Avaliação das modificações na estrutura lignocelulósica da casca de jabuticaba Myrciaria jabuticaba (Vell) Berg após tratamento químico por espectroscopia vibracional de absorção na região do infravermelho e análise termogravimétrica

Abstract

The lignocellulosic biomass is a renewable source of carbon of more abundant of the earth may be the source of biofuel of choice in the very near future. The use of lignocellulosic residues in biotechnological processes often requires, preliminary steps of preparation, can be used chemical or enzymatic hydrolysis to a greater availability of cellulosic or hemicellulosic fractions, both in the form of oligosaccharides and monosaccharides. This work deals of the characterization by Infrared Spectroscopy with Fourier Transform (FTIR) and by Thermogravimetric Analysis (ATG) of the changes undergone in lignocellulosic structure of barks jabuticaba Myrciaria jabuticaba (Vell) Berg after chemical treatment. The barks were subjected to hydrolysis with sulfuric acid (H2SO4) 1%, phosphoric acid (H3PO4) 1%, hydrogen peroxide (H2O2) 1%, hydrochloric acid (HCl) 1% and sodium hydroxide (NaOH) 1% 1:10 (w/v). The changes in functional groups of treated barks were recorded by FTIR and ATG. The spectra showed totally different absorption bands which differ from spectra of the barks before of chemical treatment, causing the extraction of lignocellulosic components depends on the type of treatment to be used, allowing handling the reaction medium according with the material to be collected. The spectra of commercial cellulose, microcrystalline cellulose and bark jabuticaba untreated were compared to the spectra of barks jabuticaba with treatment. Treatment with HCl and H2O2 pointed a predominance of lignin in the middle and a complete extraction of three compounds from lignocellulose. Treatment with H2SO4 demonstrated the predominance of cellulose in the sample and the capacity to remove hemicellulose completely while treatment with H3PO4 was obtained lower concentrations of lignocellulosic fibers besides not having a component to be obtained more preferably. In the treatment with NaOH there wasn’t removal of hemicellulose causing the lignin and more cellulose were extracted, independent this was in larger amount than the other. From the technique of thermogravimetric analysis, it was possible to observe the variations of loss of mass of each sample with and without chemical pretreatment, allowing to determine the presence and proportion of each component of lignocellulosic biomass and its behavior as a function of temperature over process. The thermogravimetry graphics of jabuticaba barks untreated suggest the quantitative presence of cellulose, hemicellulose and lignin in its constitution. These results are repeated in jabuticaba barks subjected to chemical pre-treatment, although in the samples treated with HCl and NaOH, the processes of degradation of hemicellulose and cellulose occurring simultaneously depending on the temperature range. Therefore, all the presented results were observed and recorded for the comparison between the untreated material and the after chemical pretreatment, allowing an analysis of the behavior of the lignocellulosic biomass for future experimental and/or commercial practices.