| Summary: | The ongoing transition to a circular bioeconomy and stricter legislative requirements related to waste management has forced the industry to search for a more efficient valorization of agricultural waste and by-products, such as lignin, into functional materials. As a major constituent in black liquor (25–35% of the total organic components), it is important to develop new methods for efficient isolation and valorization of lignin in some end uses. The use of other mineral acids (phosphoric acid/H3PO4) instead of chloric and sulfuric acid in the extraction process of lignin is still relatively limited. Therefore, this research work aimed to evaluate the effect of H3PO4 in various concentrations (15, 20, 25, 30, 35, and 40% v/w) on lignin characteristics derived from formacell black liquor derived from oil palm empty fruit bunches (OPEFB). The results obtained revealed that the increased concentration of H3PO4 increased the yield and methoxyl content of lignin, but decreased the equivalent weight and pH. The Fourier transform infrared spectroscopy (FTIR) analysis showed unique lignin peaks, which inferred a successful isolation method. The decrease of equivalent weight was linear to disappearing guaicyl (G) peaks at higher concentrations but opposite for the aromatic ring vibration area. Scanning electron microscopy (SEM) showed similar features of lignin morphology, but some parts of the lignin, isolated by 40% H3PO4, were more compact. The optimal lignin characteristics were obtained using H3PO4 at 40% concentration with a yield of 17.69%, equivalent weight of lignin of 127.57, methoxyl content of 28.71%, and pH of 0.4. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023.
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