Traditional views have questioned the idea that plastics with very high lignin contents might support functional mechanical behavior. The problem began more than 60 years ago with the supposition that the hydrodynamic compactness of lignin macromolecules arises from intramolecular polymer-chain crosslinking. By 2019, however, branching and crosslinking had largely disappeared from some descriptions of native macromolecular lignin structure. Actually, materials containing high levels of conventional lignin preparations are composed of well-defined associated complexes rather than individual components. The integrity of the complexes is maintained by noncovalent interactions between cofacially offset aromatic rings within their inner domains. On the other hand, the peripheral domains of the complexes embody a greater incidence of edge-on aromatic-ring arrangements that undergo inter-digitation to establish material continuity between adjoining macromolecular entities. In preferential interactions with the peripheral domains, miscible non-lignin blend components, even in small quantities, have a profound impact on the mechanical properties of the resulting lignin-based plastics. Thus, 95–98 wt% industrial kraft lignin-based plastics, with tensile strengths approaching 70 MPa, can far surpass polystyrene (46 MPa) in mechanical behavior. Neither derivatization nor fractionation of the kraft lignin is required. Appropriate formulations for these kraft lignin-based plastics are fully biodegradable. Their production costs are estimated to be well below half of current polystyrene selling prices.

Biodegradable plastics containing 95–98 wt% underivatized unfractionated kraft lignin exceed polystyrene in mechanical behavior

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.