Valorization of sugar beet pulp into cellulose nanofibers using high-speed blending: Effects of acetic anhydride and ammonium persulfate pretreatments

Sugar beet pulp (SBP), an abundant lignocellulosic by-product of the sugar industry, is a promising feedstock for producing value-added cellulose nanomaterials. In this study, cellulose was extracted and purified from dried SBP using hydrochloric acid and sodium hydroxide treatments to remove pectin, hemicellulose, and lignin. Compositional analysis showed that cellulose content increased from 22.50 ± 1.32% in raw SBP to 85.70 ± 0.89% in the purified fraction, accompanied by substantial reductions in non-cellulosic components. The purified cellulose was subsequently converted into cellulose nanofibers (CNFs) by high-speed blending following three pretreatment conditions: untreated cellulose (CNF1), acetic anhydride-treated cellulose (CNF2), and ammonium persulfate (APS)-treated cellulose (CNF3), using blending times of 45 and 60 min. For the 60-min samples, CNF2 exhibited a degree of substitution of 0.33 ± 0.04, whereas CNF3 had a carboxyl-group content of 0.89 ± 0.07 mmol g −1 . DLS, zeta potential, FESEM, XRD, and TGA/DTG analyses demonstrated clear pretreatment-dependent differences. Zeta potentials were −13.5, −28.7, and −36.9 mV for CNF1, CNF2, and CNF3, respectively. APS pretreatment combined with 60 min blending produced the smallest mean fiber diameter (85.3 ± 23.0 nm), with 74.6% of measured fibers below 100 nm. CNF2 exhibited the highest crystallinity index (64%) and maximum decomposition temperature (258 °C), whereas CNF1 showed the highest onset degradation temperature (220 °C). These results demonstrate that pretreatment chemistry effectively tailors the morphological, colloidal, crystalline, and thermal properties of SBP-derived CNFs produced by high-speed blending.