Abstract
This work demonstrates the isolation of lignocellulose micro-nanofibrils, nanocrystals and nanospheres from steam-exploded sugarcane bagasse (SEB). First, steam-explosion was carried out in sugarcane bagasse at 195 °C for 7.5 and 15 min (SEB-7.5 and SEB-15). Untreated sugarcane bagasse was also pretreated by mechanical refining (MRB) in a PFI mill for comparison. Then, SEB and MRB fibers were subjected to alkaline delignification, hypochlorite bleaching for 60 or 180 min (HB60 and HB180), enzymatic hydrolysis (endoglucanase), and high-pressure homogenization. The resulting materials were characterized regarding chemical composition by high-performance liquid chromatography, width and morphology by transmission electron microscopy, crystallinity by X-ray powder diffraction and aspect ratio (length/diameter) by rheology. Levels of glucans (mostly cellulose), hemicelluloses and lignin were: 53.8%, 19.7% and 11.6% in MRB-HB180; 87.8%, < 0.1% and 7.2% in SEB-7.5-HB60; 84.3%, < 0.1% and 4.8% in SEB-7.5-HB180, 85.9%, < 0.1% and 8.4% in SEB-15-HB60; and 82.2%, < 0.1% and 5% in SE-15-HB180, respectively. Aspect ratios and crystallinity indexes were similar among all groups (~ 100 and ~ 73%, respectively), except for SE-15-HB180 (~ 78.5 and 77%, respectively). MRB-HB180 and SE-15 (HB60 and HB180) had the lowest fiber widths (< 20 nm) with the presence of nanocrystals in SE-15-HB180, while in the SE-7.5 (HB60 and HB180), fiber widths were greater than 50 nm with the presence of lignin nanospheres in SE-7.5-HB60. Hence, lignocellulose nanomaterials with aspect ratios ranging from micro/nanofibers to nanocrystals were isolated from SEB using a cost-effective production process.
Highlights
Worldwide agro-industrial activities generate substantial amounts of residual waste streams every year
Lignocellulose nanomaterials with aspect ratios ranging from micro/nanofibers to nanocrystals were isolated from sugarcane bagasse (SEB) using a cost-effective production process
lignified nanocelluloses (LNC) with different aspect ratios were obtained with characteristics of lignocellulose nanocrystals (LCNC) and lignocellulose nanofibers (LCNF) by varying steam explosion and bleaching times. These results demonstrated that lignin-containing cellulosic nanomaterials with interesting and tailored properties and characteristics could be successfully obtained from steam-exploded sugarcane bagasse
Summary
Worldwide agro-industrial activities generate substantial amounts of residual waste streams every year. Energy savings in the range of US$ 200 to 400 can be achieved for every 1 ton of burnt wastes (dry basis) (Mathur and Srivastava 2019). Cellulosic crop residues can be utilized for the isolation of nanocelluloses, whose selling price is in the range of US$ 2,000-20,000 tonavailable, are of special interest due to their high added-value and broad spectrum of applications. Nanocellulose biocompatibility and biodegradability are key for applications in sustainable products, technological developments are still lacking to accommodate a cost-effective production process, adapted to local resources and to the type of feedstock available as raw material. Most of the commercially available nanocelluloses come from bleached chemical pulps, which leads to a low yield of the whole operation
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