Preparation and characterization of cellulose nanofiber/melamine–urea–formaldehyde composite aerogels for thermal insulation applications

Abstract The inherent flammability and low strength of pure cellulose aerogels limit their use in several applications. In this study, novel cellulose nanofibers/synthetic polymeric composite aerogels with excellent flame retardancy and increased strength were prepared under aqueous conditions with an eco‐friendly freeze‐drying and post‐curing process. This composite combined a rigid melamine–urea–formaldehyde network and pentaerythritol phosphate melamine salt as an inorganic flame retardant. The latter is positively charged; hence, it could react with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐oxidized cellulose nanofibers, which are negatively charged, by the charge neutralization of pentaerythritol. The resultant composite aerogels showed excellent flame‐retardant properties, an increased compressive modulus (up to 73.1 kPa), and low densities (8.75–10.7 mg/cm 3 ). The composite aerogels also exhibited a limiting oxygen index as high as 30.2% and a remarkable decrease in the fire indices. Therefore, we believe that the developed composite aerogel demonstrates potential as a lightweight composite thermal insulation for construction applications.