Bulgur bran as a biopolymer source: Production and characterization of nanocellulose-reinforced hemicellulose-based biodegradable films with decreased water solubility

Bulgur bran is a lignocellulosic side-stream of bulgur production factories. Separation of bulgur bran into cellulose- and hemicellulose-rich fractions paved the way of utilization of this under-exploited agro-industrial biomass. Although hemicellulose-based biodegradable food packaging films provide significant advantages, their high water solubility and low mechanical strength are obstacles to their commercialization. To overcome these bottlenecks, commercial cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) were incorporated into the hemicellulose matrix. Besides, addition of citric acid (CA) was investigated for its plasticizing effect. To minimize the film water solubility (FWS) statistical optimization by Box-Behnken design (BBD) and response surface methodology (RSM) was employed. The proposed full-quadratic model was found to have high accuracy (R² = 0.9877) within 95 % confidence interval. The results revealed that 10 % (w/w) CNC- and 10 % (w/w) CNF-incorporated films exhibited 21.3 % reduction in FWS compared to neat films. CNC- and CNF-reinforced films showed a compact structure in SEM analysis. CNC and CNF as fillers in the hemicellulose network markedly improved the tensile strength of the films. Nanocellulose incorporation caused a decrease in water vapor permeability (WVP), light transmittance, total color difference and biodegradability of the films. The properties of nanocellulose-reinforced and neat films were also compared using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). Presence of nanocelluloses in the films increased the glass transition temperature (Tg) by around 15 °C as shown by DSC analysis.