The accumulation of synthetic plastic waste derived from petroleum has been considered one of the main environmental problems worldwide, this problematic, in addition to the need for a transition towards a circular bioeconomy, generates the need to seek alternatives to these materials, a possible solution is found in biorefineries, defined as systems in which biomass is processed and integrated in order to obtain high value-added products. This chapter offers a comprehensive review of the various applications of biopolymers present in lignocellulosic materials (cellulose, hemicellulose and lignin), as well as polysaccharides present in aquatic algae, such as Sargassum (galactan, fucoidan and alginate). In addition, the extraction methods used are presented, such as hydrothermal and organosolv processes, which allow obtaining these polymers efficiently and sustainably. This review also highlights the creation of a novel biopolymer through the combination of lignin and alginate, offering a new material with significant potential in various applications. This innovative approach leverages the unique properties of each component: alginate’s excellent gelling capacity, and lignin’s mechanical strength and thermal stability. The resulting biopolymer not only enhances the performance of existing materials but also opens up new possibilities for sustainable solutions in fields such as biomedicine, packaging, and environmental protection. The integration of second and third generation biorefineries makes it possible to take advantage of renewable resources and obtain polymers with unique properties.