Valorization of underutilized river tamarind Leucaena leucocephala seeds biomass for cellulose nanocrystals synthesis

Abstract

River tamarind or scientifically Leucaena leucocephala, is one of the underutilized nanocellulose resources with the potential to be used in reinforcement materials. This work evaluated the use of the insoluble residual waste or marc obtained during the isolation of galactomannan from Leucaena leucocephala seed (LLS) as a feedstock of cellulose to obtain cellulose nanocrystals by a two-step acid hydrolysis followed by its characterization and morphological study. The first step involved acid hydrolyzation of the hemicellulose and lignin from LLS, while the second step dealt with the removal of the amorphous region to produce crystalline LLS nanocrystals (NLLS). The physicochemical properties of nanocrystals were characterized using the Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), particle size analyzer (PSA), X-ray diffractometer (XRD), thermal gravimetric analysis (TGA), and gel permeation chromatography (GPC). The NLLS isolated showed a rod-like structure in the range of 70–90nm in diameter with a crystallinity index of 76% and thermal stability at 264°C. PSA indicates that 97.5% of the size distribution of NLLS was below 136.9nm. GPC analysis also revealed that the sulphuric acid hydrolyzation during the second step caused a reduction in the molecular weight due to the cleaving of glycosidic bonds in the structure. These results indicated that LLS waste is a potential feedstock for cellulose nanocrystals preparation.