The use of lignin as feedstock to prepare lignin-containing
waterborne
polyurethane (LWPU) is of great significance for the sustainable development
of low carbon materials. However, the utilization method and function
of lignin in LWPU need to be further explored and developed. In this
study, homogeneous and stable LWPU emulsions were prepared with low-molecular-weight
lignin. Then, strong and tough LWPU/lignin nanocomposites were prepared
by blending dialyzed alkali lignin (DAL) nanomicelles with LWPU emulsions.
The well-dispersed DAL nanoparticles formed multiple hydrogen bonds
with the LWPU matrix attributed to the existence of lignin in the
polyurethane chain segments, which endowed the nanocomposites with
excellent mechanical properties. When the total lignin content was
23.8 wt %, the tensile strength and toughness of LWPU/lignin nanocomposites
reached 38.3 MPa and 173.9 MJ/m3, respectively. Benefiting
from the photothermal function of lignin, the LWPU/lignin nanocomposites
showed outstanding photothermal conversion ability, which was demonstrated
as an excellent photothermal coating for photothermo-electric power
generation. In addition, DAL nanoparticles enhanced the aging-induced
self-reinforcing properties of the LWPU/lignin nanocomposites. This
work represents a simple route for the preparation of high-performance
waterborne polyurethane materials with high lignin content and opens
up a novel value-added application of lignin in photothermal-electricity
conversion coatings.