31,792 research outputs found

    Properties of PAN Fibers Solution Spun into a Chilled Coagulation Bath at High Solvent Compositions

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    In this work, multifilament, continuous polyacrylonitrile (PAN) fiber tow was solution spun mimicking industrial processing at the small pilot scale (0.5 k tow), while carefully altering the composition of the coagulation bath, in order to determine the effect on the resulting fiber shape, density, orientation, and tensile properties at varying points in the spinning process. Novel here are the abnormally high coagulation bath solvent compositions investigated, which surpass those often reported in the literature. In addition, the coagulation bath was maintained at a slightly chilled temperature, contrary to reported methods to produce round fibers. Further, by altering the composition of the bath in a step-wise fashion during a single spinning run, variations in all other process parameters were minimized. We found that with increasing solvent composition in the coagulation bath, the fibers not only became round in cross section, but also became smaller in diameter, which persisted down the spin line. With this decrease in diameter, all else equal, came an accompanying increase in apparent fiber density via a reduction in microvoid content. In addition, molecular orientation and tensile properties also increased. Therefore, it was found that inadequate understanding of the coagulation bath effects, and spinning at low coagulation bath solvent compositions, can hinder the ability of the fiber to reach optimum properties

    Effect of coagulation time, number of coagulation bath and ingredients on properties of continuous graphene oxide fibre

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    The effect of coagulation time, the number of coagulation bath and ingredients on the properties of continuous graphene oxide fibre has been analyzed. It is observed that the number of coagulation baths and coagulation time affect the fibre morphology, electrical conductivity, and tenacity of fibre. Also, addition of the ingredient (ethylenediamine) results in lower strength and highest fibre count together with darker, curly, and rough fibre structure. It can be suggested that among all the samples, the sample with 1 coagulation bath and 2 min coagulation time can be preferred if electrical conductivity is more important than fibre tenacity. However, if fibre tenacity is the issue, preference of the sample with 3 coagulation baths and 2 min coagulation time will be more convenient

    Diffusion of solvent from a cast cellulose acetate solution during the formation of skinned membranes

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    The transport of solvent out of a cast cellulose acetate (CA) solution into the coagulation bath during membrane formation is treated as a diffusion process. From the increase of solvent concentration in the bath with time (solvent leaching experiments) an overall solvent diffusion coefficient has been calculated. In size these coefficients compare well to mutual pseudo-binary solvent-non-solvent diffusion coefficients determined by means of a classical boundary broadening method applied to ternary solutions with fixed CA concentration, but with a gradient in solvent-nonsolvent composition. Since binary polymer-solvent interdiffusion coefficients are at least one order of magnitude lower, it is concluded that the diffusion of solvent into the coagulation bath is essentially a pseudo-binary solvent-non-solvent diffusion process. Combination of experimental results with model calculations for the effect of a thin dense skin on the diffusion of solvent out of the sublayer shows that the casting-leaching diffusion coefficient can be used to describe the out-diffusion of solvent from the layer under the skin provided that the relative skin resistance is not too high, or that the skin thickness is small

    Study on the Impact of Polymer Concentration and Coagulation Bath Temperature on the Porosity of Polyethylene Membranes Fabricated Via TIPS Method

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    Microporous high density polyethylene flat membranes were fabricated via thermally induced phase separation (TIPS) method. Effects of polymer concentration and coagulation bath temperature on the membrane morphology and porosity were investigated. To the best of our knowledge, there is no work about the order of magnitude and degree of importance of influential parameters and their interactions on the microstructure of fabricated membranes. The results showed that the porosity of membranes decreased as the polymer concentration increased. It was also shown that, due to the short contact time and rapid phase inversion between coagulation bath and membrane’s outer surfaces, bath temperature mainly affects on the outer surface porosity. The results obtained from analysis of variance (ANOVA) using 95% confidence interval on the membrane porosity revealed that the effect of polymer concentration is more important than coagulation bath temperature

    Preparation and Characterization of Polysulfone/Celullose Acetate (PSF/CA) Blend Membrane

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    Blend polysulfone (PSF)/cellulose acetate (CA) membranes have prepared by phase inversion method. In here, CA was prepared from bacterial cellulose by acetylation reaction. Various temperature of coagulation bath were used as variable to investigated water uptake, water flux, porosity and thermal properties of membranes. As comparison, the CA commercial (CCA) was also investigated with the same parameters. As the result, the functional group analysis by FTIR show that CA has successfully prepared from bacterial cellulose. The parameters include water uptake, water flux and porosity have the similar trend. The parameters increase with increasing of temperature of coagulation bath. The other hand, CCA membrane have similar trend to CA membranes for parameter of water water uptake, water flux and porosity. However, CCA membrane is higher than CA membranes for all parameters. Thermal analysis by Differential Scanning (DSC) showed that all blend membranes with different temperature of coagulation bath have single transition glass temperature (Tg) that indicated that molecular homogeneity. Keywords: blend membrane, phase inversion, coagulation bath, water flux, porosity

    Wet spinning of solid polyamic acid fibers

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    The invention is a process for the production of solid aromatic polyamic acid and polyimide fibers from a wet gel or coagulation bath wet gel using N,N-dimethylacetamide (DMAc) solutions of the polyamic acid derived from aromatic dianhydrides such as 3,3',4,4' benzophenonetetra carboxylic dianhydride (BTDA) and aromatic diamines such as 4,4'-oxydianiline (4,4'-ODA). By utilizing the relationship among coagulation medium and concentration, resin inherent viscosity, resin percent solids, filament diameter, and fiber void content, it is possible to make improved polyamic acid fibers. Solid polyimide fibers, obtained by the thermal cyclization of the polyamic acid precursor, have increased tensile properties compared to fibers containing macropores from the same resin system

    Microstructures in phase-inversion membranes. Part I. Formation of macrovoids

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    A new mechanism for the formation of macrovoids in phase-inversion membranes is proposed. It is based on the observed difference in type of demixing of a thin film of a polymer solution when immersed in a nonsolvent bath: delayed or instantaneous demixing. The explanation for macrovoid formation assumes local conditions of delayed demixing in front of a certain layer of nuclei already formed, due to a change in the interfacial compositions at the advancing coagulation front, as compared to the original composition at the interface film-bath. Effects of variations in membrane formation conditions which can be calculated using the model of diffusive mass transport in thin films of polymeric solutions in combination with phase separation in phase-inversion membranes, completely support the mechanism as proposed

    PRODUCTION AND CHARACTERIZATION OF ARAMID COPOLYMER FIBERS FOR USE IN CUT PROTECTION

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    High-performance fibers such as para-aramids are used extensively in gloves for cut protection. However, the inherent cut resistance of these fibers and the relationship between cut resistance and other material properties is not known. To better understand cut resistance at the material level, an experiment was conducted using a lab-scale wet spinning system to produce and characterize aramid copolymer fibers. To facilitate the use of lab-scale equipment, the experiment was conducted as a four-factor split-plot response surface design. The four treatment factors studied were solvent concentration in the coagulation bath, the amount of salt in the coagulation bath, the degree of stretching during coagulation, and the degree of stretching after coagulation. The cut resistance of the fibers was measured using a new cut testing device developed specifically for testing single-end yarns. Other physical properties as well as the morphology of the fibers were also investigated. The cut strength of the fibers was improved by stretching after coagulation but was influenced more by the conditions of coagulation. In this experiment the optimum conditions for maximizing cut resistance occurred at slow rates of coagulation with high concentrations of solvent and salt in the bath. The resulting fibers were nearly isotropic in mechanical performance and had a coarse granular morphology that transitioned into domains of macrofibrils inside the fibers after stretching. As the coagulation rate slowed, the cross-section of the fibers became increasingly round, which also improved the cut resistance of the fibers. The tensile properties of the fibers were not significantly affected by the coagulation conditions but were improved by increasing molecular orientation as a result of stretching after coagulation. The degree of molecular orientation in the experimental fibers was relatively low, which resulted in lower tensile strength but improved transverse properties over commercial aramid fibers. Despite having low tensile strength, the cut strength of the experimental aramid copolymer fibers is predicted to exceed that of commercial aramid fibers under optimized processing conditions

    Wet spinning of solid polyamic acid fibers

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    The invention is a process for the production of solid aromatic polyamic acid and polyimide fibers from a wet gel or coagulation bath wet gel using N,N-dimethylacetamide (DMAc) solution of the polyamic acid derived from aromatic dianhydrides such as 3,3',4,4'-benzo phenone tetracarboxylic dianhydride (BTDA) and aromatic diamines such as 4,4'oxydianiline (4,4'-ODA). By utilizing the interrelationship between coagulation medium and concentration, resin inherent viscosity, resin percent solids, filament diameter, and fiber void content, it is possible to make improved polyamic acid fibers. Solid polyimide fibers, obtained by the thermal cyclization of the polyamic acid precursor, have increased tensile properties compared to fibers containing macropores from the same resin system

    Integrally skinned polysulfone hollow fiber membranes for pervaporation

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    From polysulfone as polymer, integrally skinned hollow fiber membranes with a defect-free top layer have been spun. The spinning process described here differs from the traditional dry-wet spinning process where the fiber enters the coagulation bath after passing a certain air gap. In the present process, a specially designed tripple orifice spinneret has been used that allows spinning without contact with the air. This spinneret makes it possible to use two different nonsolvents subsequently. During the contact time with the first nonsolvent, the polymer concentration in the top layer is enhanced, after which the second coagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers of ± 1 m have been obtained, supported by a porous sublayer. The effect of spinning parameters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and pervaporation experiments, using a mixture of 80 wt % acetic acid and 20 wt % water at a temperature of 70°C. Higher fluxes as a result of a lower resistance in the substructure could be obtained by adding glycerol to the spinning dope, by decreasing the polymer concentration, and by adding a certain amount of solvent to the bore liquid. Other parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent
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