New Insights on the Chemical Modification of Lignin: Acetylation versus Silylation

Soda lignin was functionalized with tert-butyldimethylsilyl groups by the reaction with tert-butyldimethylsilyl chloride. The reaction conditions leading to a quantitative derivatization of lignin, hydroxyl groups were determined by 31P and 1H NMR and compared with those of acetylation. The functionalization was also confirmed by FTIR and size exclusion chromatography. The silylation enhances the thermal stability and lowers the Tg of lignin as compared to the acetylation. In addition, the silylated lignins are soluble in a wider range of organic solvents, including solvents of low polarity and show a clear hydrophobic character with a contact angle with water higher than 100°. Neat, acetylated, and silylated lignins were then blended with low density polyethylene, and injection molded materials were analyzed with tensile tests, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). This study reveals the higher compatibility of the silylated lignin with the polyolefin matrix and hence the great potential of the silylated lignin for a use as an additive in apolar polymer matrices.