Effect of CaCl2concentration 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/CaCl2 system using the wet phase inversion method. The addition of CaCl2 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 CaCl2 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 Ca2+ ions and amide groups, leading to conformational changes in the polymer chains. Water permeability exhibited a non–linear dependence on CaCl2 concentration, with the membrane prepared using 15 wt% CaCl2 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 CaCl2 concentration is an effective parameter for tailoring the structure–property–performance relationship of nylon 6 membranes for filtration and controlled drug delivery applications