Phenyl-urethane group-modified cellulose acetate-based flat/nanofiber composite membrane for membrane distillation.

An asymmetric hydrophilic/hydrophobic cellulose acetate-based composite membrane with superior separation performance for membrane distillation was fabricated by chemically introducing hydrophobic groups into cellulose diacetate molecules through covalent bonding with the highly reactive m-tolyl isocyanate (MTIS), followed by combining with a hydrophilic cellulose triacetate nanofiber membrane and underwent reverse phase inversion. Simultaneously, the pore structure and surface roughness of the hydrophobic layer were regulated by adjusting the coagulation bath composition. The characterisation results confirmed the stable covalent bonding of MTIS. The increasing ethanol concentration in the coagulation bath significantly promoted pore formation and enhanced surface roughness of the hydrophobic layer. The synergistic effect of chemical modification and physical structuring substantially improved surface hydrophobicity, achieving a water contact angle of 116.7° and excellent separation efficiency (flux: 26.38 kg m-2 h-1, salt rejection: 96.87 %) for the optimal membrane prepared with a water/ethanol volume ratio of 67:33. In addition, chemical modification and coagulation bath optimisation positively influenced the thermomechanical properties and crystallinity of the composite membrane. This study provides a new technical basis for the construction of hydrophobic layers in cellulose-based composite membranes for membrane distillation and methodological guidance for tuning the hydrophilic and hydrophobic characteristics of cellulose-based materials.