Lignin is an abundant bioproduct derived from lignocellulosic biomass and a good source of renewable aromatic compounds. Although it has traditionally been regarded as waste, recent efforts aimed at enhancing the value and utilization of lignin has prompted researchers to take advantage of its rich functionality to fabricate bio-based vitrimer networks as an alternative to fossil-based vitrimer systems. However, its inherent heterogeneity can adversely affect the performance of lignin-derived material thus limiting its utilization. In this work, we have explored the effects of various structural features of lignin on the thermomechanical performance of lignin-based transesterification vitrimers (LVs). Lignin fractions with variable characteristics were obtained from the parent organosolv lignin via sequential fractionation in three different solvents prior to modification by carboxylation. The carboxylic acid-enriched lignins were then crosslinked with epoxidized soybean oil to form thermally stable vitrimers networks. A thorough analysis on thermomechanical properties of the synthesized vitrimer samples revealed that the OH content in lignin strongly correlated with the crosslinking density (R2 = 0.928), tensile strength (R2 = 0.997), and activation energy (R2 = 0.974), of LVs, while the molecular weight exhibited a strong correlation with thermal stability (R2 = 0.858), and glass transition temperature (R2 = 0.904). While there was no direct relationship between the measured vitrimer properties and the S/G ratio of lignin, the ratio of rigid to flexible interunit linkages in lignin had a good correlation with the mechanical performance of the synthesized vitrimers.
