An easy way of valorizing co-product lignins (from biorefineries of any kind) should be attainable through the creation of functional polymeric materials with high lignin contents. However, such means have been suppressed by a persistent working hypothesis that was conceived 60 years ago. At that time, it was declared that the hydrodynamic compactness of lignin macromolecules arises from polymer-chain crosslinking. Consequently, it was expected that lignin domains in polymeric materials would be rigid. Their brittleness would need to be cushioned by introducing (through covalent bonding or noncovalent blending) a suitable proportion of soft segments, but this remedy usually led to an incorporation limit of 40 wt% for lignin in polymeric materials with plausible functionality. In contrast, it has recently been demonstrated that materials composed solely of (native) ball-milled softwood lignin can exhibit tensile strengths that surpass polyethylene (30 MPa). Certain miscible blend components at 5–10 wt% levels can increase the tensile strengths of 90–95 wt% ball-milled lignin-based materials to values beyond that of polystyrene (46 MPa). In comparison, industrial softwood unmethylated kraft lignin-based polymeric materials are more challenging than their ball-milled softwood lignin counterparts. Nevertheless, several miscible components at 5–10 wt% levels can produce 90–95 wt% kraft lignin-based blends with tensile strengths that surpass polyethylene. Ongoing research seeks to develop analogous blends with 90–95 wt% kraft lignin contents that comfortably exceed polystyrene in tensile strength.

Plastics with high unmethylated Kraft-Lignin contents surpass polyethylene in tensile strength

2019 Spring National Meeting

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