Starch/polyvinyl alcohol with ionic liquid/graphene oxide enabled highly tough, conductive and freezing-resistance hydrogels for multimodal wearable sensors

With ever-growing demand for eco-friendly materials for wearable electronics, biopolymer-based hydrogels have drawn significant attention. As one of the most abundant and biodegradable biopolymers, starch-based hydrogels have a great potential for wearable electronics. However, mechanical fragility, low conductivity and subzero freeze restrict their applications. Here, a multifunctional hydrogel was facilely fabricated by integrating ionic liquid and graphene oxide into potato starch/polyvinyl alcohol skeleton via a green physical-crosslinking method. The abundant hydrogen-bond and electrostatic interactions endowed the hydrogel with excellent stretchability (657.5 %), strength (0.64 MPa), high conductivity (1.98 S·m-1) and good anti-freezing property (< -20 °C). Multiple characterizations and theoretical simulation (DFT) were combined to understand and confirm the interactions among different components. Taking advantage of these properties, multimodal wearable sensors were constructed for sensing tension (gauge factor: 6.04), compression (gauge factor: 3.27) and temperature (sensitivity: 0.71 %/°C), which are applied for monitoring human motion, daily-life pressure and body temperature. The sensor had a good anti-fatigue property with stable signals during 2000 cycles. Moreover, the sensor can effectively recognize handwriting and perform human-computer interaction. This work provides a promising route to develop sustainable and multifunctional biopolymer hydrogels for wearable sensors with versatile applications in human health, exercise monitors and soft robots.

In-situ visualizing selective lignin dissolution of tracheids wall in reaction wood

As a renewable biological macromolecule with aromatic structure, lignin can serve as matrix substance to maintain cell wall integrity and is regarded as the natural biomass recalcitrance. Substantial differences in the cell wall lignin topochemistry between opposite (Ow) and compression wood (Cw) trachieds in Pinus bungeana Zucc. were visualized during [Emim][OAc] pretreatment at room temperature. The ionic liqiuds treatment induced a more obvious wall swelling for highly lignified Cw tracheids than that of Ow, while dynamic Raman spectra analysis indicated the higher lignin and carbohydrates removal for Ow tracheids. Raman imaging further revealed that both lignin and carbohydrates were dissolved simultaneously within the middle lamella and secondary wall of Ow and pretreatment has little effects on Cw tracheids wall. Moreover, it was demonstrated that lignin composition was the key factor to affect the composition dissolution. In particular, lignin G-units were selectively removed from cell corner middle lamella (52.3 %) and secondary wall (62.0 %) of Ow tracheids. When cotton fiber, as a reference was treated under the same conditions, lattice conversion moving from cellulose I to II occurred. The findings confirmed the important role of lignin compostion in the dissolution behavior of carbohydrate dominant tracheids wall.

Unveiling the Migration and Transformation Mechanism of Lignin in Eucalyptus During Deep Eutectic Solvent Pretreatment

Deep eutectic solvents (DESs) have unique advantages in biomass conversion. However, the migration and transformation mechanism of lignin in the cell wall during the DES pretreatment is still elusive. In this work, Eucalyptus blocks were pretreated in choline chloride/lactic acid DES to reveal the lignin migration. Meanwhile, the remaining lignin in the pretreated residue, the regenerated DES lignin, and the solubilized degraded lignin in the recovered DES were investigated to decipher the lignin transformation. Results showed that the DES pretreatment resulted in the penetration of DES from the cell lumen to the cell wall, and lignin in the secondary wall was more easily dissolved than that in the cell corner middle lamella. The syringyl unit of lignin was better stabilized in the DES than the guaiacyl unit of lignin. The condensed lignin fraction mainly remained in the pretreated residue, while the solubilized degraded lignin fraction was monomeric aromatic ketone compounds. This study elucidates the fate of lignin during the DES pretreatment, which could also promote the development of a modern lignocellulosic pretreatment technique.

A Spatial-Temporal Analysis of Cellular Biopolymers on Leaf Blight-Infected Tea Plants Using Confocal Raman Microspectroscopy

The objective of the present study was to characterize the temporal and spatial variation of biopolymers in cells infected by the tea leaf blight using confocal Raman microspectroscopy. We investigated the biopolymers on serial sections of the infection part, and four sections corresponding to different stages of infection were obtained for analysis. Raman spectra extracted from four selected regions (circumscribing the vascular bundle) were analyzed in detail to enable a semi-quantitative comparison of biopolymers on a micron-scale. As the infection progressed, lignin and other phenolic compounds decreased in the vascular bundle, while they increased in both the walls of the bundle sheath cells as well as their intracellular components. The amount of cellulose and other polysaccharides increased in all parts as the infection developed. The variations in the content of lignin and cellulose in different tissues of an individual plant may be part of the reason for the plant's disease resistance. Through wavelet-based data mining, two-dimensional chemical images of lignin, cellulose and all biopolymers were quantified by integrating the characteristic spectral bands ranging from 1,589 to 1,607 cm^-1, 1,087 to 1,100 cm^-1, and 2,980 to 2,995 cm^-1, respectively. The chemical images were consistent with the results of the semi-quantitative analysis, which indicated that the distribution of lignin in vascular bundle became irregular in sections with severe infection, and a substantial quantity of lignin was detected in the cell wall and inside the bundle sheath cell. In serious infected sections, cellulose was accumulated in vascular bundles and distributed within bundle sheath cells. In addition, the distribution of all biopolymers showed that there was a tylose substance produced within the vascular bundles to prevent the further development of pathogens. Therefore, confocal Raman microspectroscopy can be used as a powerful approach for investigating the temporal and spatial variation of biopolymers within cells. Through this method, we can gain knowledge about a plant's defense mechanisms against fungal pathogens.

Chemical Characteristics of Wood Cell Wall with an Emphasis on Ultrastructure: A Mini-Review

Wood is complex in its chemical composition that has an important influence on its chemical behavior and mechanical strength. The complexity is reflected in the ultrastructure of the wood cell wall. In particular, the concentration of main components (cellulose, hemicelluloses and lignin) changes depending on many factors such as the different type or parts of wood, and varies in different cell wall layers. From an ultrastructural standpoint, we describe the current level of knowledge about chemical characteristics of the wood cell walls. The information of distribution of main components in the cell walls of normal wood, reaction wood and water-logged archaeological wood, the cellulose microfibrils orientation, and the interactions between main components were presented based on the use of advanced techniques including transmission electron microscopy, scanning electron microscopy, spectral imaging and nuclear magnetic resonance. In addition, the chemical changes of the wood cell wall during pretreatment are discussed. This mini-review not only provides a better understanding of wood chemistry, but also brings new insights into cell wall recalcitrance.

Comprehensive approach of methods for microstructural analysis and analytical tools in lignocellulosic biomass assessment - A review

The trend in the modern world is to replace fossil fuels with green energy sources in order to reduce their environmental impact. The biorefinery industry, within this premise, needs to establish quantitative and qualitative analytical methods to better understand lignocellulosic biomass composition and structure. This paper presents chemical techniques (chromatography, thermal analysis, HRMS, FTIR, NIR, and NMR) and physicochemical techniques (XRD, optical and electron microscopy techniques - Confocal fluorescence, Raman, SPM, AFM, SEM, and TEM) for the microstructural characterization of lignocellulosic biomass and its derivatives. Each of these tools provides different and complementary information regarding molecular and microstructural composition of lignocellulosic biomass. Understanding these properties is essential for the design and operation of associated biomass conversion processing facilities. PAT, monitored in real-time, ensures an economical and balanced mass-energy process. This review aimed to help researchers select the most suitable analytical technique with which to investigate biomass feedstocks with recalcitrant natures.

On-Line Raman Measurement of the Radiation-Enhanced Reaction of Cellobiose with Hydrogen Peroxide

Production of a chemical feedstock as a secondary product from a commercial nuclear reactor can increase the economic viability of the reactor and enable the deployment of nuclear energy as part of the low-carbon energy grid. Currently, commercial nuclear reactors produce underutilized energy in the form of neutrons and gamma photons. This excess energy can be exploited to drive chemical reactions, increasing the fraction of utilized energy in reactors and providing a valuable secondary product from the reactor. Gamma degradation of cellulosic biomass has been studied previously. However, real-time, on-line monitoring of the breakdown of biomass materials under gamma radiation has not been demonstrated. Here, we demonstrate on-line monitoring of the reaction of cellobiose with hydrogen peroxide under gamma radiation using Raman spectroscopy, providing in situ quantification of organic and inorganic system components.

Fast Track to Acetate-Based Ionic Liquids: Preparation, Properties and Application in Energy and Petrochemical Fields

Acetate-based ionic liquids (AcILs), as a kind of typical carboxylate-based ILs, display excellent structure tunability, non-volatility, good solubility to biomass, and favorable adsorption capacity, etc. These unique characteristics of AcILs make them important candidates for a range of applications in the field of energy and in the petrochemical industry. This paper intends to provide a comprehensive overview of recent advances in AcILs, including pure AcILs, AcIL-based multi-solvents, and AcIL-based composites, etc. Preparation methods, with one- and two-step synthesis, are reviewed. The relationship between properties and temperature is discussed, and some physical and thermodynamic properties of different AcILs are summarized and further calculated. The applications of AcILs in the fields of biomass processing, organic synthesis, separation, electrochemistry, and other fields are reviewed based on their prominent properties. Thereinto, the dual functions of AcILs as solvents and activators for biomass dissolution are discussed, and the roles of AcILs as catalysts and reaction mediums in clean organic synthesis are highlighted. Meanwhile, the reaction mechanisms of AcILs with acid gases are posed by means of molecular simulation and experimental characterization. Moreover, AcILs as electrolytes for zinc batteries, supercapacitors, and electrodeposition are particularly introduced. Finally, the future research challenges and prospects of AcILs are presented.

Multiple Analysis and Characterization of Novel and Environmentally Friendly Feather Protein-Based Wood Preservatives

In this study, feather was used as the source of protein and combined with copper and boron salts to prepare wood preservatives with nano-hydroxyapatite or nano-graphene oxide as nano-carriers. The treatability of preservative formulations, the changes of chemical structure, micromorphology, crystallinity, thermal properties and chemical composition of wood cell walls during the impregnation and decay experiment were investigated by retention rate of the preservative, Fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), thermoanalysis (TG), and confocal Raman microscopy (CRM) techniques. Results revealed that the preservatives (particularly with nano-carrier) successfully penetrated wood blocks, verifying the enhanced effectiveness of protein-based preservative with nano-carrier formulations. Decay experiment demonstrated that the protein-based wood preservative can remarkably improve the decay resistance of the treated wood samples, and it is an effective, environmentally friendly wood preservative. Further analysis of these three preservative groups confirmed the excellent function of nano-hydroxyapatite as a nano-carrier, which can promote the chelation of preservatives with higher content of effective preservatives.

Subcellular dissolution of xylan and lignin for enhancing enzymatic hydrolysis of microwave assisted deep eutectic solvent pretreated Pinus bungeana Zucc

The mechanism for enhancing enzymatic hydrolysis during microwave-assisted deep eutectic solvent (Mw-DES) pretreatment in deconstruction of plant cell wall was proposed by combining wet chemical analysis and microscopic measurements. Mw-DES pretreatment achieved significantly higher enzymatic conversion of 81.90% with lower lignin and comparable xylan removal (42.81% and 74.73%, respectively). While DES pretreated sample with higher lignin and xylan removal (66.59% and 74.93%, respectively) obtained limited sugar yield (45.67%). There were no significant differences with respect to chemical structures of lignin fraction between DES and Mw-DES pretreatment but primary discrepancies of topochemical and morphological changes were observed. Non- or low-substituted xylan was directly removed from secondary walls (SW) exposed more cellulose for enzyme attacking after Mw-DES pretreatment. Meanwhile, high-substituted xylan and lignin were synergistically dissolved from cell corner middle lamella (CCML). These topochemical changes of components resulted in cracked and porous cell wall structure, thus facilitating the accessibility of cellulose.

Advances in Imaging Plant Cell Walls

Understanding of cell wall architecture, including the crosslinking of cell wall polymers, provides crucial information for elucidating the relationship between cell wall structure and cell function. Moreover, examination of the cell wall informs efforts to improve biomass breakdown in bioreactor conditions. Over the past decades, imaging techniques have been used extensively to reveal the structural organization and chemical composition of cell walls, but detailed imaging of the native composition and architecture of the cell wall remains challenging. Here, we review progress in the development of cell wall imaging techniques. In particular, we focus on several advanced, label-free techniques for imaging cell walls and their potential applications in investigation of the biological functions of plant cell walls.

Multi-analysis of chemical transformations of lignin macromolecules from waterlogged archaeological wood

A large number of archaeological wooden building poles have been excavated from the Hai Menkou site (Yunnan province, China). Lignin can be transformed and altered accompanied with significant loss of carbohydrates during this process. Elucidation of chemical and structural transformations of lignin is of primary importance for understanding both the nature of degradation processes and the structure of waterlogged archaeological wood, and crucial for developing proper consolidation technology and restoring artifacts of historical and cultural value. In this study, state-of-the-art analytical techniques, including SEM, FT-IR, XRD, CP-MAS ¹³C NMR, 2D-HSQC NMR, ³¹P-NMR, CRM, GPC and TG analysis, were all employed to elucidate the structural characteristics of lignin in waterlogged and reference Pinus wood. The results interpreted by NMR analysis demonstrated the depolymerization of lignin via cleavage of β-O-4, β-5, -OCH₃ and some LCC linkages, leading to a higher amount of free phenol OH groups in the lignin from the ancient waterlogged wood as compared to that of the reference wood. Microscopically, it was found that extensive degradation of carbohydrates in cell walls was mainly occurred in secondary cell walls, while the lignin concentrations were relatively increased in CCML and S regions in the plant cell wall of the ancient wood.

Vibrational Spectroscopy of Ionic Liquids

Vibrational spectroscopy has continued use as a powerful tool to characterize ionic liquids since the literature on room temperature molten salts experienced the rapid increase in number of publications in the 1990's. In the past years, infrared (IR) and Raman spectroscopies have provided insights on ionic interactions and the resulting liquid structure in ionic liquids. A large body of information is now available concerning vibrational spectra of ionic liquids made of many different combinations of anions and cations, but reviews on this literature are scarce. This review is an attempt at filling this gap. Some basic care needed while recording IR or Raman spectra of ionic liquids is explained. We have reviewed the conceptual basis of theoretical frameworks which have been used to interpret vibrational spectra of ionic liquids, helping the reader to distinguish the scope of application of different methods of calculation. Vibrational frequencies observed in IR and Raman spectra of ionic liquids based on different anions and cations are discussed and eventual disagreements between different sources are critically reviewed. The aim is that the reader can use this information while assigning vibrational spectra of an ionic liquid containing another particular combination of anions and cations. Different applications of IR and Raman spectroscopies are given for both pure ionic liquids and solutions. Further issues addressed in this review are the intermolecular vibrations that are more directly probed by the low-frequency range of IR and Raman spectra and the applications of vibrational spectroscopy in studying phase transitions of ionic liquids.

Effect of ionic liquid treatment on the ultrastructural and topochemical features of compression wood in Japanese cedar (Cryptomeria japonica)

The morphological and topochemical changes in wood tissues in compression wood of Japanese cedar (Cryptomeria japonica) upon treated with two types of ionic liquids, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]) and 1-ethylpyridinium bromide ([EtPy][Br]) were investigated. Compression wood tracheids were swollen by both ionic liquids but their swelling behaviors were different in the types of ionic liquids used. Under the polarized light, we confirmed that crystalline cellulose in compression wood is amorphized by [C2mim][Cl] treatment whereas it changes slightly by [EtPy][Br] treatment. Raman microscopic analyses revealed that [C2mim][Cl] can preferentially liquefy polysaccharides in compression wood whereas [EtPy][Br] liquefy lignin. In addition, the interaction of compression wood with ionic liquids is different for the morphological regions. These results will assist in the use of ionic liquid treatment of woody biomass to produce valuable chemicals, bio-fuels, bio-based composites and other products.

Microscopic characterization of tension wood cell walls of Japanese beech (Fagus crenata) treated with ionic liquids

Tension wood that is an abnormal part formed in angiosperms has been barely used for wood industry. In this study, to utilize the tension wood effectively by means of liquefaction using ionic liquid, we performed morphological and topochemical determination of the changes in tension wood of Japanese beech (Fagus crenata) during ionic liquid treatment at the cellular level using light microscopy, scanning electron microscopy and confocal Raman microscopy. Ionic liquid treatment induced cell wall swelling in tension wood. Changes in the tissue morphology treated with ionic liquids were different between normal wood and tension wood, moreover the types of ionic liquids. The ionic liquid 1-ethyl-3-methylimidazolium chloride liquefied gelatinous layers rapidly, whereas 1-ethylpyridinium bromide liquefied slowly but delignified selectively. These novel insights into the deconstruction behavior of tension wood cell walls during ionic liquid treatment provide better understanding of the liquefaction mechanism. The obtained knowledge will contribute to development of an effective chemical processing of tension wood using ionic liquids and lead to efficient use of wood resources.

Probing and visualizing the heterogeneity of fiber cell wall deconstruction in sugar maple (Acer saccharum) during liquid hot water pretreatment

The S2 layer was differentiated into heavy-damaged region with more polysaccharides removed and relatively intact light-damaged region after LHW pretreatment.

Anatomical and Topochemical Aspects of Japanese beech (Fagus crenata) Cell Walls After Treatment with the Ionic Liquid, 1-Ethylpyridinium Bromide

Changes in the ultrastructure and chemical components, and their distribution in Japanese beech (Fagus crenata), during the ionic liquid 1-ethylpyridinium bromide ([EtPy][Br]) treatment were examined at the cellular level by light microscopy, scanning electron microscopy, and confocal Raman microscopy. Each of the tissues, including wood fibers, vessels and parenchyma cells treated with [EtPy][Br] showed specific morphological characteristics. Furthermore, lignin can be preferentially liquefied and eluted in [EtPy][Br] from the cell walls when compared to polysaccharides. However, the delignification was heterogeneous on the cell walls as lignin maintained a relatively high-concentration at the compound middle lamella, cell corners, inner surface of the secondary wall, and pits after [EtPy][Br] treatment.

Topochemical and morphological characterization of wood cell wall treated with the ionic liquid, 1-ethylpyridinium bromide

MAIN CONCLUSION : [EtPy][Br] is more reactive toward lignin than toward the PSs in wood cell walls, and [EtPy][Br] treatment results in inhomogenous changes to the cell wall's ultrastructural and chemical components. The effects of the ionic liquid 1-ethylpyridinium bromide ([EtPy][Br]), which prefers to react with lignin rather than cellulose on the wood cell walls of Japanese cedar (Cryptomeria japonica), were investigated from a morphology and topochemistry point of view. The [EtPy][Br] treatment induced cell wall swelling, the elimination of warts, and the formation of countless pores in the tracheids. However, many of the pit membranes and the cellulose crystalline structure remained unchanged. Raman microscopic analyses revealed that chemical changes in the cell walls were different for different layers and that the lignin in the compound middle lamella and the cell corner resists interaction with [EtPy][Br]. Additionally, the interaction of [EtPy][Br] with the wood cell wall is different to that of other types of ionic liquid.

Method for automatically identifying spectra of different wood cell wall layers in Raman imaging data set

The technique of Raman spectroscopic imaging is finding ever-increasing applications in the field of wood science for its ability to provide spatial and spectral information about the sample. On the basis of the acquired Raman imaging data set, it is possible to determine the distribution of chemical components in various wood cell wall layers. However, the Raman imaging data set often contains thousands of spectra measured at hundreds or even thousands of individual frequencies, which results in difficulties accurately and quickly extracting all of the spectra within a specific morphological region of wood cell walls. To address this issue, the authors propose a new method to automatically identify Raman spectra of different cell wall layers on the basis of principal component analysis (PCA) and cluster analysis. A Raman imaging data set collected from a 55.5 μm × 47.5 μm cross-section of poplar tension wood was analyzed. Several thousand spectra were successfully classified into five groups in accordance with different morphological regions, namely, cell corner (CC), compound middle lamella (CML), secondary wall (SW), gelatinous layer (G-layer), and cell lumen. Their corresponding average spectra were also calculated. In addition, the relationship between different characteristic peaks in the obtained Raman spectra was estimated and it was found that the peak at 1331 cm(-1) is more related to lignin rather than cellulose. Not only can this novel method provide a convenient and accurate procedure for identifying the spectra of different cell wall layers in a Raman imaging data set, but it also can bring new insights into studying the morphology and topochemistry in wood cell walls.