NLO polymers based on cellulose diacetate and a cationic chromophore

An attempt has been made to prepare second-order nonlinear optic (NLO) materials based on cellulose diacetate and melamine derivatives. The NLO cationic chromophore, composed of 1,3-dimethyl-2-(4′-N,N-dimethylaminophenyl)-azo-imidazole chloride and small amounts of 1,3-dimethyl-2-(4′-N,N-dimethylaminophenyl)-azo-imidazole methylsulfate, was incorporated into a crosslink network formed from the reaction of cellulose diacetate with trimethylol melamine or hexamethylol melamine. The poled and cured NLO materials exhibited an electro-optic coefficient (r ₁₃) of 1.03 or 1.42 pm/V, respectively, at the laser wavelength 1550 nm and a modulation frequency of 12.7 kHz; the r ₁₃ values decreased to 97% or 86.6%, respectively, of the initial values after 4 days. The laser transmission loss was 0.58 or 0.6 dB, respectively. The crosslinked materials showed better temporal stability than the material of the host/guest system with a doped cationic chromophore. The results of Fourier transform infrared spectroscopy, dielectric relaxation and thermogravimetry analyses proved the formation of a crosslink structure, and the degree of dielectric relaxation was shown to became higher if a crosslinker of too high functionality was used.     

Structural and thermal characterization of sugarcane bagasse cellulose succinates prepared in ionic liquid

The chemical modification of SCB cellulose with succinic anhydride using 1-butyl-3-methylimidazolium chloride ionic liquid/DMSO system as reaction medium was studied. The parameters including the molar ratio of succinic anhydride/anhydroglucose units in cellulose from 1:1 to 12:1, reaction time 5-120 min, and reaction temperature 85-105 °C were investigated. The results showed that the degree substitution of succinylated cellulosic preparations ranged from 0.037 to 0.53. It was found that the treatment of the native cellulose in the ionic liquid/DMSO system under the conditions given significantly degraded the cellulose and completely destroyed the cellulose crystals. FT-IR and solid-state CP/MAS ¹³C NMR spectra produced evidence for succinoylation reaction and the results showed that succinoylation occurred at positions C-6, C-2 and C-3. The thermal stability of the succinylated cellulose decreased upon chemical modification.     

Preparation and characterization of cellulose β-ketoesters prepared by homogeneous reaction with alkylketene dimers: comparison with cellulose/fatty acid esters

Cellulose was dissolved in lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI), and reacted with alkylketene dimers (AKDs) under non-aqueous and homogeneous conditions to prepare cellulose/AKD β-ketoesters with high degrees of substitution (DS). Six AKDs synthesized from octanoic, decanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic acids via their fatty acid chlorides were used in this study. The cellulose/AKD β-ketoesters obtained were gummy solid at room temperature, and had DS values ranging from 1.9 to 2.9. Cellulose/fatty acid esters with DS 2.5–2.9 were also prepared as references. ¹³C-NMR spectra of the cellulose/AKD β-ketoesters showed that cellulose carbons and substituent carbons close to cellulose chains were restricted in motion and behaved like solid in solutions. In contrast, the cellulose/fatty acid esters did not demonstrate such anomalous ¹³C-NMR spectra. The unique ¹³C-NMR patterns are characteristic for the cellulose/AKD β-ketoesters, which have long and branched alkyl substituents in each anhydroglucose unit. Size-exclusion chromatography furnished with multi-angle laser light scattering (SEC-MALLS) revealed, on the other hand, that all cellulose/AKD β-ketoesters and cellulose/fatty acid esters prepared had flexible or random-coil conformations in tetrahydrofuran (THF). There were no clear differences in conformation or stiffness of cellulose chains between cellulose/AKD β-ketoesters and cellulose/fatty acid esters.     

Molecular and crystal structure of cellulose propanoate diacetate (CPDA, 2,3-di-O-acetyl-6-O-propanoyl cellulose)

The molecular and crystal structure of cellulose propanoate diacetate (CPDA, 2,3-di-O-acetyl-6-O-propanoyl cellulose) has been determined through combined X-ray fibre diagrams and electron diffraction patterns of single crystal analysis, aided by stereochemical restraints by using a constrained linked-atom least-squares refinement. The unit cell of CPDA is orthorhombic with space group P2 ₁2₁2₁ and parameters:a =1.239 nm,b =2.498 nm and c (fibre axis)=1.044 nm. Based on these data, coupled with the observed density of the crystals, there are four chains per unit cell, distributed in two antiparallel pairs of parallel chains, and the independent repeat is the disaccharide unit in each chain. A preliminary CPDA disaccharide unit was derived based on the centre residue of cellotriose undeca-acetate, and this model was refined through a conformational analysis. The best model obtained by combining the stereochemical refinement with the diffraction intensities gave R=0.272 (R=0.259) for the three-dimensional information from the X-ray fibre diagram and R=0.248 (R=0.246) for the base plane data resulting from electron diffraction analysis.     

Thermal and liquid crystalline properties of cellulose β-ketoesters prepared by homogeneous reaction with ketene dimers

Cellulose β-ketoesters having long alkyl or alkenyl chains were prepared by homogeneous reactions with alkyl or alkenyl ketene dimmers (OKD or AKD), and were characterized by X-ray diffractometory, differential scanning calorimetry, optical microscopy with cross polarizers and others. The Cellulose/OKD and AKD β-ketoesters with degrees of substitution (DS) of more than 1.5 were gummy solid at room temperature and had birefringence due to liquid crystalline structures in wide temperature range. The liquid crystalline/isotropic phase transition points were 150–175 °C, depending on the DS and substituents introduced into cellulose hydroxyls. X-ray diffraction patterns indicated that cellulose backbones had disordered structures at room temperature, while alkyl chains in the substituents formed ordered or crystalline domains in the cellulose β-ketoesters. Films of the cellulose/AKD β-ketoesters prepared by casting their chloroform solutions on glass plates had highly hydrophobic nature, and contact angles of water droplet on the films were more than 90°. The water-contact angles on the films decreased to some extent just after heating of the films at 105 °C, whereas they were gradually recovered to the initial values by conditioning at ambient temperature.     

Simulation of X-ray diffractograms relevant to the purported polymorphs cellulose IV<Subscript>I</Subscript> and IV<Subscript>II</Subscript>

Diffractograms were simulated for model nanocrystals of cellulose I_β, using numerical summation of radiation scattered from all carbon and oxygen atoms in the nanocrystal. Diffractogram peaks were sometimes displaced by a few degrees from positions calculated by the Bragg equation, as predicted in a published study based on a different mathematical approach. Simulated diffractograms showed 2 or 3 peaks, depending on the cross-sectional size and shape of the model nanocrystal. Some of the 2-peak diffractograms resembled published results for the purported polymorph cellulose IV_I, or for cell-wall cellulose, supporting suggestions that cellulose IV_I is simply cellulose I fragmented into nanocrystals with relatively small cross-sectional dimensions. A published diffractogram for cellulose IV_II could not be simulated with acceptable precision, suggesting that this polymorph might have a crystal structure distinctly different from that of cellulose I_β.     

Thermal characterization of the clay binder of heritage Sydney sandstones

Thermal analysis has been employed in a study of the degradation of heritage Sydney sandstone used in St Mary’s Cathedral in Sydney, Australia. TG and DSC have been used to characterise the clay components removed from weathered and unweathered sandstone. Two types of kaolin clays — kaolinite and its polymorph, dickite — have been identified. A higher amount of dickite present in the clay of weathered sandstone indicates that a kaolinite-to-dickite transformation occurs upon weathering. XRD hot stage analysis was also used to demonstrate the presence of a more thermally stable polymorph of the kaolinite.     

Measuring the crystallinity index of cellulose by solid state 13C nuclear magnetic resonance

The crystallinity index of cellulose is an important parameter to establish because of the effect this property has on the utilization of cellulose as a material and as a feedstock for biofuels production. However, it has been found that the crystallinity index varies significantly depending on the choice of instrument and data analysis technique applied to the measurement. We introduce in this study a simple and straightforward method to evaluate the crystallinity index of cellulose. This novel method was developed using solid state ¹³C NMR and subtraction of the spectrum of a standard amorphous cellulose. The crystallinity indexes of twelve different celluloses were measured and the values from this method were compared with the values obtained by other existing methods, including methods based on X-ray diffraction. An interesting observation was that the hydration of the celluloses increased their crystallinity indexes by about 5%, suggesting that addition of water increased cellulose order for all the cellulose samples studied.     

The thermal expansion of cellulose II and IIIII crystals

Highly crystalline samples of cellulose II and III_II have been prepared from repeated mercerization of ramie fibers and supercritical ammonia treatment of the mercerized ramie fibers, respectively. The thermal expansion behavior of cellulose II and III_II was investigated using X-ray diffraction at temperatures ranging from room temperature to 250 °C. With increasing temperature, the unit cell of cellulose II expanded in the lateral directions and contracted in the longitudinal direction, with the a and b axes increasing by 0.54 and 3.4%, respectively, and the c axis decreasing by 0.09%. The anisotropic thermal expansion in these three directions was closely related to the crystal structure and the hydrogen bonding in cellulose II. A similar anisotropic thermal expansion was also observed in cellulose III_II. Cellulose III_II expanded in the lateral direction but contracted in the longitudinal direction.     

Insight into the extraction and characterization of cellulose nanocrystals from date pits

This study aims to extract and characterize cellulose nanocrystals (CNCs) from date pits (DP), an agricultural solid waste. Two methods were used and optimized for the cellulose nanocrystals (CNCs) extraction, namely the mechanical stirrer method (CNCs₁) and the Soxhlet apparatus method (CNCs₂) in terms of chemical used, cost, and energy consumption. The results showed that scanning electron microscopy revealed the difference in the morphology as they exhibit rough surfaces with irregular morphologies due to the strong chemical treatments during the delignification and bleaching process. Moreover, transmission electron microscopy analysis for CNCs reveals the true modification that was made through sulfuric acid hydrolysis as it presents cellulose microfibrils with a packed structure. Fourier transform infrared proved that the CNCs were successfully extracted using the two methods since most of the lignin and hemicellulose components were removed. The crystallinity index of CNCs₁ and CNCs₂ was 69.99%, and 67.79%, respectively, and both presented a high yield of CNCs (≥10%). Ultimately, both techniques were successful at extracting CNCs. Based on their cost-effectiveness and time consumption, it was concluded that method 1 was less expensive than method 2 based on the breakdown of the cost of each step for CNCs production.     

On the determination of crystallinity and cellulose content in plant fibres

A comparative study of cellulose crystallinity based on the sample crystallinity and the cellulose content in plant fibres was performed for samples of different origin. Strong acid hydrolysis was found superior to agricultural fibre analysis and comprehensive plant fibre analysis for a consistent determination of the cellulose content. Crystallinity determinations were based on X-ray powder diffraction methods using side-loaded samples in reflection (Bragg-Brentano) mode. Rietveld refinements based on the recently published crystal structure of cellulose Iβ followed by integration of the crystalline and amorphous (background) parts were performed. This was shown to be straightforward to use and in many ways advantageous to traditional crystallinity determinations using the Segal or the Ruland–Vonk methods. The determined cellulose crystallinities were 90–100 g/100 g cellulose in plant-based fibres and 60–70 g/100 g cellulose in wood based fibres. These findings are significant in relation to strong fibre composites and bio-ethanol production.     

Successive self-nucleation and annealing in the solvated state of ethylene copolymers

Summary Simultaneous TG/DSC and high temperature X-ray diffraction studies were performed on the system SrCO₃-Fe₂O₃ in an atmosphere of CO₂ from room temperature to 1300°C. SrCO₃ decomposes and reacts simultaneously with the Fe₂O₃ beginning around 850°C. A transient iron rich phase is formed initially, which soon diminishes to yield a mixture of perovskite SrFeO_3-x and the iron rich phase Sr₄Fe₆O₁₃. Upon cooling the perovskite phase predominantly orders into the brownmillerite structure Sr₂Fe₂O₅. There does not appear to be a Hedvall effect associated with the first order phase transformation in SrCO₃ at 927°C.     

Nitroxide-mediated oxidation of cellulose using TEMPO derivatives: HPSEC and NMR analyses of the oxidized products

Regenerated cellulose (viscose rayon) was oxidized using NaBr, NaClO and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) or one of ten related nitroxyl radicals in water at pH 10–11. The C6 primary hydroxyl groups in rayon were oxidized to carboxyl groups in most cases, thus giving water-soluble products. However, the oxidation times required for complete dissolution of the products varied substantially, depending on the nitroxyl radical used. Weight average degrees of polymerization (DPw) of the oxidized products were determined by means of high performance size exclusion chromatography (HPSEC) using pullulan standards. All the products had bimodal HPSEC distribution patterns, probably reflected by the solid-state structure of viscose rayon. When 4-acetamido-TEMPO and 4-carboxy-TEMPO were used, cellouronic acids having almost homogeneous chemical structures with higher DPw than for TEMPO were obtained quantitatively within 30 min. The oxidations using 4-amino-TEMPO, 4-carboxy-PROXYL and 4-carbamoyl-PROXYL gave cellouronic acids having the highest DPw, although reaction times of more than 4 h were required, and some side reactions occurred on the products.     

Tailoring the morphology and properties of waterborne polyurethanes by the procedure of cellulose nanocrystal incorporation

Polyurethane waterborne synthesis was performed using a two-step method, commonly referred to as a prepolymer method. Nanocomposites based on waterborne polyurethane and cellulose nanocrystals were prepared by the prepolymer method by altering the mode and step in which the nanofillers were incorporated during the polyurethane formation. The morphology, structural, thermal, and mechanical properties of the resulting nanocomposite films were evaluated by Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and tensile tests. FTIR results indicated that the degree of interaction between the nanofillers and the WPU through hydrogen bonds could be controlled by the method of cellulose nanocrystal incorporation. Data obtained from SAXS experiments showed that the cellulose nanocrystals as well as the step of the reaction in which they are added influenced the morphology of the polyurethane. The reinforcing effect of CNCs on the nanocomposites depends on their morphology.     

On products of reaction of imidazole with benzoyl chloride under conditions of the Regel-Buchel reaction

The reaction of imidazole with benzoyl chloride in pyridine affordedcis-1,2-bis(benzoyl-amino)ethylene (1) rather than 2-benzoylimidazole, as has been suggested previously. The structure of1 was confirmed by¹H NMR spectroscopy and X-ray diffraction study. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1593–1595, August, 1998.     

Investigation of the thermal and structural behaviour of diclofenac sodium-sugar ester surfactant systems

Sugar esters (SEs) have a wide range of hydrophilic-lipophilic balance (HLB) values (1–16) and hence can be applied as surfactants or as solubility or penetration enhancers. They can be used for hot melt technology and solvent method which are frequently applied techniques to preparation of solid dispersions. In this study drug-SE products were prepared by physical mixing, melt technology and solvent methods. The products were investigated by DSC, X-ray powder diffraction and dissolution tests. Diclofenac sodium (DS) as model drug and two SEs, P1670 (HLB=16) and S970 (HLB=9) were used for the preparation of the products. DSC curves revealed considerable melting range and enthalpy decreases for the DS-SE products. The dissolved drug molecules broke down the structures of the SEs but were not built into the crystalline phase of the carrier. The melt technology led to a solid dispersion while in the case of the solvent methods the DS was in molecularly dispersed form which resulted in faster dissolution. The drug release was influenced by the structures resulting from the various treatments, by the HLB and by the gel-forming behaviour of the SEs.     

The reaction of mono-aryl substituted methylenecyclobutanes with diphenyl diselenide in the presence of iodosobenzene diacetate and H2O

The mono-aryl substituted methylenecyclobutanes undergo an interesting reaction with diphenyl diselenide in the presence of iodosobenzene diacetate and H₂O at 40 °C in 1,2-dichloroethane to give the corresponding aryl-(1-phenylselanylcyclobutyl)methanones in moderate to good yields within 30 h. A plausible reaction mechanism has been discussed on the basis of the control and ¹⁸O-labeling experiments.     

Combination of DSC and X-ray Diffraction in the Study of the Phase Behaviour of Lipids: Mini-review

The phase behaviour and phase stability of lipids are of importance in an understanding of the biological functions of cell membranes. Among a variety of physical techniques employed to study the phase behaviour and structural properties of polar lipids, differential scanning calorimetry and X-ray diffraction have proved to be successful and are the most frequently used methods. Applications involving a combination of the two techniques, particularly when synchrotron radiation is used as the light source of X-ray diffraction, are reviewed in this article.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis,characterization, and initial reaction study of two new bicyclic hypervalent iodine(III) reagents

The synthesis of two new bicyclic hypervalent iodine(III) reagents 5 and 6 is described along with their corresponding X-ray crystal structures for the first time. A detailed comparison in the bond lengths and bond angles of reported bicyclic hypervalent iodine(III) reagents is also presented. Furthermore, an initial study shows that these two hypervalent iodine(III) reagents could promote the dipeptide coupling reaction.     

Arylation of aliphatic alcohols with tri-p-tolylbismuth and tri-p-tolylbismuth diacetate in the presence of a copper salt

Tri-p-tolylbismuth diacetate in the presence of a catalytic amount of a copper(II) salt (10.02, mol/mol) and tri-p-tolylbismuth in the presence of copper diacetate (1 2) replace the hydrogen atom of the hydroxyl groups of methanol and butanol with a tolyl group at 80 °C in up to 90 % yields.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 156–158, January, 1995.