Waste to wealth: Synthesizing hydrophobic polyurethane by cotton spinning effluent for crude tall oil separation

The effective separation of the valuable by-product, crude tall oil (CTO), from cotton spinning effluent (CSE) could simplify downstream wastewater treatment processes and enhance the economic viability of cotton spinning operations. In this study, under the 'waste-to-wealth' framework, acidic CSE sediments were transformed into renewable polyols for the synthesis of hydrophobic polyurethane (PU) sponges, which were subsequently employed to isolate CTO in upstream processes. Following oxypropylation, the functionalized CSE sediment (FCSES), characterized by aliphatic hydroxyl groups and a controlled molecular weight distribution, exhibited excellent compatibility with polyethers, resulting in PU sponges with enhanced mechanical and thermochemical properties. Upon modification for hydrophobicity, the FCSES-substituted PU sponges demonstrated a high capacity for oil separation from both model immiscible and emulsion mixtures, along with good reusability. When applied to CTO separation from CSE, the novel PU sponges exhibited remarkable efficiency in CTO removal. The findings suggest that hydrophobic PU sponges can achieve over 88 % CTO separation in initial CSE through simple adsorption and desorption, offering a potential alternative to conventional, energy-intensive, and environmentally unfriendly CTO separation techniques. • Conversion of cotton spinning effluent sediments into functional polyols Acidified sediments from cotton spinning effluent (CSE) were recycled as renewable polyols to fabricate hydrophobic polyurethane (PU) sponges, establishing a "waste-treats-waste" circular economy model. • Enhanced material properties via oxypropylation Oxypropylation-functionalized CSE sediments (FCSES) exhibited narrow molecular weight distribution and abundant aliphatic hydroxyl groups, significantly improving compatibility with polyethers and endowing PU sponges with superior mechanical strength and thermochemical stability. • Direct application in industrial wastewater treatment The hydrophobic PU sponges demonstrated potential to replace energy-intensive and polluting conventional processes in crude tall oil (CTO) separation when applied to authentic CSE treatment, advancing green upgrading of textile wastewater management. • Closed-loop system integration A synergistic "CTO separation → sediment recovery → material fabrication → wastewater treatment" closed-loop system was constructed, providing an integrated solution to reduce downstream processing costs for the textile industry.