Ultrasound-Assisted Alkaline Hydrogen Peroxide Pretreatment for Biopolymer Recovery from Exhausted Purple Corn Cobs

This study investigates the fractionation of exhausted purple corn cobs (EPCC) (a lignocellulosic byproduct remaining after bioactive compound extraction) through alkaline hydrogen peroxide (AHP) pretreatment, with and without ultrasonic assistance. Initial biomass characterization revealed a composition of 33.08% cellulose, 21.19% hemicellulose, and only 2.69% lignin, confirming its suitability as a biopolymer source. AHP pretreatment was performed under mild conditions (10% H₂O₂, pH 11.5), with ultrasound applied for 0, 1, 5, and 10 min. Mass balance analysis showed that ultrasonic assistance significantly enhanced the removal of hemicellulose and lignin. After 10 min of treatment, delignification reached 97.4%, hemicellulose removal 58.7%, and cellulose recovery 41.3%. Biopolymers were subsequently recovered from both solid and liquid fractions. Infrared spectroscopy and Principal Component Analysis (PCA) indicated progressive fractioning of EPCC. Morphology analysis revealed increased fiber compaction with longer ultrasound exposure. X-ray diffraction confirmed that cellulose crystallinity increased from 64.6% to 76.6% with ultrasound exposure, and thermal analysis showed enhanced thermal stability, with degradation occurring at 345 °C. These findings highlight the effectiveness of ultrasound-assisted AHP pretreatment for the selective extraction of cellulose, hemicellulose, and lignin from EPCC, supporting its valorization as a feedstock for biobased materials in circular bioeconomy frameworks. Moreover, the use of AHP under mild conditions aligns with green chemistry principles, offering a sustainable and environmentally friendly alternative to conventional biomass pretreatments.