Obtaining Microcellulose from Solid Agro-Waste by Ball Mill Assisted by Light Acid Hydrolysis Process

Cellulose, the most abundant biopolymer on Earth, is biodegradable, nontoxic, and derived from renewable sources. Its properties and applications depend on the extraction methods and sources, making plant waste reuse a sustainable production option. This study aimed to assess the potential of cowpea pod skin (Vigna unguiculata) as a source of microcellulose (CPMC) using a chemical-mechanical process involving ball milling combined with acid hydrolysis. For a comparative analysis of the method's efficiency and biomass performance, corn straw (Zea mays L., CSMC) and pineapple peel (Ananas comosus, PPMC) were also utilized as extraction sources. The chemical composition of microcelluloses (MCs) was investigated by Fourier Transform Infrared Spectroscopy (FTIR), thermal behavior by Thermogravimetric Analysis (TGA), crystallinity by X-ray Diffraction (XRD), morphologies by Scanning Electron Microscopy (SEM), and shape and size by Atomic Force Microscopy (AFM). In the FTIR spectra, absorption bands characteristic of cellulose were observed at 3408 cm^-1 (hydroxyl group OH stretching), 1640 cm^-1 (adsorbed water molecules), 1205 cm^-1 (O-H deformation vibration), 1165 cm^-1 (C-O-C- stretching vibration), 1113 cm^-1 (glucose ring stretching vibration), 1055 cm^-1 (CO stretching), 1028 cm^-1 (C-OH stretching), and 895 cm^-1 (β-glycosidic bonds). The TGA/DTG curves of all the samples showed three stages of mass loss, and CPMC proved to be the sample with the greatest thermal stability. The crystallinity indices of the MCs samples ranged between 69.23-75%. The micrographs show compact and lamellar materials. However, AFM measurements revealed distinct nanostructures for each of the MCs obtained, displaying lamellar structures from 20 to 280 nm. Therefore, this method was efficient for extracting MCs from different types of biomass. The analyses demonstrated greater efficiency in the CPMC and CSMC samples. In this context, they have become promising candidates for application in a wide range of industrial materials.