Extraction and Characterisation of Cellulose derived from Pearl Millet (Pennisetum glaucum) Waste for Sustainable Biomedical Applications

Abstract

The residue of pearl millet (Pennisetum glaucum L., family: Poaceae) production, widely utilised in agriculture, has high potential as a sustainable resource for scientific development of new generative materials. The stalks and husks of Pennisetum glaucum (Pearl millet or Bajra) consist mostly of cellulose content. The primary objective of this research was to extract and characterise cellulose from agricultural residue of pearl millet. The extraction of cellulose was performed via a microwave-assisted green extraction method, the extracted cellulose was further characterised through various techniques, including Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), ash value determination, contact angle measurement, swelling index assessment, moisture content analysis, chemical resistance evaluation, and biodegradability testing by burial method. The cellulose was effectively isolated by green extraction method along with alkali treatment followed by bleaching and characterised using several analytical techniques. The organoleptic assessment indicated that the cellulose possessed a fibrous texture, a colour from pale cream to light yellow, and an odourless. FTIR spectroscopy shows the efficient removal of the majority of non-cellulosic components and verified the presence of distinctive cellulose functional groups. The DSC analysis identified an apparent endothermic transition, demonstrating the thermal resistance of the extracted cellulose, while the TGA demonstrated considerable thermal stability, with primary degradation occurring at high temperatures. The coarse, porous, and fibrillated surface morphology, as illustrated the SEM micrographs, enhanced the surface area and adsorption capacity. An XRD analysis found significant diffraction peaks at 2θ values of around 16°, 22°, and 34°, confirming the formation of a highly crystalline cellulose structure. Crystalline structure abundant in polysaccharides was shown by solid-state 13C NMR spectra, which showed distinct resonances in the 60-110 ppm region. The results of the contact angle measurements showed that the surface was quite hydrophilic, which is a good indicator of its wettability. The cellulose's high purity and stability were demonstrated by its acceptable moisture content and low ash level. The ability to absorb water was demonstrated in swelling tests in acidic, phosphate buffer, and pure water settings. Chemical resistance studies found almost no degradation in acidic, buffered, and water-based conditions. The material's eco-friendliness and biodegradability were confirmed by the biodegradability study, which showed a steady weight drop over 21 days. The structural, thermal, physicochemical, and biodegradation properties of pearl millet-derived cellulose were promising for pharmaceutical, biomedical, packaging, and environmental applications as a sustainable and cost-effective biomaterial.