Alcohol solvent effect on the self-assembly behaviors of lignin oligomers

The interactions between lignin oligomers and solvents determine the behaviors of lignin oligomers self-assembling into uniform lignin nanoparticles (LNPs). Herein, several alcohol solvents, which readily interact with the lignin oligomers, were adopted to study their effects during solvent shifting process for LNPs' production. The lignin oligomers with widely distributed molecular weight and abundant guaiacyl units were extracted from wood waste (mainly consists of pine wood), exerting outstanding self-assembly capability. Uniform and spherical LNPs were generated in H2O-n-propanol cosolvent, whereas irregular LNPs were obtained in H2O-methanol cosolvent. The unsatisfactory self-assembly performance of the lignin oligomers in H2O-methanol cosolvent could be attributed to two aspects. On one hand, for the initial dissolution state, the distinguishing Hansen solubility parameter and polarity between methanol solvent and lignin oligomers resulted in the poor dispersion of the lignin oligomers. On the other hand, strong hydrogen bonds between methanol solvent and lignin oligomers during solvent shifting process, hindered the interactions among the lignin oligomers for self-assembly.