Effect of CaCl ₂ concentration on the structure, morphology, and properties of nylon 6 membranes

Abstract In this study, porous nylon 6 membranes were fabricated via decomplexation of nylon 6 in a methanol/CaCl 2 system using the wet phase inversion method. The addition of CaCl 2 significantly influenced the dissolution behavior of nylon 6 by increasing the viscosity of the casting solution, thereby modifying solvent–nonsolvent exchange during phase inversion and governing membrane formation. As a result, membrane morphology evolved from sponge–like to finger–like and mixed structures depend on CaCl 2 concentration in the polymer casting solution, accompanied by changes in thickness, density, and crystalline structure. DSC analysis revealed a reduction in crystallinity from 26.0 ± 1.0 % for pure nylon 6 to 18.9 ± 1.3–24.2 ± 0.8 % for the membranes, indicating suppressed formation of well–ordered crystalline domains during dissolution and coagulation. FTIR results further confirmed coordination between Ca 2+ ions and amide groups, leading to conformational changes in the polymer chains. Water permeability exhibited a non–linear dependence on CaCl 2 concentration, with the membrane prepared using 15 wt% CaCl 2 showing the highest permeability (18.32 ± 0.6 L m −2 h −1 bar −1 ) due to its highly interconnected porous structure. These findings demonstrate that CaCl 2 concentration is an effective parameter for tailoring the structure–property–performance relationship of nylon 6 membranes for filtration and controlled drug delivery applications.