Development and characterization of lignin microparticles for physical and antioxidant enhancement of biodegradable polymers

Abstract

As the largest aromatic polymer of natural origin, lignin arouses the interest of researchers and industries worldwide. Its three-dimensional polymeric aromatic structure, besides being complex, varies depending on its botanical origin and extraction process, which makes its use as a raw material difficult. Currently, the main destination for lignin is burning for energy production. This study presents the characterization of lignin and lignin microparticles after processing by ultrasonic irradiation. Analyzes were performed to verify the dimensional, morphological and antioxidant characteristics of the particles as well as changes in their structure after sonication. A sample of eucalyptus wood lignin isolated from kraft black liquor was used and the modifications were analyzed by X-ray diffraction analysis, zeta potential, FTIR spectroscopy, particle size, scanning electron microscopy, TGA thermogravimetric analysis, phenolic compounds total by Folin–Ciocalteau and antioxidant analysis by DPPH. The results demonstrate that there was no change in the chemical structure of lignin with the application of ultrasonic radiation, but the reduction in particle size was able to reduce zeta potential with a lower probability of agglomeration between them, and consequent greater stabilization in solution. Also, the ultrasound treatment was able to increase the thermal stability of the lignin microparticle with a decrease of the mass loss rate with the time. The reduction in particle size was also able to expose a larger number of phenolic compounds and thereby increase the total phenolic content and lignin antioxidant activity making the lignin microparticle a promising material to study and application on food-active biodegradable polymers.