Micro/Nanostructured Lignonanocellulose Obtained from Steam-Exploded Sugarcane Bagasse

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 submitted 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 SE-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.

Sustainable 2G Ethanol Production From Switchgrass Biomass via Co-Fermentation of Pentoses and Hexoses Using Novel Wild Yeasts

The production of second generation (2G) ethanol remains an interesting proposition for the implementation of sustainable and net carbon-neutral energy systems. 2G makes use of renewable lignocellulosic feedstocks, generating fermentable sugars that are converted to ethanol or other bio-based products. To be economically viable, 2G biorefineries must make use of all processing streams, including the less desirable C5 sugar stream. In this work, a strategy of sequential acid and alkaline pretreatment of the lignocellulosic feedstock switchgrass for improvement of fermentable sugar yield, and the subsequent utilization of wild yeasts for co-fermentation of its C5-C6 sugar streams are presented. Hemicellulose-enriched hydrolysates, obtained by dilute acid pretreatment of switchgrass, were fermented by a newly-isolated wild Scheffersomyces parashehatae strain–UFMG-HM-60.1b; corresponding ethanol yield (YPS) and volumetric productivity (QP) were 0.19 g/g and 0.16 g/L h, respectively. Afterwards, the remaining switchgrass cellulignin fraction was subjected to optimized alkaline delignification at 152 ºC for 30 min. The delignified solid fraction was subjected to contiguous enzymatic saccharification and fermentation, releasing a C6 sugar stream in which Saccharomyces cerevisiae 174 strain displayed a productivity of 0.46 g/g (YPS) and 0.70 g/L h (QP), whereas the S. parashehatae UFMG-HM-60.1b presented YPS and QP of 0.29 g/g and 0.38 g/L h, respectively. Upon combining the conversion of hemicellulose (37%) and cellulose-derived sugars (57%), the S. parashehatae strain provided higher yield (94%) than the generic S. cerevisiae (90%). Henceforth, our integrated pretreatment and co-fermentation process provides a pathway for maximum utilization of the switchgrass carbohydrates for 2G ethanol production.

Micro/nano-structural evolution in spruce wood during soda pulping

Alkaline delignification of wood tissue is the core of the global pulping technology and the most prominent large-scale separation of the main wood components. This work aims at improved understanding of the interplay between the topochemistry of alkaline pulping and the associated morphological changes. Morphology and chemical structure of partially soda-delignified wood chips were studied combining X-ray tomography (XRT), X-ray diffraction analysis and compositional characterization (lignin and carbohydrate content). The XRT studies of wet samples (providing 3D structural information without interfering drying effects), allowed observation of the cell wall separation as an increasing amount of lignin was removed with the increasing pulping time. Comparison between the microstructure of the surface and the central parts of the treated chips showed a more delignified microstructure at the surface, which highlights the dependence of the delignification process on the mass transport (hydroxide ions and lignin fragments) through the wood tissue. The crystallite size of cellulose increased in the <200> crystal planes during the early stage of pulping while there was little effect on the <110> plane.

The influence of bleaching scheme technology on the content of total and bound chlorine in cellulose

Наблюдается ужесточение требований по содержанию хлора в целлюлозе для санитарно-гигиенических изделий и ряда других целей. Содержание хлора в целлюлозе зависит от применяемой схемы отбелки. В процессе отбелки с применением молекулярного хлора, диоксида хлора или гипохлорита натрия небольшая часть соединений хлора присутствует в целлюлозном волокне. На большинстве современных предприятий применяется технология ECF, где в качестве альтернативы молекулярному хлору на одной или нескольких ступенях используются диоксид хлора (ClO2) или гипохлорит натрия (NaClO). Также существует технология отбелки TCF, которая позволяет полностью отказаться от применения хлорсодержащих агентов путем использования только кислородсодержащих реагентов, таких как кислород, пероксид водорода, озон. Применение полностью бесхлорных технологий ограничено в виду высокой себестоимости продукции при сравнительных качественных характеристиках продукции. Проведен анализ образцов целлюлозы различных производителей. Определение содержания общего хлора и органически связанного хлора осуществлялось путем сжигания пробы целлюлозы при температуре от 950 до 1000 С. Анализ образцов целлюлозы российских заводов показал, что в целлюлозе, полученной с использованием схем отбелки КЩОД0ЩП1Д1ЩП2Д2К и Д0ЩОПД1ЩПД2К, содержание хлора в готовой продукции меньше всего. Это может объясняться тем, что кислородно-щелочная обработка позволяет эффективно снизить содержание лигнина. Низкое содержание последнего позволяет сократить количество используемого диоксида хлора на стадиях Д. По совокупности предъявляемых к целлюлозе свойств и экономических показателей наиболее приемлемыми являются схемы отбелки с оптимизированными расходами диоксида хлора и пероксида водорода, озона без использования молекулярного хлора (ECF-light). Они позволяют достичь низкого содержания соединений хлора в целлюлозе, близкого к технологии TCF. There is a tightening of requirements for the content of chlorine in cellulose for sanitary products and a number of other purposes. The chlorine content in cellulose depends on the bleaching scheme used. In the bleaching process using molecular chlorine, chlorine dioxide or sodium hypochlorite, a small part of the chlorine compounds is replaced on cellulose fiber. Most modern plants use ECF technology, where, as an alternative to molecular chlorine, chlorine dioxide (ClO2) or sodium hypochlorite (NaClO) is used at one or several stages. There is also TCF bleaching technology, which allows you to completely abandon the use of chlorine-containing agents by using only oxygen-containing reagents such as oxygen, hydrogen peroxide, ozone. The use of completely chlorine-free technologies is limited in view of the high cost of production with comparative qualitative characteristics of the products. Pulp samples from various manufacturers were analyzed. The determination of total chlorine and organically bound chlorine was carried out by burning a cellulose sample at a temperature of from 950 to 1000 C. Analysis of cellulose samples from Russian plants showed that in the pulp obtained using the bleaching scheme O1D0EP1D1EP2D2A and D0EOPD1EPD2A bleaching schemes, the chlorine content in the finished product is the least. This can be explained by the fact that oxygen-alkaline delignification can effectively reduce the lignin content. The low content of the latter makes it possible to reduce the amount of chlorine dioxide used in stages D. According to the combination of properties and economic indicators presented to cellulose, bleaching schemes with optimized consumption of chlorine dioxide and hydrogen peroxide, ozone without the use of molecular chlorine (ECF-light) are most acceptable. It allows to achieve a low content of chlorine compounds in cellulose, close to TCF technology.

Microfibrillated Cellulose Suspension and Its Electrorheology

Microfibrillated cellulose (MFC) particles were synthesized by a low-pressure alkaline delignification process, and their shape and chemical structure were investigated by SEM and Fourier transformation infrared spectroscopy, respectively. As a novel electrorheological (ER) material, the MFC particulate sample was suspended in insulating oil to fabricate an ER fluid. Its rheological properties—steady shear stress, shear viscosity, yield stress, and dynamic moduli—under electric field strength were characterized by a rotational rheometer. The MFC-based ER fluid demonstrated typical ER characteristics, in which the shear stresses followed the Cho–Choi–Jhon model well under electric field strength. In addition, the solid-like behavior of the ER fluid was investigated with the Schwarzl equation. The elevated value of both dynamic and elastic yield stresses at applied electric field strengths was well described using a power law model (~E1.5). The reversible and quick response of the ER fluid was also illustrated through the on–off test.