Fire-retardant and ductile clay nanopaper biocomposites based on montmorrilonite in matrix of cellulose nanofibers and carboxymethyl cellulose

Nacre-mimetic clay bionanocomposites of high clay content show interesting properties although low strain to failure is a limitation. For this reason, three-component nanocomposite films were prepared based on sodium montmorrilonite clay (MTM), a water-soluble cellulose derivative (CMC) of fairly high molar mass, in combination with nanofibrillated cellulose (NFC) from wood pulp. The nanocomposite is cast from an aqueous colloidal dispersion. First, the effects of CMC content on CMC/MTM compositions with high volume fraction of MTM (36–83 vol.%) were studied by FE-SEM, XRD, UV, DMTA and TGA. In addition, fire retardance and oxygen permeability characteristics were measured. The effect of NFC nanofiber addition to the matrix phase was then evaluated. This two-phase CMC/NFC matrix phase results in significantly improved modulus, strength but also strain to failure. NFC has a favorable effect by shifting catastrophic failure mechanisms to higher strains.