Preparation and characterization of lignin nanoparticles from black pine and aspen woods by using deep eutectic solvents

This study aims to produce and characterize lignin using ChCl deep eutectic solvent from Black Pine and Trembling Aspen woods obtained from the Bartın region. The procured woods were first reduced to small particles, ground in a laboratory-type Wiley mill, and sieved through various mesh sizes to obtain 60 mesh wood chips used in the study. The ChCl solution was prepared in a heated stirrer, added to the wood chips, and after 2 hours of treatment at 90°C, the obtained black solution was filtered through an appropriate filter paper using vacuum filtration. A certain amount of distilled water was added to this solution to precipitate the lignin dissolved by the DES. The precipitated lignin was filtered again using vacuum filtration to obtain lignin. The obtained lignin was frozen for a sufficient time in a deep freezer, then dried using a lyophilizer to produce powdered lignin. The obtained lignin was subjected to yield calculations, and size and morphological analyses were conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Chemical analyses were performed using X-ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, elemental analysis, and proximate analysis, while thermal stability was investigated using thermogravimetric analysis. According to the results, the yield of lignin production was calculated to be 91% for Trembling Aspen lignin and 89% for Black Pine lignin. SEM and AFM analyses showed that the diameters of Black Pine lignins ranged between 30 and 80 nm, while the diameters of Aspen lignins were between 40 and 120 nm. However, AFM size analysis determined the diameters as 0-50.12 nm for Black Pine lignin and 0-72.49 nm for Aspen lignin. XRD analysis indicated that the lignins had similar peak points, and some differences in the intensities of peak points and wave numbers were identified in FTIR spectra. Elemental analysis and proximate analysis showed that the results were close to each other. Thermogravimetric analysis revealed that the thermal stability of Aspen wood was higher than that of Black Pine wood.