Creep/recovery behavior of open-cell foams

Static measurements have been used to predict the dynamic response of ldquo;unboundedrdquo; open-cell noninked (dry) and inked foam materials. Creep, e_c(t), and recovery, e_r(t), were determined in compression from static and dynamic modes. Force measurements, f(t), and strain decay, e(t), were used to determine the change in creep, δe_c(t). The change in creep represents the plastic strain, e_p1(t=t_h), and is uniquely defined by the recovery function, e_r(t=t_h), where t_h is the hold time. Creep and recovery results of various classes of foam materials and nonfoam materials were found to fit a master curve of the form F_r(t) =exp[–k′_r(t_h)t] = [e_r(t) - e₀₀( t_h)]/[e₀ (t = 0) - e₀₀(t_h)] at a reduced time of k′_r(t_h) t [k′_r(t_h)] C₀/(t_h)^a (where Co depends on the material's “dry” or “wet” state), a is a function of the type of material, and em is the permanent set]. These empirical results are applicable to printing ink transfer and print quality. Other important factors of concern are diffusion processes within the polymer matrix and the nature of the polymer (e. g., chemical constitution, porosity, molecular weight, and solubility). © 1995 John Wiley & Sons, Inc.     

Direct Observation of Triplet Reactions of Anthraquinone Vat Dyes Using Nanosecond Laser Photolysis

The triplet-triplet spectra of three commercial anthraquinone vat dyes (C.I. 67300, C.I. 59100 and C.I. 60515) were studied in solution at room temperature using laser photolysis. The triplet states of these dyes react with oxygen, and the rate constants for the quenching process were measured, together with the rates of energy transfer from the triplet state to anthracene. These observations are considered in relation to the photoreactivity of these dyes.     

AMMONIA CATALYZED ORGANOSOLV DELIGNIFICATION OF POPLAR

A parametric investigation of NH₄OH catalyzed solvent delignification of poplar was conducted to define pretreatment conditions which would yield an optimal separation of the biomass components and an enzymatic susceptible solid carbohydrate phase. Delignification parameters of interest included concentration of NH₄OH, time and temperature of the reaction, and type of solvent. The addition of 0.82 M NH₄OH to the delignification liquor increased lignin removal and decreased carbohydrate degradation, but increasing NH₄OH concentration had no additional effect. At lower reaction temperatures, the extent of delignification increased with reaction time; at higher temperatures, a “relignification” of the pretreated wood was observed. The delignification and hemicellulose solubilization were modelled and rate constants reported. No major difference between three potential pulping solvents—ethanol, butanol, phenol—was observed. The enzymatic susceptibility of pretreated wood samples was approximately 6-fold greater than that of the untreated poplar. UV absorbance was used to qualitatively characterize the soiubilized lignins.     

Catalyst surface at a fractal of cost—a quest for optimal catalyst loading

Intuition tells us that any decrease in the catalytically active surface area should result in an equivalent decrease in the reaction yield and efficiency. Our findings counter this by showing that the active surface and hence the catalyst loading can be reduced drastically in the diffusion-limited heterogeneous reaction systems, while the conversion rate remains essentially unchanged by using fractals for spatial distribution of the catalyst load. The results of this study provide an unusual circumstance for optimal design of chemically active surfaces and can be used to drastically reduce cost of heterogeneous chemical and biological reactors, sensors, and electrodes of fuel cells. The proposed approach can be exploited to its fullest extent in chemical microsystems by utilizing the latest advances in our abilities to manipulate matter on the micro/nano scale.     

MICROSCOPIC SPREADING CHARACTERISTICS OF NONPOLAR PERFLUOROPOLYETHER FILMS

The surface diffusion characteristics of nonpolar perfluoropolyether (PFPE) Z on carbon surfaces are investigated in two regimes, submonolayer and multilayer, for nano-thin films. For the submonolayer regime, the two-dimensional, cubic van der Waals equation of state is applied to determine the dependence of the surface diffusion coefficient on the film thickness, as experimental surface diffusion coefficients increase with increasing film thickness. For the multilayer regime, a conventional fluid mechanics analysis with position dependent viscosity and a van der Waals disjoining pressure gradient is applied to investigate the surface diffusion characteristics. The present theoretical analysis qualitatively agrees with the experimental results.     

Lipase PS-catalyzed transesterification of citronellyl butyrate and geranyl caproate: Effect of reaction parameters

Pseudomonas sp. lipase PS was immobilized by adsorption and tested for its ability to catalyze the synthesis of citronellyl butyrate and geranyl caproate by transesterification in n-hexane. The reaction parameters investigated were: enzyme load, effect of substrate concentration, added water, temperature, time course, organic solvent, pH memory, and enzyme reuse. Yields as high as 96 and 99% were obtained for citronellyl butyrate and geranyl caproate, respectively, with 300 units (approx. 15% w/w of reactants) of lipase PS. Increasing amounts of terpene alcohol inhibited lipase activity, while excess acyl donor (triacylglycerol) concentration enhanced ester production. Optimal yields were obtained at temperatures from 30–50°C after 24-h incubation time. Yields of 90 and 99% were obtained for citronellyl and geranyl esters, respectively, with 2% added water. Solvents with log P values ≥ 2.5 showed the highest conversion yields. pH 7 and 6–8 seemed to be ideal for citronellyl butyrate and geraniol caproate, respectively. The lipase remained active after reusing 12 times.     

Accessibility of man-made cellulosic fibres. Part 2: Examination of the exhaustion profiles of a series of reactive dyes on never-dried and dried lyocell, viscose and modal fibres in the presence of varying electrolyte concentrations

Reactive dyes exhibit a higher level of initial exhaustion, in the presence of small concentrations of electrolyte, on never-dried lyocell than on never-dried viscose and modal. This difference is particularly noticeable in the case of high substantivity bis-monochloro- s -triazinyl reactive dyes, which exhibit the same differentiated performance on the corresponding dried fibres. Low salt quantities (comparable to those used for applying direct dyes to cellulosic substrates) can therefore be used for applying high substantivity dyes and effect chemicals by an exhaustion process to both never-dried and dried lyocell substrates.     

Factors influencing the photofading of commercial anthraquinone dyes in solution

The photofading of two anthraquinone dyes has been studied in aqueous solution using ultraviolet-visible absorption spectroscopy and flash photolysis. The influence of alcohol concentration, pH, atmosphere, photosensitisers and stabilisers have been examined and these lead to some important conclusions on the mechanism of dye fading. Essentially, the results indicate the photoexcited triplet state of the dye undergoes a process of either electron or hydrogen-atom abstraction depending on the nature of the environment. Other factors such as aggregation and singlet oxygen also appear to play an important role in solution photofading. The relevance of these results to photofading in a polymeric phase is discussed.     

Protection of lyocell fibres against fibrillation; Mode of action of the cross-linking agent 2,4-dichloro-6-(β-sulphatoethylsulphonyl)anilino-s-triazine

2,4-Dichloro-6-(β-sulphatoethylsulphonyl)anilino- s -triazine is used as a cross-linking agent to improve the wet abrasion resistance of Lyocell fibres. The agent, which exhibits poor water solubility, is sold as an aqueous dispersion. During application to Lyocell in the presence of alkali, the agent enters a solution phase before reacting with the fibres. High pressure liquid chromatography analysis and solution studies support the view that the two electrophilic species taking part in the cross-linking reaction are vinylsulphone plus one of the chlorine atoms of the dichlorotriazine residue and that preliminary hydrolysis of one of the chlorine atoms is not the cause of the observed solubility changes.     

Beneficial Effects of Rhenium Additions on the Cyclic-Oxidation Resistance of β-NiAl + α-Cr Alloys

This study reports the effects of up to 4 at.%rhenium addition on the cyclicoxidation behavior of-NiAl + -Cr alloys having a basecomposition (in at.%) Ni-40Al-17Cr. Tests were conductedin still air at 1100°C for up to 250 1-hr cycles.The ternary alloy (without rhenium addition) exhibitedpoor cyclic-oxidation resistance, undergoing extensivescale spallation and internal oxidation. Additions of rhenium considerably improved the oxidationbehavior, reducing the extent of both scale spallationand internal oxidation. These beneficial effectsincreased with increasing rhenium content. Rhenium additions improved cyclic-oxidation resistanceby both decreasing the solubility of chromium in the phase and causing the interdendritic -Crprecipitates in the alloy microstructure to become more spheroidized and disconnected. Theseeffects aided in preventing both interdendritic attackand the dissolution of the -Cr precipitates fromthe subsurface region of the alloy. The maintenance of -Cr precipitates at the alloy-scaleinterface decreased the extent of scale spallation byproviding a lower coefficient of thermal-expansion (CTE)mismatch between the alloy and theAl₂O₃-rich scale.