Abstract
The chestnut shell from the Amazon region shared between Colombia, Brazil, and Perú is an abundant residue of the walnut used for obtaining food and cosmetic products. This residue is not yet usable due to the lack of knowledge of its properties and the environmental impact generated by its treatment through methods such as mercerization. This work presents the results of the characterization of Amazon chestnut shell residues treated by two methods, mercerization with NaOH solution and intense plasma discharge (Glow Discharge Plasma), in a reactor with argon gas in a 0,3-bar vacuum and discharge conditions of 80 mA and 600 s. The microstructural, morphological, topographic, and nanomechanical changes of the chestnut residues without treatment and with the two proposed treatments were evaluated by means of the µRaman, scanning electron microscopy, and atomic force microscopy techniques. The results showed the effectiveness of the plasma method over the mercerization method at obtaining more crystalline cellulose structures due to the reduction of hemicellulose, lignin, and the aqueous phase of walnut shell waste.
Highlights
Generating agricultural waste is inevitable, since a large amount of it can result from the harvest in the early stages of the food production chain, which causes environmental and economic problems in cultivation areas
The Raman spectra of the fibers processed by mercerization and plasma, as well as of those unprocessed, are shown in Figures 3a, b, c, and d, where the variations in the intensity of the main bands represent, among other characteristics, changes in crystallinity and the reduction of lignocellulose from the residues of the Amazonian chestnut shell due to the treatments proposed in this research
The increase in the level of crystallinity and the stiffness of the walnut shell fibers is a consequence of the covalent molecular restructuring of the carbon and oxygen bonds of the fibers, in addition to the decrease in the aqueous phase (Marcuello et al, 2019). Both the mercerization and plasma treatment on the Amazonian chestnut walnut shell generated the release of agglomerated cellulose microfibers in spirals with diameters between 1,5 and 2,5 μm, according to the Scanning Electron Microscopy (SEM) image analysis
Summary
Generating agricultural waste is inevitable, since a large amount of it can result from the harvest in the early stages of the food production chain, which causes environmental and economic problems in cultivation areas. One of the main economic activities in the Brazilian Amazon region is the Brazilian nut, whose shelling stage is a process that generates large amounts of waste, representing 90% by volume of the chestnut crops This product is part of the so-called ‘dried fruits’, which provide important nutritional benefits due to their high content of proteins, carbohydrates, unsaturated lipids, essential vitamins, and minerals (ARSUS, 2019). Brazilian nut harvesting maintains a constant demand in the international market. Bertholletia excelsa is the scientific name by which this walnut species is known, according to its taxonomy and ecology
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