Summary: Cellulose/N‐methylmorpholine‐N‐oxide monohydrate (NMMO) spinning solutions were modified with surface‐active additives to yield Lyocell fibers with functional properties. Based on cellulose fibers, a new class of materials with tailored adsorption characteristics are produced. Activated charcoal and carbon black used as additives significantly affect the thermostability of the spinning solutions. Considering the degree of filling three general tendencies become evident. It is most obvious that the onset temperature of dope decomposition is shifted towards lower values accompanied by viscosity reduction after annealing at elevated temperatures and an enhanced formation of degradations products. Morpholine, N‐methylmorpholine and formaldehyde as the main degradation products were detected in aqueous distillates by means of HPLC. To study the rate of by‐product formation during preparation of the solution kinetic measurements were carried out. Thermal instabilities are not only initiated by heavy metal ions, especially Fe(II), but also by the particle size and porosity of the charcoal. The nano‐scaled carbon black used causes autocatalytic reactions as revealed by calorimetric measurements.
Relationships between amount of Acc versus onset temperature (Ton) and concentration of N‐methylmorpholine. 相似文献
The thermal behavior of cellulose dissolved in ionic liquids was studied in comparison to NMMO solutions. The cellulose solutions were characterized by reaction calorimetry and UV‐vis spectroscopy. Generation of chromophoric substances in cellulose/IL solutions is minimized by exposing to temperatures of above 100 °C for longer time periods. Dynamic calorimetric investigations revealed first thermal activities above 180 °C applying EMIMac and above 200 °C for BMIMCl and five other ILs tested. Moreover, even in the case of modified cellulose/IL solutions, e.g., activated charcoal, only a slight decline of onset temperatures was registered compared to modified cellulose/NMMO solutions.
Abstract This paper investigates the ultrafiltration of albumin-ethanol solutions on ZrO2 mineral membranes for the preparation of human albumin from plasma. The classical process consists of a preconcentration phase of a 20% ethanol-albumin 7.5 g/L solution to raise albumin concentration to 80 g/L, then a diafiltration to reduce ethanol concentration to less than 0.3 g/L, and a final concentration to adjust albumin concentration to its final value of 210 g/L. The potential advantages of mineral membranes relative to the polysulfone membranes presently used are a longer membrane life and higher permeate fluxes in the presence of ethanol. In addition, they lend themselves to the use of back flushing or pulsatile flows for reducing membrane fouling. Using 2.7 mm i.d. Carbosep membranes with a 10 kd cut-off and velocities of 7 m/s, permeate fluxes of 40 L/hμm2 at 4[ddot]C were obtained with 50 g/L albumin, 20% ethanol solutions representative of the preconcentration phase, while 45 to 50 L/hμm2 were obtained at albumin concentrations of 100 g/L without ethanol at 8[ddot]C, representative of the final concentration phase. These fluxes compare favorably with fluxes obtained previously in our laboratory with polysulfone membranes which were respectively of 22 and 40 L/hμm2 for the same solutions. This study confirms the expectation of a smaller reduction in the presence of ethanol of the permeate flux for the mineral membranes while albumin concentration in the permeate remained generally under 0.4 g/L irrespective of retentate concentration. The superposition of pressure and flow pulsations on the filter inlet by a piston-in-cylinder system decreases concentration polarization and increases permeate flux by 50 to 60% as compared with steady flows under the same conditions. 相似文献
In order to determine the structure‐performance relationship of nonionic‐zwitterionic hybrid surfactants, N,N‐dimethyl‐N‐dodecyl polyoxyethylene (n) amine oxides (C12EOnAO) with different polyoxyethylene lengths (EOn, n = 1–4) were synthesized. For homologous C12EOnAO, it was observed that the critical micelle concentration (CMC), the maximum surface excess (Γm), CMC/C20, and the critical micelle aggregation number (Nm,c) decreased on going from 1 to 4 in EOn. However, there were concomitant increases in surface tension at the CMC (γCMC), minimum molecular cross‐sectional area (Amin), adsorption efficiency (pC20), and the polarity ([I1/I3]m) based on the locus of solubilization for pyrene. The values of log CMC and Nm,c decreased linearly with EOn lengthening from 1 to 4, although the impact of each EO unit on the CMC of C12EOnAO (n = 1–4) was much smaller than that typically seen for methylene units in the hydrophobic main chains of traditional surfactants. Compared to the structurally related conventional surfactant N,N‐dimethyl‐N‐dodecyl amine oxide (C12AO), C12EOnAO (n = 1–4) have smaller CMC, Amin, and CMC/C20, but larger pC20, Γm, and Nm,c with a higher [I1/I3]m. This may be attributed to the moderately amphiphilic EOn (n = 1–4) between the hydrophobic C12 tail and the hydrophilic AO head group. 相似文献
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