Colloidal Starch and Cellulose Nanocrystals Unite To Improve the Mechanical Properties of Paper: From Enhanced Coatings to Reinforced Nanocomposites

Emerging paper-based technologies encompassing lab-on-a-chip platforms, microfluidics, sensors, actuators, flexible electronics, and energy-storage devices, such as batteries, demand mechanically robust substrates. Current gold standards for paper and paper board reinforcement rely on petroleum-based binders and coatings, such as latex beads cured with melamine formaldehyde and urea formaldehyde resins, which have raised the red flag because of their environmental footprints. Here, we introduce an all-green reinforcing nanocomposite based on the ammonium zirconium carbonate (AZC)-mediated synergistic crosslinking of starch nanoparticles (biolatex) and a newly emerged type of nanocelluloses named anionic hairy cellulose nanocrystals. AZC, an environmentally friendly and cost-effective crosslinker, reacts with the hydroxyl groups of starch and cellulose nanocrystals, while the carboxylic acid groups of hairy nanocelluloses maintain the solution viscosity low, favoring industrial transportation, which may not be possible using conventional (nonhairy) nanocelluloses. Synergistic action of these green nanomaterials improved the mechanical properties of a glass paper by 1 order of magnitude within a broad range of temperature (<i>T</i> ∼ 25–75 °C) and relative humidity (RH ∼ 0–80%) at noticeably low nanoparticle concentrations (≤1.5 wt %) in the reinforcing dispersions. This technology may set the stage for the next generation high-performance green, renewable, and biodegradable reinforcing coatings and nanocomposites