The aim of this study is to investigate the impact of layered nanomodifiers with distinct chemical structure and morphology, namely graphene nanoplates (GnP) and sodium montmorillonite (Na-MMT), on thermal degradation of polylactic acid (PLA). The exploration was performed with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and pyrolytic gas chromatography-mass spectrometry (PyGCMS). The findings revealed a catalytic effect of Na-MMT on PLA thermal destabilization, manifested in accelerated degradation and the notable change in the composition of pyrolysis products. In contrast, the incorporation of graphene nanoplates into the PLA matrix induced a "barrier effect": it imposed diffusion limitations on the emission of volatile degradation products during pyrolysis, which enhanced the thermal stability of the PLA/GnP composite and led to quantitative alterations in the distribution of major pyrolysis products. To elucidate the underlying degradation pathways, authors proposed a model kinetic analysis of thermal degradation for both PLA/GnP and PLA/Na-MMT composites. The analysis clearly distinguished the mechanistic differences between the two systems: while Na-MMT promotes catalytic decomposition, GnP primarily acts as the physical barrier retarding mass transport and delaying the thermal degradation development. Good alignment of theoretical model-kinetic predictions with Pyrolysis-GC/MS observations confirms the robustness of the suggested kinetic modeling method.

Abstract Cold alkaline treatment of cellulose is usually used for wood cellulose enrichment with high-molecular-weight fractions, as they are not soluble even in strong alkali solutions. The processes of the dissolution of hemicelluloses are tightly related to the processes of cellulose structure partial disassembling. Considering recent results on the nature and thermodynamics of the interactions between the chiral and helical molecules and the role of the spin-spin exchange interactions in them, it was very probable that the chemical reactions in the chiral polymer matrix should be magnetosensitive. Trying to verify this assumption and using cold alkaline treatment as an example, we obtained solid experimental confirmations of the magnetosensitivity of this process and found an alternative way of nanocellulose production. The magnetic field as well as other agents promoting the cellulose structure loosening forces the destruction of the polymer at the stage of the supramolecular structure reassembling after removing alkali. The latter leads to the cleavage of the cellulose fibers and nanoscale particles forming. On the other hand, formally, the fraction of the high-molecular-weight components insoluble in strong NaOH solutions decreases, and the repeating treatment with an alkali solution causes a significant loss of mass.

In our study, we investigated the accelerated aging process of PLA under 253.7 nm UV-C irradiation with the use of the GPC, NMR, FTIR, and DSC methods and formal kinetic analysis. The results of GPC and DSC indicated a significant degree of destructive changes in the PLA macromolecules, while spectroscopic methods NMR and FTIR showed maintenance of the PLA main structural elements even after a long time of UV exposure. In addition to that, the GPC method displayed the formation of a high molecular weight fraction starting from 24 h of irradiation, and an increase in its content after 144 h of irradiation. It has been shown for the first time that a distinctive feature of prolonged UV exposure is the occurrence of intra- and intermolecular radical recombination reactions, leading to the formation of a high molecular weight fraction of PLA decomposition products. This causes the observed slowdown of the photolysis process. It was concluded that photolysis of PLA is a complex physicochemical process, the mechanism of which depends on morphological changes in the solid phase of the polymer under UV radiation.

The negative influence of water pollution by heavy metals ions on human health represents a serious ecological problem which requires effective methods in the search for its solution. The creation of eco-friendly biodegradable polymer materials capable of performing the sorption of the water media of heavy metals followed by decomposition into harmless substances after the end of their service life presents an actual task. To this aim, binary compositions synthesized from natural raw polyesters polylactide (PLA) and poly(3-hydroxybutyrate) (PHB) with polysaccharide chitosan, corresponding to these requirements, were obtained in the liquid phase. The polyesters have mechanical characteristics close to the characteristics of synthetic polymers, while the chitosan containing the amino groups is capable of performing the sorption of heavy metals. The use of compositions on their base allows one to create the new inexpensive biodegradable sorbents stable in aqueous media as well as apply them as packing materials. The sorption capacity of PLA–chitosan and PHB–chitosan compositions in relation to iron ions from aqueous solutions was explored by a method of X-ray fluorescence analysis and it was established that the sorption of Fe3+ ions by PHB–chitosan composition is more than twice as high as that by the PLA–chitosan composition (2.30 and 0.66 wt. %, correspondingly, after sorption from 0.008 mol/L FeCl3 solution during 24 h). A comparative study of thermophysical parameters and the degree of crystallinity of PLA and PHB, as well as in their initial compositions and compositions, containing sorbed iron ions, was carried out by DSC method. The DSC analysis of the PLA–chitosan and PHB–chitosan compositions, containing sorbed iron ions, showed a slight decrease in the values of Tg, Tcc, and Tm as well as an increase in the enthalpy of cold crystallization and a reduction in the degree of crystallinity of these polyesters. At the same time, an increasing of the thermal stability of polyester compositions in the presence of iron ions was established. The influence of UV irradiation on the structure of PLA and PHB for 2, 5, 24, and 144 h was analyzed by FTIR spectroscopy and significant changes in the spectrum were observed. Based on the analysis of the IR spectra of PHB and PLA, it was concluded that, under the action of UV radiation, the destruction of ester bonds takes place, which is expressed in the appearance of intense bands characterizing the formation of new structural units, resulting in the decrease in the molecular weight of polyesters.

The synthesis of ionic liquids based on 1-butyl-3-methylimidazolium with different anions—Cl–, Br– and CH3C(O)O– was performed. [BMIm]Cl and [BMIm]Br were obtained by direct interaction of the corresponding butyl halide with N-methylimidazole in acetonitrile solution under heating. [BMIm]OAc was obtained by the ion exchange reaction of [BMIm]Cl with silver acetate. It was found that to obtain homogeneous mixtures of wood pulp LS-0 with ionic liquids, its preliminary impregnation with solutions of imidazolium salts in acetonitrile is preferable. The effective formation temperature of the cellulose solution in ionic liquids is 110°C. The most efficient dissolution occurs in [BMIm]Cl, and when [BMIm]OAc is used, the reaction of attachment of imidazolium to the aldehyde group of hexoses occurs.

The flax ( Linum usitatissimum) is widely used as a source of linen oil and fiber. As a rule, the flax varieties serve to produce either seeds (oil), or stem fibers, as the "fiber'' varieties bring the low amount of seeds, while the "oil'' varieties have poor fibers that cannot be used in textile. The straw of the oil flax has not been applied in industry and has to be burned or degrade naturally in the field. However, it contains a low degree of polymerization cellulose, which can be used at least for varnish production. The main challenge in the industrial application of the oil flax cellulose is the necessity of separating the cellulose fibers and shive enriched in lignin. On the other hand, the low cost of the final products restricts the set of available tools. Here we describe a machine designed for oil flax straw stripping and several ways of further conversion of the obtained tow into microcrystalline or fluff-like cellulose. The supposed processes run at the temperatures below the water boiling point and at the atmospheric pressure and could be held in the plastic reactors.

Composites of polylactide containing graphite nanoplates as a filler in the concentration range 1–20 wt% were prepared in methylene chloride using the sonication technique. The thermal characteristics and phase transitions were studied by DSC and TGA methods. The temperatures and heats of glass transition, crystallization, and melting were determined, and the degree of crystallinity during primary and secondary heating was calculated. It is shown that the introduction of graphite nanoplates leads to an increase in the elastic modulus and a decrease in the breaking stress and elongation at break. These changes are especially pronounced at 20% GNP content in the composition, when the corresponding mechanical parameters are characteristics of brittle polymer systems. The study of the electrical properties of the composites showed that the percolation threshold in these materials is close to 7 wt%, which is significantly lower than in the case of spherical particles of comparable density. The SEM study of the filled composites showed a system of pores, which were apparently formed during the evaporation of solvent in the process of their preparation. Diverse structures of PLA/GNP composites films after hot pressure were established by the SEM method.

This study was aimed to investigate the effect of reduced graphene oxide (rGO) on the pyrolysis of polylactide composites (PLA4042D/rGO) prepared in solution. GC-MS analysis of PLA4042D/rGO pyrolysis products showed that introduction of rGO into the composition with PLA leads to a significant change in the ratio of main degradation products. A sharp decrease of five-membered dioxolanones accompanied by a growth in the content of lactides and cyclic oligomeric lactides was observed in PLA4042D/rGO pyrolysis products as compared with pristine PLA. DSC studies of PLA4042D crystallization in the melt showed that the adsorption of PLA macromolecules on rGO surface can cause the decrease in their segmental mobility. Apparently, a decrease in the segmental mobility of PLA chains hinders the formation of dioxolanones via the intramolecular nonradical ester interchange reaction. At the same time, the role of intermolecular reactions with the formation of cyclic oligomers of lactides increases.

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.

Abstract The cold alkaline treatment or mercerization of cellulose is widely used in industry to enrich the cellulose raw with high-molecular-weight $$\alpha$$ α -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.

The development of high-end targeted drugs and vaccines against modern pandemic infections, such as COVID-19, can take a too long time that lets the epidemic spin up and harms society. However, the countermeasures must be applied against the infection in this period until the targeted drugs became available. In this regard, the non-specific, broad-spectrum anti-viral means could be considered as a compromise allowing overcoming the period of trial. One way to enhance the ability to resist the infection is to activate the nonspecific immunity using a suitable driving-up agent, such as plant polysaccharides, particularly our drug Panavir isolated from the potato shoots. Earlier, we have shown the noticeable anti-viral and anti-bacterial activity of Panavir. Here we demonstrate the pro-inflammation activity of Panavir, which four-to-eight times intensified the ATP and MIF secretion by HL-60 cells. This effect was mediated by the active phagocytosis of the Panavir particles by the cells. We hypothesized the physiological basis of the Panavir proinflammatory activity is mediated by the indol-containing compounds (auxins) present in Panavir and acting as a plant analog of serotonin.

The paper presents the results of drop tests performed to measure ignition delay for ionic liquids under various experimental conditions. Factors that strongly affect correct determination of ignition delay are indicated. Processes preceding ignition upon contact between various quantities of a fuel and an oxidizer are explained. It is argued that well-defined experimental conditions are required to ensure correct comparison when using benchmark fuels.

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.

Man-made fibers were spun from solutions of cotton and wood cellulose in ionic liquid (1-butyl-3-methyl-imidazolium chloride, [B-mim] Cl. Depending on the concentration, cellulose dissolved in [B-mim] Cl. down to macro- molecules 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 ((similar to)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 (similar to)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.

Studies of thermal and fire-resistant properties of the polyethylene/graphite nanoplates (PE-GNP) nano-composites prepared by means of in situ polymerization are discussed. The key factor of influence of graphite nanoplates on the thermal degradation and combustion of PE-GNP nanocomposites is analyzed using the sets of the data acquired with the aid of thermogravimetry (TG) and gas chromatography - mass spectrometry (GC MS) experiments. It has been found that the addition of graphite nanoplates changes the composition of polyethylene pyrolysis products resulting in dramatically increase the fraction of heavy hydrocarbons. The results of cone calorimetric tests lead to traditional conclusion that formation of GNP protective shield plays a key role in the mechanism of flame retardation for PE-GNP nanocomposites. On the other hand, the decrease in PE-GNP nanocomposites combustibility can also be a result of the reduction in the diffusion rate of the degradation products in the liquid pyrolysis phase and gaseous phase of combustion.

Syntheses of trans-1,2-di-tert-butylpyrazolidine 1, d,l- and semi-meso-1,2-diisopropyl-3,5-dimethylpyrazolidines, 2a and 2b, respectively, have been developed. Activation parameters of the nitrogen inversion in 1 (ΔG≠=123kJmol−1 at 110°C, ΔH≠=114kJmol−1, ΔS≠=−15JK−1mol−1) have been determined. The steric veto of the nitrogen inversion in 2a has been confirmed. Chemical transformations of 1 have been studied, and the crystal structures of 2a·picrate and 2b·HCl determined.

We found that (PriNH)2 with MeCHO form only pyrazoline 1 because of the competitive crotonization of the latter followed by reaction with hydrazine; pyrazoline 2, pyrazolidinones 6 and 9, pyrazolidinol 8 and pyrazolidine 7, in which the inversion of nitrogen atoms is hindered by bulky PriN substituents, were prepared for the first time, and the inversion barriers were determined.

N,N′-Diisopropyl-substituted 1,3,4-oxadiazolidine3c, 1,3,4-thiadiazolidine6, 4,5-benzo-1,2,3,6-tetrahydropyridazine8, and new 3,4-dialkyl-1,3,4-oxadiazolidines9–14 were synthesized and studied. The configurational stability of the N atoms does not change on going from compound3c to itsS-analog6 and decreases in the case of pyridazine8. 3,4-Di-tert-alkyl-1,3,4-oxadiazolidines3d and11–14 were found to be promising objectes for optical resolution.