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Deep eutectic solvent (DES) treatment has been considered as a promising approach to lignocellulose deconstruction and valorization. Nevertheless, some aspects such as high energy consumption and cellulose residue loss limited bioconversion efficiency. Herein, neutral DESs based on choline chloride (ChCl) and zinc acetate (ZAC) in different molar ratios were designed for ultra-fast treatment on bamboo holocellulose with the assistance of microwave radiation for the first time. ZAC/ChCl-1 promoted the glucose conversion yield to 67.3%, due to more hydrophobic sites exposed on crystallite surfaces caused by fibrils swelling and enlarged gaps between adjacent glucan chains after the treatment. Furthermore, the proposed DES also displayed the ability to exfoliate cellulose nanofibrils with high aspect ratios from microfibrils at high treatment temperature (120 °C). With a large amount of negative charge on surface, the nanocellulose maintained satisfying dispersion stability and homogeneity, which achieved the full use and tunable dual conversion of bamboo cellulose. Thus, the present study provides a deeper understanding of novel DES pretreatment for biomass conversion and widens the scope of high-efficiency biorefinery. [Display omitted] • Zinc acetate based DESs pretreatments assisted by microwave were developed. • Fast and efficient co-production of glucose and nanocellulose was achieved. • Cellulose structure variations contribute to high-yield enzymatic hydrolysis. • Nanofibrils with high aspect ratio and stability were demonstrated. [ABSTRACT FROM AUTHOR]

A facile and sustainable strategy for preparing bamboo holocellulose nanofibrils (HCNFs) via zinc acetate/ choline chloride deep eutectic solvents treatment assisted with mild acetic acid (HAc) was developed in the present work. The treatment was performed under fast microwave irradiation and followed by mechanical homogenization, resulting in HCNFs with considerable amounts of xylan hemicellulose (15 %−19 %) remained. Less HAc consumption was achieved, which is beneficial for fabricating nanofibrils with higher aspect ratios (>800). More xylan contents and higher degrees of acetylation on cellulose were investigated, resulting in greater charge repulsion and steric hindrance between HCNFs and favoring the fibrils dissociation. Moreover, the HCNFs maintained high crystallinity of 70 %− 80 % and good thermal stability, confirming the intact hydrogen bonding linkages between cellulose and xylan hemicellulose. Transparent films prepared from the HCNFs suspensions by vacuum drying approach displayed better mechanical strength (>40 MPa) and well-mimicked the complex of polysaccharides interactions in plant cell walls. [Display omitted] • Bamboo HCNFs were prepared by ZnAc/ChCl DES with mild HAc and microwave assistance. • Acetylation and charge repulsion favored the holocellulose nanofibrillated. • Higher DES ratios fabricated HCNFs with greater aspect ratios and xylan content. • HCNFs films present high transparency and improved mechanical strength. [ABSTRACT FROM AUTHOR]

Green bioconversion technology has been regarded as a fundamental solution to energy challenges and environmental issues. During bioconversion, a combination of mechanical and enzymatic treatment on lignocellulosic biomass can not only conformity with environmental concepts but also enable efficient conversion. In this study, a ball milling assisted enzymatic treatment was applied for full utilization of bamboo cellulose. In addition to the production of soluble saccharides, the residues that remained after enzymatic hydrolysis were collected for producing high-quality nanocellulose. Ball milling efficiently broke the hydrogen bonding interactions between glucan chains thus promoting the following xylanase and cellulase conversion. The highest Xylo-oligosaccharides (XOS) yield reached 21.6%. Meanwhile, xylanase facilitated cellulase hydrolysis by separation of hemicellulose on cellulose. With a low commercial cellulase loading of 5 FPU/g glucan, a maximum yield of 76.6% glucose and 53.3% xylose was reached. Finally, nanocellulose was extracted from the enzymatic hydrolyzate residue with a minimum width of 3.5 nm and an average size of 294.8 nm. The present study proposed an efficient combination of mechanical treatment assisted enzymatic digestion, which is not only environmentally friendly but also allows for complete bioconversion of bamboo cellulose. [Display omitted] ● A ball milling assisted enzymatic hydrolysis treatment was developed. ● 21.6% of XOS yield without chemical additions was achieved. ● 76.6% of high glucose yield at low cellulase loading (5 FPU/g glucan) was achieved. ● Nanocellulose fibrils were derived from residues after enzymatic treatment. [ABSTRACT FROM AUTHOR]

Exploration and application of novel and sustainable deep eutectic solvents (DESs) on lignocellulose pretreatment are promising approaches to efficient bioconversion. However, comprehensive understanding on efficient DESs selection and inner mechanisms of lignocellulose deconstruction are still limited. Herein, bio-based acetylcholine chloride (AChCl) was firstly utilized as hydrogen bond acceptor in cooperation with lactic acid, urea and glycerol respectively for microwave-assisted pretreatment on moso bamboo in short time. High enzymatic conversion yield of bamboo cellulose (∼85%) was achieved by lactic acid-AChCl DES due to its lower pH value and viscosity, followed by glycerol-AChCl and urea-AChCl DES. In addition to the features of proposed DESs, changed chemical and physical properties of highly recalcitrant bamboo biomass after pretreatments were systematically determined. Besides of great amount of lignin (∼90%)/ xylan (100%) removal, micro- to nano-scale variations of cellulose structures including more dissociated microfibrils, lowered crystallinity, and enlarged crystallite sizes all played key roles in promoting bioconversion yields. Moreover, the multi-factors contributing to improved hydrolysis performance were integrated to evaluate the effects of novel DESs pretreatments on lignocellulose deconstruction, which may provide new strategies on bioconversion enhancement and process optimization. [Display omitted] • Acetylcholine chloride was firstly served as HBA for fast DES treatment on bamboo. • Boosted enzymatic conversion yield of 85% was achieved for AL-10 and AL-20. • Multi-factors inhibiting enzymatic conversion of biomass were summarized. • Cellulose supramolecular structures are key factors impacting the glucose yield. [ABSTRACT FROM AUTHOR]