Potassium permanganate oxidation as a carboxylation and defibrillation method for extracting cellulose nanofibrils to fabricate films with high transmittance and haze

Abstract

Cellulose-based films have attracted significant attention in the fields of flexible photoelectric products and energy equipment by virtue of their abundant sources, biodegradability, renewability, sustainability, and optical properties, of which high transmittance and high haze are important parameters. In this study, we proposed a green and efficient defibrillation and carboxylation method of KMnO₄ synergized with slight homogenization to produce fine carboxylated cellulose nanofibrils (COOH-CNFs) with a high yield of 96%. The oxidation reaction was carried out under mild conditions (50 °C, 2 h). The as-prepared COOH-CNFs well-retained the crystalline structure of the pulp with coexisting crystalline and amorphous regions. This structure gave the COOH-CNF film unique optical properties, including a transmittance above 80% at a wavelength of 550 nm, a haze reaching 97.45%, and no obvious absorption in the ultraviolet-visible range. The resulting COOH-CNFs were characterized in terms of fibrillation yield, morphological features, crystal structure, surface chemistry, and mechanical behavior. This CNF preparation approach is advantageous over traditional methods owing to a reduced reactant dosage and enhanced efficiency, which represents a potential green route in industry and makes it a promising candidate for fabricating films for flexible lighting, energy, and sensing devices.