Wiley
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Investigation into the rheological properties of PES/NMP/nonsolvent membrane‐forming systems Abstract From the perspective of a polymer solution, the rheological properties of the popular polyethersulfone (PES)/N ‐methyl‐2‐pyrrolidone (NMP)/nonsolvent (NS) membrane‐forming system were investigated thoroughly with a controlled stress rheometer (HAAKE RS75, Germany). The scope of the study included measurements of the controlled‐stress flow curve, creep recovery, and dynamic oscillation. H2 O, 1‐butanol, ethylene glycol, and diethylene glycol were used as NS additives. The effects of the polymer concentration and the quality of the solvent mixture, as characterized by the approaching ratio, on the rheological behavior of the dopes were studied. Up to 38 wt % PES and extremely adjacent to the phase separation (i.e., the approaching ratio of the dope was 0.95), the viscous property dominated all the dopes, which behaved as Newtonian fluids. Moreover, all the membrane‐forming dopes investigated were in the crossover regime in the semidilute region, in which the chains were overlapping but unentangled. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 283–291, 2001
Wiley - Tập 82 Số 2 - Trang 283-291 - 2001
Low dose γ‐irradiation of some fluoropolymers: Effect of polymer chemical structure Abstract The effect of low dose (1–20 Mrad) γ‐irradiation on five fluoropolymers (PVF, PVDF, ETFE, FEP, PFA), differing in fluorine content and chain structure, was studied. The radiation effect, reflected by changes in thermal and mechanical properties, as well as NaOH etched surface morphology, was investigated. The main chain structure was found to predominate the irradiated polymers' behavior. The tensile strength of PVF and its resistance to etching increased with radiation dose, while its degree of crystallinity and melting temperature decreased. These changes were correlated with network formation by irradiation and by the incorporation of crosslinked segments into the crystalline phase during recrystallization. Solvent extraction of PVDF (no solvents were found for the other fluoropolymers) revealed increased gel formation with increasing dose. The degree of crystallinity and the tensile strength dependence on radiation dose for PVDF and ETFE reflected the competition between crosslinking and chain scission events. FEP and PFA undergo predominantly chain scission accompanied by reduction of their mechanical properties. PFA even exhibited an increase in both its melting temperature and degree of crystallinity, stemming from a massive degradation process forming shorter chains. Chemical mechanisms are discussed in an attempt to correlate the irradiation effects with the polymers' chain structure.
Wiley - Tập 45 Số 5 - Trang 783-795 - 1992
Water‐ethanol separation by pervaporation through plasma graft polymerized membranes Abstract Water‐ethanol permselective membranes were prepared through plasma graft polymerization of acrylic acid, methacrylic acid, and acrylamide onto porous polypropylene film. In these membranes, the functions of permseparation and mechanical properties are shared respectively to the graft polymer layer and the substrate film. Higher permselectivity of water is achieved with the ionization of the acrylic acid and the methacrylic acid‐grafted membranes. Permselectivity is dependent on the degree of grafting, and it is necessary to fill the pores of substrate film with graft polymers. Permseparation of water was investigated with respect to the feed ethanol concentration and also to the temperature dependence.
Wiley - Tập 34 Số 3 - Trang 1159-1172 - 1987
Flow properties of various irradiated resins of PTFE (teflon) Abstract Changes in the melt viscosity of PTFE exposed to various radiation doses in air were measured using a capillary rheometer. The melt viscosity decreases dramatically after exposure to 2.5 MRad, but between 2.5 and 5 MRad there is an increase in viscosity which is attributed to the formation of branches and crosslinks. Above 5 MRad, the melt viscosity decreases with dose. Plots of log apparent melt viscosity vs. log apparent shear rate are given for PTFE exposed to various radiation doses. The data in each of these plots can be fit by a straight line (power law), and changes in the slopes of these lines are interpreted to indicate changes in the molecular weight distribution. It is postulated that the observed decrease in the slopes of these lines after irradiation is caused by a narrowing of the molecular weight distribution because of the decrease in the number of molecules at the high molecular weight end of the distribution. The melt viscosity of a PTFE sample irradiated to a given dose was less for a sample of low preirradiation crystallinity than for an otherwise identical sample of higher crystallinity. This crystallinity dependence of viscosity is related to differences in oxygen diffusion properties of crystalline and amorphous PTFE.
Wiley - Tập 27 Số 10 - Trang 3769-3786 - 1982
Proton exchange membranes by radiation grafting of styrene onto fep films. III. Structural investigation Abstract Structural investigation on proton‐exchange membranes, obtained by the radiation grafting of styrene onto FEP films and subsequent sulfonation, was carried out by differential scanning calorimetry. The membrane crystallinity was found to show a decreasing trend with increasing degree of grafting. The melting temperature of all the membranes also showed a slight decrease as compared to the ungrafted FEP. The results have been explained in terms of the cumulative effect of the decrease in the crystalline/amorphous ratio by the incorporation of amorphous polystyrene grafts and of disruption of spherulitic crystallites of the FEP component in the membranes. The glass transition temperature of the membranes with different water contents was also evaluated. A correlation of the glass transition temperature with the residual water in dried membranes was established. © 1994 John Wiley & Sons, Inc.
Wiley - Tập 54 Số 4 - Trang 469-476 - 1994
Some effects of ionizing radiation on tetrafluoroethylene copolymers
Wiley - Tập 29 Số 4 - Trang 1335-1344 - 1984
LbL‐coated microcapsules as systems for encapsulation of optical brightening agent Abstract We report the encapsulation of optical brightening agent (OBA) into hollow microcapsules prepared by the controlled Layer‐ by‐Layer (LbL) self‐assembly process, achieved by the sequential adsorption of oppositely charged polyelectrolytes using negatively charged silica template. Loading takes place by spontaneous deposition method which was proved by confocal laser scanning microscopy (CLSM) using rhodamine 6G (Rd6G) as a fluorescent probe. The loading of the OBA into the microcapsules was found to be dependent on the feeding concentration, pH of the medium, and loading temperature. The encapsulation efficiency of OBA decreased on increasing feeding concentration. Maximum loading was observed at pH 4 and amount of OBA loaded decreased with increase in pH. The loaded OBA was released in a sustained manner for 8 h. No degradation of the OBA was observed during the process of encapsulation and release. Polyelectrolyte capsules potentially offer an innovative way of encapsulating large amounts of active materials for a variety of applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Wiley - Tập 127 Số 3 - Trang 1609-1614 - 2013
Simultaneous diffusion of benzyl alcohol into plasticized poly(vinyl chloride) and of plasticizer from polymer into liquid Abstract The diffusion of benzyl alcohol and plasticizer in compression‐molded sheets of plasticized poly(vinyl chloride) was studied over the temperature range 30–55°C. A simultaneous diffusion occurred for benzyl alcohol into polymer and for dioctyl phthalate as plasticizer from polymer into liquid when the polymer was soaked in benzyl alcohol. The concentration of benzyl alcohol in polymer increased, rose to a maximum, and then decreased. Diffusion coefficients were measured by considering a nonsteady‐state phenomenon for plasticizer concentration of 25, 38, and 50 wt %, both for dioctyl phthalate and benzyl alcohol. Plasticizer concentration and temperature were found to play an important role.
Wiley - Tập 26 Số 7 - Trang 2315-2324 - 1981
Plasticizer transfer from plasticized PVC into ethanol–water mixtures Abstract The transfer of plasticizer from compression‐molded sheets of plasticized poly(vinyl chloride) into ethanol–water mixtures was studied over the temperature range of 30–55°C. A simultaneous diffusion occurred for ethanol and water into polymer and for dioctylphthalate plasticizer from polymer into liquid. The concentration of ethanol transferred into the polymer was found to increase, rise to a maximum, and then decrease. Equations of diffusion in unsteady state were found to correlate well with experiments on plasticizer transfer, over the plasticizer concentration range of 25–50 wt %. Stirring, temperature, water concentration in ethanolic solutions, and plasticizer concentration were found to play important roles.
Wiley - Tập 27 Số 10 - Trang 3945-3955 - 1982
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