Sustainable and low oxidative damage bleaching strategy for degummed ramie cellulose fibers using NHPI selective...

In this study, a novel bleaching method for ramie cellulose fibers with low oxidative damage was developed by utilizing the properties of sodium percarbonate contained in tea saponin, which slowly releases hydrogen peroxide in the catalytic oxidation system of N-hydroxyphthalimide (NHPI). First, the bleaching process was optimized using response surface design, followed by comparison and characterization of fiber properties prepared under different bleaching systems. Finally, the energy consumption, water consumption, and toxicity of the NHPI/tea saponin system were evaluated. The results demonstrated that fibers bleached by catalytic oxidation with the NHPI method (COBM-N) exhibited a 170 % increase in whiteness and a 5.16 % improvement in breaking tenacity compared with degummed ramie fiber, while the specific work of rupture (SWR) decreased by only 2.4 %. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FT-IR) analyses revealed that non-cellulosic substances in raw cellulose fibers were further removed after bleaching. X-ray diffraction (XRD) analysis showed that fiber crystallinity was closely related to SWR. The crystallinity of degummed ramie fibers, COBM-N fibers, and oxidation-bleached fibers without NHPI (OBM) was determined to be 89.92 %, 89.13 %, and 88.26 %, respectively. Furthermore, the SWR of these fibers also decreased sequentially. Selective oxidation of cellulose fibers at the C6 position was confirmed by ¹³C nuclear magnetic resonance (NMR) analysis. Raman mapping analysis showed that the intensity of the absorption peak at 1604 cm^-1 decreased after bleaching, confirming that colored groups were removed by oxidation. Life Cycle Assessment (LCA) indicated that, compared with the sucrose octaacetate (SOA) system, the NHPI/tea saponin system reduced energy consumption by about 37.84 % and water consumption by 35.80 %, with a lower environmental impact.