Physical, Chemical and Biochemical Modifications of Industrial Softwood Kraft Lignin for Different Applications

Abstract: Various technical lignins, e.g. industrial Softwood Kraft lignin (SKL), are now largely available while they are generally underutilized due to their heterogeneous and complicated structures and/or the poor properties. SKL has here been modified by physical, chemical and biochemical methods for preparation of lignin microspheres, phenol substitution in phenol-formaldehyde (PF) resin preparation and preparation of highly efficient fertilizers.Physically, a brand-new slow and exhaustive solution evaporation process was developed for the highly efficient and productive preparation of microsphere structures. Highly homogenous SKL hollow microspheres were obtained and for the first time, urea encapsulating SKL microspheres were similarly prepared which could be an excellent controlled release urea fertilizer.Chemically, Mannich reaction (one type of amination) was deeply investigated by including for the first time an LC-MS study of vanillin reaction, resulting in the establishment of a fast and reliable lignin reactivity (for phenol substation in PF resin) quantification method. In addition, SKL was functionalized using the Mannich reaction or esterification, leading to an improved hydrophobicity and compatibility for blending with polylactic acid (PLA). Using dip-coating technique for the first time, PLA-functionalised SKL-coated urea pellets were prepared, leading expectedly to a highly efficient urea fertilizer with simultaneous controlled- and slow- release and biological stabilization effects.Biochemically, SKL was demethylated via incubation with different laccase-mediator combinations, which in principle will increase its reactivity in PF resin preparation. However, polymerization occurred which would decrease the reactivity.  The overall effects need to be further investigated.Conclusively, broader or larger scale SKL applications can expectedly be realized after the development of SKL modifications tailored towards the optimum desired structures and properties.