Self-Fibrillating Cellulose Fibers: Rapid In Situ Nanofibrillation to Prepare Strong, Transparent, and Gas Barrier Nanopapers

Cellulose nanofibrils
(CNFs) prepared from wood biomass are promising
candidates to replace oil-based materials in, for example, packaging
applications. However, CNFs’ affinity for water combined with
their small size leads to very slow and energy-demanding processes
for handling and removal of water. To a large extent, this is the
major roadblock that prevents a feasible production of dry CNF-based
materials on an industrial scale. In this work, self-fibrillating
fibers (SFFs) from wood, where the fibrils can be liberated by external
stimuli, were prepared via sequential TEMPO and periodate oxidation
reactions. Papers made from these modified fibers using conventional
laboratory papermaking methods were then in situ nanofibrillated via
a modest pH increase. With a dewatering time of less than 10 s for
a 3 g/L dispersion, SFFs represent a major improvement over conventional
CNF nanopapers that take approximately 6 h to dewater. Moreover, 100
g/m2 nanopapers obtained through in situ fibrillation exhibited
comparable, if not superior, properties to those reported for conventionally
made CNF films. A tensile strength of 184 MPa, a Young’s modulus
of 5.2 GPa, a strain at break of 4.6%, 90% optical transmittance,
and an oxygen permeability of 0.7 cm3 μm m–2 d–1 kPa–1 at 50% RH were measured
for SFF nanopapers. Furthermore, in situ nanofibrillation of the SFFs
can also be achieved from already dried papers, facilitating numerous
possibilities in terms of logistics and handling for an industrial
scale-up and transportation of nanomaterials. Overall, stimuli-induced
SFFs indeed enable a rapid production of strong, transparent, gas
barrier nanopapers, which likely can be industrially scaled up and
eventually compete with the oil-based plastics in the market for packaging
materials.