Revealing the structural variation and degradation mechanism of cellulose during ozone oxidation treatment

Abstract

Despite numerous studies on the use of ozone for the removal of non-cellulosic substances from lignocellulosic fibers, the mechanism underlying cellulose degradation and the oxidized group formation during ozone oxidation treatment remain unclear. This study focuses on the extraction of α-cellulose from flax fibers. The effect of ozone oxidation on the degree of polymerization (DP) and oxidized groups in α-cellulose under different operational conditions (ozone concentration, oxidation time, water pick-up value, initial pH value) were thoroughly investigated. Additionally, the quality of α-cellulose oxidized under different phases (gas and liquid) of ozone reaction was systematically compared. Results showed that the DP value of α-cellulose-O3-Gas-80% (130 mg·L−1·min−1, 15 min, WPV 80%, pH 2.0) was lower than that of α-cellulose-O3-Liquid (130 mg·L−1·min−1, 15 min, 1:30 g·mL−1, pH 2.0) and α-cellulose-O3-Gas-0% (130 mg·L−1·min−1, 15 min). However, the carboxyl and carbonyl contents showed the opposite trends. FTIR results showed a new peak (carboxyl peak) for α-cellulose and a reduction of hydrogen bonding interactions in molecules after ozone oxidation. In addition, the crystallinity and thermal stability of α-cellulose decreased after ozone oxidation, with α-cellulose-O3-Gas-80% exhibiting the most significant decline. SEM analysis showed that the morphology of α-cellulose was changed after ozone oxidation. This study provides some guidance to mitigate ineffective degradation of cellulose and assist in the selection of cellulose protectors during the process of extracting lignocellulosic fibers by ozone oxidation.