Alkoxylation of cellulose nitrates

Reactions of high nitrogen-containing cellulose nitrate with a series of aliphatic alcohols are studied. In the course of physicochemical studies most probable pathways of chemical reaction were established. They include substitution of nitrate groups by alkoxy group, opening of glucopyranose ring with the addition of the fragment of alcohol by the free bonds formed and formation of the carbonyl group, and also saponification of nitrate groups while studying the process in alkaline medium.     

Synthesis of bacterial cellulose nitrates

Russian Chemical Bulletin - The conceptual possibility to synthesize bacterial cellulose nitrates with the use of commercial mixed acid was demonstrated. The initial bacterial cellulose was...     

High-resolution solid-state 13C-NMR spectroscopy of cellulose nitrates

Solid-state ¹³C-NMR spectroscopy has been used to investigate the structure of cellulose nitrates prepared from cotton linters. The solid-state technique has the advantage that the entire range of substitution can be studied, which is not possible at present by solution methods. The spectra change progressively with increasing degree of substitution (DOS = 3 for cellulose trinitrate), and can be used to quantify the extent of substitution at C6, C2, and C3. Progressive nitration leads to elimination of the original C6 resonances of native cellulose by DOS = 1.39. The first nitration of C6 occurs in the amorphous regions, and this is complete by DOS = 0.50. Substitution at C6 is accompanied by decrystallization, as indicated by the decrease in the resonance assigned to crystalline C4, which also disappears at DOS = 1.39. A new resonance assigned to C1 appears at DOS = 0.28 at 101 ppm; the original C1 resonance for cellulose declines steadily and disappears by DOS = 2.65. This change is assigned to nitration of C2, based on the published solution spectra. Finally, development of intensity at 82 ppm at DOS = 1.83 is assigned to the effect of nitration at C3. There is no indication of any rearrangement of the unsubstituted regions analogous to those that occur on Mercerization of native cellulose.     

Molecular weight parameters of cellulose nitrates modified with alcohols

We have studied molecular weight parameters of the products prepared via chemical modification of cellulose nitrates with aliphatic alcohols. Proceeding from the quantum-chemical simulation data the most probable pathways of degradation of cellulose nitrate macromolecules have been elucidated.     

Carboxymethylation of cellulose in unconventional media

Carboxymethylation of cellulose in the new and highly efficient aqueous solvent Ni(tren)(OH)₂, [tren=tris(2aminoethyl)amine] and in melts of LiClO₄· 3H₂O or NmethylmorpholineNoxide (NMMNO), which is now widely applied for cellulose fibre production, was investigated. In case of Ni(tren)(OH)₂, a totally homogeneous carboxymethylation of cellulose with sodium monochloroacetate, in the presence of an aqueous NaOH solution is possible for the first time. Structure analysis by means of HPLC and ¹ HNMR after chain degradation showed results comparable with findings for CMC obtained by the heterogeneous slurry process, that is, a statistic distribution of substituents along the polymer chain and functionalisation of the hydroxyl groups in the order C6 C2 > C3. The etherification of cellulose in a melt of LiClO₄· 3H₂O, a new type of cellulose solvent, was shown to be possible and gave products of a statistic functionalisation pattern as well. In contrast, carboxymethylation starting from solutions of cellulose in NMMNO initiated with solid NaOH particles yields polymers with a nonstatistic distribution of functional groups along the chain, as observed for cellulose ethers prepared in reactive microstrctures starting from solutions of cellulose intermediates in dimethyl sulfoxide as well as of unmodified cellulose dissolved in N,Ndimethyl acetamide/LiCl.     

Enzymatic Degradation of (Ligno)cellulose

Glycoside‐degrading enzymes play a dominant role in the biochemical conversion of cellulosic biomass into low‐price biofuels and high‐value‐added chemicals. New insight into protein functions and substrate structures, the kinetics of recognition, and degradation events has resulted in a substantial improvement of our understanding of cellulose degradation.     

咪唑类高铼酸盐催化微晶纤维素降解反应研究

以咪唑类高铼酸盐为催化剂,以离子液体1-烯丙基-3-甲基咪唑氯盐([Amim]Cl)为溶剂降解微晶纤维素(MCC)。分别考察反应温度、反应时间、反应物浓度、催化剂用量和结构对纤维素降解反应的影响。结果表明,以5%1-(3-磺酸)丙基-3-甲基咪唑高铼酸盐([mim-(CH_2)_3SO_3H]ReO_4)为催化剂,在微波辅助加热条件下,0.1 g纤维素在2.0 g离子液体[Amim]Cl中于160℃降解30 min,还原糖收率(TRS)和葡萄糖收率最高可达89.6%和46.7%。研究还对咪唑类高铼酸催化纤维素降解反应的催化机理进行讨论,认为催化剂芳环阳离子、ReO-4中Re=O与纤维素分子中羟基的相互作用是促进纤维素降解的关键     

Interdiffusion and phase equilibrium in systems based on cellulose nitrates and low-volatile solvents

Phase equilibrium and interdiffusion in systems based on cellulose nitrates with different contents of nitrogen and several organic solvents, such as ethyl carbitol, dimethyl carbonate, and diethyl carbonate, have been studied. Cellulose nitrate containing 12.2 wt % nitrogen forms homogeneous systems with all studied solvents over the entire composition range. Systems based on cellulose nitrate with a high content of nitrogen (13.2 wt %) possess limited compatibility with the solvents. Phase diagrams constructed for these systems testify to the fact that the region of homogeneous solutions widens with a decrease in temperature. For the system composed of cellulose nitrate containing 13.2 wt % nitrogen and ethyl carbitol, the lower critical mixing temperature is ?10°C. The presence of water in ethyl carbitol causes widening of the region of unstable solutions and leads to a reduction in the lower critical mixing temperature.     

Degradation of wood cellulose with Lewis acids with the aim to prepare powder cellulose

The influence of various factors on degradation of wood cellulose with Lewis acids was studied. The physicochemical characteristics of the resulting products were analyzed.     

Degradation of TEMPO-oxidized cellulose fibers and nanofibrils by crude cellulase

The biodegradation behavior of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose fibers (TOCs) suspended in water and TEMPO-oxidized cellulose nanofibrils (TOCNs) dispersed in water by a commercial crude cellulase was studied. Products crude cellulase-treated for 0–7 days were separated into water/ethanol-insoluble and -soluble fractions. Weight recovery ratios and viscosity-average degrees of polymerization of the water/ethanol-insoluble fractions clearly decreased with crude cellulase-treatment time, showing that both TOCs and TOCNs have biodegradability. Water/ethanol-soluble fractions were subjected to size-exclusion chromatography (SEC) with photodiode array (PDA) detection to obtain SEC elution patterns detected by reflective index and UV spectra of each SEC pattern elution slice. SEC–PDA and ¹³C-NMR analyses showed that glucuronosyl unit-containing molecules present on microfibril surfaces in TOCs and TOCNs were primarily cleaved by hydrolyzing enzymes present as contaminants in the crude cellulase to form glucuronic acid as one of the major water-soluble degradation compounds. After the glucuronosyl units in TOCs and TOCNs were degraded and removed from microfibril surfaces by the hydrolyzing enzymes, cellulose chains newly exposed on the microfibril surfaces were rapidly hydrolyzed by cellulases predominantly present in the crude cellulase to form cellobiose. Both TOCs and TOCNs having sodium carboxyl groups are thus biodegradable, but TOCN having free carboxyl groups had clearly low biodegradability by the crude cellulase. Thus, biodegradation behavior may be controllable by controlling the structure of carboxyl group counter ions in TOCs and TOCNs.     

4.3 Degradation and modification of cellulose acetates by biological systems

A survey is given on recent findings in the enzymology of cellulose acetate degradation. Acetyl esterases have been identified as the principal enzymes, initiating cellulose acetate degradation as a prerequisite for endoglucanase-catalyzed cellulose acetate depolymerisation. Acetyl esterases are provided by nature to deacetylate naturally occurring partly acetylated polysaccharides, i.e. xylan and chitin. Accordingly they are not designed to attack high DS cellulose acetate. Under these circumstances acetyl esterases require a pretreatment of cellulose acetate, leading to some reduction in DS, in case highly substituted material should be degraded. One of these treatments is composting under the conditions of which a partial deacetylation may occur under the action of heat and high pH, facilitating the accessibility for acetyl esterases. However from the present knowledge it cannot be excluded that certain microbial specialists exist, being capable to degrade high DS cellulose acetate.     

Surface functionalization of nanofibrillated cellulose using click-chemistry approach in aqueous media

In the present work, amino functionalized nanofibrillated cellulose (NFC) was prepared using click-chemistry in aqueous reaction conditions. First, reactive azide groups were introduced on the surface of NFC by the etherification of 1-azido-2,3-epoxypropane in alkaline water/isopropanol-mixture at ambient temperature. Then the azide groups were reacted with propargyl amine utilizing copper catalyzed azide-alkyne cycloaddition (CuAAC), leading to pH-responsive 1,2,3-triazole-4-methanamine decorated NFC. The reaction products were characterized using Fourier transform infrared spectroscopy, elemental analysis and X-ray photoelectron spectroscopy. The presence of the attached azide groups was also confirmed by reacting them with 5-(dimethylamino)-N-(2-propyl)-1-naphthalenesulfonamide by CuAAC, yielding highly fluorescent NFC. In addition, atom force microscopy and rheology studies confirmed that the original NFC nanostructure was maintained during the synthesis.     

Degradation of historic cellulose triacetate cinematographic film: The vinegar syndrome

The degradation of cellulose triacetate based cinematographic film has been studied by moisture regain, viscometry, uv absorption, pH and degree of insolubilisation. Analysis of naturally aged films indicates a correlation between moisture regain, acidity and degree of degradation. Artificial ageing studies at various temperatures and at different humidities show that temperature, moisture regain and pH are important related factors in the degradation mechanism. The results show conclusively that the degradation of acetate based film, which is often accompanied by the release of acetic acid, is associated with an acid catalysed hydrolysis of the ester groups resulting in a consequent reduction in the molecular weight of the polymer.     

Degradation mechanism of green biopolyester nanocomposites with various cellulose nanocrystal based nanohybrids

Oceans and soils have been contaminated with traditional plastic due to its lack of degradability. Therefore, green biopolymer composites reinforced with cellulose nanocrystal-zinc oxide hybrids (ZnO hybrids) with good biodegradation ability provided a positive impact on reducing environmental challenges. In this work, the effect of various morphologies of ZnO hybrids on the biodegradation ability of poly(butylene adipate-co-terephthalate), PBAT) under seawater, soil burial, and UV aging conditions were investigated. Sheet-like ZnO hybrids (s-ZnO hybrid) efficiently enhanced the mechanical, UV-blocking properties and biodegradation ability of PBAT nanocomposite films. Compared to neat PBAT, the best tensile strength of PBAT nanocomposite with 2 wt% s-ZnO hybrid was increased by 15.1%, meanwhile this nanocomposite films showed the highest biodegradation rate after 80 days of soil degradation and 90 days of seawater degradation. Besides, three possible biodegradation mechanisms of green PBAT nanocomposite films were presented, hinting that such PBAT nanocomposite have great promising packaging applications.

Graphic abstract

     

Enzymatic saccharification of cellulose in aqueous-ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate-DMSO media

Ionic liquid (IL) 1-ethyl-3-methylimidazolium dimethylphosphate ([Emim]DMP) was chosen as an environment-friendly solvent to enzymatically hydrolyze cellulose in situ. Under optimal reaction condition, 80.2 % of cellulose (10 mg mL⁻¹) were converted to glucose in aqueous-IL-DMSO (φ _r = 74: 25: 1) media at 55°C in 18 h. Finally, fermentability of the recovered hydrolyzates was evaluated using Saccharomyces cerevisiae which is able to ferment hydrolyzates efficiently, the ethanol production was 0.44 g g⁻¹ of glucose within 24 h of the process. Such information is vital for the saccharification of more complex cellulose materials and for the fermentation of hydrolyzates into biofuel.     

Thin-Layer chromatography of inorganic ions on cellulose phosphate in sulfuric acid-organic solvent media

Summary Thin-layer chromatographic behavior of 49 inorganic ions on cellulose phosphate (P-cellulose) has systematically been surveyed with binary solvent mixtures consisting of sulfuric acid and an organic solvent such as methanol or acetone. The R_f values of many bivalent and monovalent ions as well as Te(VI) decrease on the P-cellulose layer with an increasing concentration of the organic solvent. Polyvalent ions which form strong phosphato-complexes and precipitate insoluble sulfate are strongly retained on P-cellulose. Oxy-anions, Au(III) and Pt(IV) are not adsorbed on the cellulose to any great extent. Feasibilities of the separation of multicomponent mixtures are demonstrated on the P-cellulose layer.     

Separation of rhenium by thin-layer chromatography with polyethyleneimine cellulose in hydrochloric acid media

Summary The thin-layer chromatographic behavior of 49 inorganic ions on polyethyleneimine (PEI) cellulose has been investigated in hydrochloric acid media (0.01–1.0 mol dm⁻³). The sorption on the cellulose decreases with increasing acid concentration for most of the ions, but As(III), Ti(IV) and Te(VI) do not exhibit any R_f variation with the acid concentration. The R_f spectra of TI(I), Cd(II), Pb(II) and Zn(II) have a maximum. Ag(I), Bi(III), Nb(V), Ta(V), Mo(VI) and W(VI) are retained tightly on the layer, due to either insoluble salt formation or extensive hydrolysis. The extremely low R_f values of Hg(II), Pd(II), Au(III), Ru(III) and Pt(IV) are accounted for by stability of their chlorocomplexes. Re(VII) distributes chromatographically, having moderate R_f values between 0.3 and 0.6, so that the selective separation of Re(VII) from the other ions is feasible.