Comparative evaluation of cellulose nanocrystals from bagasse and coir agro-wastes for reinforcing PVA-based composites

In order to increase resilience of planters against climate change and bring additional economic benefits, agro-wastes can be exploited for extracting nanocellulose to produce eco-friendly composites. This paper focused on extracting nanocellulose from sugarcane bagasse and coir (cocos nucifera) using chemical methods including mercerisation, bleaching and acid hydrolysis. Taguchi Design of Experiment showed that the optimum alkaline treatment conditions of bagasse were at 2 wt% NaOH at 90 °C for 16 h. The morphological changes occurring along each treatment stage were observed using Fourier-Transform Infrared spectroscopy and Scanning Electron Microscopy. The differences in the nanoparticles extracted from the two biomass were studied through the determination of crystallinity indexes and particle size. Cellulose nanocrystals (CNCs) from coir exhibited a total crystallinity index (TCI) of 1.03 and an average particle size of 137.3 nm while CNCs extracted from sugarcane bagasse under similar treatment conditions had a TCI of 0.85 and an average particle size of around 48 µm. Dynamic Light Scattering findings showed risks of agglomeration after freeze drying. Bio-nanocomposite films with polyvinyl alcohol (PVA) as matrix were manufactured by the solvent casting process. The highest tensile strength (38.2 MPa) was obtained for CNCs extracted from coir at a CNC/PVA loading of 0.5 wt%, representing a 96.9% increase in the tensile strength as compared to the unreinforced PVA matrix. This study showed that sugarcane bagasse and coir are suitable sources of nanocellulose and can be used to prepare bio-composites with considerably high tensile strengths.