Síntese de nanofibras de carbono pela técnica da fiação por sopro em solução a partir de poli(álcool vinílico) e lignina proveniente do substrato pós-cultivo de cogumelos comestíveis

Abstract

The growing increase in the production of edible mushrooms and consequently, in the disposal of the post-cultivation substrate (SMS - Spent Mushroom Substrate) has motivated companies in the field to seek ways to dispose of this material in an ecologically correct manner. For every ton of mushrooms produced, 1 to 2 tons of SMS are generated. Thus, a viable alternative to take advantage of this material is employing it in the development of new materials. Lignin, which is also present in SMS, has characteristics that suggest a high potential for replacement of polyacrylonitrile (PAN) in the synthesis of carbon nanofibers (NFCs), and is one of the most abundant natural resources on earth, besides having a renewable origin and a high carbon concentration. In this work, a route of synthesis of NFCs spun by the method of solution blow spinning (SBS - Solution Blow Spinning) and formulated from of a lignin solution extracted from the SMS from the cultivation of edible mushrooms and poly(vinyl alcohol) (PVA) was investigated. Lignin was extracted by employing the alkaline method and characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TGA), differential scanning calorimetry (DSC) and spectroscopy in the region of ultraviolet-visible (UV-Vis). All the analyzes performed on the extracted lignin displayed characteristic results, suggesting that the mushroom blocks, even after biotransformation by lignocellulolytic fungi, that is, lignin and cellulose degraders, still result in SMS with lignin content. For the wiring in the SBS, two solutions containing 30% (solution A) and 23% (solution B) of lignin were formulated and used. The synthesized lignin/PVA nanofibers were characterized by scanning electron microscopy (MEV), FTIR, TGA and DSC. FTIR, TGA and DSC characterizations were also performed in the pure PVA. The average diameters obtained for the lignin/PVA nanofibers were 370 nm for solution A and 463 nm for solution B. This indicates that the lignin content has a direct influence on the diameter of the nanofibers. FTIR analysis showed that the lignin and PVA can form intermolecular bonds with each other, which led to the formation of nanofibers during spinning. NFCs were characterized by SEM and elementary analysis. The average diameters obtained for the NFCs were 286 nm and 322 nm. It was observed that there was a reduction in the diameter of the nanofibers after carbonization due to the volatilization of non-carbon components of the samples, such as nitrogen, hydrogen, oxygen, among others. Therefore, it was possible to synthesize NFCs from the lignin extracted from SMS associated with PVA. In addition, the SBS can be the precursor method of spinning the lignin/PVA solution.