Lignin is one such complex biopolymer present in plant cell walls. Due to its chemical versatility and abundance, it has been considered as a potential renewable resource for development in advanced materials. However, its hydrophilic nature and structural complexity impede its integration into hydrophobic polymer matrices, thus limiting its broader utility. This chapter explores a new approach to overcome these challenges by modifying lignin surfaces using cetyl trimethyl ammonium bromide, a cationic surfactant. Modification involves adsorption of cetyl trimethyl ammonium bromide (CTAB) on the lignin surface, through electrostatic interaction, changing its surface energy to be more hydrophobic. For preliminary evaluation, the modified lignin was incorporated into a polypropylene matrix as a reinforcing filler. In this case, the measured properties of the mechanical test augmented interfacial adhesion and dispersion, bringing about increased tensile strength and general mechanical properties. Such results point toward potential uses for CTAB-modified lignin as a biobased material for developing composite materials. This chapter underlines surface-functionalized lignin’s huge potential, from compatibility with hydrophobic polymers to more extensive industrial application. Through an innovative mechanism of surface treatment, lignin can become the central ingredient in the turn toward sustainable, renewable, high-performance biocomposites.