Valorization of agarwood (Aquilaria spp.) bark waste: Impact of a re-bleaching treatment on the physicochemical properties of extracted cellulose microfibrils

The valorization of agricultural waste is critical for developing a sustainable bioeconomy. Agarwood ( Aquilaria spp. ) bark, a significant byproduct of the agarwood industry, represents an underutilized source of high-quality cellulose microfibrils (CMFs). This study examines the effect of a sequential chemical treatment, with a specific focus on the re-bleaching step, on the properties of CMFs derived from this waste material. The extraction process involved alkaline treatment, initial bleaching, and final re-bleaching. The results demonstrate that the re-bleaching treatment is a crucial step for significantly enhancing CMFs properties. The cellulose content increased progressively from 49.89 % in the raw fibers to 85.86 % in the re-bleached CMFs, while the lignin content was reduced to 3.11 %. Fourier-transform infrared (FTIR) spectroscopy confirmed the systematic removal of non-cellulosic components, including hemicellulose and lignin. Morphological analysis by scanning electron microscopy (SEM) revealed a transformation from rough, bundled raw fibers (average diameter 10.01 ± 3.37 μm) to smooth, uniform CMFs (average diameter 5.30 ± 0.84 μm). Furthermore, X-ray diffraction (XRD) analysis showed a significant increase in the crystallinity index from 46.69 % to 60.38 % after re-bleaching. Thermogravimetric analysis (TGA) confirmed a substantial improvement in thermal stability, with the onset decomposition temperature rising from 229.16 °C for raw fibers to 345.35 °C for the final CMFs. These findings highlight the significance of the re-bleaching process in producing high-purity, highly crystalline, and thermally stable CMFs from agarwood bark waste, indicating their potential use as reinforcing agents in advanced biocomposite materials.