Comparative property investigation of raw and treated coconut shell biomass for potential polymer composite application

Abstract

The use of environmentally friendly materials for industrial applications has increased tremendously in the past decades due to environmental concerns associated with using synthetic materials. The present comparative investigation studied the properties of raw and chemically-treated coconut shell biomass for possible polymeric composite applications. The coconut shell biomass was treated with alkali (NaOH), bleaching and combined NaOH-bleaching solutions and investigated the surface morphology, chemical transformations, and thermal stability. Untreated and chemically modified coconut shell biomass was characterized through the determination of chemical constituents, X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), thermogravimetric (TGA), and morphological analyses. Chemically treated coconut shell biomass reported a significant increase in cellulose constituents, reaching 74.72% for combined NaOH-bleach treated samples with accompanying reductions in lignin and hemicellulose, as confirmed by FTIR spectroscopy. Further, the study reported an increase in crystallinity index with chemical treatment. For instance, combined NaOH-bleach treatment reported a maximum crystallinity index of 80.29% compared to 44.82% for untreated biomass. Alkali treatment improved thermal stability as indicated by an increase in the onset temperature of degradation to 255°C from 250°C for raw samples. Post-treatment, improved surface purity and roughness were observed, indicating enhanced fibre/matrix interlocking during composite fabrication. Moreover, combined NaOH-bleaching treatment exhibited enhanced surface hydrophobicity, as indicated by a maximum C/O ratio of 0.93 compared to 0.64 for untreated samples. In conclusion, combined NaOH-bleaching treatment significantly improved the chemical, structural and morphological properties of coconut shell biomass, suggesting its potential for developing low-cost, lightweight, renewable, and sustainable composite materials.