Síntese e caracterização de compósitos de polianilina e lignina

Abstract

Since antiquity, polymeric materials have been widely used in everyday life. However, the understanding of these materials from a molecular perspective only began in the 20th century, with the concept of macromolecules proposed by Hermann Staudinger. Until the 1970s, polymers were considered insulating materials; this view changed after the discovery that polyacetylene, after doping, could exhibit a significant increase in conductivity. This advance gave rise to the class of conductive polymers, among which polyaniline (PANI) stands out. Due to its stability, ease of synthesis, and reversible redox behavior, PANI has great potential for application in devices such as supercapacitors. Despite its advantages, conductive polymers have some limitations, such as low mechanical stability and loss of performance throughout charge and discharge cycles. One strategy to overcome these limitations is the formation of composites, such as the combination of PANI and lignin. Lignin is a biopolymer composed of phenylpropanoid units (H, G, and S), whose composition varies according to the plant origin. The incorporation of lignin into PANI can result in improvements in structural, mechanical, and electrochemical properties. The objective of this work was to produce PANI-lignin based composites for application in electrochemical systems. The materials were synthesized by oxidative polymerization, followed by doping, deprotonation, and composite formation processes with different lignin proportions. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-Vis and infrared spectroscopies (FTIR), as well as electrical conductivity measurements. The results indicated that the addition of lignin reduces the crystallinity of PANI, evidenced by the decrease in peak intensity in XRD and the increase in the amorphous character of the material. Morphological analyses revealed greater structural heterogeneity in the composites, while UV-Vis and FTIR spectra showed alterations in electronic states and chemical interactions as a function of lignin concentration and type. Electrical measurements demonstrated that conductivity depends directly on the proportion and nature of the incorporated lignin. Thus, it is concluded that lignin significantly influences the structural, morphological, and electrical properties of PANI-lignin composites, highlighting their potential for applications in energy storage devices, such as supercapacitors.