Effect of VUV-excimer lamp treatment on cellulose fiber

Vacuum ultra-violet-excimer lamp effect on cellulose fiber was studied to examine the effect on surface chemistry of cellulose. We focused on composition of a superficial layer of cellulose, which was studied by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Along with the surface composition, surface morphology was studied by scanning electron microscopy. The vacuum ultra-violet-excimer exposure in various atmospheres can be advantageously utilized as cellulose pre-treatment with tailored properties. N₂ atmosphere is suitable for cleaning of cellulose surface, NH₃ atmosphere for functionalization with amine and amide groups, and air atmosphere for increase or decrease of wettability, depending on exposure time.     

Adsorption of four non-ionic cellulose derivatives on cellulose model surfaces

The adsorption of four commercial non-ionic cellulose derivatives onto two different model surfaces of cellulose fibres has been studied with surface plasmon reflectance. The model surfaces of cellulose were ultrathin films of either nano fibrillated cellulose or regenerated cellulose on Au(s). Partial least squares models were used in the analysis of the data and it was found that the type of cellulose model surface seems to be most important for both the total adsorption and the initial adsorption rate of the studied cellulose derivatives. It is believed that this can be explained by morphological differences between the surfaces, and it was found that the properties of the cellulose derivatives that affect the adsorption of the two types of cellulose surface differ. For adsorption onto a NFC-based model surface, the type of cellulose derivative and the polydispersity index (PDI) of the cellulose derivative seem to be the two most important variables for the observed adsorption of these cellulose derivatives. For the regenerated cellulose surface the three most important variables are the M _n of the cellulose derivatives, the DS _NMR of the methyl celluloses, and PDI of the cellulose derivatives. Thus the adsorption of cellulose derivatives on the NFC-based cellulose model surface is strongly affected by the type of substituent, while the same cannot be said for a surface regenerated from N-methylmorpholine-N-oxide. Additionally, the DS _NMR of methyl celluloses affects their adsorption differently on the investigated cellulose model surfaces.     

Comparative Study of Intercalation of Zero-Valent Silver into the Cellulose Matrix by Raster and Transmission Microscopy

Diffusion-reduction interaction between microcrystalline cellulose and aqueous solution of AgNO₃ was studied in the absence (taking into account the reducing properties of cellulose) and in the presence of specific reductants. The resulting intercalates of cellulose and zero-valent silver were examined by raster and transmission electron microscopy. The morphological changes in cellulose after intercalation of silver nanoclusters as well as the nanocluster size distribution in the cellulose matrix were characterized.     

Studies on Non-natural Deoxyammonium Cellulose

Summary: Ammonium group containing cellulose derivatives are prepared from homogeneously synthesized cellulose p-toluenesulfonic acid esters (tosyl cellulose) by conversion with sodium azide and subsequent reduction of the azido moiety applying NaBH₄/CoBr₂/2,2′-bipyridine as reagent. Regarding the tosylation, cellulose samples of different degree of polymerization and hemicellulose content possess a different reactivity. The deoxyamino cellulose is water soluble in the protonated state. Elemental analysis, FTIR- and NMR spectroscopy were carried out to analyze the degree of substitution and functionalization pattern. It was also studied to synthesize deoxyazido celluloses without isolation of the tosyl cellulose. However, a predominant formation of deoxychloro moieties occurs.     

Influence of UV pretreatment on the abies wood catalytic delignification in the medium “acetic acid–hydrogen peroxide–TiO2”

Some regularities of abies-wood oxidative delignification by acetic acid–hydrogen peroxide mixture under the action of suspended TiO₂ catalyst and UV pretreatment of wood pulp were studied. The combined action of TiO₂ catalyst and of UV-pretreatment of abies-wood allow to produce at optimal conditions of the delignification process the chemically pure cellulose containing no residual lignin. The major characteristics of cellulose product obtained from abies-wood correspond to the characteristics of microcrystalline cellulose.     

Glass transition temperature and thermal decomposition of cellulose powder

Cellulose powder and cellulose pellets obtained by pressing the microcrystalline powder were studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermal gravimetry (TG). The TG method enabled the assessment of water content in the investigated samples. The glass phase transition in cellulose was studied using the DSC method, both in heating and cooling runs, in a wide temperature range from −100 to 180 °C. It is shown that the DSC cooling runs are more suitable for the glass phase transition visualisation than the heating runs. The discrepancy between glass phase transition temperature T _g found using DSC and predictions by Kaelbe’s approach are observed for “dry” (7 and 5.3% water content) cellulose. This could be explained by strong interactions between cellulose chains appearing when the water concentration decreases. The T _g measurements vs. moisture content may be used for cellulose crystallinity index determination.     

The coagulation of cellulose from anisotropic solutions in the NH3/NH4SCN solvent system

Coagulation of cellulose has been studied in cellulose/ammonia/ammonium thiocyanate anisotropic solutions. The effect of coagulation variables such as coagulant, bath temperature, and cellulose concentration on the coagulation process is reported. The coagulation rate was measured by microscopic observation of the moving boundary associated with coagulation. Results indicate that the coagulation rate increases with increasing cellulose concentration and bath temperature. Methanol has the highest coagulation power among the coagulants employed. Mass transfer rate difference and equilibrium swelling were also measured. The results on the mass transfer rate differences show that the mass transfer rate of NH₃/NH₄SCN is greater than those of the respective coagulants under all coagulation conditions. The equilibrium swelling decreases with increasing bath temperature and cellulose concentration.     

Template synthesis of mesoporous silicas with the use of nanocrystalline cellulose

The porous structure of silica samples prepared via sol–gel synthesis with the use of nanocrystalline cellulose particles as a template has been studied by low-temperature nitrogen adsorption. The influence of the concentration of a nanocrystalline cellulose dispersion, template content in the nanocrystalline cellulose/SiO₂ composite, and the conditions of the sol–gel synthesis on the porous structure of silica has been investigated.     

Lyotropic mesophases of cellulose in the ammonia/ammonium thiocyanate solvent system: Phase relationships

Mesophase formation of the cellulose/NH₃/NH₄SCN system has been studied as a function of system composition at 25°C. Compositions for incipience of mesophase formation and for wholly anisotropic phase formation have been determined and relevant phase diagrams constructed. The biphasic gap narrowed when the solvent composition approached 75.5 weight percent NH₄SCN and as the cellulose concentration decreased. As solvent composition was changed, the minimum cellulose volume fraction for mesophase formation ranged between 0.02 to 0.045.     

Effect of Molecular Structure on the GasPermeability of Cellulose Aliphatate Esters简

In this work, four kinds of cellulose aliphatate esters, cellulose acetate （CA）, cellulose propionate （CP）, cellulose butyrate （CB） and cellulose acetate butyrate （CAB） are synthesized by the homogeneous acylation reactions in cellulose/AmimC1 solutions. These cellulose aliphatate esters are used to prepare gas separation membranes and the effects of molecular structure, such as substituent type, degree of substitution （DS） and distribution of substituents, on the gas permeability are studied. For CAs, as the DS increases, their gas permeabilities for all five gases （02, N2, CH4, CO and CO2） increase, and the ideal permselectivity significantly increases first and then slightly decreases. At similar DS value, the homogenously synthesized CA （distribution order of acetate substituent： C6 〉 C3 〉 C2） is superior to the heterogeneously synthesized CA （distribution order of acetate substituent： C3 〉 C2 〉 C6） in gas separation. With the increase of chain length of aliphatate substituents from acetate to propionate, and to butyrate, the gas permeability of cellulose aliphatate esters gradually increases. The cellulose mixed ester CAB with short acetate groups and relatively long butyrate groups exhibits higher gas permeability or better permselectivity than individual CA or CB via the alteration of the DS of two substituents.     

Theoretical investigation of azo dyes adsorbed on cellulose fibers: 1. Electronic and bonding structures

Structural, bonding and electronic characteristics of complexes of anthraquinone and 1-arylazo-2-naphtol dyes and cellulose I _β are studied using B3LYP density functional method with 6-31G** basis set based on the partially and fully optimized structures. Results reveal that for both partially and fully optimized complexes, there is a stabilizing attraction between dyes and cellulose surface. The hydrazone (Hy) tautomer in anionic state (Hy–SO₃ ^?) shows the strongest interaction with the cellulose surface. Natural bond orbital (NBO) and atoms-in-molecules (AIM) analyses have been carried out to study the nature of azo dyes-cellulose bonds in detail. According to NBO analysis, a remarkable charge transfer occurs between the –SO₃ ^? and –SO₃H functional groups of the dye and the cellulose surface which can be regarded as the main source of the large dye–cellulose interaction energy. AIM analysis confirms the existence of hydrogen and van der Waals bonds between the azo dyes and cellulose. Furthermore, a very good agreement is observed between the number of hydrogen bonding sites and dye–cellulose interaction energies.     

Removal of uranyl ions from wastewaters using cellulose and modified cellulose materials</p> </p>

Summary Three silylcellulosic derivatives with different substitution degree were examined as sorbents for uranyl ions. The adsorption rate and capacity of cellulose and modified cellulose were investigated in aqueous media, at various pH and temperature values. The polymer - metal complexes of UO₂²⁺ were characterized by infrared and electronic spectra, and thermogravimetry. The thermal behavior of cellulose (C), trimethylsilyl - cellulose (tmsc, SD= 2.85) and triphenylsilyl - cellulose (TPSC1, SD=2.89 and TPSC2, SD =2.70) and their complexes with uranyl ions in atmospheric air has been studied between room temperature and 600 °C. The Coats-Redfern method was applied to estimate the kinetic parameters. The results revealed that the complexation of C and TMSC with UO₂²⁺ increases the thermal stability.</p> </p>     

Beyond a solvent: the roles of 1-butyl-3-methylimidazolium chloride in the acid-catalysis for cellulose depolymerisation

In this report, 1-butyl-3-methylimidazolium chloride ([C₄C₁im]Cl) is demonstrated to enhance the kinetics of acid-catalysed hydrolysis of 1,4-β-glucans in binary solvent mixtures. [C₄C₁im]Cl plays other roles in the reaction beyond acting as a solvent for cellulose, as currently accepted. In fact, the presence of the IL increases the Hammett acidity of the catalyst dissolved in the reaction medium. The kinetic data from cellobiose and cellulose hydrolysis directly correlate with the acid strength found for p-toluenesulfonic acid in the different reaction media studied here. The current report identifies neglected, but yet very important phenomena occurring in cellulose depolymerisation.     

Vibrational sum-frequency-generation (SFG) spectroscopy study of the structural assembly of cellulose microfibrils in reaction woods

The cellulose microfibril assemblies in secondary cell walls of tension wood and compression wood were studied with vibrational sum frequency generation (SFG) spectroscopy. The tension wood contains the gelatinous layer with highly-crystalline and highly-aligned cellulose microfibrils. The SFG spectral features of tension wood changed depending on the azimuth angle between the polarization of the incident IR beam and the preferential alignment axis of the cellulose microfibrils. The SFG spectra of the compression wood did not show any dependence on the azimuth angle, implying that the overall orientation of cellulose microfibrils in compression wood is not highly aligned. Instead, the decrease of cellulose content in compression wood brought about larger separation between cellulose microfibrils, which was manifested as changes in CH₂/OH intensity ratio in SFG spectra. These results implied that SFG spectral features are sensitive to cellulose microfibril alignments and inter-fibrillar separations.     

Structure and properties of cellulose graft copolymers. III. Cellulose–methyl methacrylate graft copolymers synthesized by the ceric ion method

The ceric ion-initiated graft copolymerization of methyl methacrylate onto wood cellulose was found to depend on the concentrations of initiator, monomer, and cellulose. The structure of cellulose—methyl methacrylate graft copolymers was studied by hydrolyzing away the cellulose backbone to isolate the grafted poly(methyl methacrylate) branches. The molecular weights and molecular weight distributions of the grafted poly(methyl methacrylate) were determined by using gel-permeation chromatography. The number-average (M?_n) molecular weights ranged from 36 000 to 160 000 and the polydispersity ratios (M?_w/M?_n) varied from 4.0 to 7.0. The grafting frequency or the number of poly(methyl methacrylate) branches per cellulose chain calculated from the per cent grafting and molecular weight data varied from 0.38 to 3.2. The structure of cellulose—methyl methacrylate graft copolymers and the effect of stepwise addition of initiator on the structure are discussed.     

Formation of free radicals in photoirradiated cellulose. I. Effect of wavelength

Formation of free radicals in photoirradiated cellulose has been studied by means of ESR spectroscopy at 77°K. Three kinds of light sources with different wavelengths between 2500 and 4000 ÅR were employed. No radicals detectable by ESR were recorded when cellulose was irradiated with light of wavelength longer than 3300–3400 ÅR. Hydrogen atoms that generated a doublet spectrum (ΔH = 508 G) were observed when cellulose was irradiated with light longer than 2800 ÅR. Hydrogen atoms and formly radicals that generated doublet spectra with splitting constants of 508 and 129 G, respectively, were observed when irradiated with light shorter than 2800 ÅR. The scission of the polymer chain in cellulose is evident from decrease of the degree of polymerization, and the results of mass spectrometric analysis indicated H₂, CO, CO₂, and H₂O to be the main volatile products of cellulose upon photoirradiation.     

Molecular parameters of sodium cellulose xanthate in dilute solution

Molecular parameters of sodium cellulose xanthate in NaOH solution have been determined by means of light scattering and viscometry. The effect of the degree of substitution on the molecular configuration of sodium cellulose xanthate has been studied for three series of samples of varying degree of substitution. The expansion factor has been determined from the expression due to Orofino and Flory. The effective bond length b and the ratio of the unperturbed dimension to the dimension assuming free rotation of the chain units (R?_o²/R?_f²)^1/2, have also been determined. It is concluded that sodium cellulose xanthate in dilute solution is a loosely coiled molecule, comparable to other cellulose derivatives in chain stiffness.     

Synthesis of SiO2-TiO2 binary composites with cellulose as the substrate

A procedure for the synthesis of the SiO₂-TiO₂ binary material was developed. The procedure includes the formation of the silica matrix by impregnating cellulose plates with tetraethoxysilane followed by hydrolysis of the organometallic compound and burning-out of the cellulose constituent; activation of silica with HF; and deposition of titanium dioxide on the surface of the silica matrix by impregnating it with a solution of tetrabutoxytitanium, which is hydrolyzed in water-ammonia atmosphere. The physicochemical properties of the obtained material were studied.     

Degradation processes in the cellulose/<Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide system studied by HPLC and ESR. Radical formation/recombination kinetics under UV photolysis at 77 K

Degradation processes of N-methylmorpholine-N-oxide monohydrate (NMMO), cellulose and cellulose/NMMO solutions were studied by high performance liquid chromatography (HPLC) and electron spin resonance (ESR) spectroscopy. Kinetics of radical accumulation processes under UV (λ = 248 nm) excimer laser flash photolysis was investigated by ESR at 77 K. Beside radical products of cellulose generated and stabilized at low temperature, radicals in NMMO and cellulose/NMMO solutions were studied for the first time in those systems and attributed to nitroxide type radicals ∼CH₂–NO^•–CH₂∼ and/or ∼CH₂–NO^•–CH₃∼ at the first and methyl ^•CH₃ and formyl ^•CHO radicals at the second step of the photo-induced reaction. Kinetic study of radicals revealed that formation and recombination rates of radical reaction depend on cellulose concentration in cellulose/NMMO solutions and additional ingredients, e.g., Fe(II) and propyl gallate. HPLC measurements showed that the concentrations of ring degradation products, e.g., aminoethanol and acetaldehyde, are determined by the composition of the cellulose/NMMO solution. Results based on HPLC are mainly maintained by ESR that supports the assumption concerning a radical initiated ring-opening of NMMO.     

Cellulose conversion to polyols on supported Ru catalysts in aqueous basic solution

It is of great significance and challenge to achieve direct conversion of cellulose to specific polyols, e.g., ethylene glycol and propylene glycol. For such selective conversion, a novel one-pot approach was studied by combination of alkaline hydrolysis and hydrogenation on supported Ru catalysts. A wide range of bases including solid bases, e.g., Ca(OH)₂ and La₂O₃, and phosphate buffers were examined in the cellulose reaction in water, and the cellulose conversions and polyol products depended largely on the basicity or pH values in the aqueous solutions. Ethylene glycol, 1,2-propanediol, and especially 1,2,5-pentanetriol were obtained with selectivities of 15%, 14% and 22%, respectively, at 38% cellulose conversion at pH 8 in phosphate buffer solution. These preliminary results provide potentials for efficient conversion of cellulose to targeted polyols by using the advantages of bases.