Influence of water on the dissolution of cellulose in selected ionic liquids

Cellulose (7% water) was thoroughly dispersed in various ionic liquids (IL) and the turbidity of the mixture was investigated to distinguish real dissolution from fine dispersion. The dissolving ability of 1-butyl-3-methylimidazolium chloride (BMIMCl know cellulose solvent) and 11 other commercial IL (not reported as cellulose solvents) was studied. From the latter, only 1,3-dimethylimidazolium dimethylphosphate (DMIMDMP) could dissolve cellulose. The influence of water content on the real dissolution of cellulose in these two IL was investigated. The maximum theoretical amount of dissolved anhydrous cellulose in the IL was determined by extrapolation methodology at different temperatures. For cellulose in BMIMCl, it was 8.75 g/100 g of IL at 95 °C. DMIMDMP could achieve real cellulose dissolution only in a practically anhydrous system (2.3 g/100 g of IL at 30 °C) but dissolution was physically limited by high viscosity.     

Influence of biodegradation on crystallization of poly (butylene adipate‐co‐terephthalate)

The biodegradation of aromatic‐aliphatic biodegradable polyester poly (butylene adipate‐co‐terephthalate) (PBAT) was studied under mesophilic (37°C) and thermophilic (55°C) anaerobic conditions. Anaerobic sludge from municipal wastewater treatment plant was utilized as an inoculum. Non‐isothermal crystallization kinetics of PBAT before and after biodegradation was explored by differential scanning calorimetry. Under mesophilic anaerobic conditions (37°C), the biodegradation after 126 days was only 2.2%, molecular weight changed from 93 000 to 25 500 g/mol, and the crystallization behavior was changed only slightly. However, biodegradation under thermophilic anaerobic conditions (55°C) caused much bigger changes: biodegradation according to biogas production reached after 126 days 8.3%, molecular weight changed from 93 000 to 9430 g/mol, and the crystallization behavior was changed significantly. While T_m increased only slightly, T_c on the other hand increased significantly for the sample after biodegradation at 55°C. Also, the crystallization rate was slower (particularly at lower cooling rates), but crystallinity was slightly higher. The diffraction pattern was observed by X‐ray diffraction.     

Processing stability of polypropylene impact-copolymer during multiple extrusion - Effect of polymerization technology

Three commercially available polypropylene impact-copolymers (ICPP) produced by Innovene (INN), Spheripol (SPH) and Unipol (UNI) technologies were subjected to multiple extrusion using a twin-screw extruder W&P ZSK25 at 220 °C. Processing stability and changes in properties induced by extrusion were investigated. The materials were of similar MFR ∼6 dg/min, similar ethylene contents ∼7.5 wt. % and the same type and level 1200 ppm of phenol/phosphite stabilizer system was used. Ranking INN < UNI < SPH in processing and long-term (LTHA) stabilities observed was primarily related to the reactivity of catalyst residues rather than to other factors, such as contents of ethylene, quantity of extractables, EPR phase composition, levels of ash or individual elements in it. The mechanically demanding multiple extrusion conditions and consequently different extent of processing degradation, however, induced only minimum changes in morphology and impact strength of the solid ICPP matrix. Thus, regardless of changes in melt-flow properties induced by extrusions, all the three grades even after 5th extrusion at 220 °C exhibited Charpy notched impact strength at 23 °C only minimally changed.     

Thermal degradation mechanism of dodecylbenzene sulfonic acid- hydrochloric acid co-doped polyaniline

Co-doped polyaniline (PANI) was synthesized in microemulsion by hydrochloric acid (HCl) and dodecylbenzene sulfonate (SDBS) then thermal treated in air at 160 and 200 °C for 0.5 h, respectively. The changes of structure, thermal stability, micromorphology and electrical conductivity after thermal treatment were studied by Fourier transformed infrared (FT-IR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM) and four-probe technique. It was found that the conductivity of PANI decreased about 50% after thermal treated at 160 °C, and droped by 2 orders of magnitude at 200 °C. This may be explained by that only a fraction of total mass of HCl losses during thermal treatment at 160 °C, but after heating at 200 °C, the dedoping of dodecylbenzene sulfonic acid (DBSA) along with cross-linking, chain scission and oxygen incorporation in a form of carbonyl groups take place, resulting in destruction of crystal structure, decrease of the emeraldine sequence, lower thermal stability and heterogeneous micromorphology.     

Counterpoise-corrected potential energy surfaces of simple H-bonded systems

Geometries and stabilization energies of various simple H-bonded complexes (water dimer, hydrogen fluoride dimer, formamide dimer, formic acid dimer) have been determined by a gradient optimization that eliminates the basis set superposition error (BSSE) by the counterpoise (CP) method in each gradient cycle as well as by the standard gradient optimization. Both optimization methods lead to different potential energy surfaces (PES). The difference depends on the theoretical level used and is larger if correlation energy is considered. Intermolecular distances from the CP-corrected PES are consistently longer, and this difference might be significant (∼0.1 ?); also angular characteristics determined from both surfaces differ significantly. Different geometries were obtained even when passing to larger basis sets (aug-cc-pVDZ). The standard optimization procedure can result in a completely wrong structure. For example, the “quasi-linear” structure of the (HF)₂ (global minimum) does not exist at the standard MP2/ 6-31G** PES (where only cyclic structure was detected) and is found only at the CP-corrected PES. Stabilization energies obtained from the CP-corrected PES are always larger than these from the standard PES where the BSSE is added only a posteriori for the final optimized structure; both energies converge only when passing to a larger basis set (aug-cc-pVDZ). Received: 11 March 1998 / Accepted: 19 June 1998 / Published online: 4 September 1998 RID=" ID=" <E6>Acknowledgements.</E6> The project was supported by the Grant Agency of the Czech Republic (Grant No. 203/98/1166). RID=" ID=" <E5>Correspondence to</E5>: P. Hobza     

Characterization of aqueous rose bengal dye solution for the measurement of low doses of gamma radiation

Aqueous solution of rose bengal dye has been studied spectrophotometrically as a gamma-ray dosimeter for the measurement of low doses of radiation. The useful dose range was found to be from 50 to 1000 Gy when the measurements were made at 549 nm. The effects of temperature and light conditions on the stability of response during post-irradiation storage were also investigated. When stored in dark at room temperature, the dosimetric solutions showed a stable response up to 22 days. The storage of irradiated solutions in diffused sunlight showed a stable response only up to 6 days. When exposed to direct sunlight, very prominent and fast bleaching of dye solution occurred. At low storage temperature (ca. 11 °C), dosimetric response was found to be stable up to 22 days while at higher temperature (ca. 30 °C), the response of dosimetric solution was stable only up to 6 days. The rose bengal aqueous solution showed promising characteristics as a low dose radiation dosimeter when stored at lower temperatures (<25 °C) in dark.     

Effect of temperature and pH on the aggregation and the surface hydrophobicity of bovine κ-casein

κ-Casein (κ-CN) aggregation by heating has been studied at pH 7.2 and 5.2 using UV-visible spectrophotometry, sodium dodecyl sulfate polyacrylamide gel electrophoresis, spectrofluorometric study of the 1–8 aniline naphtalene sulfonate (ANS)–κ-CN binding and circular dichroism (CD) spectroscopy. The aggregation process to form aggregates like micelles or submicelles and the structural characteristics of these aggregates were pH dependent. Far-UV CD showed that the aggregates obtained by heating presented changes in the κ-CN secondary structure. Near-UV CD spectra showed a certain degree of tertiary organization in the Tyr environment for the protein heated or unheated, only at pH 5.2. ANS binding at both pH was quite different and depends on the self-association process. Heating produced exposition of hydrophobic binding sites only at pH 7.2, including those in the neighborhood of the κ-CN Trp residue.     

Synthesis, characterization and application of a novel mercapto- and amine-bifunctionalized silica for speciation/sorption of inorganic arsenic prior to inductively coupled plasma mass spectrometric determination

A bifunctional sorbent, (NH₂ + SH)silica, containing both amine and mercapto functionalities was prepared by modification of silica gel with 3-(triethoxysilyl)propylamine and (3-mercaptopropyl)trimethoxysilane. In addition to the bifunctional sorbent, silica gel was modified individually with the functional mercapto- and amino-silanes, and the mono-functional sorbents, namely (SH)silica and (NH₂)silica, were also mechanically mixed ((NH₂)silica + (SH)silica) for the sake of comparison of sorption performances. It has been demonstrated that (SH)silica shows quantitative sorption only to As(III) at two pH values, 1.0 and 9.0, while (NH₂)silica displays selectivity only towards As(V) at pH 3.0. On the other hand, the bifunctional (NH₂ + SH)silica possesses the efficient features of the two mono-functionalized sorbents; for example, it retains As(III) at a wider pH range, from 1.0 to at least 9.0 with the exception at pH 2.0, and it also shows quantitative sorption to As(V) at pH 3.0. This property gives the bifunctional (NH₂ + SH)silica a better flexibility in terms of sorption performance as a function of solution pH. The mechanically mixed (NH₂)silica + (SH)silica exhibits a similar but less efficient sorption behavior compared to the bifunctional sorbent. Desorption of both As(III) and As(V) species can be realized using 0.5 M NaOH. The validity of the proposed method was checked through the analysis of a standard reference material and a good correlation was obtained between the certified (26.67 μg L⁻¹) and determined (27.53 ± 0.37 μg L⁻¹) values. Spike recovery tests realized with ultrapure water (93.0 ± 2.3%) and drinking water (86.9 ± 1.2%) also confirmed the applicability of the method.     

Hydrolysis of poly(l-lactic acid) using microwave irradiation

Poly(l-lactic acid) (PLLA) was hydrolyzed using microwave irradiation, and yields of the resultant lactic acid and reaction time were compared with those obtained by conventional heating. In both cases, the reaction temperature was maintained at 170 °C and the weight ratio of PLLA:H₂O was 3:1. Under conventional heating, the lactic acid yield reached saturation after 800 min at 45%, whereas only 120 min was required to reach the same yield level under microwave irradiation. The optical purity under conventional heating decreased with hydrolysis of the PLLA and dropped to 94%ee when the lactic acid yield reached at 45%. Under microwave irradiation, however, the optical purity decreased only after the equilibrium state of hydrolysis was attained. Therefore, to maintain the optical purity at 98%ee, it was necessary to stop microwave irradiation when the lactic acid yield reached 45%.     

Two-Step Pretreatment of Corn Stover Silage Using Non-ionic Surfactant and Ferric Nitrate for Enhancing Sugar Recovery and Enzymatic Digestibility of Cellulose

Corn stover silage (CSS) is regarded as a promising feedstock for bioethanol production. The two-step pretreatment using a sequential non-ionic surfactant and ferric nitrate pretreatment was investigated for improving the enzymatic hydrolysis of CSS. The first-step pretreatment using non-ionic surfactant (Tween-80, 2.0 wt.%) at 60 °C for 60 min achieved 30.48% the removal of lignin. Compared with the raw material, the cellulose content of first-step treated CSS increased by 15.86%. The second step using ferric nitrate resulted in 94.56% hemicellulose removal and achieved 72.53% cellulose purity at 130 °C for 30 min, while the yields of furfural and HMF were only 0.36 and 0.32 g/100 g dry material, respectively. The maximum enzymatic digestibility of the two-step treated CSS was 90.98% with a low cellulose dosage (15 FPU/g-glucan), which was approximately 32.07% higher than that of the first-step pretreatment only with Tween-80.

     

Production of submicron-sized poly(methyl methacrylate) particles by dispersion polymerization with a poly(dimethylsiloxane)-based azoinitiator in supercritical carbon dioxide

 Submicron-sized, comparatively monodisperse poly (methyl methacrylate) particles were produced by dispersion polymerization of methyl methacrylate with a poly(dimethylsiloxane)-based azoinitiator in supercritical carbon dioxide at 30 MPa for 24 h at 65 °C. The initiator operated not only as a radical initiator but also as a colloidal stabilizer, and was named an “inistab”. Received: 13 February 2001 Accepted: 20 June 2001     

Effect of Laser Thermal Injury on Langerhans Cells in Mouse and Hairless Guinea Pig Epidermis

To examine the effect of laser thermal injury on Langerhans cells (LC) within the epidermis, the dorsal skin of mice and hairless guinea pigs was exposed to varying levels of laser irradiation using a thulium laser at a wavelength of 2.0 μm. At 6, 24 and 48 h post irradiation, animals were euthanized, skin samples prepared for histology and the epidermis obtained and stained by major histocompatibility complex‐II staining (mice) or ATPase assay (hairless guinea pigs) for the enumeration of LC. Mouse skin exhibited histological evidence of thermal damage at 24 h post irradiation at even the lowest dose (0.14 W) and decreases in the numbers of epidermal LC were observed at all doses and decreases were proportional to dose. In contrast, hairless guinea pig skin only showed consistent histological evidence of thermal damage at the highest dose of irradiation (0.70 W) at 24 and 48 h post irradiation and exhibited a statistically significant decrease in numbers of epidermal LC only at this dose. Thus, epidermal LC depletion occurred in the skin of both mice and hairless guinea pigs in response to laser treatment and the magnitude of depletion directly correlated with the extent of thermal damage both within and between species.     

The Influence of Corona Electrodes Thickness on the Efficiency of Plasmachemical Oxidation of Acetone

Current–voltage characteristics (CVC) and acetone vapors oxidation in atmospheric pressure corona discharge (CD) of negative and positive polarity were studied in double wires-to-plate geometry. Negative CD was more stable than positive one towards breakdown and allowed to reach higher current. CVC for negative CD can be well described by model for cylindrical geometry with correction in one coefficient only. The ignition voltage of negative CD obeys Peek’s law. The rate of acetone vapors oxidation increased with the increase of corona wire radius in the range of discharge power 15–60 W. The highest oxidation rate was obtained at power 60 W, negative polarity and wire radius 400 μm but the highest energetic efficiency (g/kWh) was obtained at maximum wire radius (400 μm) and minimum power level (15 W). The oxidation rate was directly proportional to the volume of discharge area which grows together with the increase of wire radius.     

Hexacyanoferrate(III) as a mediator in the determination of total iron in potable waters as iron(II)-1,10-phenanthroline at a single-use screen-printed carbon sensor device

Hexacyanoferrate(III) was used as a mediator in the determination of total iron, as iron(II)-1,10-phenanthroline, at a screen-printed carbon sensor device. Pre-reduction of iron(III) at −0.2 V versus Ag/AgCl (1 M KCl) in the presence of hexacyanoferrate(II) and 1,10-phenanthroline (pH 3.5-4.5), to iron(II)-1,10-phenanthroline, was complete at the unmodified carbon electrode surface. Total iron was then determined voltammetrically by oxidation of the iron(II)-1,10-phenanthroline at +0.82 V, with a detection limit of 10 μg l⁻¹.In potable waters, iron is present in hydrolysed form, and it was found necessary to change the pH to 2.5-2.7 in order to reduce the iron(III) within 30 s. A voltammetric response was not found at lower pH values owing to the non-formation of the iron(II)-1,10-phenanthroline complex below pH 2.5.Attempts to incorporate all the relevant reagents (1,10-phenanthroline, potassium hexacyanoferrate(III), potassium hydrogen sulphate, sodium acetate, and potassium chloride) into a modifying coated PVA film were partially successful. The coated electrode behaved very satisfactorily with freshly-prepared iron(II) and iron(III) solutions but with hydrolysed iron, the iron(III) signal was only 85% that of iron(II).     

The stability of poly(m-carborane-siloxane) elastomers exposed to heat and gamma radiation

Poly(m-carboranyl-siloxane) elastomers containing a mixture of di-methyl- and methylphenyl-silyl units were synthesised using the ferric chloride catalysed condensation reaction between di-chloro-diorganosilane and bis(di-methylmethoxysilyl)-m-carborane. These elastomeric materials were originally developed to have greater stability to extreme thermal environments and retain tailorable physical and chemical properties relative to comparable non-carborane containing elastomers. Prepared samples were aged either by heating in air at elevated temperatures or by gamma irradiation from a ⁶⁰Co source. Multinuclear (¹H, ¹³C and ¹¹B) solid and solution state nuclear magnetic resonance (NMR) was used to assess degradation. This included measurements of segmental chain dynamics using a solid-echo pulse sequence reflecting changes in crosslink density and assessing changes to the carborane fragment by ¹¹B and ¹H Magic Angle Spinning (MAS) methods. Thermogravimetric measurements were also performed to assess thermal stability. Gamma radiation (to a dose of 1 MGy) was found to induce only a small degree of elastomer hardening as evidenced by a reduction in segmental chain dynamics. The carborane cage however, remained intact at these dose levels. Thermal degradation was observed to lead to oxidative crosslinking, the degree of which is dependent on temperature. At temperatures below 350 °C, only small changes in segmental dynamics were observed commensurate with only minor weight loss at this temperature. At temperatures above 350 °C, the degradation of the elastomer increased dramatically with decreased segmental dynamics and presumed partial oxidation of the carborane cage. The integrity of the m-carborane cage and the segmental dynamics were found to be significantly reduced at temperatures above 580 °C, in line with the known cage rearrangement temperature for icosahedral carboranes.     

Measurement of alligator (Alligator mississippiensis) serum angiotensin converting enzyme (ACE) using a miniaturized colorimetric assay

Oftentimes enzyme assays can be difficult when utilizing tissues from rare, endangered or exotic animals due to limited tissue supplies. We have miniaturized a common assay for angiotensin converting enzyme (ACE) to a microtiter plate format. The assay is based on the reduction of the optical density at 340 nm when the substrate 2-furanacryloyl-l-phenylalanylglycylglycine (FAPGG) is enzymatically-converted to the product 2-furanacryloyl-l-phenylalanine (FAP). The assay was used to measure ACE activity in alligator serum. The optimal pH for this assay was 7, while the ionic strength-dependence was optimal at 25–50 mM NaCl. ACE enzyme activity requires zinc, and thus the assay was sensitive to the presence of EDTA. Inclusion of only 0.2 mM EDTA-inhibited ACE activity by more than 70%. The assay only required the use of only 10 μL of sample for measurable activity, and maximal activity was recorded using 60–65 μL of serum, making it ideal for use with small amounts of blood or tissue extract.     

Preparation,characterization and application of a novel thermal stable composite nanofiltration membrane

A thermal stable composite membrane was prepared by interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) on poly(phthalazinone ether amide) (PPEA) ultrafiltration membrane. The effect of reaction parameters on the performance of composite membranes was studied and optimized. The surface morphologies of the composite membrane and the substrate were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The rejection of optimized composite membrane for dyes Congo red (CGR) and Acid chrome blue K (ACBK), the molecular weight (MW) of which is over 400, was over 99.2%, with a flux at about 180 L m⁻² h⁻¹. While the rejection for NaCl was only 18.2% with a flux over 270 L m⁻² h⁻¹, when tested at 1.0 MPa 60 °C. The composite membrane was applied in the desalination-purification experiment of dye ACBK and NaCl mixed solution. The flux of the membrane increased obviously as the operation pressure and/or temperature increased, while the rejection for dye was constant and kept over 99.3%. The purification experiments were accomplished effectively at 1.0 MPa, 80 °C. Only after five rounds of desalination-concentration experiment, about 160 min, the salt mixed in dye solution was fully removed. The initial flux of the eighth cycle was about 254 L m⁻² h⁻¹, which was only 20 L m⁻² h⁻¹ lower than that of the first round. The rejection of the membrane was constant and kept over 99.3% through out the eight cycles of purification experiment.     

Potentiometric Study of the Effect of Sodium Dodecylsulfate and Dioxane on the Hydrolysis of the Aluminum(III) Ion

Hydrolytic equilibria of the aluminum(III) ion were studied in the presence of a surfactant, sodium n-dodecylsulfate (SDS) and, separately, in mixed water + dioxane and water + dioxane + surfactant media at 298.15 K, by using potentiometric measurements with a glass electrode. The concentration of SDS was between 1.25 and 25.0 mmol-dm⁻³, whereas the volume percent of dioxane was varied from 10 to 50. The supporting strong electrolyte was 0.1 mol-dm⁻³ LiCl. A general least-squares treatment of the data indicates the formation of mononuclear hydrolytic complexes of the form Al(OH)_m^{3 − m} (m = 1–3) at all studied compositions. At lower concentrations of SDS (≤ 12.5 mmol-dm⁻³) it was necessary to include polynuclear hydrolytic complexes in the hydrolytic model. On increasing the concentration of SDS, the formation of polynuclear complexes is suppressed, and at the SDS concentration of 25.0 mmol-dm⁻³, only Al(OH)²⁺ and Al(OH)₂⁺ are observed in solution. At lower volume percentages of dioxane, the speciation involved polynuclear complexes in addition to mononuclear complexes. At dioxane concentrations higher than 20 vol% only mononuclear complexes are formed. The simultaneous presence of the SDS and dioxane as ionic medium modifiers produces only the mononuclear complexes Al(OH)²⁺ and Al(OH)₂⁺, which have significantly higher stability constants than in the pure ionic medium.     

Studies on substituted phenols by differential pulse cathodic stripping voltammetry: 1. Pentachlorophenol

A study of chlorophenols using differential pulse cathodic stripping voltammetry (dpcsv) is reported. Of the wide range of chlorophenols investigated, only pentachlorophenol and 2,3,4,6-tetrachlorophenol yield stripping peaks.For pentachlorophenol in water, two peaks are obtained at stripping potentials of –1.2 V and –1.58 V versus SCE. In methanol, pentachlorophenol shows one peak with a stripping potential at –1.6 V versus SCE.In the case of 2,3,4,6-tetrachlorophenol in water, two peaks are observed at –1.06 V and –1.6 V versus SCE, while in methanol only one peak arises at a stripping potential of –1.6 V. A procedure was developed for the determination of pentachlorophenol in natural waters.     

Synthesis and some transformations of 2- and 2,2′-substituted bis(ethylenedioxy)biphenyls containing cyclopropane fragments

3,4: 3′,4′-Bis(ethylenedioxy)biphenyl undergoes bromination, nitration, and cyclopropylcarbonylation only at the 2-position. Analogous reactions with 2-substituted bis(ethylenedioxy)biphenyls occur regioselectively at the 2′-position. The reactions of 2-cyclopropylcarbonyl- and 2,2′-bis(cyclopropylcarbonyl)bis(ethylenedioxy)biphenyls with complex metal hydrides afforded the corresponding arylcyclopropylcarbinols which tended to undergo intramolecular alkylation of the aromatic ring with conservation of the cyclopropane fragment (monosubstituted derivatives) and formation of cyclopropyl-containing cyclic ethers (disubstituted ethylenedioxybiphenyls). The reduction of the nitro group in 2′-cyclopropylcarbonyl-2-nitro-4,5: 4′,5′-bis(ethylenedioxy)biphenyl was accompanied by intramolecular cyclization involving spatially close functional groups, the cyclopropane fragment remaining intact.