Synthesis and characterization of nanofibrilated cellulose films modified with blocked isocyanates in aqueous media and their barrier properties to water vapor and oxygen

•Modification of nanofibrillated cellulose with blocked isocyanates in aqueous emulsion.•Films prepared by emulsion casting followed by drying and thermal treatment.•Chemical modification avoided water plasticizing effect and enhanced barrier properties to water vapor and oxygen.•Young's modulus up to 5 GPa for urethane modified nanofibrillated cellulose films in wet state.•Reduced water-vapor transmission rate of 40 g m−² day−1was obtained for NFC films. Hydrophobic nanofibrilated cellulose (NFC) films were prepared by the casting of a mixture of NFC suspension in an aqueous emulsion of two blocked isocyanates - one prepared by the reaction of 4,4′- methylenebis (phenyl isocyanate) and phenol (MDI-2Ph) and a commercial one from trimethylol propane and toluene diisocyanate (Desmodur AP Stabil®) (TMP-TDI-3Ph),). The drying procedure was performed in two steps, i.e., first at 60 °C for 24 h and then at 170 °C for 10 min. Infrared spectroscopy (FT-IR), elemental analysis, and 13 CNMR confirmed the chemical modification of cellulose. The NFC modified films showed an approximately 40 g m−2.day−1 water vapor transmission rate, which is almost 75% lower than that of non-modified NFC films (153 g m−2.day−1). The film modified with TMP-TDI-3Ph showed a very low oxygen transmission rate and lower than that with MDI-2Ph When exposed to a wet environment, the modified films maintained their stiffness with Young's modulus around 5 GPa, whereas that of non- modified films decreased from approximately 6.5 GPa to below 0.1 GPa. [Display omitted]