Development of polypropylene microporous hydrophilic membranes by blending with PP-g-MA and PP-g-AA

Cast films based on polypropylene (PP) blended with commercial maleic anhydride or acrylic acid grafted polypropylene (PP-g-MA and PP-g-MA) at different weight ratios were prepared by melt extrusion. These films were used to produce hydrophilic microporous membranes. The membranes were prepared by annealing at elevated temperatures followed by cold and hot stretching, respectively. DSC, FTIR and SAXS analyses showed that the addition of the modifiers changed the crystalline lamellar structure and, consequently, the membrane morphology. Membrane morphology observations using SEM showed smaller pore size and lower number of pores as the modifier content increased. Porosity and pore dimensions of the microporous membranes were also measured using mercury porosimetry and their results confirmed SEM observations. Oxygen content of the precursor film surface was analyzed using XPS. Water vapor permeability was increased significantly at low concentrations of the modifiers, compared to the neat PP. This was attributed to the presence of sufficient concentration of polar groups on the surface with a minimal change in the crystalline structure. Finally, the tensile properties of the precursor films in the machine directions (MD) as well as the puncture resistance of the precursors and the membranes in the normal direction (ND) were evaluated.