62.3% compared to a commercial organic PCM. Demonstrating a circular economy approach, end-of-life C-ah-HDI was successfully upcycled as a reactive modifier for a commercial polybenzoxazine (PH-ddm). At an optimal loading of 5 wt%, the copolymer exhibited a 18.4% increase in impact strength and a 7.8% increase in tensile strength, transforming a potential waste stream into a value-added reinforcing and toughening agent. This work presents a compelling strategy for molecular design of organic PCMs integrating performance, safety, and sustainability.