Optimization and characterization of cellulose extraction from olive pomace

Olive pomace (OP) was used as raw material to extract cellulose by multi-step chemical method, and the extracted cellulose was characterized. The two steps of alkali treatment (alkali concentration, reaction time and reaction temperature) and bleaching (H2O2 concentration, NaOH concentration, bleaching time and bleaching temperature) were optimized. The results showed that the optimum conditions for alkali treatment were as follows: alkali concentration 6%, reaction time 2 h, reaction temperature 95 °C; the optimal bleaching conditions were as follows: 7.5% H2O2 solution, 5% NaOH, bleaching time 2 h, bleaching temperature 75 °C. After multi-step chemical treatment, the cellulose content of the final OP cellulose was (86.41 ± 0.27) %, the lignin content was (6.77 ± 0.55) %, the extraction process yield was 20.36%. By scanning electron microscopy, the surface of OP cellulose changes from dense smooth structure to rough irregular structure with different treatment degrees. Fourier transform infrared spectroscopy (FTIR) proved the removal of hemicellulose and lignin in OP fibers after chemical treatment. The crystallinity of OP fiber increased from 34.80 to 68.69% after treatment. Thermogravimetric analysis (TGA) showed that OP cellulose had high thermal stability. The study provides a new idea for the conversion of industrial processing by-products into high-quality cellulose, and proves that it is feasible to extract cellulose from olive pomace.