The fibrils untwisting limits the rate of cellulose nitration process

Cellulose Nitrates-Blended Composites from Bacterial and Plant-Based Celluloses

Cellulose nitrates (CNs)-blended composites based on celluloses of bacterial origin (bacterial cellulose (BC)) and plant origin (oat-hull cellulose (OHC)) were synthesized in this study for the first time. Novel CNs-blended composites made of bacterial and plant-based celluloses with different BC-to-OHC mass ratios of 70/30, 50/50, and 30/70 were developed and fully characterized, and two methods were employed to nitrate the initial BC and OHC, and the three cellulose blends: the first method involved the use of sulfuric-nitric mixed acids (MAs), while the second method utilized concentrated nitric acid in the presence of methylene chloride (NA + MC). The CNs obtained using these two nitration methods were found to differ between each other, most notably, in viscosity: the samples nitrated with NA + MC had an extremely high viscosity of 927 mPa·s through to the formation of an immobile transparent acetonogel. Irrespective of the nitration method, the CN from BC (CN BC) was found to exhibit a higher nitrogen content than the CN from OHC (CN OHC), 12.20-12.32% vs. 11.58-11.60%, respectively. For the starting BC itself, all the cellulose blends of the starting celluloses and their CNs were detected using the SEM technique to have a reticulate fiber nanostructure. The cellulose samples and their CNs were detected using the IR spectroscopy to have basic functional groups. TGA/DTA analyses of the starting cellulose samples and the CNs therefrom demonstrated that the synthesized CN samples were of high purity and had high specific heats of decomposition at 6.14-7.13 kJ/g, corroborating their energy density. The CN BC is an excellent component with in-demand energetic performance; in particular, it has a higher nitrogen content while having a stable nanostructure. The CN BC was discovered to have a positive impact on the stability, structure, and energetic characteristics of the composites. The presence of CN OHC can make CNs-blended composites cheaper. These new CNs-blended composites made of bacterial and plant celluloses are much-needed in advanced, high-performance energetic materials.

A state-of-the-art review on plant-derived cellulose-based green hydrogels and their multifunctional role in advanced biomedical applications

The most prevalent carbohydrate on Earth is cellulose, a polysaccharide composed of glucose units that may be found in diverse sources, such as cell walls of wood and plants and some bacterial and algal species. The inherent availability of this versatile material provides a natural pathway for exploring and identifying novel uses. This study comprehensively analyzes cellulose and its derivatives, exploring their structural and biochemical features and assessing their wide-ranging applications in tissue fabrication, surgical dressings, and pharmaceutical delivery systems. The use of diverse cellulose particles as fundamental components gives rise to materials with distinct microstructures and characteristics, fulfilling the requirements of various biological applications. Although cellulose boasts substantial potential across various sectors, its exploration has predominantly unfolded within industrial realms, leaving the biomedical domain somewhat overlooked in its initial stages. This investigation, therefore, endeavors to shed light on the contemporary strides made in synthesizing cellulose and its derivatives. These innovative techniques give rise to distinctive attributes, presenting a treasure trove of advantages for their compelling integration into the intricate tapestry of biomedical applications.

Structure and properties of nitrocellulose: approaching 200 years of research

This review brings together almost 200 years of fragmented research on the structure of nitrocellulose to give an overview that covers production to application in composite materials. As a mouldable plastic, energetic rocket propellant and biomolecular binding membrane, nitrocellulose still finds widespread practical application today despite the inception of synthetic plastics. The influence of different cellulose source materials affects the structure and properties of nitrocellulose in ways that are not fully understood, and so this review brings together relatively recent developments in the understanding of cellulose nanostructures to highlight where the gaps in understanding now reside. The influence of nitration conditions on the material properties of nitrocellulose is described, together with the proposed mechanisms and equilibria associated with these synthetic routes. The reported crystal structures of nitrocellulose are also reviewed, and the confirmed structural features are separated from those yet to be proven. We also consider how nitrocellulose interacts with other compounds, to help explain the distinct properties of its composite materials. This review points to further work that is required to obtain well founded structural models of nitrocellulose, while highlighting opportunities to control and direct its structure to improve its material properties.

Green composites based on thermoplastic starch reinforced with micro- and nano-cellulose by melt blending - A review

Starch is a biodegradable biopolymer, a sustainable material that can replace conventional petrochemical-based plastics. However, starch has some limitations, as it must be processed by heating and treated mechanically with a plasticizer to become thermoplastic starch (TPS). Different variables such as mixing speeds, amount, and kind of plasticizers play a vital role in preparing TPS by melting. Despite this, the properties of the TPS are not comparable with those of traditional plastics. To overcome this limitation, microcellulose or nanocellulose is added to TPS by melt mixing, including the extrusion and internal mixing process, which enables large-scale production. This review aims to compile several studies that evaluate the effect of plasticizers, as well as the relevance of incorporating different cellulosic fillers of different dimensions on the properties of TPS obtained by melt mixing. Potential applications of these materials in food packaging, biomedical applications, and other opportunities are also described.

Promising Energetic Polymers from Nanostructured Bacterial Cellulose

This study investigated the nitration of nanostructured bacterial cellulose (NBC). The NBC, obtained using symbiotic Medusomyces gisevii Sa-12 as the microbial producer and then freeze-dried, was nitrated herein by two methods, the first using mixed sulphuric-nitric acids (MA) and the second using concentrated nitric acid in the presence of methylene chloride (NA+MC). The synthesized samples of NBC nitrates (NBCNs) exhibited 11.77-12.27% nitrogen content, a viscosity of 1086 mPa·s or higher, 0.7-14.5% solubility in an alcohol-ester mixture, and 0.002% ash. Scanning electron microscopy showed that the nitration compacted the NBC structure, with the original reticulate pattern of the structure being preserved in full. Infrared spectroscopy for the presence of functional nitro groups at 1658-1659, 1280, 838-840, 749-751 and 693-694 cm^-1 confirmed the synthesis of cellulose nitrates in particular. Thermogravimetric and differential thermal analyses showed the resultant NBCNs to have a high purity and high specific heats of decomposition of 6.94-7.08 kJ/g. The NBCN samples differ conceptually from plant-based cellulose nitrates by having a viscosity above 1086 mPa·s and a unique 3D reticulate structure that is retained during the nitration. The findings suggest that the NBCNs can be considered for use in novel high-tech materials and science-driven fields distinct from the application fields of plant-based cellulose nitrates. The NBCN sample obtained with NA+MC has the ability to generate an organogel when it is dissolved in acetone. Because of the said property, this NBCN sample can find use as a classical adhesive scaffold and an energetic gel matrix for creating promising energetic polymers.

Recent Advances in Cellulose-Based Hydrogels: Food Applications

In the past couple of years, cellulose has attracted a significant amount of attention and research interest due to the fact that it is the most abundant and renewable source of hydrogels. With increasing environmental issues and an emerging demand, researchers around the world are focusing on naturally produced hydrogels in particular due to their biocompatibility, biodegradability, and abundance. Hydrogels are three-dimensional (3D) networks created by chemically or physically crosslinking linear (or branching) hydrophilic polymer molecules. Hydrogels have a high capacity to absorb water and biological fluids. Although hydrogels have been widely used in food applications, the majority of them are not biodegradable. Because of their functional characteristics, cellulose-based hydrogels (CBHs) are currently utilized as an important factor for different aspects in the food industry. Cellulose-based hydrogels have been extensively studied in the fields of food packaging, functional food, food safety, and drug delivery due to their structural interchangeability and stimuli-responsive properties. This article addresses the sources of CBHs, types of cellulose, and preparation methods of the hydrogel as well as the most recent developments and uses of cellulose-based hydrogels in the food processing sector. In addition, information regarding the improvement of edible and functional CBHs was discussed, along with potential research opportunities and possibilities. Finally, CBHs could be effectively used in the industry of food processing for the aforementioned reasons.

Role of the Exchange Interactions in the Stability of the Cellulose

The problem of the origin of biochirality and the related problem of the initial monomers' selection are still under discussion, and the main point here is not the mechanics of...

On the orientation of the chains in the mercerized cellulose

The cold alkaline treatment or mercerization of cellulose is widely used in industry to enrich the cellulose raw with high-molecular-weight [Formula: see text]-cellulose. Washing out of hemicelluloses by alkalies is accompanied by the rearrangement of the cellulose chains' packing, well known as a transition between cellulose I and cellulose II. Cellulose II can also be produced by the precipitation of the cellulose solutions (regeneration). The currently accepted theory implies that in cellulose II, both mercerized and regenerated, the macromolecules are arranged antiparallelly. However, forming such a structure in the course of the mercerization seems to be significantly hindered, while it seems to be quite possible in the regeneration process. In this work, we discuss the sticking points in the theory on the antiparallel structure of mercerized cellulose from a theoretical point of view summarizing all of the available experimental data in the field.

New insensitive high-energy dense biopolymers from giant reed cellulosic fibers: their synthesis, characterization, and non-isothermal decomposition kinetics

Renewable giant reed has been explored for the first time to develop new advanced high-energy dense biopolymers through carbamate surface functionalization and nitration of native cellulose and cellulose microcrystals.

Zhurkov's Stress-Driven Fracture as a Driving Force of the Microcrystalline Cellulose Formation

Microcrystalline cellulose (MCC) is a chemically pure product of cellulose mechano-chemical conversion. It is a white powder composed of the short fragments of the plant cells widely used in the modern food industry and pharmaceutics. The acid hydrolysis of the bleached lignin-free cellulose raw is the main and necessary stage of MCC production. For this reason, the acid hydrolysis is generally accepted to be the driving force of the fragmentation of the initial cellulose fibers into MCC particles. However, the low sensibility of the MCC properties to repeating the hydrolysis forces doubting this point of view. The sharp, cleave-looking edges of the MCC particles suggesting the initial cellulose fibers were fractured; hence the hydrolysis made them brittle. Zhurkov showed that mechanical stress decreases the activation energy of the polymer fracture, which correlates with the elevated enthalpy of the MCC thermal destruction compared to the initial cellulose.

A promising energetic biopolymer based on azide-functionalized microcrystalline cellulose: Synthesis and characterization

In the current investigation, azidodeoxy-microcrystalline cellulose nitrate (AMCCN) as a novel promising nitrogen-rich energetic biopolymer was synthesized, and its features were compared to those of azidodeoxy-pristine cellulose nitrate (APCN), conventional cellulose nitrate (PCN) and microcrystalline cellulose nitrate (MCCN). The produced nitrated samples and their precursors were fully characterized using various analytical techniques. In addition, the heats of combustion and mechanical sensitivities of all nitrated biopolymers were evaluated, and their energetic performances were predicted by EXPLO5 V6.04 software. The obtained results provide evidence for the effectiveness of the applied chemical functionalization approach to synthesize the relatively insensitive AMCCN and APCN with nitrogen content of 22.75 % and 22.50 %, density of 1.718 g/cm³ and 1.706 g/cm³, and detonation velocity of 7707 m/s and 7533 m/s, respectively, which are higher than those of PCN. This work opens avenues to design promising energetic biopolymers based on renewable microcrystalline cellulose for potential application in advanced high performance solid propellants and explosives.

Recent advances in composites based on cellulose derivatives for biomedical applications

Cellulose derivatives represent a viable alternative to pure cellulose due to their solubility in water and common organic solvents. This, coupled with their low cost, biocompatibility, and biodegradability, makes them an attractive choice for applications related to the biomedicine and bioanalysis area. Cellulose derivatives-based composites with improved properties were researched as films and membranes for osseointegration, hemodialysis and biosensors, smart textile fibers, tissue engineering scaffolds, hydrogels and nanoparticles for drug delivery. The different preparation strategies of these polymeric composites as well as the most recent available experimental results were described in this review. General aspects such as structure and properties of cellulose extracted from plants or bacterial sources, types of cellulose derivatives and their synthesis methods were also discussed. Finally, the future perspectives related to composites based on cellulose derivatives were highlighted and some conclusions regarding the reviewed applications were drawn.

Chirality Driven Twisting as a Driving Force of Primitive Folding in Binary Mixtures

The N-trifluoroacetylated α-aminoalcohols (TFAAAs) are able to form quasi-one-dimensional supramolecular fibers (strings) when chirally pure, and isometric precipitates in the racemate. The strings' formation leads to the reversible gelation of the solution. The fresh gels occupy all the available volume, however during the incubation, they contract and concentrate in the central region of the tube. The microscopic observations revealed the growth of the strings' diameter and their rotation in the course of the incubation at the hour time-scale. The rotation provides for the hairpins forming that serve as hooks on the rotating string, which provides for coiling of the strings, which was observed as gel contraction. The morphology of the twisted strings resembles the structures observed in modern proteins, which allows drawing an analogy between the folding of biopolymers and the formation of the clew of strings. In addition, the rotation found in the TFAAA gels is an example of a simple system converting the energy of intermolecular agglutination to the rotational movement, so they could be considered as molecular motors.

Bacterial Nanocellulose Nitrates

Bacterial nanocellulose (BNC) whose biosynthesis fully conforms to green chemistry principles arouses much interest of specialists in technical chemistry and materials science because of its specific properties, such as nanostructure, purity, thermal stability, reactivity, high crystallinity, etc. The functionalization of the BNC surface remains a priority research area of polymers. The present study was aimed at scaled production of an enlarged BNC sample and at synthesizing cellulose nitrate (CN) therefrom. Cyclic biosynthesis of BNC was run in a semisynthetic glucose medium of 10-72 L in volume by using the Medusomyces gisevii Sa-12 symbiont. The most representative BNC sample weighing 6800 g and having an α-cellulose content of 99% and a polymerization degree of 4000 was nitrated. The nitration of freeze-dried BNC was performed with sulfuric-nitric mixed acid. BNC was examined by scanning electron microscopy (SEM) and infrared spectroscopy (IR), and CN was explored to a fuller extent by SEM, IR, thermogravimetric analysis/differential scanning analysis (TGA/DTA) and 13C nuclear magnetic resonance (NMR) spectroscopy. The three-cycle biosynthesis of BNC with an increasing volume of the nutrient medium from 10 to 72 L was successfully scaled up in nonsterile conditions to afford 9432 g of BNC gel-films. CNs with a nitrogen content of 10.96% and a viscosity of 916 cP were synthesized. It was found by the SEM technique that the CN preserved the 3D reticulate structure of initial BNC fibers a marginal thickening of the nanofibers themselves. Different analytical techniques reliably proved the resultant nitration product to be CN. When dissolved in acetone, the CN was found to form a clear high-viscosity organogel whose further studies will broaden application fields of the modified BNC.

Spontaneous Resolution and Super-coiling in Xerogels of the Products of Photo-Induced Formose Reaction

This work addresses the supramolecular self-organization in the xerogels of formose reaction products. The UV-induced formose reaction was held in over-saturated formaldehyde solutions at 70∘C without a catalyst. The solutions of the obtained carbohydrates were dried on a glass slide, and the obtained xerogels demonstrated a prominent optical activity, while the initial solutions were optically inactive. The xerogels contained highly elongated crystalline elements of a helical structure as well as the isometric ones. Thus xerogel formation was accompanied by a spontaneous resolution of enantiomers and separation of different-shaped supramolecular structures. The thick helices were twisted of thinner ones, while the latter were twisted of elementary structures having a diameter much smaller than 400 nm. Similar structural hierarchy is typical of biological macromolecules (DNA, proteins, and cellulose). Summarizing the obtained results, we proposed a hypothetical mechanism explaining the amplification of the initial enantiomeric excess, as well as chiral and chemical purification of the substances which were essential for the evolution of Life to start.

Twisting of Fibers Balancing the Gel⁻Sol Transition in Cellulose Aqueous Suspensions

Cellulose hydrogels and films are advantageous materials that are applied in modern industry and medicine. Cellulose hydrogels have a stable scaffold and never form films upon drying, while viscous cellulose hydrosols are liquids that could be used for film production. So, stabilizing either a gel or sol state in cellulose suspensions is a worthwhile challenge, significant for the practical applications. However, there is no theory describing the cellulose fibers' behavior and processes underlying cellulose-gel-scaffold stabilizing. In this work, we provide a phenomenological mechanism explaining the transition between the stable-gel and shapeless-sol states in a cellulose suspension. We suppose that cellulose macromolecules and nanofibrils under strong dispersing treatment (such as sonication) partially untwist and dissociate, and then reassemble in a 3D scaffold having the individual elements twisted in the nodes. The latter leads to an exponential increase in friction forces between the fibers and to the corresponding fastening of the scaffold. We confirm our theory by the data on the circular dichroism of the cellulose suspensions, as well as by the direct scanning electron microscope (SEM) observations and theoretical assessments.