O uso de corantes naturais como temática central para o ensino de química

Abstract

Natural dyes have been utilized for thousands of years to color fibers, fabrics, and other materials derived from plants, insects, and minerals. As a sustainable alternative to synthetic dyes, they have garnered attention from researchers and entrepreneurs for their potential application in textile dyeing. Due to the structural diversity of natural dyes, their varied sources, and extraction methods, this topic is the central focus of this dissertation. The objective was to extract dyes from fruits, vegetables, and spices for teaching chemical concepts, such as separation of mixtures, pH, organic functions, and intermolecular i0nteractions, in high school classes. The work was divided into two stages. In the first stage, the raw materials and their respective extraction methods were investigated. The selected raw materials were beetroot, black beans, hibiscus, annatto, onion skins, turmeric, and red cabbage. Solvent extraction under heating was used to obtain the dyes, and the color palette obtained by dyeing cotton fabrics was evaluated. The second stage consisted of planning and executing a workshop with students from Colégio Estadual José Veríssimo and Centro Educacional Imperial, both located in the city of Magé, in the metropolitan region of Rio de Janeiro. The workshop was divided into three meetings: the first consisted of a theoretical class covering the chemistry content involved in the practice; in the second, students carried out the practice of extracting natural dyes and participated in a discussion group; and in the third, students applied the extracted dyes in a cotton fabric dyeing activity using the Tie-Dye technique, combining art and science. The learning assessment was conducted the week after the third meeting, in the form of a questionnaire containing discursive and objective questions about the topics discussed during the workshop. It was observed that the activities encouraged students to take a leading role, as they carried out all the practical work autonomously. Additionally, they had a voice in the entire teaching and learning process, especially in the discussion group. They were able to relate chemistry to their daily lives, seeing it beyond chemical formulas. However, even using active teaching methodologies, some chemistry topics considered more abstract were still more challenging for students to understand, resulting in fewer correct answers to these questions. All the steps of the teaching sequence, including the workshop, are recorded in an e-book entitled "Exploring the Colors of the Earth: The Use of Natural Dyes as a Facilitator of Chemistry Teaching", a free digital resource that other teachers can access and use as a teaching tool.