Recycling the sediment of cotton spinning effluent for rigid polyurethane foams.

Sediment from the effluent of cotton spinning industry was valorized as the renewable bio-based polyols substitute for the rigid polyurethane (RPUFs), targeting to generate the economic and environmental benefits. Before reaction with the isocyanate, the sediment was functionalized by hydroxymethylation, in order to increase the density of the active hydroxyl groups for higher reactivity. The structural characterization results of the functionalized sediment indicated the material exhibited narrow molecular weight distribution, high hydroxyl groups content, and highly aromatic skeleton, which can be qualified as the renewable polyols for the RPUFs. In the crosslinking process, the effect of the polyols substitute rate of the sediments on the physio-chemical properties and the thermo-resistant performances of the resulting RPUFs was investigated. Specifically, in the group with 30 wt% of polyols substitution, the received foam exhibited comprehensive superiorities in compressive strength (0.58 MPa), apparent density (58 kg m^-3), and thermo-conductivity (0.032 W m^-1 K^-1). Attractively, the RPUFs also exhibited good flame retardancy. The burning time can be extended by 30 % compared to the control group that without the sediment's substitution. Moreover, the RPUF also possessed good degradability, allowing for harmless recycling. The current work provided a potential route for the valorization of the hazardous waste effluent from the cotton spinning industry.