Colloidal dispersions
of cellulose nanofibrils (CNFs) are viable
alternatives to cellulose II dissolutions used for filament spinning.
The porosity and water vapor affinity of CNF filaments make them suitable
for controlled breathability. However, many textile applications also
require water repellence. Here, we investigated the effects of postmodification
of wet-spun CNF filaments via chemical vapor deposition (CVD). Two
organosilanes with different numbers of methyl substituents were considered.
Various surface structures were achieved, either as continuous, homogeneous
coating layers or as three-dimensional, hairy-like assemblies. Such
surface features reduced the surface energy, which significantly affected
the interactions with water. Filaments with water contact angles of
up to 116° were obtained, and surface energy measurements indicated
the possibility of developing amphiphobicity. Dynamic vapor sorption
and full immersion experiments were carried out to inquire about the
interactions with water, whether in the liquid or gas forms. Mechanical
tests revealed that the wet strength of the modified filaments were
almost 3 times higher than that of the unmodified precursors. The
hydrolytic and mechanical stabilities of the adsorbed layers were
also revealed. Overall, our results shed light on the transformation
of aqueous dispersions of CNFs into filaments that are suited for
controlled interactions with water via concurrent hydrolysis and condensation
reactions in CVD, while maintaining the moisture buffering capacity
and breathability of related structures.
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