From a circular economy
perspective, one-pot strategies for the
isolation of cellulose nanomaterials at a high yield and with multifunctional
properties are attractive. Here, the effects of lignin content (bleached
vs unbleached softwood kraft pulp) and sulfuric acid concentration
on the properties of crystalline lignocellulose isolates and their
films are explored. Hydrolysis at 58 wt % sulfuric acid resulted in
both cellulose nanocrystals (CNCs) and microcrystalline cellulose
at a relatively high yield (>55%), whereas hydrolysis at 64 wt
% gave
CNCs at a lower yield (<20%). CNCs from 58 wt % hydrolysis were
more polydisperse and had a higher average aspect ratio (1.5–2×),
a lower surface charge (2×), and a higher shear viscosity (100–1000×).
Hydrolysis of unbleached pulp additionally yielded spherical nanoparticles
(NPs) that were <50 nm in diameter and identified as lignin by
nanoscale Fourier transform infrared spectroscopy and IR imaging.
Chiral nematic self-organization was observed in films from CNCs isolated
at 64 wt % but not from the more heterogeneous CNC qualities produced
at 58 wt %. All films degraded to some extent under simulated sunlight
trials, but these effects were less pronounced in lignin-NP-containing
films, suggesting a protective feature, but the hemicellulose content
and CNC crystallinity may be implicated as well. Finally, heterogeneous
CNC compositions obtained at a high yield and with improved resource
efficiency are suggested for specific nanocellulose uses, for instance,
as thickeners or reinforcing fillers, representing a step toward the
development of application-tailored CNC grades.