摘要:

AbstractThe reverse osmosis separation of toluene from water has been studied using an asymmetric cellulose acetate membrane at different temperatures, pressures, and feed concentrations. The finely porous transport model is used to describe the performance of the membrane as a function of the operating conditions. Based on experimental data, the transport parameters for the membrane are estimated. These parameters include the pore size of the membrane, the frictional parameter for the solute in the membrane pore, the relative porosity of the membrane surface, and the partition coefficients on the high and low pressure sides of the membrane. The influence of operating temperature on some of these parameters is presented and discussed. A modified form of the finely porous model which includes the effect of temperature is presented.

ISSN:0021-8995    

DOI:10.1002/app.1988.070350501

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

年代:1988

数据来源: WILEY

摘要:

AbstractPolyimide was pyrolyzed in an argon atmosphere at various temperatures, and thermally converted to amorphous carbon films. The irreversible change of polyimide under progressive heat treatment is characterized by three successive structural changes: pyrolysis, carbonization, and graphitization. X‐ray photoelectron spectroscopy (XPS) studies show that the polyimide starts to dissociate at pyrolysis temperatures above 500°C. At temperatures higher than 650°C most functional groups of polyimide decompose to evolve gases from the sample. The polyimide then gradually becomes more carbon rich. It is believed that at pyrolysis temperature higher than 650°C the polyimide starts to form heterocyclic structures with residual oxygen and nitrogen incorporated into the heterocyclic carbon rings. X‐ray analyses indicate that the polyimide at pyrolysis temperatures less than 1000°C is amorphous carbon and no long‐term periodic structure can be detected. At pyrolysis temperatures higher than 2000°C, the polyimide is converted to microcrystallin

ISSN:0021-8995    

DOI:10.1002/app.1988.070350502

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe long‐term behavior of high density polyethylene (HDPE) and poly(vinyl chloride) (PVC) under static mechanical load is investigated. The long‐term behavior is determined as a function of stress and temperature. The applicability of the equation proposed by the authors which describes the dependence between the time‐dependent failure, stress, and temperature of the two polymers is examined. The equation, derived on theoretical considerations, represents a modification of the Arrhenius equation for the chemical reaction rate. It is found that there is a complete agreement between the experimentally determined long‐term behavior of PVC and HDPE and that calculated by the equation over the whole examined range of temperatures and stresses, with the exception of narrow intervals for HDPE where an intensive plastic deformation is de

ISSN:0021-8995    

DOI:10.1002/app.1988.070350503

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe grafting of acrylamide onto guar gum in aqueous medium initiated by KMnO4/oxalic acid redox system has been studied gravimetrically at the temperature 35 ± 0.2°C. The effect of redox components, acrylamide concentration and quantity of guar gum has been studied in terms of percentage and efficiency of grafting. A plausible mechanism of grafting and a suitable rate expression has been suggested. The rate of grafting was found to increase with increase in temperature and concentrations of redox components and acrylamide, but, at high concentration of guar gum, the rate was found to decreas

ISSN:0021-8995    

DOI:10.1002/app.1988.070350504

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

年代:1988

数据来源: WILEY

摘要:

AbstractIn recent years polymers have been utilized as binding sites for transition metal catalysts (e.g. crosslinked polystyrene beads). However, general problems exist with the above system. The rate of reaction depends on the presence of solvents that adequately swell the polystyrene bead in order to allow access to the catalyst sites. Differences in polarity and reactant size can inhibit diffusion into the bead. Recently a new system has been developed where the catalyst is bound to polyethylene single crystal surfaces, this has solved the above problems. However, polyethylene single crystals are small and plate‐like causing a new problem, when trying to filter the separate product the crystals cause clogging of the filtering system and limit the reactions to batch process. This paper describes the use of fine microporous polyethylene hollow fibers as the supporting polymer. This gives the advantages of the single crystal support, plus allows for the use of a fixed‐bed flow reaction sys

ISSN:0021-8995    

DOI:10.1002/app.1988.070350505

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

年代:1988

数据来源: WILEY

摘要:

AbstractMembranes consisting of ionically crosslinked polyacrylic acid (PAA) and Nylon 6 were prepared and tested for the pervaporation separation of acetic acid‐water mixtures. The polyacrylic acid (PAA) membranes were crosslinked in aluminum nitrate aqueous solution while the polyacrylic acid (PAA)‐Nylon 6 blends were cast from homogeneous PAA‐Nylon 6 mixtures to appropriate thicknesses and then crosslinked in aqueous aluminum nitrate solutions. Optimum pervaporation results were obtained from blends of Nylon 6 and PAA in the weight ratio of 60–75 wt% Nylon 6 and 25–40 wt% PAA which have separation factors (water/acetic acid) of over 60 and flux rates higher than 100 g/m2h at 15°C for the separation of acetic acid‐water mixtures. The flux rates and separation factors could be altered by changing the blend composition of the membrane. The effects of the feed composition on the separation factors were

ISSN:0021-8995    

DOI:10.1002/app.1988.070350506

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

年代:1988

数据来源: WILEY

摘要:

AbstractTwo types of semiflexible mesogenic random copolyesters which contained both nematic and smectic type repeating units within the main chain were prepared and the thermal properties as well as the mesomorphic structures were characterized by differential scanning calorimetry and by polarizing microscope. The first type of copolymer (copolymer I) contained two repeating units which differed in the rigid mesogenic groups and the second (copolymer II) contained repeating units which differed in the length of flexible segment. Copolymerization disrupted the structural regularity of the crystal, lowered the crystal–mesophase transition temperature, and destabilized the molecular order of the smectic phase. These effects were more pronounced for copolymer II. However, the isotropization temperature was changed only slightly with the incorporation of the other mesogenic component. The crystal melting temperatures of both copolymers exhibited a eutectic behavior. A smectic to nematic transition, which was not observed for the homopolymers, occurred in the range of 0.4‐0.6 mole fractions of the smectic units for copolymer I and 0.5–0.85 for copolymer II. The molecular order of the nematic phase was slightly increased as the smectic units were incorporated, while those of the smectic phase became more disordered upon addition of the nematic

ISSN:0021-8995    

DOI:10.1002/app.1988.070350507

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

年代:1988

数据来源: WILEY

摘要:

AbstractFifteen different pure polymers were studied by thermal methods under air, nitrogen, and nitrous oxide in order to determine their tendency to char in relation with their structure and the experimental conditions used. Styrene polymers and aliphatic polyolefines give chars under air and total volatilization without carbonization under nitrogen and nitrous oxide, showing the essential part played by oxygen in the charring process. On the opposite, ambient oxygen has some effect on the carbonization of polymers containing aromatic rings in their main chain. A schematic mechanism of the charring process is discussed in which condensed phase oxidation, formation of olefinic bonds and crosslinking, dehydrogenation–aromatization are postulate

ISSN:0021-8995    

DOI:10.1002/app.1988.070350508

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

年代:1988

数据来源: WILEY

摘要:

AbstractPhotochemical degradation of natural rubber yielded hydroxyl‐terminated liquid natural rubber (HTNR) when carried out in solution in presence of H2O2. Ultraviolet radiation from a medium pressure mercury vapor lamp and sunlight were found to be almost equally effective in bringing about the depolymerization and hydroxylation of natural rubber. The variations in the composition of the reagents and exposure time on the extent of depolymerization was conducted, and a suitable procedure for the large scale preparation of HTNR was described. A probable mechanism leading to the formation of HTNR as well as the side products is discussed based on the analytical dat

ISSN:0021-8995    

DOI:10.1002/app.1988.070350509

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe kinetics of grafting of acrylic acid onto poly(ethylene terephthalate) fabrics initiated by benzoyl peroxide has been studied. Extent of grafting depended upon time, concentration of the initiator and the monomer, as well as the presence of the activator used. From the temperature dependence of the initial rate of grafting the overall activation energy for grafting was found to be 90 kJ/mol. The results of the monomer and temperature dependence found in this study are consistent with the rate expression derived from a normal kinetic scheme for grafting.

ISSN:0021-8995    

DOI:10.1002/app.1988.070350510

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

年代:1988

数据来源: WILEY