Polyvinyl difluoride (PVDF) membranes prepared from casting solution including the biopolymer kappa-carrageenan (kCg) as an additive demonstrate improved structure and properties. The resulting asymmetrical structure has a thin layer on the upper surface, a porous sublayer with reduced volume of macro void space and increased porosity, and a spongy layer beneath the sublayer. This results in an increased hydrophilic nature, and provides enhanced wetting, membrane porosity, and water permeability—all important properties making these membranes suitable for a wide range of uses.