Lignins upgrade the lignocellulosic cell-wall domains in all vascular plants; they embody 20-30% of terrestrial organic carbon. For 50 years, mistaken assumptions about the configuration of lignin have hindered the development of useful polymeric materials with a lignin content above 40 wt%. Now, polymeric materials composed only of methylated softwood lignin derivatives can exhibit better tensile behavior than polystyrene. Marked improvements may be achieved with small quantities (5-10 wt%) of miscible blend components as simple as poly(ethylene glycol). These observations contradict commonly held views about crosslinking or hyper-branching in lignin chains. The hydrodynamic compactness of the macromolecular lignin species arises from powerful noncovalent interactions between the lignin substructures. Individual lignin components undergo association to form macromolecular complexes that are preserved in plastics with a very high lignin content. Material continuity results from interpenetration between the peripheral components in adjoining lignin complexes. Through interactions with the peripheral domains, miscible blend components modulate the strength and ductility of these utterly original lignin-based plastics.
Bibliographical noteFunding Information:
This work was funded by Agriculture and Food Research Initiative Grant no. 2011-67009-20062 from the USDA National Institute of Food and Agriculture, and a Subaward (115808 G002979) from the “Northwest Advanced Renewables Alliance” led by Washington State University and supported by the Agriculture and Food Research Initiative Competitive Grant no. 2011-68005-30416 from the USDA National Institute of Food and Agriculture. X-ray powder diffraction studies and atomic force microscopy were carried out in the Characterization Facility at the University of Minnesota, which receives partial support from NSF through the MRSEC program.