摘要:

AbstractThis study reports on the use of static secondary ion mass spectroscopy (SSIMS) to chemically characterize complex methacrylate copolymers used in the pharmaceutical industry for controlled drug delivery. Ions diagnostic of the component monomer residues were detected, which could be interpreted using a fragmentation model for alkylmethacrylate homopolymers proposed previously. This model is extended to include the SSIMS analysis of nitrogen‐containing methacrylate copolymer residue

ISSN:0021-8995    

DOI:10.1002/app.1990.070390901

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractCellulase enzymes produced by the microorganismsAspergillus nigerandTrichoderma viridehave been immobilized on Ponilex type ion exchangers, both by ionic and by covalent bonding. Immobilization efficiency has been determined for enzyme preparations obtained, by their activity, as well as by that of the resulted effluent, on using as substrate carboxymethyl cellulose, cellobiose, and filter paper. The catalytic activity of the immobilized products has been tested against solutions of carboxymethyl cellulose and a series of hemicellulose containing alkaline extracts resulted from the alkaline pretreatments of some vegetal materials. The presence of polyphenol compounds in the latter ones determines a series of peculiarities in the behavior of the enzyme preparations, such as the transformation of the hydrolysis products and reduction of thecatalytic activity of the enzyme, after a certain period of reaction.

ISSN:0021-8995    

DOI:10.1002/app.1990.070390902

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper presents the results of a systematic study of the effect of different additives on the degradation of acrylamide–acrylic acid copolymers at high temperature. Under conditions of current applications in enhanced oil recovery (without oxygen and in the presence of ferrous ions), the effects of sodium azide, sequestrant DTPA, and isobutanol have been separately tested. It is shown that DTPA enhances degradation when ferrous ions are present. A new process of stabilization which may be efficient in most of the conditions is propose

ISSN:0021-8995    

DOI:10.1002/app.1990.070390903

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractEquilibrium constants (nK) for the binding of Chrysophenine G by methyl cellulose (MC) and poly(vinyl alcohol) (PVA) were determined spectrophotometrically in the temperature range 15–40°C. The polymer chains of PVA extended by the dye binding but those of MC shrank slightly. The enthalpy change and the entropy change for the binding by MC were negative and positive, respectively, whereas those for the binding by PVA were both negative. When the dye was bound to the extended polymer chains, the contribution of the entropy term to the binding increased. The rate of the dye bindings was studied by means of the temperature jump method. For the dye binding to PVA, the whole relaxation process finished in a very rapid step. On the other hand, for dye binding to MC, the initial rapid step was followed by two successive slower steps; the relaxation times for the slower steps were independent of the polymer concentration. The results were interpreted in terms of the stiffness of polymer chain of MC; the conformational change of the stiff chains to accommodate the dye in stable states seems to be the rate determining step in each slow relaxati

ISSN:0021-8995    

DOI:10.1002/app.1990.070390904

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA polycarbonate (PC)/carbon fiber (CF) composite system has been examined with regard to interfacial adsorption and crystallization by altering times and temperatures of annealing. Times up to 180 min and temperatures of 245, 275, and 300°C have been investigated. Tranverse tensile, tranverse toughness, and scanning electron microscopy results on unidirectional, continuous‐fiber composites indicate improved fiber/matrix adhesion at longer times and higher temperatures of annealing. Improvements in transverse toughness and transverse tensile strength of a factor of two is achieved. The data indicate that primarily adsorption rather than secondary interfacial crystallization is the likely mechanism for increased adhension. Isothermal transverse toughness values have been found to fit well to a Langmuir‐type expression. The temperature dependence of adsorption as measured by transverse toughness is described well by an Arrhenius equation. The dependence of transverse toughness on PC molecular weights fromMw= 26,600 to 39,800 was found to be large, with higher molecular weights adsorbing more effecti

ISSN:0021-8995    

DOI:10.1002/app.1990.070390905

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA method based on diffuse reflection Fourier transform infrared (FT‐IR) spectroscopy has been developed for determining the state of crystallinity in composite materials made from poly(phenylene sulfide) (PPS) reinforced with carbon fibers. Using this technique, good‐quality spectra can be obtained directly from the surface of prepreg or molded composite; thus the method is rapid and nondestructive. Several peaks in the spectrum are sensitive to the crystallinity and can be used for quantitative characterization purposes. The recommended indicator is the ratio of the heights of the peaks at 1075 and 1093 cm−1. Using a range of samples of varying crystallinity prepared by annealing amorphous prepreg, it has been shown that there is a very good correlation between this ratio and the enthalpy of crystallization as determined by differential scanning calorimetry. The effects of such annealing, as well as heating in air at high temperatures, have been investi

ISSN:0021-8995    

DOI:10.1002/app.1990.070390906

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA heat‐resistant rubber blend of natural rubber NR and styrene butadiene rubber (SBR‐1502) was prepared according to the standard techniques. The rubber blend was loaded with different concentrations of LAMP black and general purpose furnace (GPF) black for obtaining conductive rubber composites. The obtained vulcanizates were subjected to electrical conductivity measurements over a wide range of temperature and electric field. It was found that all samples showed negative values of temperature coefficient of conductivity (TCC). The temperature developed inside the samples by the Joule heating effect was recorded as a function of time (T–t) at different values of the initial applied DC‐electric power. TheT–tdependence was found to obey an exponentially growing function with a time constant (τ), which was found to be dependent on the concentrations as well as the type of carbon black and the value of the initial applied power. The current–voltage characteristics of the samples showed a negative resistance behavior after a characteristic voltage (V*). It was noticed thatV*decreases as the carbon black concentrati

ISSN:0021-8995    

DOI:10.1002/app.1990.070390907

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe structure of the effective separating layer of an asymmetric polysulfone hollow fiber membrane with a graded density skin was studied by SEM, TEM, and osmium tetroxide vapor adsorption and compared to that of a bilayer asymmetric hollow fiber membrane prepared from a solvent/nonsolvent mixture. The studies revealed the presence of micropores which transverse the effective separating layer of the membrane with graded density skin. The structural units which constituted the effective separating layer of this membrane are less tightly packed and distorted than are the entities forming the effective separating layer of its congener prepared from the traditional solvent/nonsolvent mixture. These results indicate that the enhanced free volume in an asymmetric hollow fiber membrane with a graded density skin exists in the effective separating layer as well as in the membrane interior.

ISSN:0021-8995    

DOI:10.1002/app.1990.070390908

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractEnergy‐absorbing simultaneous interpenetrating networks (SINs) based in polyether‐type polyurethanes (PUs) and poly(methyl methacrylate) (PMMA) networks were prepared by a prepolymer procedure. The products are translucent and appear to have single and broad glass transitions, suggesting some degree of phase separation. The percent energy absorption determined from dynamic properties and pendulum impact tests, the resistance to fatigue crack growth and fracture toughness (K1c) all increase with polyurethane content. The fracture behavior changes from brittle to ductile failure with increasing PU. The fatigue fracture surfaces of the SINs show extensive stress whitening associated with cavitation around the polyurethane domains, and localized shear deformation rather than craz

ISSN:0021-8995    

DOI:10.1002/app.1990.070390909

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractOxygen plasma ablation has been used to define the structure of polysulfone hollow fiber membranes spun from Lewis acid:base complex solvents in which the molar ratio of propionic acid toN‐methylpyrrolidone was varied. It was found that the helium/nitrogen separation factor of the unetched samples increases with increasing PA/NMP molar ratios. This increase implies a decrease in surface porosity of the resultant hollow fiber as larger fractions of the total NMP in the solvent are complexed with propionic acid. The results also suggest that the differences between the outer separating layer and the supporting matrix increase with increases in the PA/NMP molar ratios. Therefore, a more rapid transition from the separating layer to the porous supporting matrix exists in hollow fiber membranes spun from the higher PA/NMP ratio

ISSN:0021-8995    

DOI:10.1002/app.1990.070390910

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY