Anisotropic and flame-retardant phase change aerogels derived from upcycled waste paper: A comprehensive case study on building thermal management

Developing low-cost, flame-retardant phase change materials (PCMs) for passive building energy conservation remains a critical challenge. Here, we report a comprehensive case study on an ultra-low-cost phase change composite aerogel (P/WPA) skillfully derived from upcycled industrial waste corrugated paper. A structurally reliable, vertically aligned cellulose scaffold (WPA) is fabricated via directional freezing, followed by vacuum infiltration with disodium hydrogen phosphate dodecahydrate (DHPD) and sealing with a polydimethylsiloxane/expanded graphite (PDMS/EG) protective skin. Thermal characterizations reveal that the P/WPA composite delivers a high melting enthalpy of 189.31 J/g and exhibits a unique spatially decoupled heat transfer mechanism, combining a low through-thickness thermal conductivity of 0.48 W/(m·K) for insulation with rapid lateral heat spreading. Interfacial hydrogen bonding achieves a 43% reduction in supercooling degree (down to 16.2 °C) and ensures excellent cycling reliability (merely 3.6% enthalpy fade over 200 cycles). Crucially, outdoor engineering case tests performed under real plateau environment show that integrating P/WPA into building envelopes dramatically buffers thermal fluctuations, reducing peak indoor temperatures by 6–8 °C. Boasting a highly competitive overall manufacturing cost of ∼$0.0123/g (including processing energy overheads), this study provides a practical, sustainable, and commercially compelling case paradigm for green building energy storage.