TEMPO-oxidized cellulose nanofibril/layered double hydroxide nanocomposite films with improved hydrophobicity, flame retardancy and mechanical properties

High-performance and environment-friendly biomass-based composite films have drawn much attention recently. Here, bio-nanocomposites of TEMPO-oxidized cellulose nanofibrils (TOCNs) reinforced with layered double hydroxides (LDHs) were prepared through an environmentally benign pathway by aqueous dispersion. The results showed that LDHs could be uniformly dispersed in the cellulose nanofibril matrix to form an intercalated nanolayered structure due to good compatibility and the formation of ionic and hydrogen bonds between LDHs with positive charges and TOCNs with negative charges. The TOCN-LDH composite films exhibited high light transmittance, which exceeded 80% with an LDHs content of less than 10%. Moreover, the incorporation of LDHs improved not only the mechanical properties of the cellulose nanofibrils, but also their thermal stability, flame retardancy and hydrophobicity. More specifically, the highest Young's modulus and tensile strength reached 39.3 GPa of TOCN-LDH20 and 358 MPa of TOCN-LDH5, which were 364% and 178% of the neat TOCN film, respectively. The water contact angle and limiting oxygen index of the TOCN-LDH composite film increased from 46 degrees to 103 degrees, and from 25 to 31, respectively, with the LDH content increase from 0 to 20 wt%.