S. T. Gonggo, C. L. Radiman, B. Bundjali, and I. M. Arcana, “Properties of Polymer Electrolyte Membranes Prepared by Blending Sulfonated Polystyrene with Lignosulfonate”, J. Math. Fund. Sci., vol. 44, no. 3, pp. 285-295, Aug. 2014.