ABSTRACT
For the first time, a systematic study to investigate the electrospinnability of cyclic olefin polymer (COP) was performed. Different solvents and mixtures were tested together with different electrospinning parameters and post-treatment types to prepare bead-free fibers without defects. These were successfully obtained using a chloroform/chlorobenzene (40/60 wt.%) solvent mixture with a 15 wt.% COP polymer, a 1 mL/h polymer solution flow rate, a 15 cm distance between the needle and collector, and a 12 kV electric voltage. COP fibers were in the micron range and the hot-press post-treatment (5 MPa, 5 min and 120 °C) induced an integrated fibrous structure along with more junctions between fibers, reducing the mean and maximum inter-fiber space. When the temperature of the press post-treatment was increased (from 25 °C to 120 °C), better strength and less elongation at break of COP fibers were achieved. However, when applying a temperature above the COP glass temperature (Tg = 138 °C) the fibers coalesced, showing a mechanical behavior similar to a plastic film and a low elongation at break with a high strength. The addition of a high dielectric constant non-solvent, N,N-dimethylacetamide (DMAc), resulted in a considerable reduction in the COP fiber diameter. Based on the cloud point approach, it was found that the use of DMAc and the solvent chloroform or chlorobenzene improved the electrospinnability of COP polymer solution.
ABSTRACT
Treatment of textile wastewater using ultrafiltration membranes was carried out in this study. Since membrane fouling is a major operational problem that decreases the membrane separation efficiency, wastewater was treated with polyaluminum chloride (PACl) and alum (aluminum sulfate) as coagulant to decrease the fouling of ultrafiltration membranes. PACl was selected as the best coagulant in the experiments. Also, chitosan was used as coagulant aid upon developing the hybrid process. The obtained optimum dosage of PACl coagulant was 100 mg/L, and maximum turbidity and COD removal of 35% and 66% were attained, respectively. The pretreated wastewater by coagulation was sent to ultrafiltration process for further removal of turbidity and COD. Three ultrafiltration hollow-fiber membranes made of polypropylene (PP), polyvinylidene fluoride (PVDF), and polyethersulfone (PES) were applied in this study. In general, the filtration results were evaluated for two types of samples treated under coagulation and without treatment; the results were unfavorable for the second type. The effects of transmembrane pressure (TMP) and cross velocity on membranes performance were also investigated for process optimization. The obtained results showed that PVDF membrane had the highest flux and turbidity removal, whereas the PES membrane had the highest COD removal. Also, the results revealed that turbidity and COD removal by all membranes were decreased by increasing TMP and cross velocity.
