Controlling Lignin Solubility in Nonpolar Lubricating\nOil via Multiple Fatty Chains Modification Strategy

In this study, we developed a multiple\nfatty chains modification\nstrategy to utilize lignin effectively. First, different biomass materials\n(hardwood, softwood and herbaceous) were used to extract and modify\nlignin with uniform molecular weight and aliphatic hydroxyl alkylation\nunder mild conditions using dodecyl aldehyde as an inhibitory polycondensation\nagent. Palmitoyl chloride was then used to tether the long fatty chain\nbranches to the phenolic hydroxyl groups. Nuclear magnetic resonance\n(NMR), gel permeation chromatography (GPC), and Fourier-transform\ninfrared spectroscopy (FTIR) were used to analyze the structural changes\nduring lignin modification. The experimental results demonstrated\nthat the contact angle of lignin increased from 74.2 to 114°\nafter the modification, and the modified lignin exhibited complete\nsolubility in nonpolar lubricating oil over a long-term. In addition,\nthe COSMO-RS results indicated that the influence of alkylation treatment\non solubility was greater than that of the molecular weight. Modified\nlignin improved the tribological properties of nonpolar lubricants\nby reducing the friction coefficient and wear volume by 10.6 and 81.3%,\nrespectively. These findings are expected to contribute significantly\nto the development of lignin based value-added products.