RHEOLOGICAL PROPERTIES OF FILM-FORMING SOLUTIONS BASED ON BIOPOLYMERS CONTAINING CELLULOSE NANOFIBER FROM SOYBEAN STRAW

The effect of cellulose nanofiber (CNF) from soybean straw on the rheological properties of film-forming solutions (FFS) based on gelatin, pectin or chitosan was investigated. CNF was prepared by enzymatic hydrolysis (pH=4, 50°C/42h), followed by mechanical homogenization and sonication. FFS were produced with 4 g gelatin (Type A or B) or pectin, or 1 g chitosan/100 g FFS and 0, 1, 3 and 5 g CNF/100g biopolymer. Rheological essays were performed in a rheometer using concentric cylinders (radius=14/15 mm, gap= 1000 μm) and conic geometries (cone angle= 4°, diameter=60 mm, gap=128 μm) at 40°C. Steady flow analysis was performed (0-100 s^-1), and oscillatory analyses consisted in frequency and temperature sweeps (0.01-10 Hz and 50-5-50 °C, respectively). CNF presented micrometric length and nanometric diameter (16.8±1.2 nm). FFS presented a shear-thinning behavior described by Ostwald de Waele model (R²>0.98).The increase of CNF concentration (0-5%) raised consistency index and decreased flow behavior index for FFS from type-A gelatin (K=4.4±0.3-13.3±1.6 mPa.s^-n; n=0.98-0.73) and type-B gelatin (K=4.2±0.3-11.3±0.7 mPa.s^-n; n=0.94-0.77), pectin (K=114.5±0.3-148.1±5.3 mPa.s^-n; n=0.94-0.91), except for chitosan (K=35.9±2.2 mPa.s^-n; n=0.96). From oscillatory essays, FFS presented an exponentially increasing trend for G' and G'' (1-10 Hz), characteristic of dilute solutions. Gelatin FFS showed a weak gel behavior (G’>G’’, 0.01-1 Hz); while polysaccharides behave as dilute solutions (G’’>G). Tan δ varied between 30 and 85. The presence of NFC (0-5%) decreased the viscous behavior of gelatin B solutions and increased it for type A gelatin FFS, suggesting greater interaction between type-B gelatin and CNF, without notable trends for polysaccharides. Temperature scans showed that CNF did not alter the thermal transitions of gelatin FFS. The CNF presence did not change the structural behavior of polysaccharides FFS.