Lignins embody 20−30% of terrestrial organic carbon.  Yet, it has been surprisingly difficult to create functional polymeric materials with lignin-derivative contents approaching 100 wt%.  This problem has delayed the dawn of profitability in converting lignocellulosic plant materials to commodity organic chemicals or liquid fuels.  However, it has recently become evident that, on their own, methylated native softwood lignins can form polymeric materials with tensile properties surpassing those of polystyrene.  Small quantities (just 5 wt%) of non-biobased blend components as common as poly(ethylene glycol) are capable of increasing tensile strength by 40%.  Even without methylation, miscible blends containing 95 wt% native softwood lignin can exceed the tensile strength of polystyrene by a substantial margin.  These striking results have been achieved with softwood lignin preparations exhibiting weight-average molecular weights around 2300.  In contrast, the polystyrene typically used as an industrial material has a molecular weight that is two orders of magnitude higher.  The macromolecular species in materials containing 85−100 wt% levels of simple softwood lignin derivatives are associated complexes composed of two distinct domains.  Their integrity is maintained by strong non-covalent interactions between cofacially offset aromatic rings in the interior.  On the other hand, the peripheral domains, through which continuity between neighboring complexes is established, embody a high proportion of edge-on arrangements of interacting aromatic rings.  Non-lignin blend components interact as plasticizers preferentially with the peripheral domains of the complexes.  Their efficacy is reflected in the propensity of the peripheral domains to expand in response to the non-biobased components in the blend.

Blend configuration in polymeric materials with very high lignin-derivative contents

253rd National Meeting (2017)

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