Controlling lignin particle size for polymer blend applications

Softwood lignin produced by the LignoForce System (TM) was physically processed using different milling approaches to ascertain effective and scalable means to yield micro to submicron particles of controllable and uniform size. Our work suggests that wet ball-milling using a small milling medium is the most reliable method in terms of processing efficiency and particle-size controllability. Controllable particle size reduction would permit lignin to be used as an effective filler in polymer blends. We show that wet-milled lignin could, subsequently, be oven-or spray-dried, and, subsequently, blended with, for instance, polypropylene (PP) through coextrusion. The spray-drying method produced spherical lignin aggregates smaller and more uniform than oven-dried ones. As a consequence, spray-dried lignin demonstrated a more uniform distribution within the polymer melt, leading to noticeable improvement in the strain-or flexibility-of the lignin-PP polymer blends. Furthermore, it is confirmed that the investigated drying methods had no effect on the thermal stability of the resulting lignin-PP blends. (C) 2016 Wiley Periodicals, Inc.