Fractionation and characterization of lignin from waste rice straw: Biomass surface chemical composition analysis

•Rice straw was fractionated to extract the lignin by alkaline and acidic treatment process.•Structural characterization of the SHT-lignin and OAT-lignin fractions were analyzed by UV, FTIR and 1H NMR technique.•Surface characterization of UT-RS, SHT-RS and OAT-RS biomass were carried out by SEM, XRD and FTIR technique.•Surface chemical composition changes of SHT-RS and OAT-RS analysis by XPS survey, Cls and O1s spectra. Waste rice straw (RS) was fractionated to extract the lignin using alkaline (sodium hydroxide) treatment (SHT) and organic acid (Formic acid/Acetic acid) treatment (OAT) process. Rice straw fractionation by the acetic OAT and alkaline SHT methods resulted in the recovery of OAT-lignin and SHT-lignin respectively. The structural characterization of the extracted lignin fractions was done by UV–vis spectroscopy, FTIR and 1H NMR technique. Total phenolic content (TPC) present in SHT-lignin and OAT-lignin were determined to be 28.87 mg GAE/g and 24.75 mg GAE/g respectively. The DPPH radical scavenging activity 59.50% was observed in SHT-lignin and 45.74% in OAT-lignin using the DPPH test for 30 min of incubation. Surface characterization of untreated rice straw (UT-RS) and treated rice straw (SHT-RS and OAT-RS) were carried out by XRD, FTIR and SEM. X-ray photoelectron spectroscopy (XPS) survey, C1s, and O1s spectra were used to determined the surface carbon and oxygen composition changes in RS after SHT and OAT. These structural characterizations of lignin and biomass are beneficial for further processing in bio-refinery industry.