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Lignin is among one of the largest natural resources in the world, with aromatic structures that can serve as a raw material in the synthesis of high value-added chemicals, the production of bioenergy, and the development of carbon-based products, among others. A better understanding of the chemical structure of lignin and its valorization methods is necessary to overcome current technological challenges for industrial scale applications. The main challenge found to provide the most abundant source of aromatics in the world is the fractionation of lignin. Current studies propose a way to fractionate lignin to obtain more homogeneous and less complex fractions, because of the fact that aromatic compounds are essential intermediates in the manufacture of polymers, and lignin is the main source of biologically aromatic-based substrates. Numerous review articles have addressed research aimed at understanding the structure of lignin, however, a limited focus has been given to its fractionation methods. This article aims to review papers published in recent years using different lignin fractionation techniques, focusing on the four main types of fractionations: in organic solvents, gel permeation chromatography in preparatory scale, ultrafiltration and precipitation by varying acid gradient. This a Review summarizes the most recent innovations in the area of biorefineries for the chemical valorization of lignin derived from various botanical sources through different fractionation methods.

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This study show influence of alkaline treatment on sisal fiber (SF) in different composites of starch matrices (SM) and cellulose acetate matrices (CAM). SF were modified with an aqueous 0.5M NaOH solution. Composites were prepared in proportion of 3% fiber/matrix (m/m) using casting method. The samples were characterized by Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy by Attenuated Total Reflection (FTIR-ATR), Thermogravimetric Analysis (TGA) and Dynamic-mechanical thermal analysis (DMA). Through results obtained in FTIR and TGA, it was possible to verify that alkaline treatment partially removed hemicellulose and SF lignin. With SEM, best fiber/matrix adhesion in composites prepared with modified fiber (TSF) has been proven to change fibre morphology. Through DMA analysis it was possible to observe that after addition of SF and TSF, SM composites showed improvements in mechanical properties, while TGA showed an increase in initial temperature of thermal degradation in CAM composites with addition of fiber.

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