Advancing robust and fire-retardant nanopaper through intrinsic crosslinking of functionalized cellulose nanofibers

Abstract

Functionalized cellulose nanopaper, derived from sustainable biobased materials, has shown impressive strength and lightweight properties. This study introduces a simple method to produce a flame-retardant, ductile, and robust phosphorylated cellulose nanopaper (PCNP). First, the phosphorylation and mechanical defibrillation of cellulose microfibers (CMFs) resulted in the formation of phosphorylated cellulose nanofibers (PCNFs) which were effectively dispersed in water. The fibrillation treatment facilitated the separation of PCNFs bundles into a nanonetwork of extensively disordered, elongated, and pliable nanofibers, with a width of 5.2 ± 1.3 nm. Furthermore, the physicochemical, structural, rheological and thermal properties of the produced PCNFs were investigated through various analytical techniques, including conductometric titration, FTIR, ¹³C/³¹P NMR, XPS, rheology, and TGA-MS. Second, crosslinked phosphorylated cellulose nanopaper (Cr-PCNP) was prepared using solvent casting, followed by a crosslinking reaction through a heat treatment stage. The Cr-PCNP revealed notable tensile strength (reaching up to 72.65 MPa) and Young's modulus (reaching up to 2.41 GPa), along with excellent flexibility. As revealed by the micro combustion calorimeter, the heat release rate (HRR) of Cr-PCNP significantly decreased by 61.76 %, compared to CMFs. This work shows a novel approach to developing a promising robust cellulose nanopaper for fire retardation purposes.