Thermochromic Phase-Change Polyurethane Composites with High Enthalpy and Visual Responsiveness for Industrial Wastewater Heat Recovery

Addressing the global demand for energy efficiency and sustainability, this study designed novel, high-performance, intelligent thermochromic cross-linked polyurethane-encapsulated tetradecanol phase-change composites (TC-PU/TDs). These materials aim to overcome the limitations of traditional phase-change materials (PCMs) like low phase-change enthalpy and leakage while enabling visual monitoring of thermal energy utilization. We first prepared SP-NO2/OH, a dihydroxyl and dinitro-modified thermochromic molecule. Subsequently, SP-NO2/OH, along with xylitol as a chain extender, was incorporated into a poly(ethylene glycol)-based prepolymer, forming crystallizable solid–solid thermochromic phase-change polyurethanes (ssTC-PUs). High-enthalpy tetradecanol (TD) was then encapsulated within this network, resulting in TC-PU/TDs, shape-stabilized composite materials with dual phase-change components. TC-PU/TDs exhibit excellent structural stability, shape retention, phase-change stability, and thermochromic repeatability. Through the optimization of the cross-linked network structure, the encapsulation rate of TD reached an impressive value of 72%, and the melting enthalpy achieved 159.7 J/g with an enthalpy efficiency of 87.2%. Exploratory applications confirmed the outstanding thermal energy absorption/release of TC-PU/TDs in industrial wastewater heat recovery, with color changes intuitively reflecting the thermal state. This study provides an innovative strategy for intelligent thermal management and energy visualization monitoring, showcasing broad application prospects.