Obtenção de nanolignina a partir da casca e fibra do coco verde (Cocos sp.)

Abstract

The lignin, the second most abundant biopolymer in nature, plays vital roles in plants and possesses attractive properties for industrial applications. Various methods of lignin extraction are mentioned, with acetosolv pulping being highlighted for its efficacy and sustainability. This research aimed to obtain nanolignin from lignin derived from green coconut (Cocos nucifera) husk and fiber using the acetosolv method. The research began with the collection of green coconut residues, available near the Federal University of Alagoas, and their preparation to obtain flour. The flour was then characterized for total extractives, ash content, lignin, moisture, holocellulose, alpha-cellulose, and hemicellulose. Acetosolv pulping was conducted in two stages, varying temperature conditions and the presence or absence of extractives. Lignin was obtained through precipitation and subsequently characterized through chemical and morphological analyses. The study comprised five main stages. Analysis of the primary components of coconut husk and fiber showed a lignin content of 40%, cellulose of 15.90%, and hemicellulose of 15.86%, within the ranges found in other studies. Physicochemical characterization of green coconut flour revealed extractive contents between 2.6 to 19.26%, moisture from 9.22 to 10.5%, ash from 0.98 to 5.12%, and proteins between 3.56 to 8.27%. These results indicate that green coconut husk and fiber are rich sources of lignin compared to other lignocellulosic biomasses. Next, nanolignin was produced through ultrasonication. The characteristics of the obtained products were analyzed, considering the influence of temperature and the presence of extractives. Finally, the nanolignin under the best condition underwent comprehensive qualitative and quantitative characterization. The results revealed an average yield of 13.86%, with variations related to temperature and biomass type. The purity of lignin was confirmed by moisture, ash, and Klason lignin content, indicating consistent values. Thermogravimetric analysis demonstrated thermal stability of lignin, while FTIR revealed typical lignin characteristics such as ketone groups, aromatic structure, and methylation. Scanning electron microscopy highlighted the formation of clusters and porosities in lignin, suggesting a complex structure. These results contribute to a comprehensive understanding of acetosolv lignin extraction and its structural properties.