The role of exchange interactions in the stability of cellulose.

The problem of the origin of biochirality and the related problem of the initial monomer selection are still under discussion, and the main point here is not the mechanics of enantiomer separation but the problem of the role of chirality in the very early stages of evolution. A recent breakthrough in understanding the influence of a static magnetic field on non-magnetic systems can shed light on this complex problem. The phenomenon of magnetosensitivity of non-magnetic systems was reported for only chiral systems and was closely related to the ability of some chiral substances to self-assemble. We suppose the chirality was essential due to the quantum spin-related effects arising between the interacting chiral molecules and providing for the self-assembly phenomenon. Here we demonstrate the magnetosensitivity of the supramolecular packing of cellulose chains, directly indicating the reliability of the supposition above.

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.

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.

Structure and properties of helical fibers spun from cellulose solutions in [Bmim]Cl.

Man-made fibers were spun from solutions of cotton and wood cellulose in ionic liquid (1-butyl-3-methyl-imidazolium chloride, [Bmim]Cl). Depending on the concentration, cellulose dissolved in [Bmim]Cl down to macromolecules or nanofibrils. The artificial fibers had a diameter of about 100 nm, were uniform, transparent, helical, and optically active. The fibers were composed of the core and shell (∼20% of the radius). The core was composed of the dense helical pseudofibrils of about 30 nm in thick occupying of about 40% of the area of the fiber core cross-section. The tensile strength of the whole fiber was, on average, 250 MPa, while that of the individual pseudofibrils was ∼1.1 GPa. The tensile-strength dependencies were two-stage with drastically different Young's modules. We explain the shape of the loading curves as well as the strength of the fibers by the friction between the twisted pseudofibrils in the core.

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.