Characterization of Bast Fiber of Sterculia villosa (Roxb.) and Bauhinia vahlii and Fabrication of Biomass-based Nano-composite Membrane

Abstract

Lignocellulose biomass performs an important role in both traditional and next-generation composite materials. Different stages of chemo-mechanical processing are required to achieve the desired properties from the biomass. Commercial alkali is used extensively in the pulp, paper, and related industries for the purpose of bleaching raw fiber and/or recycling waste. It would be beneficial to have a low-cost substitute for commercial alkali in order to lower manufacturing and recycling costs and lower global alkali consumption. The performance of composites may be better understood by knowing the material characteristics of lignocellulose fiber. Cellulose nanocomposite materials have interesting uses in antimicrobial packaging and photocatalytic activity. In this study, material properties of comparatively fewer investigated and traditionally significant wild plant species Sterculia villosa (Roxb.) (Local name Murgilo or Mudilo) and Bauhinia vahlii fibers (local name Bharlo) were explored. Water sorption kinetics was one of the material characteristics investigated in its various forms; including untreated, commercial, and wood ash alkali retted. In addition, alkali-treated fibers were compared in terms of sorption data. Fibers treated with alkali were examined for their mechanical strength in both their sorbed and dry states. Specific focus is given to the material properties of fiber mats made from these plant species. Additionally, the antimicrobial and photocatalytic activity of the Ag-ZnO/cellulose nanocomposite prepared were studied. In the water retting study, many properties of raw Sterculia villosa (Roxb.) and Bauhinia vahlii fiber samples (n = 8) were thoroughly evaluated after they were retted for 0, 20, 30, and 55 days. After water retting, both lignin and extractive levels dropped significantly (p<0.05), but cellulose levels increased. Fiber bundle strength increased significantly (R2 = 0.7) with retting time in Sterculia villosa (Roxb.), but not in Bauhinia vahlii (p > 0.05). The Sterculia villosa (Roxb.) fiber treated with 5% sodium hydroxide and the fiber processed with wood-ash alkali (WAA) were evaluated in terms of their material properties. A net weight loss of 29.1±2.6% was seen after WAA treatment, whereas a net weight loss of 41±3.3% was observed after sodium hydroxide treatment. The elimination of hemicellulose and lignin may be responsible for the weight loss in both procedures. Cellulose fiber produced by the two processes was thoroughly compared with regard to their crystallinity, surface morphology, and thermal stability. The average diffusion coefficient, sorption coefficient, water permeability, and diffusion coefficients at the early and late sorption phases were calculated after the Fickian model was fitted to the experimental kinetic data. For Sterculia villosa (Roxb.) average diffusion coefficient (D) for untreated, wood ash alkali and commercial alkali treated was found to be 10.6 × 10-13 m2/ sec, 3.08 × 10-12 m2/sec, and 2.35 × 10-12 m2/sec; respectively. Bauhinia vahlii had the corresponding values of 6.8 x 10-13 m2/sec, 3.80 x 10-12 m2/sec, and 3.46 x 10-12 m2/sec. Finally, the physico-mechanical, and optical properties of the cellulose mat prepared were examined. Ag-ZnO nanoparticles were doped in the mat using a single-pot hydrothermal synthesis procedure. The materials' properties were investigated by FE-SEM, EDS, XRD, FTIR, and UV-Vis spectroscopy. Images taken with a FE-SEM demonstrated that the nanoparticles were distributed uniformly throughout the mat. The paper disc diffusion method was used to evaluate the antimicrobial efficacy against Escherichia coli, Bacillus subtilis, and Candida albicans. Methylene blue was utilized to evaluate photocatalytic performance in an ultraviolet light environment. It is interesting to note that water retting improved the stability of both kinds of fibers at high temperatures and increased their resistance to water. Fibers made by alkali and WAA retting methods have very comparable mechanical strengths. These findings suggested that WAA treatment of lignocellulosic biomass might be a low-cost alternative. The elimination of cementing components and the subsequent rise in crystallinity both contributed to a significant reduction in the equilibrium water sorption of the alkali-treated fiber. Sorbed fibers lose mechanical strength. The produced nanocomposite showed promising photocatalytic and antibacterial activity. These outcomes point out that the nanocomposite mat is suitable for antibacterial and photodegradation in water resources. Keywords: Lignocellulose biomass, Diffusion coefficient, Paper and pulp, Water retting, Photodegradation, Nanocomposite