Physicochemical characteristics of lignins from corncob and agave tequila bagasse warrant their use for sustainable materials

Corncob and agave tequila bagasse are agricultural residues composed of lignin, cellulose and hemicelluloses. Despite being the second most abundant biopolymer, commercial applications of lignin are restricted owed to its heterogeneous and complex chemical structure. However, lignin properties (UV-absorption, biodegradation, biocompatibility, antioxidant, etc.) forecast production of sustainable high-added value materials. The aim of this contribution was to characterize the material properties of organosolv lignins from corncobs (CC) and agave tequila bagasse (T), to aid in the development of sustainable materials. The physicochemical characteristics of both polymers were determined. The degree of polymerization was 16, determined by GPC for both residues, resulting in similar thermal properties (TGA and DSC). Infrared and nuclear magnetic resonance spectroscopies showed that T was composed mainly of syringyl (S) units, while CC contains p-hydroxyphenyl (H), syringyl (S), and guaiacyl (G) units. The surface composition as investigated by XPS, showed that T has more hydroxyl groups available on the surface and a higher surface area (12.2 m ² /g) as compared to CC. Hydrodynamic size, determined by light scattering, ranged from 255–712 nm for T, while CC particles had a wider distribution (from 70-1000 nm), with an 8-fold polydispersity index as compared with T; the z potential was in the vicinity of -30 mV for T and − 20 mV for CC. Spherical nanoparticles with diameters of 42 nm for T and 49 nm for CC were observed. Based upon the specific material properties of each lignin, sustainable, high value-added products can be obtained.