Advanced approaches to wound healing have attracted much attention in the last decades due to the use of novel types of dressings that provide a moist environment and take an active part in wound ...protection and tissue regeneration processes. The materials for novel wound dressings should have a set of features that will contribute to efficient skin recovery. The use of bacterial cellulose (BC) is attractive for advanced wound management because of the favorable characteristics of BC, such as its biocompatibility, non-toxicity, mechanical stability, and high moisture content. Numerous approaches can be taken to modify BC to address the shortcomings of the native material and to optimize its biocompatibility, water uptake and release, and antimicrobial activity. This review highlights possible pathways for functionalization of BC, affecting all levels of its structural organization. The focus is on post-production treatment of BC, although selected studies concerning in situ modifications during the biosynthesis process are also emphasized.
•Critical review on bacterial cellulose applied to wound dressing•Categorization of different approaches to modify bacterial celluloses with regard to wound dressing•Discussion of chemical/physical or biological modifications to increase biocompatibility and to add antimicrobial activity•Emphasis on factors influencing the water holding capacity and morphology
The remarkable efficiency of chemical reactions is the result of biological evolution, often involving confined water. Meanwhile, developments of bio-inspired systems, which exploit the potential of ...such water, have been so far rather complex and cumbersome. Here we show that surface-confined water, inherently present in widely abundant and renewable cellulosic fibres can be utilised as nanomedium to endow a singular chemical reactivity. Compared to surface acetylation in the dry state, confined water increases the reaction rate and efficiency by 8 times and 30%, respectively. Moreover, confined water enables control over chemical accessibility of selected hydroxyl groups through the extent of hydration, allowing regioselective reactions, a major challenge in cellulose modification. The reactions mediated by surface-confined water are sustainable and largely outperform those occurring in organic solvents in terms of efficiency and environmental compatibility. Our results demonstrate the unexploited potential of water bound to cellulosic nanostructures in surface esterifications, which can be extended to a wide range of other nanoporous polymeric structures and reactions.
The purpose of this article is to provide the reader with an overview of the methods used to determine the molecular weights of cellulose. Methods that employ direct dissolution of the cellulose ...polymer are described; hence methods for investigating the molecular weight of cellulose in derivatized states, such as ethers or esters, only form a minor part of this review. Many of the methods described are primarily of historical interest since they have no use in modern cellulose chemistry. However, older methods, such as osmometry or ultracentrifuge experiments, were the first analytical methods used in polymer chemistry and continue to serve as sources of fundamental information (such as the cellulose structure in solution). The first part of the paper reviews methods, either absolute or relative, for the estimation of average molecular weights. Regardless of an absolute or relative approach, the outcome is a molecular weight average (MWA). In the final section, coupling methods are described. The primary benefit of performing a pre-separation step on the molecules is the discovery of the molecular weight distribution (MWD). Here, size exclusion chromatography (SEC) is unquestionably the most powerful and most commonly-applied method in modern laboratories and industrial settings.
Knowledge about the carbohydrate composition of pulp and paper samples is essential for their characterization, further processing, and understanding the properties. In this study, we compare ...sulfuric acid hydrolysis and acidic methanolysis, followed by GC–MS analysis of the corresponding products, by means of 42 cellulose and polysaccharide samples. Results are discussed and compared to solid-state NMR (crystallinity) and gel permeation chromatography (weight-averaged molecular mass) data. The use of the hydrolysis methods in the context of cellulose conservation science is evaluated, using e-beam treated and artificially aged cellulose samples.
Sugar‐based biorefineries have faced significant economic challenges. Biorefinery lignins are often classified as low‐value products (fuel or low‐cost chemical feedstock) mainly due to low lignin ...purities in the crude material. However, recent research has shown that biorefinery lignins have a great chance of being successfully used as high‐value products, which in turn should result in an economy renaissance of the whole biorefinery idea. This critical review summarizes recent developments from our groups, along with the state‐of‐the‐art in the valorization of technical lignins, with the focus on biorefinery lignins.
A beneficial synergistic effect of lignin and cellulose mixtures used in different applications (wood adhesives, carbon fiber and nanofibers, thermoplastics) has been demonstrated. This phenomenon causes crude biorefinery lignins, which contain a significant amount of residual crystalline cellulose, to perform superior to high‐purity lignins in certain applications. Where previously specific applications required high‐purity and/or functionalized lignins with narrow molecular weight distributions, simple green processes for upgrading crude biorefinery lignin are suggested here as an alternative. These approaches can be easily combined with lignin micro‐/nanoparticles (LMNP) production. The processes should also be cost‐efficient compared to traditional lignin modifications.
Biorefinery processes allow much greater flexibility in optimizing the lignin characteristics desirable for specific applications than traditional pulping processes. Such lignin engineering, at the same time, requires an efficient strategy capable of handling large datasets to find correlations between process variables, lignin structures and properties and finally their performance in different applications.
One for all? Forget it: In this Review, the current approaches towards utilization of technical lignins in different biorefinery scenarios are critically discussed. The review focuses on cellolignins whose potential as precursors for biomaterials in high‐value applications has been widely overlooked, to date.
Cellulose is often described as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials ...is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding and definitive analysis remain elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 min. X-ray diffraction results were analyzed with the Rietveld method; DNP (dynamic nuclear polarization) natural abundance 2D NMR studies in the next paper in this issue assisted with the interpretation of the 1D analyses in the present work. A conventional NMR model’s paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum frequency generation (SFG) spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and field emission-scanning electron microscopy results showed the changes in particle size; molecular weight and carbonyl group analyses by gel permeation chromatography confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier transform infrared (FTIR) and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability. Although understanding of structural changes as cellulose is amorphized by ball milling is increased by this work, continued effort is needed to improve agreement between the synchrotron and laboratory X-ray methods used herein and to provide physical interpretation of the SFG results.
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•Novel wet type solution blow spinning using water mist/vapor coagulant.•Preparation of fine regenerated cellulose fibers from an ionic-liquid solution.•Fibers with an average ...diameter of ˜1 μm, high crystallinity, and high orientation.•Spinning conditions decisive for fiber structure and tensile properties.
A wet type solution blow spinning system with a water-mist coagulation chamber was developed to spin fine regenerated cellulose fibers from the non-volatile ionic liquid solvent 1-ethyl-3-methylimidazolium diethyl phosphate. The molecular weight distribution of cellulose, and the rheological properties and spinnability of its spinning solution were evaluated. Scanning electron microscope observations indicated that the fine water mist/vapor was important for efficient coagulation of the stretched solution jets. Under optimized spinning parameters, a non-woven fabric was obtained consisting of fine fibers with an average diameter of 0.98 ± 0.62 μm. The tensile strength of the samples was greatly influenced by the fabric structure formed upon regeneration of cellulose from solution. X-ray diffraction and polarized optical microscopy measurements revealed that the prepared cellulosic non-woven fabric was highly crystalline and had a well-defined molecular orientation, respectively, which might have contributed to the increased tensile strength.
Determination of molecular weight parameters of native and, in particular, technical lignins are based on size exclusion chromatography (SEC) approaches. However, no matter which approach is used, ...either conventional SEC with a refractive index detector and calibration with standards or multi‐angle light scattering (MALS) detection at 488 nm, 633 nm, 658 nm, or 690 nm, all variants can be severely erroneous. The lack of calibration standards with high structural similarity to lignin impairs the quality of the molar masses determined by conventional SEC, and the typical fluorescence of (technical) lignins renders the corresponding MALS data rather questionable. Application of MALS detection at 785 nm by using an infrared laser largely overcomes those problems and allows for a reliable and reproducible determination of the molar mass distributions of all types of lignins, which has been demonstrated in this study for various and structurally different analytes, such as kraft lignins, milled‐wood lignin, lignosulfonates, and biorefinery lignins. The topics of calibration, lignin fluorescence, and lignin UV absorption in connection with MALS detection are critically discussed in detail, and a reliable protocol is presented. Correction factors based on MALS measurements have been determined for commercially available calibration standards, such as pullulan and polystyrene sulfonate, so that now more reliable mass data can be obtained also if no MALS system is available and these conventional calibration standards have to be resorted to.
Size matters: Size exclusion chromatography in combination with multi‐angle light scattering (MALS) detection at 785 nm is applied to eliminate the fluorescence effect and to get reliable mass data for all types of technical lignins. The result is a correction factor based on MALS measurements determined for commercially available calibration standards, such as pullulan and polystyrene sulfonate.
Despite the structural, load‐bearing role of cellulose in the plant kingdom, countless efforts have been devoted to degrading this recalcitrant polysaccharide, particularly in the context of biofuels ...and renewable nanomaterials. Herein, we show how the exposure of plant‐based fibers to HCl vapor results in rapid degradation with simultaneous crystallization. Because of the unchanged sample texture and the lack of mass transfer out of the substrate in the gas/solid system, the changes in the crystallinity could be reliably monitored. Furthermore, we describe the preparation of cellulose nanocrystals in high yields and with minimal water consumption. The study serves as a starting point for the solid‐state tuning of the supramolecular properties of morphologically heterogeneous biological materials.
Vapor over the cracks: The adsorption of hydrogen chloride vapor on water‐covered cellulose microfibrils results in rapid degradation and increased crystallinity without a change in fiber morphology. This process constitutes an example of supramolecular tuning of native biological materials directly in the solid state.
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