pH indicators by nanofibril hydrogels from sugarcane leaves

This research focuses on the development of hydrogels derived from sustainable biomass nanocellulose for use as pH indicators. First, the cellulose nanofibrils (CNFs) were extracted from sugarcane leaves. Then, the CNFs with 0 %, 0.4 %, and 1 % were added to the hydrogels. The scanning electron microscopy (SEM) revealed a transition from a compact structure of PVA to a microporous network when CNFs were added. The average pore size of CNFs 0.4 % and 1 % were 0.61 ± 0.29 μm and 0.35 ± 0.13 μm, respectively. Fourier transform infrared spectroscopy (FTIR) showed the removal of lignin and hemicellulose, along with stronger hydroxy bonding interactions with PVA-CNFs. X-ray diffraction (XRD) confirmed the presence of cellulose phase, and the addition of CNFs resulted in the increased crystallinity (from 49.7 % to 57.6 %) and crystallite size (from 6.8 nm to 21.9 nm). The hydrogel containing 0.4 % CNFs had maximum values of stress and strain (682 kPa and 80.34 %). The water swelling increased with time for all samples; however, at 3 h, the values were ~ 47 % (0 % CNF), 45 % (0.4 %), and 41-42 % (1 %), reflecting a higher effective physical crosslink density at higher CNF content. The UV light absorption revealed many regions of pH response, including the single band (530-540 nm) at pH 1-3, the mixed band (530-540 nm, and 600-620 nm) at pH 4-10, the mixed band (450-470 nm, and 600-620 nm) at pH 11-12, and the single band (450-470 nm) at pH 13. The color difference analysis indicated the potential pH indicator of the hydrogel in testing with pork, chicken, and bean sprouts. The results showed that the pH indicator of nanofibril hydrogels could detect food spoilage, potentially serving as an alternative pH indicator for the food industry.